Note: Descriptions are shown in the official language in which they were submitted.
1115785
FIELD OF THE INVENTION
The present invention relates to temperature responsive
power supply apparatus for electrical resistance heating, and is
useful in particular, but not exclusively, for the preheat treat-
ment and stress relief of pipe welds and other welds.
DESCRIPTION OF THE PRIOR ART
In United States Patent 3,851,148, issued November 26,
1974 jointly to Heinz E. Schonert and the present inventor, there
is disclosed a power control apparatus for weld stress relief by -~
I0 means of which temperature signals corresponding to the tempera-
tures at different workpiece zones are employed to actuate switch
means controlling the voltage applied to a saturable reactor. The
saturable reactor, in turn, controls the supply of electrical
power from a power supply transformer to two electrical resistance
heating elements. When the apparatus is inoperation, both of the
heating elements are initially energized to heat upper and lower
portions of apipe. Heated air inthe interior ofthe pipe rises,
- and the uppermost portion of the pipe is therefore subjected to -
greater heating than the lowermost portion of the pipe. By opera-
tion of the saturable reactor, the heating element heating the
uppermost portion ofthe pipe is de-energized, when necessary, while
the heatingofthe lowermost portion of the pipe is maintained by
the other heating element.
The two heating elements are connectedinseries with one
another across a secondary winding of the power supply transformer.
OBJECT OF THE INVENTION
It is an object of the present invention toprovide a
novel and improved power supply apparatus for electrical resist-
ance heating which provides greater flexibility of operation than
has been available hitherto.
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~157~5
BRIEF SUMMARY OF THE INVENTION
According to the present invention, there is provided
power supply apparatus for selectively energizing first and
second electrical resistance heating elements, comprising power
supply transformer means for transforming an electrical supply
current; the power supply transformer means comprising first
and second secondary winding means in series with one another
for delivering electrical power from the power supply trans-
former means; first, second and third conductors for connection .-
to the first and second heating elements; first and second con-
necting means for connecting the first and second conductors .
to respective opposite ends of the secondary winding means; third
connecting means for connecting the third conductor between the
first and second secondary winding means; first and second tem-
perature sensing means for providing first and second temperature ;
signals corresponding to the temperatures of zones heated by ~ ~ :
the first and second heating elements, respectively; first and ~:
second temperature responsive control means for providing power ~-
supply control signals in response to the first and second tem-
perature signals, respectively; first and second control signal
responsive means for varying the current flow through the first
and second connecting means in response to the power supply con-
trol signals; switch means for connecting the first and second :
temperature responsive control means to the first and second
control signal responsive means, respectively, to control the
latter independently of one another, in a first switch posi~ion
and for connecting the first temperature responsive control means :~
to both of the first and second control signal responsive means,
to effect common control of the latter, and disconnecting the
second temperature responsive control means for the second con-
trol signal responsive means in a second switch position; whereby
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111578S
the apparatus can be operated to deliver electrical power in
a first operational mode from both of the secondary winding means
in a single heating circuit, in a second operational mode from
the first and second secondary winding means in two respective
heating circuits and in a third operational mode from one of
the first and second secondary winding means in a single heating
circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more readily understood from
the following description of a preferred embodiment thereof given,
by way of example, with reference to the accompanying drawings,
in which:-
Figure 1 shows a power supply transformer, a pair ofsaturable reactors and three current conductors or leads forming
parts of a temperature responsive power supply apparatus;
Figure 2 shows a circuit diagram of temperature control
and switching means forming part of the same apparatus;
Figures 3 to 5 show heating elements connected for
energization by the apparatus of Figures 1 and 2 in first, second
and third operational modes, respectively, for heating a single
pipe; and
Figure 6 shows heating elements connected for energiza-
tion by the apparatus of Figures 1 and 2 in the second operational
mode for heating two different pipes.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in Figure 1, a power supply transformer, in-
dicated generally by reference numeral 10 has a centre-tapped
secondary winding S. Three electrical conductors lla, llb and
llc are provided for connecting the secondary winding S to heat-
ing elements, as described in greater detail hereinafter.
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1115785
The conductors lla and llc are connected through linked
on-of~ switches 12, ammeter A and saturable reactors, indicated
generally by reference numerals 14 and 15, to opposite terminals
17 and 18 of the transformer secondary winding S.
The on-off switches 12 may be provided as a double pole
circuit breaker incorporating isolator means and overload/short
circuit protection, and it will be appreciated that, while the `
switches 12 are preferably linked for safety reasons, it is al-
ternatively possible to employ separate switches, i.e. switches
which are not linked or otherwise connected together, in which
case when only one of the switches is closed, a voltage would ~-
still exist between the conductor llb and the conductor lla or
llc connected to the closed switch.
Referring now to Figure 2, reference numerals 20a and
20b indicate generally two temperature control devices, and
reference numeral 21 indicates generally a switchlng arrangement `~
for controlling the connection of the temperature control devices
;~ 20a and 20b to the saturable reactors 14 and 15. ~/ -
For convenience, the components of the two temperature
control devices 20a and 20b have been indicated by the same
reference numerals followed, respectively, by the letters "a"
and "b", and only the temperature control device 20a will be
described hereinafter, it being understood that the temperature
contxol device 20b is similar.
The temperature control device 20a comprises a thermo-
couple 22a connected to a temperature control unit 23a.
; The temperature control unit 23a has normally open
contacts C which are closed when power is applied to the tempera-
ture control unit 23a and the temperature sensed by the thermo-
couple 22a is below a predetermined value. A variable trans-
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: . , , . . ~, . :
~1578S
former 24a is provided for applying a variable voltage across
a rectifier bridge indicated generally by reference numeral 25a
on closure of the contacts C.
The temperature control devices 23a and 23b are com-
mercially available temperature controllers, for example those
marketed under Model No. 32103 by Thermo Electric Co. Inc. of
Saddle Brook, New Jersey, and are therefore not described in
greater detail herein. However, it will be understood by those
skilled in the art that such a controller operates by opening
the contacts C when a temperature signal supplied thereto from
its thermocouple reaches the above-mentioned predetermined value,
which can be preset by manual adjustment of the controller.
The circuitry illustrated inFigure 2 isenergized by an
a.c. current supply through supply conductors 26 and 27. The
supply conductor 26 is connected to one endof the variable trans-
former 24a through conductors 28, 29 or 30, the switching ar- ;-~
rangement 21 and conductors 31 and 32.
~ The opposite endofthe variable transformer 24ais con-
nected through conductors 34 and 35 to the othersupply conductor 27.
The temperature control unit 23a is connected to supply
conductor 27 and, via conductors 36, 32 and 31, switching ar-
rangement 21, conductor 29 or 30 and conductor 28, to the supply
conductor 26 for energization of the temperature control unit 23a.
Normally open contacts C of temperature control unit
23a are respectively connected by conductor 38a to one arm of
the rectifier bridge 25a and by conductor 39a, provided with
fuse 40a, to arm 41a of the variable transformer 24a.
The opposite arm of the bridge 25a is connected by
conductor 42 to the supply conductor 27.
The switching arrangement 21 has eight movable contacts
or switches 21a to 21h which are linked for simultaneous actua-
l~S785
tion and which are actuatable into three different positions
to make contact with fixed contacts Cl, C2 and C3. Cl represents
the "off" positions of the contacts 21a to 21h.
Contacts C2 and C3 of the two switches 21~ and 21b
are connected by respective conductors 44 and 45 to the control
terminals 14a and 14b of the saturable reactor I4.
Contacts C3 of the switches 21c and 21d are connected
by conductors 46 and 47 to the control terminals 15a and 15b of
the saturable reactor 15, and contacts C2 of the switches 21d and
21f are connected by respective conductors 48 and 49 to the con-
ductors 46 and 47 and thus, likewise, to the saturable reactor
control terminals 15a and 15b. Switches 21a and 21e are con-
nected, by conductors 50 and 51, and switches 21b and 21f are
connected by conductors 52 and 53, to opposite arms of the `
rectifier bridge 25a.
Swltches 21c and 21d are connected by conductors 54
and 55 to opposite arms of the rectifier bridge 25b.
One arm of the rectifier bridge 25b is connected by
conductor 38b to the normally open contacts C of the temperature
control unit 23b and the opposite arm is connected to conductors
57 and 42 to the supply conductor 27.
Switch 21h is connected by conductor 58 to one end of
saturable reactor 24b, the other end of which is connected to
the conductor 35 and thus to the supply conductor 27. Tem-
perature control unit 23b, for energization thereof upon closure
of switch 21h, is connected by conductors 59 and 60 across con-
ductors 58 and 35.
Referring again to Figure 1, three electrical plug
and socket connectors 16a, 16b and 16c are provided for connect-
ing the conductors lla to llc to the power supply transformer 10,
11~57~35
the connectors 16a and 16c being in series with the on-off :
switches 12 and the connector 16b being connected to a centre-
tapping CT of the transformer secondary winding S.
The conductors lla to llc are in the form of insulated
electrical cables and are provided, at their ends remote from the :~
power supply transformer 10, with terminals l9a, l9b and l9c.
Any two or all three of the conductors lla to llc may .
be utilized at the same time, as required, and due to the pro-
vision of the connectors 16a to 16c, any one of the conductors
lla to llc which is not in use may be readily disconnected and .
stored in a convenient place.
,.~ . . . ~, . . .
Before the operation of the above-described apparatus
is explained, the various ways in which the heating elements may
be connected to the power supply transformer 10 by the conduc-
tors lla to llc will firstly be described with reference to . -
Figures 3 to 6.
It will be understood that the heating elements
:
referred to herein each comprise, in practice, a plurality of
individual electrical resistance heating elements, commonly
referred to as "finger elements", connected in series.
Referring now to Figure 3, which illustrates a first~:
operational mode of the above-described apparatus, a heating
element 60, which comprises a plurality of finger elements con-
nected in series, is provided for heating the upper and lower
portions of a pipe P, the heating element 60 being connected
across the conductors lla and llc, and thus across the entire
transformer secondary winding S.
In this first operational mode, the conductor llb and ~ ~-
the thermocouple 22b are removed. The thermocouple 22a, which
as shown is associated with the upper portion of the pipe P for
:
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1~15785
sensing the temperature at that location, is connected by a dual
lead 21a to terminals 62a and 63a of the temperature control unit
23a. This first operational mode thus provides temperature sen-
sing at a single location.
In Figure 4, which shows a second operational mode,
the heating element 60 again extends around the upper and lower
portions of the pipe P, but in this case the conductor llb is
employed as a common conductor connected between the heating
element 60, at a point midway between the ends of the heating
element 60, and, through connector 16b, the centre-tapping CT
of the transformer secondary winding S. In other words, the
two halves of the heating element 60 are connected across op-
posite halves of the secondary winding S.
Also, both thermocouples 22a and 22b are in use for
sensing the temperatures of the lower and upper portions,
respectively, of the pipe P, i.e. at two separate locations.
In a third operational mode, illustrated in Figure 5, a
heating element61is associated with the upper and lower portions
of a pipe Pl and connected by conductors lla and llb across the
transformer end terminal 17 and the centre-tapping CT, i.e.
across only half of the secondary winding S. The pipe Pl is of
smaller diameter than the pipe P and therefore requires less
electrical power for heating, and thus only half of the secondary
winding S need be utilized in this case. The thermocouple 22b
is again omitted, only the thermocouple 22a being in use.
Figure 6 shows the same mode of operation as Figure 4,
i.e. the second operational mode. ~owever, as shown in Figure 6,
two pipes P2 and P3 are being heated, the heating element 60 in
this case being replaced by heating elements 60a and 60b res-
pectively associated with the two pipes P2 and P3.
111578S
.:
The thermocouples 22a and 22b are in this case res-
pectively associated with the pipes P2 and P3.
As will be apparent, the heating element 60a is con- -~
nected across transformer end terminal 17 and centre-tapping CT,
i.e. across one half of the secondary winding S, and the heating
element 60b is connected across the transformer end terminal 18
and the centre-tapping CT, i.e. across the other half of the
secondary winding S.
It will also be apparent that, in the second opera-
10 tional mode illustrated in Figure 6, the conductor llb again ~
serves as a common conductor in which the currents through the -
heating elements are balanced.
The operation of the temperature control devices il-
lustrated in Figure 2 will now be described.
As explained above, each of the switches 21a to 21h
has three possible positions, corresponding to its respective `
fixed contacts Cl, C2 and C3, and the fixed contacts Cl represent
the "off" position of the switching arrangement 21, in which
the temperature control devices 20a and 20b are disconnected
20 ~ from the saturable reactors 14 and 15 from the current supply
conductor 26.
When the switches 21a to 21h are in the positions
shown in Figure 2, in which they make contact with fixed con-
tacts C2, the bridge rectifier 25a of temperature control device
20a is connected, via switches 21a, 21b, to the control ter-
minals 14a, 14b of the saturable reactor 14.
The rectifier bridge 25a is also connected, via
switches 21e, 21f, to the terminals 15a, 15b of the saturable
reactor 15.
Thus, with the switching arrangement 21 in a first
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11~57~5
closed condition, i.e. with the switches 21a to 21h contacting
the fixed contacts C2, the temperature control device 20a con-
trols both of the saturable reactors 14 and 15.
Electrical current is supplied through movable switch
contact 21g to the temperature control device 20a. ;
Current supply to the temperature control device 20b
is interrupted by the open movable switch contact 21h, and the
conductors 54 and 55 of the associated recitifer bridge 25b are
connected to the open movable switch contacts 21c and 21d.
The switching condition which has just been described
is employed when only the thermocouple 22a ia in use, as shown
in Figure 3 or 5, in which case the thermocouple 22b and its
lead 21b may be disconnected from the temperature control unit
23b and placed in storage.
When, for example, the heating element 60 is connected
as shown in Figures 3 or 5, the switches 21a to 21h are in en-
gagement with the fixed contacts C2, so that the temperature con-
trol unit 23a is controlling both saturable reactors 14 and 15
and the thermocouple 22b is not in use; and the switches 12 are
20 closed to energize this heating element, the temperature of the -
pipe P or Pl will rise. ;
When the temperature sensed by the thermocouple 22
rises to a predetermined value, the temperature con~rol unit
23a responds by opening its closed contacts C to interrupt
a control voltage applied to the rectifier bridge 25a and thus
to interrupt the d.c. voltage applied by the latter across the
control terminals of the saturable reactors 14 and 15. Conse-
quently, the a.c. windings of the saturable reactors develop a
high impedance and the current supply to the heating element 60
is reduced.
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~11578S
When it is desired to employ both thermocouples 22a
and 22b for independent operation of the saturable reactors 14
and 15, for example in the second operational mode illustrated
in Figures 4 and 6, the switching arrangement 21 is actuated so
that the switches 21a to 22h are moved to the fixed contacts C3.
The bridge rectifier 25a of the temperature control
device 20a is then again connected, by the closed switches 21a
and 21b, to the terminals 14a, 14b of the saturable reactor,
but the switches 21e and 21f are now open, so that the bridge
rectifier 25a is no longer connected to the saturable reactor
15.
The temperature control devices 20a and 20b are both
energized via the closed switches 21g and 21h.
The bridge rectifier 25b is, in this case, connected
to the terMinals 15a, 15b of the saturable reactor 15 via the
closed switches 21g, 21h.
Thus, the two temperature control devices 20a and 20b
are in this case connected for independently controlling the
saturable reactors 14 and 15, respectively, and thus for in-
dependently controlling the current flow through the conductorslla and llc.
The temperatures at which the saturable reactors 14
and 15 are operated can be varied by adjustment of the tem-
perature control units 23a and 23b to vary the temperatures at
which the normally closed contacts C are opened.
By adjustment of the variable transformers 24a, 24b,
the magnitudes of the d.c. control voltages applied by the
rectifier bridges 25a, 25b to the saturable reactors 14, 15 can
be infinitely varied to adapt the apparatus to a wide range of -
pipe diameters and heating element sizes, i.e. numbers of finger
. .
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11~ÇL5785
elements.
An important advantage of the above-described apparatus -
is its ability to control the heating of two pipes of different
diameters by passing different currents through two heating
elements respectively associated with the two pipes, as illustra-
ted in Figure 6. In this case, the common conductor 116 carries
the out of balance current difference between the two heating
elements.
Furthermore, the present apparatus is extremely
versatile in enabling various sizes of pipes and weld~ to be
heat treated, with simultaneous or staggered heating of the
various pipes and/or heating of some pipes while others are
cooled, which allows the apparatus to be utilized to maximum
advantage in any given situation.
If required, for example in the case of a large dia-
meter pipe, the apparatus may be employed for simultaneously
heating different sections or zones of the pipe, the thermo-
couples being respectively associated with the pipe sections or
zones.
As will be readily apparent to those skilled in the
art, various modifications may be made in the above-described
apparatus within the scope of the invention as defined by the
following claims. For example, instead of the saturable reactors
14, 15, thyristors triac assemblies or other solid state means
may be employed as current controllers.
Also, the temperature control units 23a, 23b, instead
of being the temperature controIlers described above, may com-
prise programmers for varying the predetermined temperatures, at
which the contacts C open, in accordance with predetermined pro-
grams. In this way, the temperature signals supplied by the
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~15785
thermocouples are compared with signals which are generated
within the programmers and which vary with time, thus causing
the temperature variations of the pipes being heated to occur in
accordance with the programs preset in the programmers. A com-
mercially available programmer which is suitable for this purpose
is Digital Control Programmer DCP7700 sold by Honeywell Corpora-
tion of Fort Washington, Pa.
