Note: Descriptions are shown in the official language in which they were submitted.
CA 02274184 1999-06-10
BACKGROUND OF THE INVENTION
The present invention is directed to a collar for a watt-hour meter, and more
particularly to a meter collar which is configured for a use with an interface
circuit
that facilitates using an on-site energy source in lieu of or in addition to
commercial
power from an electric utility company. The interface circuit may isolate the
utility
company's power lines when the on-site source is used, or it may permit the on-
site
power source to be used in parallel with commercial power. The invention is
also
directed to an interface circuit itself, whether it is used in conjunction
with a meter
collar or is instead associated with other components of a customer's private
electrical distribution system, such as a meter socket box or a circuit
breaker box.
Some customers of commercial electrical utility companies would like the
option of using power which they, the customers, generate or store locally, or
on-site.
The customer's on-site power source may comprise, for example, a generator
which
is powered by a gasoline or diesel engine or a combustion turbine, a solar
cell array
which charges storage batteries that then supply electricity to an inverter
for
conversion to alternating current, a fuel cell and an inverter, or simply back-
up
storage batteries which are kept charged using commercial power and which
supply
power through an inverter when necessary.
Among the problems that typically confront a customer who wants the option
of using either his or her on-site power source or the utility company's power
is that
-2-
CA 02274184 1999-06-10
the modifications in the wiring of the customer's private electrical
distribution
system (at the customer's residence, for example, or at a small business
establishment receiving two-phase service) to accommodate the on-site power
source
are relatively expensive. Another problem is that the customer's electrical
distribution system should either be isolated from the utility company's power
lines,
or connected to the power lines in a carefully controlled manner, when the on-
site
power source is used. The isolation option not only prevents possible damage
to the
utility company's distribution system and to the loads of other customers, it
also
protects technicians who may be working on the utility company's power lines
from
electricity generated by the customer's on-site power source. Safety is a
paramount
concern for utility companies, which train their line technicians to make sure
the
lines they are working are on are electrically isolated from the utility
company's
generating facilities. It is not customary for line technicians to also
isolate the
segments they are working on from the customers, however, unless the
technicians
have been specifically trained to do so.
Despite this potential hazard, it may desirable to permit a customer to use
his
or her own on-site power source in parallel with the utility's power, so that
both the
on-site power and the utility's power can be consumed by the customer's loads.
If
the utility permits, parallel operation would also allow excess on-site power
to be
coupled to the utility's power lines for distribution to other customers.
Figure 1 illustrates a typical prior art arrangement illustrating how a
utility's
distribution system may be connected to the private distribution system of a
customer
who receives two-phase service (such as a residential customer with 110-
volts/220-
volt service or a small business owner with 110-volt/220-volt service). A
utility
-3-
' CA 02274184 1999-06-10
substation 20 receives power at a high voltage from a generating station (not
illustrated) and distributes this power (at a stepped-down but nevertheless
relatively
high voltage and in three phrases) to a network which includes a step-down
transformer 22. The primary winding of the transformer 22 receives one of the
phases from the substation 20, and the secondary winding in center-tapped. The
center tap, which is grounded, is connected to a neutral power line 24. A "leg
1 "
of the secondary winding is connected to a leg-1 power line 26 and a "leg 2"
of the
secondary winding is connected to a leg-2 power line 28. The potential
difference
between the leg-1 power line 26 and the neutral line 24 is typically 110 volts
(average) and the potential difference between the leg-2 power line 28 and
is also typically 110 volts (average). However, leg-1 power line 26 is
180° out of
phase with the leg-2 power line 28. Consequently, a load which is connected
between the neutral line 24 and either of the leg-1 or leg-2 power lines 26
and 28
receives 110 volts while a load connected between the leg-1 and leg-2 power
lines 26
and 28 receives 220 volts. The two-phase service that is illustrated in Figure
1 can
thus supply power to both 110 volt loads and 220 volt loads that are connected
to a
customer's private distribution system.
Figurel also shows the front side of a meter socket box 30 and the back side
of a watt-hour meter 32. The socket box 30 has a recessed socket 34 with
utility-side
contacts 36 and 38 and customer-side contacts 40 and 42. Each of the contacts
includes a pair of electrically conductive arms (not numbered). The socket 34
also
includes a neutral contact 44 that is connected by a neutral service line 46
to the
neutral power line 24 and to a neutral line 48 of the customer's private
distribution
system. The arms of the contact 36 are connected via a leg-1 service line 50
to the
-4-
CA 02274184 1999-06-10
leg-1 power line 26 and the arms of the contact 38 are connected via a leg-2
service
line 52 to the leg-2 power line 28. The arms of the contact 40 are connected
to a leg-
1 line 54 of the customer's distribution system while the arms of the contact
42 are
connected to leg-2 line 56 of the customer's distribution system
With continuing reference to Figurel, the back side of the meter 32 is
provided with four contacts, 58, 60, 62, and 64. When the meter 32 is plugged
into
the socket 34 as indicated schematically by arrow 66, the contact 60 is wedged
between the arms of the contact 36 to form a connection, the contact 58 is
wedged
between the arms of the contact 38 to form a connection, the contact 64 is
wedged
between the arms of the contact 40 to form a connection, and the contact 62 is
wedged between the arms of the contact 42 to form a connection. Meter 32 is an
electromechanical meter having a Farraday motor and a gear train (not
illustrated)
which turns dials (not illustrated) when the motor rotates. The meter includes
a low
resistance winding (not numbered) between the contacts 58 and 62 and another
low
resistance winding (also not numbered) between the contacts 60 and 64. The
meter
also includes a high resistance winding (not numbered) between the contacts 62
and
64. The net result is that, when the meter 32 is plugged into the socket 34,
the leg-1
line 54 of the customer's distribution system is connected to leg-1 power line
26, the
neutral line 48 of the customer's distribution system is connected to neutral
power
line 24, and the leg-2 line 56 of the customer's distribution system is
connected to
the leg-2 power line 28. The meter 32 records the watt-hours consumed by the
loads
connected to the customer's distribution system.
-5-
CA 02274184 1999-06-10
SUMMARY OF THE INVENTION
One object of the present invention is to provide a meter collar which houses,
in whole or in part, or which is connected to, an interface circuit that
permits easy
connection of an on-site power source to a customer's loads while reliably and
automatically disconnecting the utility's power lines from the loads.
Another object is to provide a meter collar which houses, in whole or in part,
or which is connected to, an interface circuit that permits easy connection of
a on-site
power source to a customer's loads in parallel with the utility.
Another object is to provide a meter collar which houses, in whole or in part,
or is connected to, an interface circuit that responds to a tone waveform that
is
superimposed on a power waveform (typically 60 Hz) carried by the utility's
power
lines.
Another object is to provide an interface circuit for performing one or more
of the above functions, regardless of whether the interface circuit is housed
in whole
or in part in a meter collar or is connected to a meter collar, or whether it
is used
without a meter collar at a location that is electrically downstream from the
meter,
such as in the meter socket box or in the circuit breaker box.
According to one aspect of the invention, these and other objects which will
become apparent in the ensuing detailed description can be attained by
providing a
meter collar which is configured as an adapter inserted between the meter
socket box
and the meter, the meter collar including a housing which is provided with
first
contacts for connection with utility-side contacts of the meter socket box and
which
is also provided with second contacts for connection with customer-side
contacts of
the meter socket box. The housing is additionally provided with contacts for
-6-
CA 02274184 1999-06-10
connecting the meter. The meter collar also includes an interface circuit
having
conductors which connect the first contacts to the meter and having means for
selectively connecting either the meter or an on-site power source to the
second
contacts. This means includes primary detection means, such as a relay and an
associated input circuit for the relay, for detecting whether the on-site
power source
is on and a second detection means, such as another relay and associated input
circuit, for detecting whether the utility's power lines are energized, the
second
detection means being connected to the first detection means.
According to another aspect of the invention, an interface method for
connecting a load or loads to either an on-site power source or to power lines
of a
utility, regardless of whether a meter collar is used, includes the steps of
detecting
whether the on-site power source is supplying, and opening first switches
between
the power lines and load or loads if the on-site power source is indeed
supplying
power. After the first switches have been opened, second switches between the
on-
site power source and the load or loads are closed. The method additionally
includes
the step of detecting whether the power lines are supplying power, but only if
power
supplied by the on-site power source has not been detected. The second
switches are
opened if power supplied by the power lines is detected, and then the first
switches
are closed.
In accordance with yet a further aspect of the invention, a meter collar for
use
between a watt-hour meter and a socket having utility-side contacts which are
connected to power lines of a utility and having customer-side contacts which
are
connected to a load or loads, includes a housing having first contacts for
connection
to the utility-side contacts of the socket and second contacts for connection
to the
CA 02274184 1999-06-10
customer-side contacts of the socket, the housing also having further contacts
for
connection with the meter. A means is provided for detecting whether a plug is
received in a receptacle that is connected to an on-site power source. The
meter
collar additionally includes an interface circuit having conductors which
connect the
first contacts to the meter, means for connecting the second contacts to the
meter if
the plug is not received in the receptacle, and means for connecting the
second
contacts to the receptacle if the plug is received in the receptacle.
Yet another aspect of the invention provides that a meter collar for use
between a watt-hour meter and a socket having utility-side contacts which are
connected to power lines of the utility and having customer-side contacts
which are
connected to a load or loads, includes a housing having first contacts for
connection
to the utility-side contacts of the socket and second contacts for connection
to the
customer-side contacts of the socket, the housing additionally having further
contacts
for connection with the meter. The meter collar also includes an interface
circuit
having conductors which connects the first contacts to the meter and having
means
for selectively connecting the second contacts to one or both of the meter and
the on-
site power source. This means for selectively connecting includes means for
detecting whether the on-site power source is supplying power, along with
means for
connecting the on-site power source to the second terminals, regardless of
whether
the meter is also connected to the second terminals.
According to still another aspect of the invention, a meter collar for use
between a watt-hour meter and a socket having utility-side contacts which are
connected to power lines of the utility and having customer-side contacts
which are
connected to a load or loads, with a tone generator being connected to the
power
_g_
CA 02274184 1999-06-10
lines, includes a housing having first contacts for connection to the utility-
side
contacts of the socket and second contacts for connection to the customer-side
contacts of the socket, the housing additionally having further contacts for
connection with the meter. The meter collar also includes an interface circuit
having
conductors which connect the first contacts to the meter. The interface
circuit
additionally has a detector for the tone from the tone generator, and means
for
selectively connecting the second contacts to either the meter, if the tone is
detected,
or to the on-site power source, if it is not detected.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic drawing illustrating a typical example of how a public
utility company's power distribution system supplies two-phase power via a
meter to
a customer;
Figure 2 is a schematic diagram illustrating a generalized embodiment of a
meter collar with an interface circuit according to the present invention;
Figure 3 is an exploded perspective view illustrating a specific embodiment
of a meter collar along with associated components;
Figure 4 is a left-side view of the meter collar shown in Figure 3;
Figure 5 is a right-side view of the meter collar shown in Figure 3;
Figure 6 is a front view of the meter collar shown in Figure 3;
Figure 7 is a schematic diagram illustrating a first embodiment of an
interface
circmt;
Figure 8 is a schematic diagram illustrating a second embodiment of an
interface circuit;
-9-
CA 02274184 1999-06-10
Figure 9 is a schematic diagram illustrating a third embodiment of an
interface circuit; and
Figure 10 is a schematic diagram illustrating a fourth embodiment of an
interface circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 2 illustrates a generalized embodiment of a meter collar 68 with an
interface circuit 70, which in this case is disposed within the meter collar
68. The
right-hand side of the meter collar 68 plugs into the meter socket 34 and has
contacts
(not illustrated in Figure 2) which engage the contacts 36-40. The meter 32,
in turn,
plugs into the left-hand side of the meter collar 68, which has contacts (not
illustrated
in Figure 2) for engagement with the contacts 58-64 of the meter. The meter
collar
68 thus acts as an adapter between meter 32 and the meter socket box 30,
providing
access to the lines 48, 54, and 56 of the customer's distribution system. An
on-site
power source 72 is connected to the interface circuit 70. Several embodiments
of
suitable interface circuits will be discussed hereafter. As will become
apparent
during these discussions, depending upon the circuitry employed, the interface
circuit
70 may disconnect the power lines 24-28 from the customer's distribution
system if
the commercial power fails and connect the on-site power source 72 instead, or
it
may disconnect the commercial power when the customer wants to use his or her
on-
site power source 72 even though the commercial power has not failed, or the
interface circuit 70 may permit that both the utility's power lines 24-28 and
the on-
site power source 72 to be connected to the service lines 48, 54, and 56 of
the
customer's distribution system, so that both power sources (commercial and on-
site)
may be said to supply power to the customer "in parallel."
-10-
CA 02274184 1999-06-10
Turning next to Figures 3-6, a more specific embodiment of a meter collar in
accordance with the present invention will now be described. In these figures,
the
meter collar will be identified by reference number 74.
The meter collar 74 includes a right-side housing member 76 which is joined
end-to-end to a left-side housing member 77. The housing member 76 includes a
cylindrical wall 78 having a pair of windows 79 in it. A flange 80 is provided
at one
end of the housing member 76 and a panel 81 is provided within cylindrical
wall 78
at a position that is recessed from the flange 80. An insulated wire 82 which
terminates in a connector member 83 extends through an opening (not numbered)
in
panel 81.
Four legs 84 extend from the panel 81. Furthermore, metal contacts 85, 86,
87, and 88 extend through openings (not numbered) in panel 81. A cable 90,
which
terminates in a fitting 92, includes wiring (which will be discussed later)
that extends
into the interior of the collar 74.
The left-side housing member 77 includes a cylindrical wall 94, a flange 96 at
one end of the wall 94, and a panel 98 at the other end. Contacts 100, 102,
104, and
106 extend through openings (not numbered) the panel 98, each of these
contacts
including a metal inner arm 108 and a metal outer arm 110 that is split into
two
segments. An elongated actuator member 112 protrudes through a keyhole-shaped
opening (not numbered) in panel 98 (the actuator member 112 is a mechanical
part of
an electrically controllable latching switch assembly 212 that will be
discussed later
in conjunction with the embodiment of an interface circuit that is shown in
Figure 7).
The housing members 76 and 77 may be made, for example, from injection-
molded plastic. When the housing members are assembled end-to-end in the
manner
-11-
CA 02274184 1999-06-10
shown in Figures 3 and 6, the space between the panel 81 of member 76 and the
panel 98 of the member 77 provides a hollow region within the meter collar 74.
A
printed circuit board 114 for an interface circuit, various embodiments of
which will
be described later, can be mounted within this space.
S Figure 3 illustrates an example of how the meter collar 74 can be employed
between the meter socket box 30 and the meter 32 in practice. The socket box
30 is
attached to a wall 114 at the premises of a customer for two-phase electric
power,
typically 110 volts and 220 volts as was discussed in the "Background of the
Invention" section of this document. When meter collar 74 is inserted into a
the
socket of the box 30, the contact 86 engages the contact 36 (see Figure 1 ) to
form a
connector 116 (see Figure 7); the contact 85 engages the contact 38 to form a
connector 118 (Figure 7); the contact 88 engages the contact 40 to form a
connector
120 (Figure 7); and the contact 87 engages the contact 42 to form a connector
122
(Figure 7 again). The wire 82 is connected to the neutral contact 44 before
the meter
collar 74 is plugged in. The flange 80 of the meter collar abuts against a
flange 124
on the socket box 30, and the meter collar 74 is secured to the socket box 30
by a
screw-tightened clamp 126 which engages the flanges 80 and 124. When the meter
32 is plugged into the meter collar 64, the contact 60 (see Figure 1) engages
the
contact 100 (see Figure 4) to form a connector 128 (see Figure 7); the contact
58
engages the contact 102 to form a connector 130; the contact 62 engages the
contact
106 to form a connector 132; and the contact 64 engages the contact 104 to
form a
connector 134. The meter 32 has a flange 136 which abuts against the flange 96
of
meter collar 74. A screw-tightened clamp 138 engages the flanges 96 and 136 to
secure the meter 32 to the collar 74.
-12-
CA 02274184 1999-06-10
With continuing reference to Figure 3, the cable 90 is connected by a fitting
140 to a box 142 which is closed by a cover 144. The box has a window 146 and
a
receptacle (not illustrated) for receiving a plug 148.
A connector assembly 150 includes a threaded pipe portion 152 which
extends through an opening (not illustrated) in the box 142 and which receives
a nut
(not illustrated) to thereby connect the assembly 150 to the box 142. (The
threaded
region of pipe portion 152 is illustrated in Figure 3 in order to facilitate
the
description but would in actual practice extend inside the box 142). The
assembly
150 also includes a mounting portion 154 having holes 156. Screws (not
illustrated)
extend through the holes 156 in order to mount the assembly 150 (and thus also
the
box 142) on the wall 114. T'he connector assembly 150 also includes a
receptacle
portion 158 having a spring-loaded flap 160 which is normally closed to keep
out
moisture and debris. An electrical receptacle 162 (see Figure 7) is mounted
inside
portion 158.
A power cable 164 extends from an on-site power source 166 and terminates
in a plug 168 that mates with the receptacle 162 (Figure 7). A signal cable
170
extending from the power source 166 terminates in the plug 148. Clamps 172 tie
the
cable 170 to the cable 164.
A first embodiment of an interface circuit 60a for use with the meter collar
74
will now be discussed with reference to Figure 7. In Figure 7, a leg-1
conductor 200
couples the connector 116 to the connector 128 and another leg-1 conductor,
202,
couples the connector 134 to the connector 120 via a switch 204. A leg-2
conductor
206 couples the connector 118 to the connector 130, and a leg-2 conductor 208
couples the connector 132 to the connector 122 via a switch 210.
-13-
CA 02274184 1999-06-10
Switches 204 and 210 are part of an electrically controllable latching switch
assembly 212 which additionally includes a solenoid 214 and an SPDT switch 216
having a "trip" contact or position 218 and a "close" contact or position 220.
The
switch 216 is mechanically linked to the switches 204 and 210, as is indicated
by the
S dotted line in the figure. The operation of switch assembly 212 can be
briefly
described as follows: When current flows in one direction through the solenoid
214
for a period of time exceeding a brief minimum, the switches 204 and 210 are
closed
and latched in the closed position and the switch 216 moves to trip position
218 and
is latched in the trip position. When current flows through a solenoid 214 in
the
opposite direction for a period of time exceeding the brief minimum, the
switches
204 and 210 are opened and locked in the open position and the switch 216
moves to
close position 220 and is latched in the close position. Further information
about the
construction and operation of switch assembly 212 is available in U.S. Patent
4,430,579, which is incorporated herein by reference. Switch assembly 212 is
commercially available from Automatic Switch Company of Florham Park, New
Jersey, USA.
The interface circuit 60a also includes three interconnected relays - a
secondary detection relay 222, a switchover relay 224, and a primary detection
relay
226. The secondary detection relay 222 includes a solenoid 232, a normally
closed
switch 234, and a normally opened switch 236. When the solenoid 232 is
energized,
the normally closed switch 234 opens and the normally opened switch 236
closes.
The solenoid 232 is connected to an input circuit 238 which includes a step-
down
transformer 240, a rectifying diode 242, a smoothing capacitor 244, a load
resistor
246, and a flyback diode 248. The input circuit 238 steps down the voltage
received
-14-
CA 02274184 1999-06-10
by the primary winding of transformer 240, and converts the stepped-down
voltage
to DC. The input circuit 238 has a time constant whose value is determined
primarily by capacitor 244 and resistor 246.
The switchover relay 224 includes a normally opened switch 248, a normally
open switch 250, and a solenoid 252, the solenoid being connected to an input
circuit
254. The primary detection relay 226 includes a normally closed switch 256, a
normally open switch 258, and a solenoid 260. The solenoid 260 is connected to
an
input circuit 262. The time constants of input circuits 254 and 262 may be the
same
as that of input circuit 238.
The cathodes of flyback diode 264, steering diodes 266 and 268, and flyback
diode 270 are connected to one end of solenoid 214. The anodes of steering
diodes
272 and 274 are connected respectively to the close contact 220 and the trip
contact
218 of latching switch assembly 212. A conductor 276 connects the leg-1
conductor
200 to a fuse 278 and a conductor 280 connects the fuse 278 to the anode of
diode
266. The leg-2 conductor 206 is connected to a fuse 282 by a conductor 284,
and a
conductor 286 connects the fuse 282 to the fixed contact of switch 256. A neon
glow
lamp 288 is connected between conductors 276 and 284 and another neon glow
lamp, 290, is connected between conductors 280 and 286. Physically, the glow
lamps 288 and 290 are located behind windows 79 (see Figure 6).
One contact of receptacle 162 is connected via a leg-1 conductor 292 and a
circuit breaker 294 to the movable contact of switch 250. The fixed contact of
switch 250 is connected to leg-1 conductor 202. Another contact of the
receptacle
162 is connected via a leg-2 conductor 296 and a circuit breaker 298 to the
movable
contact of switch 248. The fixed contact of switch 248 is connected to leg-2
-15-
CA 02274184 1999-06-10
conductor 208. A neon glow lamp 300 is connected between the first and second
leg
contact 292 and 296. Physically, the neon glow lamp 300 is disposed behind
window 146 (see Figure 3). A third contact of the receptacle 162 is connected
by a
conductor 302 (which includes the wire 82 shown in Figures 3 and 5) to the
neutral
contact 44.
A conductor 304 connects conductor 280 to one end of the primary winding
of transformer 240. The other end of the primary winding is connected by a
conductor 306 to the movable contact of switch 256. A conductor 308 connects
the
conductor 306 to the fixed contact of switch 236, the movable contact of which
is
connected by a conductor 310 to the anode of diode 264 and the cathode of
diode
272. A conductor 312 connects the fixed contact of switch 234 to the anode of
diode
270, the cathode of diode 274, and to a fuse 314. The fuse 314 in turn is
connected
by a conductor 316 to the fixed contact of switch 258. The movable contact of
switch 258 is connected via a fuse 318 to the leg-1 conductor 292.
The anode of diode 268 is connected by a conductor 320 to one end of a fuse
322, whose other end is connected to the leg-2 conductor 296.
One end of the primary winding of the transformer in input circuit 254 is
connected to the conductor 320, while the other end is connected via a
conductor 322
to the movable contact of the switch 234. One end of the primary winding of
the
transformer in input circuit 262 circuit is connected via the fuse 318 to the
leg-1
conductor 392, and the other end is connected via the fuse 322 to the leg-2
conductor
296.
The on-site power source 166 may take many forms, and the example shown
in Figure 7 is depicted only schematically. This example includes a generator
324
-16-
CA 02274184 1999-06-10
which is driven by gasoline engine (not illustrated). The generator 324 is
connected
via circuit breakers 326 and connectors 328 to the cable 164 (also see Figure
3). A
generator start/run controller 330 is provided for starting the gasoline
engine using a
battery (not illustrated) within the controller 330 and for controlling the
speed of the
engine thereafter. The controller 330 thus indirectly controls the generator
324 by
way of the engine, and this control is indicated schematically by arrow 331. A
manual start switch 332 is connected to the controller 330. Furthermore, the
controller 330 is connected to the cable 170 (also see Figure 3) by way of
connectors
334. The cable 170 is connected by connectors 336 (which include the plug 148
shown in Figure 3 and a receptacle, not shown, in box 142) to conductors 338
and
340. The conductor 338 is connected to conductor 286 and the conductor 340 is
connected to conductor 280.
It has been found that the steering diodes 266 and 268 may be damaged, in
regions where a utility's power lines are subject to unusually strong surges,
if the
peak inverse voltage ratings of these diodes is not high enough. Diodes with a
PIV
of a thousand volts are recommended. If surges approaching a thousand volts
(or
higher) are encountered in a particular region, the latching switch assembly
212 may
be modified by adding another SPDT switch (not shown), like switch 216 but
connected electrically on the other side of solenoid 214 from switch 216.
Latching
switch assemblies that are commercially available from Automatic Switch
Company
at Florham Park, New Jersey are configured to permit another switch to be
added.
The movable contact of the added switch would be connected to solenoid 214 and
the two fixed contacts would be connected to the cathodes diodes 266 and 268.
The
-17-
CA 02274184 1999-06-10
added SPDT switch would isolate the diodes from high reverse voltages during
surges.
It is noted that diodes 266 and 272 both have a steering function and turn on
simultaneously, so the steering function could be performed by one of the
diodes and
the other could be omitted. Similarly, one of the diodes 268 and 274 could be
omitted.
The operation of interface circuit 60a will now be described, with reference
to
several cases.
In the first case, Case A, assume the following initial conditions: The
utility's power is off (that is, the voltage between leg-1 conductor 200 and
leg-2
conductor 206 is zero), the on-site power source 166 is turned off (that is,
the voltage
between leg-1 conductor 292 and leg-2 conductor 296 is zero), switches 204 and
210
are open and switch 216 is at close position 220, and the capacitors in input
circuits
238, 254, and 262 are discharged. Now turn on the commericial power, so that
the
voltage between leg-1 and leg-2 conductors 200 and 206 rises to approximately
220
voltage AC (average) while the on-site power source 166 remains off. A circuit
between leg-1 conductor 200 and leg-2 conductor 206 exists via conductor 276,
fuse
278, conductor 304, the primary winding of transformer 240, conductor 306,
normally closed switch 256, conductor 286, fuse 282, and conductor 284.
Because
of this circuit, the voltage across capacitor 244 in input circuit 238 begins
to rise.
Primary detection relay 226 is in a deactuated state and remains deactuated
because
the primary winding of the transformer in input circuit 262 is connected
across leg-1
and leg-2 conductors 292 and 296, which have been assumed to have a zero
potential
difference. Switchover relay 224 is in a deactuated state and remains
deactuated
_18_
CA 02274184 1999-06-10
because one end of the primary winding of the transformer in input circuit 254
is
connected via conductor 322, normally closed switch 234, conductor 312, fuse
314,
and conductor 316 to normally open switch 258 of relay 226. Although normally
closed switch 234 does not open until capacitor 244 has charged sufficiently
for relay
222 to be actuated, normally open switch 258 keeps current from flowing
through
this circuit (regardless of the state of switch 234).
After the voltage across voltage capacitor 244 rises sufficiently, secondary
detection relay 222 is actuated and this causes normally closed switch 234 to
open
and normally open switch 236 to close. The closure of switch 236 connects leg-
2
conductor 206 to leg-1 conductor 200 via conductor 284, fuse 282, conductor
286,
normally closed switch 256, conductors 306 and 308, the now-closed but
normally
open switch 236, diode 272, switch 216, solenoid 214, diode 266, conductor
280,
fuse 278, and conductor 276. The diodes 272 and 266 become conductive during
the
first positive half cycle of the utility company's electricity after secondary
detection
relay 222 has been actuated, so current flows through solenoid 214. This
causes
switches 204 and 210 to close and causes switch 216 to move from the close
position
220 to the trip position 218, thus removing current from solenoid 214. The
switches
204, 210 and 216 are latched at their new positions and thus do not change
states
when the current through solenoid 214 is reduced to zero. The result is that
the
utility company's leg-1 and leg-2 power lines 50 and 52 are connected to the
leg-1
and leg-2 service lines 54 and 56 of the customer's distribution system during
Case A
while leg-1 and leg-2 conductors 292 and 296 remain disconnected.
In Case B, assume that the utility company's power is turned on, that the
circuitry of input circuit 60a is initially in the state that it assumed at
the conclusion
-19-
CA 02274184 1999-06-10
of Case A, and that the on-site power source 166 is then manually turned on by
actuating switch 332 and begins supplying power by way of plug 168 and
receptacle
162 (that is, assume that the voltage between leg-1 and leg-2 conductors 292
and 296
changes from 0 volts to 220 volts). A circuit exists between leg-1 and leg-2
conductors 292 and 296 via fuse 318, the primary winding of the transformer in
input
circuit 262, and fuse 322. Consequently, primary detection relay 226 is
actuated
after the capacitor in input circuit 262 has charged sufficiently, whereupon
switch
256 is opened and switch 258 is closed. With the opening of switch 256,
current
ceases to flow through the primary winding of transformer 240 (however,
secondary
detection relay 222 remains actuated briefly due to energy stored by capacitor
244).
The closure of switch 258 creates a circuit from leg-1 conductor 292 to leg-2
conductor 296 via fuse 318, switch 258, conductor 316, fuse 314, diode 274,
switch
216, solenoid 214, diode 268, conductor 320, and fuse 222. Current begins
flowing
through this circuit during the first negative half cycle of generator 324
after relay
226 has been actuated. The current through solenoid 214 opens switches 204 and
210 and moves switch 216 to close position 220, thus preventing continued flow
to
solenoid 214. The switches 204, 210, and 216 are latched in their new
positions.
When capacitor 244 discharges sufficiently for secondary detection relay 222
to be deactuated, the switch 236 opens and switch 234 closes . A circuit
between
leg-1 and leg-2 conductors 292 and 296 is created when switch 234 closes, via
the
fuse 318, switch 258 (which is closed due to the actuation of primary
detection relay
226), conductor 316, fuse 314, conductor 312, switch 234, conductor 322, the
primary winding of the transformer in input circuit 254, conductor 320, and
fuse 322.
Switchover relay 224 is therefore actuated shortly after secondary detection
relay 222
-20-
CA 02274184 1999-06-10
becomes deactuated. This closes switches 248 and 250, thereby coupling leg-1
conductor 292 to leg-1 conductor 202 and coupling leg-2 conductor 296 to leg-2
conductor 208. As a result, the customer receives power from his or her on-
site
power source 166 even though commercial power is available. By turning the on-
site power source on, the customer elects to switch to it from commercial
power.
In Case C, assume that the utility's power is on, that the on-site power
source
166 is also on, and that the interface circuit 60a is in the state discussed
above at the
conclusion of Case B. Then assume that on-site power source 166 is turned off
and
the voltage between leg-l and leg-2 conductors 292 and 296 falls to zero. As a
result, current ceases to flow through the primary winding of the transformer
in
input circuit 262 and it also ceases to flow through the primary winding of
the
transformer in input circuit 254. Primary detection relay 226 and switchover
relay
224 are deactuated shortly thereafter, when the capacitors in their input
circuits have
discharged sufficiently. The deactuation of switchover relay 224 disconnects
leg-1
and leg-2 conductors 292 and 296 from leg-1 and leg-2 conductors 202 and 208.
The
deactuation of primary relay 226 opens switch 258 and closes switch 256, thus
causing current to flow through the primary winding of transformer 240. After
the
expiration of the time constant of input circuit 238, secondary detection
relay 222 is
actuated and switch 234 is opened while switch 236 is closed. The closure of
switch
236 creates a circuit between leg-1 and leg-2 conductors 200 and 206 via
conductor
284, fuse 282, conductor 286, switch 256, conductor 306, conductor 308, switch
236,
diode 272, switch 216, solenoid 214, diode 266, conductor 280, fuse 278, and
conductor 276. The completion of this circuit causes latching switch assembly
212
to change state, so that switches 204 and 210 are closed and latched in their
closed
-21-
CA 02274184 1999-06-10
position and so that switch 216 moves to trip position 218 and is latched in
that
position. The net result is that the interface circuit 60a switches back to
the utility's
power after on-site power source 116 is turned off.
In case D, assume that the utility's power is on, that the on-site power
source
116 is on, and that the interface circuit 60a is in the state discussed above
at the
conclusion of Case C. Then assume that the utility's power goes off, due
perhaps to
damage to the power lines during a storm. The voltage between conductors 280
and
286 thus falls to zero, information that is conveyed to generator start/run
controller
330 via conductors 338 and 340, connectors 336, signal cable 170, and
connectors
334. In response the controller 330 starts the engine (not illustrated) that
drives
generator 324. The voltage between leg-1 conductor 292 and leg-2 conductor 296
rises to 220 volts. Operation then proceeds along the lines discussed above
with
respect to Case B, so that the service lines 50 and 52 are disconnected from
the
customer's distribution lines 54 and 56 and the on-site power source 166 is
connected instead. Case D provides an "automatic-start" feature which
initiates an
automatic change from the utility's power to the on-site power source 166 if
the
utility's power is lost. Of course, the customer also has the option of
actuating
manual start switch 332 in order to intentionally initiate a change from the
utility's
power to on-site power, as was described above in the explanation of Case B.
The
customer might want to intentionally change to on-site power if (for example)
a
possible commercial power outage is anticipated due to a severe storm.
Some final observations about interface circuit 60a will now be presented,
before proceeding to the next embodiment. Relay 226 has been called a "primary
detection" relay because it detects whether on-site power source 166 is on or
off.
-22-
CA 02274184 1999-06-10
That is, subject to delays due to input circuit 262 (and particularly its
capacitor) and
the relatively modest response speed of the relay itself, the relay 226 is
actuated
when on-site power source 166 is on (meaning above some predetermined minimum
average voltage) and deactuated when it is off. Relay 222 has been called a
"secondary detection" relay because it detects whether the commercial power is
on
or off but is subservient to the primary detection relay 226. That is, subject
to delays
due to input circuit 238 (and particularly capacitor 244) and the relatively
modest
response speed of the relay itself, the relay 222 is actuated when the
commercial
power is on (meaning above some predetermined minimum voltage) and deactuated
when it is off, but only if the primary detection relay 226 is in a deactuated
state.
This is due to the fact that switch 256 of primary detection relay 226 is
connected to
the input circuit 238 for secondary detection relay 222, thereby operationally
interlocking the relays. Relay 224, which is operationally interlocked to both
the
primary and secondary detection relays 226 and 222 by virtue of their
respective
switches 258 and 234, has been named a "switchover" relay to suggest its
function --
connecting on-site power source 166 to leg-1 and leg-2 conductors 202 and 208,
in
lieu of commercial power from the utility company if the commercial power was
on
when on-site power source 166 was turned on, depending on the states of
primary
and secondary detection relays 226 and 222.
As was noted previously, the switch 256 of primary detection relay 226 is
present in order to isolate the input circuit 238 for secondary detection
relay 222
from the commercial power (i.e., conductor 206) when on-site power source 166
is
on and primary detection relay 226 is actuated. The purpose of switch 258 is
to
avoid a problem that might otherwise arise if on-site power source 116 is
turned on
-23-
CA 02274184 1999-06-10
while the commercial power is on. With the commercial power on and the on-site
power source off, primary detection relay 222 is in its actuated state,
switches 204
and 210 are closed, and switch 216 is at trip position 218. After on-site
power source
166 is turned on, there is a brief delay before primary detection relay 226 is
actuated.
S If switch 258 were absent, so that conductor 316 were connected permanently
to fuse
318, the trip contact 218 of latching switch assembly 216 would be permanently
connected to leg-1 conductor 292. Consequently, latching switch assembly 216
would be actuated when on-site power source 166 is turned on, thereby opening
switches 204 and 210 and shifting switch 216 to the close position 220. But
switch
256 of primary detection relay 226 would still be closed due to the previously
mentioned time delay associated with relay 226, and switch 236 of secondary
detection relay 222 would also be closed. As a result, latching switch
assembly 212
would be actuated again, closing switches 204 and 210 and shifting switch 216
back
to its trip contact 218. This back-and-forth actuation of latching switch
assembly
212 would continue until the delay period associated with activation of
primary
detection relay expired. Furthermore, without switch 258 to isolate the
transformer
in input circuit 254 from the leg-1 conductor 292, switchover relay 224 might
be
actuated before primary detection relay 226. This would lead to the
possibility that
switches 248 and 250 of switchover relay 224 might be closed at the same time
as
the switches 204 and 210 of latching switch assembly 212, connecting the on-
site
power source 166 to the service lines 50 and 52. Since it is unlikely that on-
site
power source 166 would just happen to be matched in phase with the utility,
this
could cause damage. These adverse consequences can be avoided by including
switch 258 in the primary detection relay 226, in order to control the timing
of the
-24-
CA 02274184 1999-06-10
actuation of latching switch assembly 212 and the connection of input circuit
254
across leg-1 and leg-2 conductors 292 and 296.
Turning next to switch 236 of secondary detection relay 222, this switch is
present to ensure that switches 204 and 210 do not close before switches 248
and 250
of switchover relay 224 are opened. It has already been explained (see Case C,
above) how switches 204 and 210 are closed to connect the utility to the lines
54 and
56 of the customer's distribution system if the utility is on when the on-site
power
source 166 stops supplying power. First the primary detection relay 226 is
deactuated and then the secondary detection relay is actuated, closing switch
its 236
to permit the latching switch assembly 212 to also close its switches 204 and
210 so
as to thereby connect the service lines 50 and 52 to the lines 54 and 56 of
the
customer's distribution system. If switch 236 were not present, so that
conductor
308 were connected directly to diode 272, latching switch assembly 212 might
close
its switches 204 and 210 while switchover relay 224 is still in its actuated
state (if the
delay associated with the switchover relay 224 were slightly greater than the
delay
associated with primary detection relay 226). The primary windings of the
transformers in input circuits 254 and 262 stop receiving current at the same
time
when on-site power source 166 is turned off, so the primary detection relay
226 and
the switchover relay are deactuated at about the same time, but slight timing
differences might arise due to incidental differences in the delays associated
with the
relays. However, the presence of switch 236 means that the delay period
associated
with secondary detection relay 222 does not even start until primary detection
relay
226 is deactuated, and this in turn ensures that switches 248 and 250 are
opened
before switches 204 and 210 are closed.
-25-
CA 02274184 1999-06-10
Switch 234 of the secondary detection relay 222 is also present for timing
purposes. Consider what might happen if switch 234 were not present and
conductor
322 were connected directly to conductor 312. Then the transformer in input
circuit
238 would stop receiving current when primary detection relay 226 is actuated
and,
at the same time, the transformer in input circuit 254 would start receiving
current.
Whether switchover relay 224 would be actuated before or after secondary
detection
relay 222 is deactuated could not be predicted with precision due to
incidental
variations in the delay times associated with these relays. The presence of
switch 234
means that the delay associated with switchover relay 224 when it is being
actuated does not
start until the delay associated with secondary detection relay 222 when it is
being
deactuated has expired.
Figure 8 illustrates another embodiment of an interface circuit, this
embodiment being designated by reference number 60b. It includes a leg-1
conductor 342 which links the connectors 116 and 128 and a leg-2 conductor 344
which links the connectors 118 and 130. A conductor 346 connects the neutral
contact 44 to one power input terminal of a battery charger 348. The other
power
input terminal of the charger 348 is connected to a conductor 350.
The interface circuit 60b also includes relays 352, 354, 356, 358. The relay
352 has a solenoid 360 and a normally closed switch 362. The relay 354
includes a
solenoid 364 and a normally open switch 366. Relays 356 and 358 have solenoids
368 and 370 respectively, with relay 356 also including a normally closed
switch 372
and relay 358 including a normally open switch 374.
A normally open switch 376 is connected to the connectors 336 and thus also
to the controller 330. The switch 376 is mechanically linked to a normally
open
-26-
CA 02274184 1999-06-10
switch 378. The switches 376 and 378 are mounted in the connector assembly 150
(see Figure 3) in such a manner that they are engaged by plug 168 (or engaged
by a
linkage arrangement, not illustrated, which in turn is engaged by the plug
168) when
the plug 168 is inserted into the receptacle 162. Such engagement causes the
switches 376 and 378 to close. The switch 378 is connected by a conductor 380
to
the negative terminal of a rechargeable battery 382, and by a conductor 384 to
one
end of solenoid 364 and one end of solenoid 370.
One contact of receptacle 162 is connected by a leg-1 conductor 386 to the
fixed contact of switch 366. Another contact of the receptacle 162 is
connected by a
leg-2 conductor 388 to the fixed contact of switch 374. Another contact of the
receptacle 162 is connected by a conductor 390 to the conductor 346.
A leg-1 conductor 392 links the connector 134 to the fixed contact of switch
362. Another leg-1 conductor 394 links the connector 120 to the movable
contact of
switch 362 and to the movable contact of switch 366. A leg-2 conductor 396
links
the connector 132 to the fixed contact of switch 372, and another leg-2
conductor
398 links the connector 122 to the movable contact of switch 372 and to the
movable
contact of switch 374.
The operation of interface circuit 60b will now be described. Unless plug
168 is plugged into receptacle 162, the leg-1 service line 50 is connected to
the leg-1
line 54 of the customer's distribution system by way of leg-1 line 342, meter
32, leg-
1 line 392, normally closed switch 396, and leg-1 line 394. The leg-2 service
line 52
is also connected to the customer's leg-2 line 56 by way of leg-2 line 344,
the meter
32, leg-2 line 396, normally closed switch 372, and leg-2 line 398. The leg-1
line
-27-
CA 02274184 1999-06-10
394 is isolated from the leg-1 line 386 by normally open switch 366, and the
leg-2
line 398 is likewise isolated from the leg-2 line 388 by the normally open
switch 374
If the plug 168 is plugged into receptacle 162, however, switches 376 and 378
are closed. The closure of switch 376 enables controller 330 to start the
gasoline
engine (not illustrated) which drives generator 324 when switch 332 is
manually
actuated. That is, the generator 324 cannot be started unless the plug 168 is
plugged
into the receptacle 162. The closure of switch 378 permits current from
battery 382
to flow through the series connection of solenoids 360 and 364 and also
through the
series connection of solenoids 368 and 370. The switches 362 and 372 are thus
opened, isolating leg-1 conductor 392 from leg-1 conductor 394 and also
isolating
leg-2 conductor 396 from leg-2 conductor 398. Furthermore, switches 366 and
374
are closed, thus connecting leg-1 conductor 386 to leg-1 conductor 394 and
also
connecting leg-2 conductor 388 to leg-2 conductor 398. As a result, the
customer's
distribution system receives power from on-site power source 166 and the
utility
company's power lines are disconnected. When the generator 324 is turned off
and
plug 168 is withdrawn, the utility's power lines are connected to the
customer's
distribution system again.
Protective devices (e.g., fuses and circuit breakers) and indicator lamps have
been omitted from the embodiment shown in Figure 8 (and from embodiments that
are to be described hereafter) to facilitate the description. Those skilled in
the art
will appreciate, however, that protective devices and possibly also indicator
lamps
would, in practice, normally be employed, as in the embodiment shown in Figure
7.
-28-
CA 02274184 1999-06-10
Those skilled in the art will also appreciate that relays 352 and 354 could be
replaced by a SPDT relay and that relays 356 and 358 could likewise be
replaced by
a SPDT relay. Or relays 352-358 could all be replaced by a DPDT relay.
Figure 9 illustrates another embodiment of a protective circuit, designated by
reference number 60c. It includes a leg-1 conductor 398 linking the connectors
116
and 128, a leg-2 conductor 400 linking the connectors 118 and 130, a leg-1
conductor 402 that is connected to the connector 134, a leg-1 conductor 404
that is
connected to the connector 120, a leg-2 conductor 406 that is connected to the
connector 132, and a leg-2 conductor 406 that is connected to the connector
122.
Relays 410 and 412 include normally closed switches 414 and 416,
respectively. The fixed contact of switch 414 is connected to leg-1 conductor
402
and the fixed contact of switch 416 is connected to leg-2 conductor 406. Relay
410
also includes a solenoid 418, one end of which is grounded, and relay 412
includes a
solenoid 420, which likewise has an end that is grounded. Relays 422 and 424
have
normally open switches 326 and 328 whose fixed contacts are connected
respectively
to conductors 430 and 432. Relays 422 and 424 also include solenoids 434 and
436,
respectively. One end of each of these solenoids is grounded. The movable
contact
of switch 414 and the movable contact of switch 426 are connected to the leg-1
conductor 404, and likewise the movable conductor of switch 416 and the
movable
conductor of switch 428 are connected to leg-2 conductor 408.
A battery charger 438 has a first power input terminal that is connected by a
conductor 440 to the leg-1 conductor 402 and a second power input terminal
that is
grounded. The charger 438 charges a battery 442, whose negative terminal is
grounded and whose positive terminal is connected to electrically controlled
switches
-29-
CA 02274184 1999-06-10
444 and 446. The ungrounded terminals of solenoids 418 and 420 are connected
to
switch 444 and the ungrounded terminals of solenoids 434 and 436 are connected
to
switch 446. When switch 444 is closed, current from battery 442 flows through
solenoids 418 and 420 and consequently switches 414 and 416 are opened,
thereby
disconnecting leg-1 conductors 402 and 404 and also disconnecting leg-2
conductors
406 and 408. On the other hand, when switch 446 is closed, current flows
through
solenoids 434 and 436, so that switches 426 and 428 are closed and leg-1 and
leg-2
conductors 430 and 432 are connected respectively to leg-1 and leg-2
conductors 404
and 408.
The interface circuit 60c also includes manually operable switches 448 and
450, which are connected between ground and pull-up resistors 452 that in turn
are
connected to the positive terminal of battery 442. The switch 448 is
accessible to the
owner of on-site power source 166, but switch 450 is not accessible to the
owner.
The owner closes switch 448 if he or she wants the utility company's power
lines to
be automatically disconnected when the on-site power source 166 is running.
Switch
450 is placed in a closed position by an agent of the utility company if the
utility
company will permit its power lines to be connected in parallel to the on-site
power
116. If switch 450 is open, of course, the position of switch 448 makes no
difference
since switches 414 and 416 will be opened automatically (as will be explained
below) when the on-site power 166 begins running, regardless of the setting of
switch 448. Switches 448 and 450 provide input signals to a microprocessor
454.
The interface circuit 60c includes a sensor group 456 that receives signals
from leg-1 and leg-2 conductors 402 and 406 and from leg-1 and leg-2
conductors
430 and 432. Signals from the sensors are supplied over a mufti-conductor
analog
-30-
CA 02274184 1999-06-10
bus 458 to a selector 460, which receives selection signals from the
microprocessor
454 over a digital bus 462. The selected sensor signals pass through the
selector 460
and are converted to digital by an A/D converter 464 to provide input signals
to the
microprocessor 454. The sensor group 456 preferably includes voltage sensors,
current sensors, and a phase-locked loop. The PLL in sensor 456 provides a
signal
that is conveyed via a conductor 466 and the connectors 336 to the generator
start/run controller 330. The controller 330 uses the signal to adjust the
speed of the
engine driving generator 324 so that its output matches the utility company's
power
in frequency and phase. In the case of an on-site power supply of the type
that
includes batteries or some other DC source and an inverter, the signal from
the PLL
would be used to control the inverter so that its output would match the
utility
company's power in frequency and phase.
The operation of interface circuit 60c will now be described. Microprocessor
454 normally emits digitally low signals to switches 444 and 446. This keeps
the
switches open and isolates the solenoids of all four relays from the battery
442. In
this state, the switches 426 and 428 are open, and switches 414 and 416 are
closed to
connect the leg-1 conductors 402 and 404 and the leg-2 conductors 406 and 408.
The microprocessor 454 also repeatedly controls the selector 460 to pass
sensor
signals which indicate the voltage across leg-1 and leg-2 conductors 430 and
432. If
the sensed voltage across conductors 430 and 432 rises past a predetermined
level,
the microprocessor checks the state of switches 448 and 450. If switch 448 is
closed,
indicating that the owner of on-site power source 166 wants to use the source
166
only and to disconnect the utility, the microprocessor waits until the voltage
and
frequency on leg-1 and leg-2 conductors 430 and 432 are within a first
acceptable
-31-
CA 02274184 1999-06-10
range (the frequency can be determined by microprocessor 454 by repeatedly
sampling the voltage over a time interval corresponding to a few cycles of the
commercial power). If the sensed voltage and frequency are within the first
acceptable range, the microprocessor 454 emits a digitally high signal to
switch 444,
thus actuating relays 410 and 412 to disconnect the leg-1 and leg-2 conductors
402
and 406, and then emits a digitally high signal to switch 446, thus actuating
relays
422 and 424. This connects the leg-1 and leg-2 conductors 430 and 432 to the
leg-1
and leg-2 conductors 404 and 408 via the switches 426 and 428.
What has been described as the "first acceptable range" is provided for the
protection of the owner of the on-site power source 166. The first acceptable
range
can be rather loose, excluding only voltages and/or frequencies that would
probably
be unacceptable to the owner of the on-site source 166 and possibly damage his
loads. That is, the first acceptable range is a complimentary protective
feature that is
designed to keep the owner's on-site power source from damaging the owner's
own
loads.
A second acceptable range is employed by the microprocessor 454 if the
switch 448 is opened (indicating that the owner of the on-site power source
would
like to operate it in parallel with the utility) and if the switch 454 is
closed (indicating
that the utility company is willing to permit such parallel operation). If
parallel
operation is desired by the owner and permitted by the utility company, as
indicated
by switches 448 and 450, after microprocessor 454 detects that the voltage
across
leg-1 and leg-2 conductors 430 and 432 has risen past the predetermined level
it also
detects whether the voltage, frequency, and phase on the conductors 430 and
432
closely match the voltage, frequency, and phase on conductors 402 and 406. If
so,
-32-
CA 02274184 1999-06-10
the microprocessor 454 closes switch 446 while keeping switch 444 open, thus
closing switches 426 and 428 so as to connect on-site power source 166 in
parallel
with the service lines SO and 52.
It is possible that the on-site power source 166 may malfunction in some way
after parallel operation has been initiated. However, the on-site power source
166
would normally have a power capability that is substantially smaller than that
of the
utility company, and it is believed that a malfunction which develops after
the
initiation of parallel operation would not seriously perturb the utility
company's
distribution network or harm other customers. Nevertheless, after the
microprocessor 454 initiates parallel operation it continues to monitor the
current
through leg-1 and leg-2 conductors 402 and 406, and deactuates relays 410 and
412
to open switches 414 and 416 if the current becomes excessive.
Once interface circuit 60c has initiated parallel operation, it maintains
parallel
operation until the on-site power source 116 is turned off unless, as was
mentioned
above, the current carried by conductors 402 and 406 becomes excessive. The
microprocessor 454 decides that the power source 166 has been turned off if
the
current through leg-1 and leg-2 conductors 430 and 432 falls below a
predetermined
level. The microprocessor thereupon emits a digitally low signal to the switch
446,
thereby deactuating the relays 422 and 424 and opening switches 426 and 428.
This
returns the interface circuit 60c to the original state before the parallel
operation
began.
Those skilled in the art will appreciate that relays 410 and 412 can be
replaced by a DPST relay, and so can relays 422 and 424.
-33-
CA 02274184 1999-06-10
The interface circuits 60a and 60b that were described previously with
reference to Figures 7 and 8 automatically disconnect the utility company's
power
lines when on-site power is used. This protects the utility company's power
distribution network and other customers from damage that might be caused by
an
out-of specification or out-of phase on-site power source. It also protects
technicians
who may be working on a segment of the power lines that they have disconnected
from the utility company's substation 20 (see Figure 1 ). A portion of the
utility
company's distribution network that has been disconnected from a substation is
sometimes called an "island" and for safety purposes it is desirable to ensure
that
such as island is not electrified by distributed on-site power sources (unless
the line
technicians have been trained to isolate the segment of the power lines they
are
working on not only from the substation, but also from customers). It would
therefore be desirable to provide an interface circuit with an anti-islanding
feature.
One way to provide such an anti-islanding feature would be for the utility
company to superimpose what will be called an "anti-islanding tone" on its
power
lines. The frequency of the anti-islanding tone should be selected to be
higher than
the power distribution frequency (e.g., 60 Hz) but not a harmonic of the
distribution
frequency. The frequency selected for the anti-islanding tone should be low
enough
that the impedance of the distribution network at the selected frequency does
not
become excessive. If such an anti-islanding tone is superimposed on the power
lines,
the sensor group 456 of the interface circuit 60c that is shown in Figure 9
may
include sensors to detect its presence. Absence of the tone means that there
is a
break in the power lines or a purposeful disconnection between the anti-
islanding
tone source and the interface circuit 60c -- meaning that the circuit 60c is
connected
-34-
CA 02274184 1999-06-10
to an isolated island of the utility's power distribution network -- so the
microprocessor 454 should not permit parallel operation if the anti-islanding
tone
disappears unless the utility company's line technicians have been suitably
trained.
Figure 10 illustrates an interface circuit 60d having a tone detector 518 for
detecting whether a tone is present. The interface circuit 60d includes a leg-
1
conductor 468 which links connectors 116 and 128, a leg-1 conductor 470 which
is
connected to connector 134, and a leg-1 conductor 472 which is connected to
connector 122. A leg-2 conductor 474 links connectors 118 and 130. A leg-2
conductor 476 is connected to connector 132 and another leg-2 conductor, 478,
is
connected to connector 122.
The interface circuit 60d also includes a relay 480 having a solenoid 482 and
a normally closed switch 484; a relay 486 having a solenoid 488 and a normally
open
switch 490; a relay 492 having a solenoid 494 and a normally closed switch
496; and
relay 498 having a solenoid 500 and a normally open switch 502. One end of
each
solenoid is grounded. The other ends of solenoids 482 and 494 are connected to
an
electrically controlled switch 504. The other ends of solenoids 488 and 500
are
connected to an electrically controlled switch 506. The switches 504 and 506
are
also connected to the positive terminal of a rechargeable battery 508, whose
negative
terminal is grounded. A battery charger 510 supplies a charging current to the
battery 508.
One contact of receptacle 162 is connected to the fixed contact of switch 490
by a leg-1 conductor 512, and another contact of the receptacle 162 is
connected to
the fixed contact of switch 502 by a leg-2 conductor 514. The neutral contact
of
receptacle 162 is connected to neutral contact 44 by a conductor 516, which is
-3 5-
CA 02274184 1999-06-10
grounded. The movable contact is switch 490 is connected to the movable
contact of
switch 484, and both are connected to the leg-1 conductor 472. Similarly, the
movable contact of switch 502 is connected to the movable contact of switch
496,
and both are connected to leg-2 conductor 478.
The interface circuit 60d also includes the tone detector 518, which has input
terminals that are connected to the leg-1 and leg-2 conductors 470 and 476.
The tone
detector 518 emits output signals on conductors 520 and 522. The signal on
conductor 520 is conveyed to a control circuit 524 and the signal on conductor
522 is
ultimately conveyed to the controller 330.
The interface circuit 60d cooperates with a tone generator, not illustrated,
that
is coupled to the utility company's power lines. For example, a tone generator
which
provides a 275 Hz sinusoidal output that is capacitively coupled to the leg-1
and leg-
2 ends of the secondary winding of transformer 22 in Figure 1 could be
employed.
The tone detector 518 would also be tuned to 275 Hz. The presence of the 275
Hz
tone at detector 518 means that both the leg-1 power line 26 and the leg-2
power line
28 are operative at least as far as the location of the tone generator.
Consequently,
when the tone can be detected, detector 518 emits an output signal on
conductor 520
and, in response, the control circuit 524 keeps switches 504 and 506 open. As
a
result, normally closed switch 484 connects a leg-1 conductor 472 to the leg-1
conductor 470 and the normally open switch 490 keeps the leg-1 line 512
disconnected. Similarly, the normally closed switch 496 keeps the leg-2
conductor
478 connected to leg-2 conductor 476 while the normally open switch 502 keeps
leg-
2 conductor 514 disconnected. Should the 275 Hz signal disappear, however,
detector 518 emits a signal on conductor 522 which causes controller 330 to
start the
-36-
CA 02274184 1999-06-10
generator 324. It also emits a signal via conductor 520 to control circuit
524, which
then closes switch 504 to actuate relays 480 and 492 and cause switches 484
and 496
to open. Moments later the control circuit 524 also emits a signal to close
switch
506, which actuates relays 486 and 498 so as to close switches 490 and 502.
When
the 275 Hz tone is thereafter detected again by detector 518, meaning that the
power
lines have been restored, relays 486 and 498 are deactuated to disconnect the
on-site
power source 166 and then relays 480 and 492 are deactuated to reconnect the
power
lines to the customer's distribution system. A signal emitted on conductor 522
causes
the controller 330 to shut down the engine which drives generator 324.
It will be understood that the above description of the present invention is
susceptible to various modifications, changes, and adaptations, and the same
are
intended to be comprehended within the meaning and range of equivalents of the
appended claims. Several such modifications, changes, or adaptations will be
specifically mentioned below.
Although the embodiments of an interface circuit that are illustrated in
Figures 7-10 all employ electro-mechanical relays, solid state relays or other
switching arrangements could be employed instead. Similarly, in lieu of the
electrically controllable latching switch assembly 212 that is shown in Figure
7, a
solid state arrangement could be used. Such a solid state arrangement might
include,
for example, a pair of solid state relays.
The embodiments of an interface circuit shown in Figures 7, 9, and 10 may
be located completely within the meter collar, with the possibility of also
locating
one or more components of the interface circuit in the box 142 shown in Figure
3 (in
the embodiment shown in Figure 8, however, it is desirable for the switches
376 and
-3 7-
CA 02274184 1999-06-10
378 to be mounted in the connector assembly 150). In particular, the
switchover
relay 224 and input circuit 254 shown in Figure 7 may be located in box 142,
with
the remaining components being located in the meter collar. However, it is
also
possible to mount the switchover relay 224 and the input circuit 254 in the
meter
collar along with the remaining components of the interface circuit, in which
case the
box 124 can be omitted. The cable 90 would then lead directly to the connector
assembly 150.
The receptacle 162 can be mounted directly on the meter collar, without a
separate connector assembly 150 that is attached to the wall 114, but using
the
connector 150 reduces the mechanical stress that would otherwise be placed on
the
meter collar when the on-site power source is connected or disconnected.
Using a meter collar in conjunction with a interface circuit provides a
convenient and economical way for a customer with a conventional meter and
meter
socket box to connect an on-site power source. That is, the customer's
existing
installation can be retrofit by way of the meter collar so as to accommodate
an on-
site power source. However it is anticipated that, in the future, the private
distribution systems of residential customers or small business customers may
be
designed of ab initio to accommodate an on-site power source. In such a case,
the
interface circuit could be used without the meter collar by placing the
interface
circuit in the customer's meter socket box or circuit breaker box, for
example.
The meter itself has been described as an electro-mechanical meter, but an
ordinarily skilled person would appreciate that an all-electrical meter could
be
employed instead.
-3 8-
