Note: Descriptions are shown in the official language in which they were submitted.
CA 03059517 2019-10-09
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ELECTRICAL POWER TRANSMISSION
This invention relates to an electrical power transmission network
designed to compensate for the power factor which arises due to reactive loads
on
the network and to a load control device to be used at subscriber premises on
the
network.
BACKGROUND OF THE INVENTION
The most challenging problems power systems face today are; power
factor control, transformer load imbalance, and nonlinear loads, adding to
transformer
imbalance and inject disruptive harmonic currents into the system. All of
these
problems erode the efficiency and stability of the power system, in some cases
over
40% of power is lost en route to the customer.
Power system compensation is presently done from the top down, high
voltage and high power correction equipment is installed at distribution
substations.
This can include static or switched capacitor banks and/or switched reactors
for power
factor or voltage correction, universal power flow controllers to balance
loads and
control bus voltages. These devices can address some of the challenges but,
the
costs are significant and the solutions are less than optimal. They require a
large
investment in engineering, custom equipment, infrastructure to mount
equipment,
have a low fault tolerance and require maintenance.
SUMMARY OF THE INVENTION
According to the invention there is provided a load control device for
use in an electrical power transmission network where the network comprises:
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a plurality of subscriber premises for receiving electrical power from a
power supply system;
where the power supply system has a natural time constant of the
response time of the power supply system;
each subscriber premises including a plurality of user devices on a
power supply circuit;
transmission lines supplying electrical power from the power supply
system with each of the subscriber premises having a drop from one of the
transmission lines to a power supply inlet;
the load control device being arranged for controlling the power
supplied from the power supply inlet to the user devices on the power supply
circuit,
the load control device comprising:
a sensing system for detecting variations in power load caused
by switching on or off of a load caused by one of said user devices;
and an arrangement for creating soft load changes arranged
whereby:
when a load is switched on, instead of the full load power being
supplied by the power system, power is supplied by a power supply component at
the
subscriber premises for a short time and this power supplied is reduced over a
time
period substantially matching or greater than said natural time constant of
the power
supply system;
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and when a load is switched off, instead of the full load power being
released, it is used to charge the power supply component for a short time and
this
charging is reduced over a time period again substantially matching or greater
than
said natural time constant of the power supply system.
Preferably the power is supplied by the power supply component
though a current inverter.
Preferably the current inverter comprises one or more half bridges.
Preferably the power is supplied by the power supply component
drawn from the component through a half bridge 357 onto a DC bus and charges a
lo DC link capacitor where this charge is then immediately inverted out onto
power
supply BUSes via half bridges.
According to a second aspect of the invention there is provided a load
control device for use in an electrical power transmission network where the
network
comprises:
a plurality of subscriber premises for receiving electrical power from a
power supply system;
each subscriber premises including a plurality of user devices on a
power supply circuit;
transmission lines supplying electrical power from the power supply
system with each of the subscriber premises having a drop from one of the
transmission lines to a power supply inlet;
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the load control device being arranged for controlling the power
supplied from the power supply inlet to the user devices on the power supply
circuit,
the load control device comprising an arrangement for balancing loads
between a first phase on a first BUS and a second phase on a second BUS by
calculating a required correction current by adding load currents from the
first and
second phases which are then divided by the number of phases to determine the
load
current needed in each to be balanced where the differences between this
average
and the actual current in each phase determines a balancing correction current
order.
Preferably the current orders cause the first BUS to draw current from
the system side while the second BUS is caused to deliver an equal and
opposite
current to the load side.
Preferably the current is absorbed by the first BUS and is delivered to
the second BUS hence balancing out the currents as viewed by the system or
utility
side.
Preferably the current flows to the first BUS through a first half bridge
charging a DC link capacitor which is discharged through a second half bridge
onto
the second BUS.
Preferably the sensing system comprises a meter generating data
relating to the standard true RMS values of voltage, current and Real Power.
These
values can then be used by the control system to calculate the power factor to
generate a value of a required capacitive load to improve the power factor.
CA 03059517 2019-10-09
The power factor can where possible be improved to the maximum
unity power factor so that only real power is flowing in the system. However
in some
cases it is necessary to apply a load which provides an improvement without
reaching
the theoretically optimum situation. Either the system is at maximum
compensation
5 or the system is configured to improve transformer imbalance.
Transformer imbalance is a result of unsymmetrical loading of each
phase of a typical three phase system. By compensating the capacitive load of
each
phase independently improvements to transformer imbalance can be made. While a
less than optimal solution to both power factor and load imbalance will result
using
just capacitor compensation the overall operation efficiency may be a best
solution
with available resources. The present invention in its simplest form is
passive
capacitive compensation for one phase only. More control of load imbalance can
be
made with the addition of reactive compensation components and multiphase
implementation of the control, where current imbalances can be redirected
within the
control to balance phase currents. These improvements come with a price in
complexity and costs. The addition of distributed solar/wind generation can
aid in the
imbalance issues by sourcing this power to heavily loaded phases.
In some cases the system can be used to correct the waveform of the
power supply to remove distortions caused by noise, improving power quality.
Such
noise can arise from many different user devices which do not provide linear
power
use. In order to correct for the noise and thus better balance the waveform of
the
power supply, the sensing system generates data relating to FFT spectra of the
power
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supply waveform. The control system then uses the data from the FFT analysis
to
provide a correction signal at a rate significantly greater than the frequency
of the
power supply waveform. That is the sensing system can be used from this
analysis
to generate data relating Total Harmonic Distortion (THD).
A reference current waveform is in phase with the voltage wave and is
sinusoidal. The error signal is built up of the results from the FFT spectra
of the load
current. The fundamental current frequency components are removed since no
compensation is necessary. All other frequency components reduce the power
quality
and make up the error signal. The reference signal minus the error signal
provides
correction pulses to an Active Power Factor Control (APFC). The APFC shapes
the
incoming current into sinusoidal waves removing the power noise and improving
power quality.
The APFC produces a DC current to charge a local capacitor to a high
voltage. This energy can be re-inverted back into the system using a power
inverter,
bled away, or can be another energy source for local solar / wind generation
systems.
It should be mentioned this system does nothing for the power quality within
the
premises. The power quality is improved as viewed from the system side and
limits
noise from effecting premises nearby. The present invention can be used to
reduce
noise of problem loads within a premises, such as variable speed drives in
industrial
zo settings. Where the control is installed to monitor and compensate a
specific load or
group of loads.
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Preferably the sensing system comprises a first meter generating data
at the drop and a second meter generating data downstream of the power
correction
system. Both meters provide the same parameters obtained from the power supply
so that the data can be compared. For example, the control system can be used
to
compare the output data from the second meter with the output data from the
first
meter to determine a level of improvement in the power factor obtained by the
power
correction system. This comparison provides a self-accounting function where
the
level of ongoing improvement in the power factor can be monitored. This value
can
be used if required in a calculation of a rebate to the customer for that
improvement
and can be used to monitor over a set of premises on a particular transmission
line
where and how improvements are being made at the premises level which can be
compared with improvements detected at the macro level at the relevant
transformer.
That is the load control device is arranged to communicate using the
communication
system data relating to the improvement to the network control system. In
addition
the load control device can be arranged to communicate data relating to the
Real
power to the network control system. This provides data to the network
management
system of the operation of the system and the premises allowing better control
of the
network at the supply end.
Typically the power correction system comprises static or switched
capacitor banks. These banks can be switched in and out as required by the
control
system to provide a value of capacitive load to manage the power factor. For
example
a binary system can be employed using a number n of capacitors each twice the
value
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of the previous to provide up to 2^n different values for close management of
the
capacitive load. Finer power factor control can be achieved with a switched
reactor in
parallel with the capacitor bank. Adjusting the firing angle on the reactor,
an infinite
resolution of current can be achieved from its maximum current rating to zero.
This
enables the system to track the power factor very accurately.
In addition to the control of the capacitive load, it is also possible in
some cases to provide in the power correction system an Active Power Factor
Control
(APFC). This is a known arrangement which can be switched at high rate to
filter out
the noise and Total Harmonic Distortion detected by the FFT analysis. The
switch,
which can be operated at high rate of multiple times per cycle, connects in
and out of
the circuit an inductor which therefore changes the input current draw in a
manner to
smooth out the effects generated by the noise from the user devices. The
switch is
thus operated in response to the error signal derived from FFT analysis of the
waveform of the power supply for current correction. This system draws energy
from
the system which can be bled away with a resistor, be another energy source
for local
solar/wind generation, or be the source for a local power inverter. Ideally
this should
be coupled with a local solar / wind generator since these systems already
have an
integrated power inverter saving installation costs. Wasting this energy
through a
bleeding resistor is only convenient if the losses are minimal and doesn't
warrant the
additional costs of a power inverter.
In addition the load control device can include a system for
disconnecting from the power supply circuit within the user premises certain
ones of
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the user devices for load shedding. This is typically carried out by a switch
on one or
more of the drop cables of the circuit to disconnect high load items such as
heating
and cooling systems.
The control system can also be programmable to change the response
to variations detected by the sensing system. That is the control system can
use
adaptive intelligence to change the output controlling the power correction
system in
response to detected variations depending on different circumstances. Such
change
of the output might use time of day or the input voltage or power factor as
parameters
_
in the programming. The system operates to maintaining a power factor or
voltage at
a point or a weighted combination of several parameters to meet a required
condition.
In addition, the control system can be programmable by data received
by the communication system from the network control system. That is the
network
control system may communicate to the individual control systems of the load
control
devices instructions which depend on the state of the network as detected at
the head
end of the network. This instruction may be to control the components
particularly
the power correction system in a manner different from that which would be
used by
the system in the absence of information from the network control. Thus
voltages
and load shedding can be controlled centrally by instructions from the
network. In this
way an interactive communication system can be set up where the communication
system operated bi-directionally to supply information to the network control
system
and to receive instructions obtained from the network either as a result of
that
information or from other data obtained conventionally from the network.
CA 03059517 2019-10-09
Typically the communication protocol is not set up to require high
speed communication of complex instructions in real time to the multitude of
subscriber premises but instead the system typically will be adaptive to
generate
programming over time which changes in response to detected data. Thus the
central
5 network control can communicated programs to the load control devices
over time
which are implemented on a real time basis depending on data detected locally.
However high speed communication techniques can be used to manage the system
in real time. The communication system can be setup to provide a synchronizing
pulse periodically to controls in the field. This enables the system to take a
global
10 snap shot of measures throughout the system enabling better tracking of
power and
accessing of system stability.
As is well known the voltage on the transmission line can vary
depending on the distance from the head end and also it is known that the
voltage
can be managed by reactive loads particularly capacitive loads applied to the
transmission line at various positions along the line. Using this knowledge,
the control
system at all or some of the individual premises can be operated to change
voltage
at the respective drop in response to data provided by or communicated by the
network control system. That is the local control system can be used to add
capacitive
load or to shed loads in response to data from the network control system. In
this
way instability in the network can be detected early by data from the local
load control
devices and can be better managed by operating the local load control devices
to
take steps to ameliorate the stability problems. For example a voltage profile
along
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the transmission line can be managed in this way. The network control system
can
arrange the individual premises control systems to react to system events in
order to
maintain stability. Much like cruise control setting the voltage and turning
loads on or
off to keep the voltage measure constant. This method has a net effect of
leveling the
voltage graduation along a transmission line such that the overall voltage
drop across
a line is reduced.
Power systems are beginning to employ variable voltage transformers
to manage overall power usage of systems during peak periods. By lowering the
system voltage, loads draw less current which means less overall power is
delivered
making the most of available resources. Variable voltage transformer
efficiencies are
increased by the ability of the arrangement herein to minimize the overall
drop of a
distribution line, thus allowing greater voltage drops while still maintain
rated voltage
tolerances within each premises.
The network herein also can be used to control a power supply system,
such as solar power stored in battery banks, at the subscriber premises for
adding
power to the power at the premises. That is the control system can be arranged
to
control the capacitor banks, any load shedding and any power added by the
power
supply system in response to the detected variations. The local variations can
be
used in conjunction with data communicated from the network control system to
control these components to better manage the network.
According to a second aspect of the invention there is provided a load
control device for use in individual subscriber premises of an electrical
power
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transmission network comprising a plurality of subscriber premises for
receiving
electrical power, each including a plurality of user devices on a power supply
circuit,
at least some of which cause power factor variations when operated;
transmission
lines supplying electrical power; and a network control system for controlling
the
supply of power on the transmission lines where each of the subscriber
premises has
a drop from one of the transmission lines to a power supply inlet;
the load control device being arranged for connection to a respective
one of the power supply inlets for controlling the power supplied from the
power
supply inlet to the user devices on the power supply circuit,
the load control device comprising:
a sensing system for detecting variations in power factor caused
by the user devices;
a power correction system for applying a capacitive load to the
power supplied by the drop to the subscriber premises;
a control system for controlling the power correction system in
response to variations detected;
and a communication system for communicating between the
load control device and the network control system.
The load control device can be arranged to provide any one or more of
the above stated features of the network.
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The arrangement as described herein therefore uses a bottom up
approach to power system compensation and monitoring. Instead of one large
installation, many thousands of small units are distributed across a system,
ideally at
individual power services or loads. Point of load compensation (PLC) is the
optimal
s
placement to minimize losses and maximize system stability. Several design
factors
contribute to dramatically reduce costs when compared with top down solutions.
Designing compensation equipment for the low voltage side reduces
component costs, increases reliability and component availability.
Installation costs
are minimal using well established models from the telecommunications
industry.
Typical distances from substation to load are many kilometers and the
top down compensation has limited effect on these transmission lines.
Installing
compensation closer to loads and finer resolution of compensation reduce
losses
even further and increases system stability and flexibility.
Deployment of these devices at the point of load gives rise to a natural
communication network, the power system voltages, currents, and phasors
themselves. A global communication network is provided for overall system
control
and synchronization. But in the absence of global communication, individual
units
operate as a reflexive type of control, monitoring the power system's line
values and
reacting to changes with best operating practices. By providing a much faster
response to disturbances than a traditional system, both system stability and
availability is increased. This network of power monitors and compensators
gives a
unique insight into the workings of each installation. Using this information,
self-
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organizing and learning algorithms extract best operating practices for each
individual
system. This information can aid in almost every aspect of power system
management including power theft. Current trends are pushing towards a
distributed
generation model with the advent of small scale solar and wind generation. The
distributed generation model presents many challenges to current supervisory
control
and Data Acquisition (SCADA) systems, based on a centralized control ideology.
The
present unit can easily integrate the distributed generation model into the
system and
use them as active elements in power generation, system control and
compensation.
One form of the present invention includes two metering points: one at
the system side and one at the load side. Power compensation modules are
installed
between these two metering points. This unique scheme allows the effects of
compensation to be measured and quantified, and forms the basis for
performance
contract accounting. Meter outputs from the load side (and/or system side) can
be
used as feedback by active compensation modules. This allows modules to
nullify or
reduce noise generated from problematic SMPS, CFL, LED lighting and similar
nonlinear loads. Outputs from the system side meter show the results of such
efforts.
Each metering point is capable of measuring the standard true RMS values of
voltage,
current, Real Power, as well as accurately determining power factor, FFT
spectra,
Total Harmonic Distortion (THD), and many more. These meters are field
updatable
and under software control so that they may be programmed, tuned or focused on
important aspects of the data to aid in control or monitoring tasks.
CA 03059517 2019-10-09
The dual meter structure enables compensation of visible loads and
conditions avoiding any opportunity of over compensation. And hence any
possibility
of instability created by the compensation actions of the device. The device
is
inherently stable by design and can only provide compensation or actions that
will
s improve system stability. This is all done without the need of
communication with any
other device, power network control, etc. This has a profound effect on
network
security. Where disruption of the power network by commanding (potentially
millions
of) these devices to do system harm is impossible!
Using a current inverter as the compensation element dramatically
10 improves the flexibility and stability of the present invention. A
current inverter
measures current injected and system voltage as feedback to control the amount
of
current injected and the position of this current with respect to the system
voltage.
With the current inverter or Universal compensator any passive element or
combination of (capacitor, resistor, inductor, and negative resistor) can be
15 implemented with software using this structure. Current injection
feedback control
avoids any resonant interaction with external system components highlighting
its
inherent stable characteristic. Structures are built from half bridges which
interface
DC link bus(es) with AC systems or renewable energy sources. Current Inverters
can
be constructed with half bridges to interface to any number of AC phases or
renewable energy sources (as shown in fig 5). At a minimum only one half
bridge is
required to interface a renewable energy source such as solar, wind or battery
with a
DC link bus. This structure has a natural modular design topology, where
additions to
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the compensator can be made as needed. Multiple half bridges can be assembled
in
parallel to service an AC phase or energy source to increase current transfer
capability and reduce operation noise through interleaving techniques.
Current Injection compensation uses a two meter structure with the
compensation injected in-between these two meters points. When power flows
from
the system to the service side compensation action is determined by the
service
meter. Injection of correction currents, enables the entire service side to
appear from
the systems side as a resistive load (PF=1). The harmonic cleansing and power
factor
correction has a great benefit to the system. Stability margin is dramatically
increased
3.0 and systems with older relaying equipment benefit by removing undetectable
harmonics. As local renewable energy sources are added to the service side,
energy
will flow both to the system and service loads. With the present two meter
structure
and injecting the renewable energy again in-between these two metering points
the
flow of this energy can be metered and conditioned using the current injection
inverter
used for compensation.
The system acts as a universal compensator in that the dual meter
structure is particularly useful in this instance to enable reverse flow of
power.
Connecting a renewable source such as solar panels, wind generators, and
batteries
at the point of compensation between the two meter structure using a generic
half
bridge. This enables the inverter to not only compensate for VARs but inject
real
power from these renewable sources and add the required VAR compensation to
these sources before they are injected into the system. The dual meter enables
the
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tracking of this real power, the quantity and where it is delivered whether to
the
system, service or both. This is an important distinction from current systems
available where power delivered is measured but without tracking and VAR
compensation. And if VAR compensation is provided, a communication network is
s necessary to provide the Power and VAR orders. However in the present
invention
communication is not required for the device to provide VAR compensation and
maintain system stability.
The inverter can be configured as a single phase, bi-phase, three
phase delta or Y connected inverter, or most any poly-phase arrangement can be
3.0 accommodated. If more than one phase is compensated the Inverter
can also balance
out the phase currents as a part of compensation, without external
communication.
The net effect of a multiphase compensator is the power is balanced with a
unity
power factor and the harmonics are scrubbed from the system. This load is now
viewed from the distribution transformer as an ideal balanced resistive load.
15 The system provides distributed compensation in that SMPS and CFL
devices, especially low wattage ones, tend by design to concentrate the drawn
current
at the voltage peaks. The spike of current is very narrow and large in
magnitude,
resembling an impulse function. This creates a large number of high current
harmonics injected into the system. Further, multiple devices function to
increase this
20 peak amplitude independent of manufacturer and is an industry design
practice for
minimal cost. These types of loads may saturate compensation devices. The
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distributed compensation described herein enables multiple units in the wiring
path to
aid in the compensation of these loads.
Where, some attached devices may require more compensation than
available at the point of load. Now all devices on a wiring path can
contribute to this
compensation.
The distributed compensation for VARs, Harmonic Distortion, Real
Power, if a renewable power source is locally available, can take the form of
devices
installed along wiring paths to compensate for hardwired loads and renewables
attached to these devices. Compensators built into outlets can replace
standard
outlets with added features for load shedding and demand side management of
attached loads. Communications between these devices enable management of
black out and reassertion where priority loads are reinstated first and as
more power
sources become available more loads are reinstated. Priorities can be hard
set, by
location, or digital identification tags attached to the pluggable loads such
as
refrigerators to set priority wherever they are plugged-in. Communication is
not strictly
necessary to perform the compensation functions, but is required to implement
prioritized load reinstatement.
The arrangement disclosed herein provides the following unique
features and advantages:
1) Dual meter
structure: allows power flow reversal and accounting.
2)
Distributed compensation placement improves performance and
overall efficiency.
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3) It can be used to remove the need for PFC circuitry to be included
within consumer devices, saving costs to manufacture, the environment, time to
market, and the consumer. Power network infrastructures are expected to last
decades if not centuries. Whereas, consumer products have an average life of 3-
5
s years. If the current device circuitry is built within the power network
it becomes
adaptable and more resilient, reducing or eliminating the need for such
circuitry to be
included within consumer devices. This action can have a major impact on
society
and the environment.
4) It enables more useful power to be delivered through individual
io breaker circuits without tripping breakers or violating electrical
codes. This can be
very significant in older neighbourhoods where the electrical distribution
network has
lower capability. Typical homes in these neighbourhoods have service sizes in
the 40
to 80 Amp range. This may not be enough current to run modern appliances such
as
air conditioners which have low power factors. By employing the present
is compensation methods another 20 to 30% of power would become available
to help
satisfy these added loads. This can be achieved without affecting the local
distribution
network in an adverse way, but indeed improve its operation, stability, and
maximize
power sales for the utility.
The arrangement herein can take many forms including a panel at the
20 service entrance, as described in detail hereinafter. However it can
also be provided
as a black box along the individual wiring paths. In this form it can be used
to replace
outlets or can be moulded within power cords.
CA 03059517 2019-10-09
The arrangement herein can be used with a system for dual phase
services. In this case, the outlets along wiring paths with both phases can
now select
which phase will be used to source loads in order to improve phase balance in
a
natural and transparent way.
5 Further, if a SMPS load is identified as the load and can
operate more
efficiently at 240V as opposed to 120V it can be sourced with 240V again in a
natural
and transparent way. Most Voltage adaptors available today are of universal
voltage
construction which can be sourced by 90 to 260 VAC and compatible with
worldwide
markets. The downside is the lower the source voltage, the lower the overall
efficiency
io of the adaptor. Where, this new adaptation would allow these loads to
operate at peak
design efficiency even in 120 VAC environments.
One of the largest problems facing power systems today is the how to
accommodate a large number of distributed renewable energy sources close to
load
centers. In some areas these distributed sources are larger than the power
systems
is grid tie connection. The problem arises when the system suffers a power
outage. How
do you reinstate literally thousands of generators (distributed renewable
energy
sources) and thousands of loads in an orderly and stable fashion?
Traditionally, the
grid tie is the strongest or only source, after a power outage. The system is
restarted
but has to start under load of any load that was on before the power outage.
This can
zo add up to a significant load size. One of which in the near future will
be beyond the
grid ties capability and in this situation current methods will not work. A
solution using
the present invention is possible. By detecting grid instability and opening
the inlet
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supply switch 17, the local system can be isolated from the grid. Using the
available
renewable energy sources and removing any non-priority loads this isolated
system
can continue to operate. After the grid tie connection is reestablished and
stable then
the local system can resynchronize with the grid and reassert switch 17,
connecting
the local with the greater grid once more. Demand side management is an
important
function of modern power system design and is an integral part of solving this
most
difficult power system management problem. The present invention can perform
demand side management with load priority. Where the most important loads are
serviced first and as more power becomes available further loads are
reinitialized.
io Demand side management can aid in reducing the number of power outages or
brownouts by removing non-priority loads when detecting signs of a weak grid
(voltage droop, line frequency droop, etc) or being instructed by the network
to do so.
Sequencing and prioritizing of attached loads. This has a profound
effect on current power systems during reinstating a power outage. With higher
and
is higher levels of distributed generation sources expected in power systems,
coordinating and synchronizing these many sources becomes increasingly
difficult.
Especially in systems dominated by distributed sources where the grid tie is
weak
and cannot be used as a synchronizing source. Where in the present scheme,
loads
are removed leaving only the highest priority ones, this makes the load side
weak and
20 allow the grid tie to function as the synchronizing source for the
distributed sources.
As more sources become available more loads in the priority structure are
reinstated.
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Again, this provides a natural and transparent way of solving a very difficult
power
network problem. And further can be done with little or no communication.
The arrangement herein can also be used for creating soft load
changes. When electrical loads are turned on and off they represent a
discontinuous
change to the power system. These sharp changes have many negative effects on
the system and in particular the magnetic forces on movable components within
loads
including generators, transformers, and transmission lines. These magnetic
forces
exert mechanical forces on the components in this equipment that can shorten
their
service life, cause instability, and cause failures.
Since loads change instantaneously these magnetic forces can be
significant since this force is proportional to the derivative of change.
Governors for
generators are typically over excited to improve their response. But the
effect
obtained is limited by the ability of the prime mover to change speed and
input power.
The difference between what the system wants and what the prime mover is
currently
is
delivering causes torsion forces and stress on the equipment, with the larger
the
change the larger the force. All of these motor generator systems have a
natural time
constant which is a value known to the system. If a rate of change of the load
can be
kept above this natural time constant, minimum force is exerted on the
equipment.
Typical systems use a combination of high gain governors and high speed
control
communication networks to maintain stability and load response. With typical
times
of communication in the several millisecond range, this adds significant costs
and
potential reliability issues to power systems.
CA 03059517 2019-10-09
23
According therefore to a further aspect of the invention there is
provided a load control device for use in an electrical power transmission
network
where the network comprises:
a plurality of subscriber premises for receiving electrical power from a
s power supply system;
where the power supply system has a natural time constant of the
response time of the power supply system;
each subscriber premises including a plurality of user devices on a
power supply circuit;
transmission lines supplying electrical power from the power supply
system with each of the subscriber premises having a drop from one of the
transmission lines to a power supply inlet;
the load control device being arranged for controlling the power
supplied from the power supply inlet to the user devices on the power supply
circuit,
the load control device comprising:
a sensing system for detecting variations in power load caused
by switching on or off of a load caused by one of said user devices;
and an arrangement for creating soft load changes arranged
whereby:
when a load is switched on, instead of the full load power being
supplied by the power system, power is supplied by a power supply component at
the
subscriber premises for a short time and this power supplied is reduced over a
time
CA 03059517 2019-10-09
24
period substantially matching or greater than said natural time constant of
the power
supply system;
and when a load is switched off, instead of the full load power being
released, it is used to charge the power supply component for a short time and
this
charging is reduced over a time period again substantially matching or greater
than
said natural time constant of the power supply system.
Preferably the power is supplied by the power supply component
though a current inverter.
Preferably the current inverter comprises one or more half bridges.
Preferably the power is supplied by the power supply component
drawn from the component through a half bridge 357 onto a DC bus and charges a
DC link capacitor where this charge is then immediately inverted out onto
power
supply BUSes via half bridges.
Thus the present invention can be used to remove these sharp load
changes as seen by the power system.
The system can use the same configuration as shown and described
herein of half bridges, one for each controlled phase and one for the neutral
line. In
addition, one half bridge is provided controlling an attached small
rechargeable
battery or other power supply storage and supply device such as a
supercapacitor
acting as a supplementary power supply. However other arrangements of
controlling
the supply of power from the storage device can be used.
CA 03059517 2019-10-09
The battery, if used, can be of any size but typically a very small battery
can be used which only needs to be about 30Whr, such as a typical battery used
on
a rechargeable drill.. Then when a load is switched on, instead of the full
load power
being supplied by the power system, it is supplied by this battery for a short
time and
5 this power supplied is reduced over a short period matching or greater
than the natural
time constant of the power systems response time. Similarly when a load is
switched
off, instead of the full load power being released, it is used to charge the
battery for a
short time and this charging is reduced over this period again matching or
greater
than the natural time constant of the power system. The profile of the load
change as
10 seen by the power system can be tailored in software. If all loads or
services use this
device the system as a whole will have a longer service life, stability margin
will
increase, and reduce the need of' high speed control communications networks.
The natural time constant of a motor or power generator machinery,
the time it takes for this combination to change the output power to match the
power
15 of the loads attached, which happens continuously as power is supplied
and the load
changes. As an example a steam turbine and generator has a time constant to
change
the active output power. Where it takes time to physically open or close steam
valves
and time to adjust generator settings to provide the requested active power
and once
again bring the overall system into equilibrium (power output = power
consumed). If
20 the active power of loads is constrained by the system to change at a
rate slower than
this time constant then there is never a mismatch (or a very insignificant
one) between
CA 03059517 2019-10-09
26
power output and power consumed. Each motor/generator set has a time constant
and a characteristic transfer curve where most are typically exponential in
nature.
With distributed generation in the form of Solar or Wind and the power
electronics used in these devices the power transfer curves may be quite
varied. With
the present invention this load transition curve is software programmable to
match
any as required by the attached motor / generation equipment. The change in
the
load seen by the power supply system can be controlled to provide any selected
transition shape in the power requirement including a simple linear ramp or
more
complex.
The system herein can also be used for active load balancing between
phases. With the present system, given more than one phase, loads between the
various phases can be balanced. The load currents from the different phases
are
added then divided by the number of phases to determine the load current
needed in
each to be balanced. The differences between this average and the actual
current in
each phase determines the balancing correction current order. It is important
to note
this function has little cost impact on the system. The system now can provide
total
power quality control in other words every load appears to be a balanced
resistive
load no matter its makeup.
According to a further aspect of the invention there is provided a load
control device for use in an electrical power transmission network where the
network
comprises:
CA 03059517 2019-10-09
27
a plurality of subscriber premises for receiving electrical power from a
power supply system;
each subscriber premises including a plurality of user devices on a
power supply circuit;
transmission lines supplying electrical power from the power supply
system with each of the subscriber premises having a drop from one of the
transmission lines to a power supply inlet;
the load control device being arranged for controlling the power
supplied from the power supply inlet to the user devices on the power supply
circuit,
the load control device comprising an arrangement for balancing loads
between a first phase on a first BUS and a second phase on a second BUS by
calculating a required correction current by adding load currents from the
first and
second phases which are then divided by the number of phases to determine the
load
current needed in each to be balanced where the differences between this
average
and the actual current in each phase determines a balancing correction current
order.
Preferably the current orders cause the first BUS to draw current from
the system side while the second BUS is caused to deliver an equal and
opposite
current to the load side.
Preferably current is absorbed by the first BUS and is delivered to the
second BUS hence balancing out the currents as viewed by the system or utility
side.
CA 03059517 2019-10-09
28
Preferably current flows to the first BUS through a first half bridge
charging a DC link capacitor which is discharged through a second half bridge
onto
the second BUS.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is a schematic illustration of a power network according to the
present invention.
Figure 2 is a schematic illustration of the power correction circuit of
Figure 1.
Figure 3 is a schematic illustration of a power network according to the
present invention similar to that of Figure 1 but including further features.
Figure 4 is a schematic illustration of the power correction circuit of
Figure 3.
Figure 5 is a schematic illustration of a half bridge to be used in the
arrangement of Figures 3 and 4.
Figure 6 is a schematic illustration of a power network similar to that of
figure 1 showing an arrangement where the compensators are built into the
outlets.
Figure 7 is a schematic illustration of the power correction circuit of
Figure 4 modified to show active load balancing between phases.
CA 03059517 2019-10-09
29
Figure 8 is a schematic illustration of the switching of a load and the
operation of the battery in the soft load system of Figure 7.
In the drawings like characters of reference indicate corresponding
parts in the different figures.
DETAILED DESCRIPTION
An electrical power transmission network 10 includes a power supply
11 generally at a transformer supplying one or more transmission lines 12 and
managed by a network control system 9 using many systems for detecting
parameters of the network and for controlling various components of the
network to
maintain voltage stability on the transmission lines.
On the transmission line is a plurality of subscriber premises 13 for
receiving electrical power, each including a plurality of user devices 14 on a
power
supply circuit 15. Each of the subscriber premises 13 has a drop 16 from the
transmission line to a power supply inlet board 17 typically including a main
inlet
control switch. Typically in the drop is provided a meter for measuring power
usage.
In the present invention the meter is replaced by an integral component
defining a
load control device 18 connected to the power supply inlet 17 for controlling
the power
supplied from the power supply inlet to the user devices on the power supply
circuit
15.
Each load control device includes a sensing system 19 for detecting
variations in power factor caused by the user devices 14, a power correction
system
CA 03059517 2019-10-09
20 for applying load corrections to the power supplied by the drop to the
subscriber
premises and a control system 21 for controlling the power correction system
in
response to variations detected. The control system 21 connects to a
communication
system 91 for communicating between the load control device 19 and the network
5 control system 9.
The sensing system comprises a first meter 22 and a second meter 23
each of a generally known construction. Each acts to monitor the waveform of
the
power supply and to generate data relating to the standard true RMS values of
voltage
and current and relating to the Real Power. The sensing system can also have
1.0 systems which generate data relating to FFT spectra of the power supply
wave form
by analyzing the waveform using conventional Fast Fourier Transform
techniques.
This can also be used to generate data relating Total Harmonic Distortion
(THD).
The first meter is located at the drop and the second meter is located
downstream of the power correction system and the control system 21 which
receives
15 the data from both acts to compare the output data from the second meter
with the
output data from the first meter to determine a level of improvement in the
power
factor obtained by the power correction system 20.
The load control device is arranged to communicate data relating to
the improvement measured and to the Real Power consumed to the network control
20 system 9. This can be done in real time but typically is periodic
As shown in Figure 2, the power correction system 20 comprises
switched capacitor banks 24 including a switch 25 operated by the control 21
which
CA 03059517 2019-10-09
31
switches in selected capacitors 26 in a binary switching system. The system 20
further includes a switched reactor circuit 38 for voltage correction. This
includes an
inductor 28 and a switch 29 connecting the inductor across the power supply
buses
30 and 31. The switch 29 is operated by the control 21 in response to a
leading power
factor, provides greater control of power factor by varying the firing angle.
Typically
systems over-compensate the power factor with capacitors and use the reactor
switch
combination to fine tune the power factor to unity. The system 20 further
includes an
active power factor correction circuit 40 for noise correction and current
shaping. This
is composed of rectifier 41 across the supply buses 30 and 31 feeding into an
inductor
42 with a switch 43 connected to the rectifier return forming a boost circuit.
Output
from the boost circuit feeds diode 44 and holding capacitor 45. The switch 43
is
operated by the control 21 in response to noise and FFT analysis of the
downstream
loads. A sinusoidal waveform of the fundamental frequency minus the sum of FFT
waveforms minus the fundamental is used as the input to switch 43 modulated to
a
high frequency. This circuit 40 shapes the load current into a sinusoid based
on the
measured noise from downstream loads. The charge deposited onto capacitor 45
can
be bled off with a resistor (not shown), fed into a local solar/wind battery
charging
system, or re-inverted back onto the supply bus.
The load control device further includes a system for disconnecting
certain ones of the user devices for load shedding provided by a switch 33
operated
by the control 21.
32
The control system includes a processor which is programmable from
external input from the communication system or is programmed to change the
response to variations detected by the sensing system so that the response is
different in different circumstances. In this way the whole system can be
interactive
or can be adaptive to provide improved response to better manage the whole
system
depending on various aspects such as time of day and voltage levels locally or
globally in the system.
In particular, the control system is operated by its program to change
voltage at the drop by changing the capacitive load in response to data from
the
io network control system or other factors so as to provide another tool to
the network
management system to better control voltages and to better maintain stability.
Some or all of the subscriber premises can include a power supply
system 34 at the subscriber premises for adding power to the power. This can
comprise any of the known power supply systems such as solar panels,
generators
is and other local systems. For example the power supply as shown includes
a solar
generator 35 connected to a battery bank 36 operated by a switch 37 controlled
by
the control 21 to take power from the drop 16 or to add power to the drop
depending
on data and or program instructions from the sensor system 19 or from the
network
control 9. Thus the control system is arranged to control the capacitor banks
and the
20 power added by the power supply system in response to the detected
variations.
The dual meter structure 22, 23 enables compensation of visible loads
and conditions avoiding any opportunity of over compensation. And hence any
CA 3059517 2020-03-11
CA 03059517 2019-10-09
33
possibility of instability created by the compensation actions of the device.
The device
is inherently stable by design and can only provide compensation or actions
that will
improve system stability. This is all done without the need of communication
with any
other device, power network control, etc. This has a profound effect on
network
security. Where disruption of the power network by commanding (potentially
millions
of) these devices to do system harm is impossible.
Turning now to Figures 3 and 4, there is shown an arrangement for
connection of solar panels 351, wind generators 352, other power supplies 353
and
battery banks 354 to the power correction circuit 20. In figure 4 the
arrangement for
1.0 the connection is provided which includes a series of current inverters
355, 356 and
357 arranged in a row along a pair of conductors 358 and 359. Across these
conductors is also connected a pair of further current inverters 361 and 362.
A
capacitor 363 is also connected to the conductors 358, 359 and located between
the
current inverters 361 and 362.
The construction of each current inverter is shown in figure 5 and
comprises an upper switch and flyback diode 364 and the lower switch and
flyback
diode 365 connected across the conductors 358, 359, where the relevant input
from
the power source is connected at 366. When connecting to an input power source
such as a solar panel, wind generator, or charged battery, the inverter acts
like a
boost regulator. Typically the DC link voltage is much higher than the voltage
sourced
by the attached renewable power sources, hence a boost conversion is
necessary.
The return or ground of the renewable energy source(s) is connected to point
359.
CA 03059517 2019-10-09
34
The lower switch is turn on until a desired current "I" measured with 367 is
built up
through inductor 368. The lower switch 365 is then turned off. The inductor
has a
stored charged which now will discharge through the upper switch 364 flyback
diode,
charging the DC Link capacitor 363 connected between point 358 and 359 and
finally
complete the circuit through the return to the energy source connected. In
this way
the DC Link capacitor 363 is charged with energies that can be inverted back
into the
AC system via inverters 361 and 362 shown in Fig 4. To reverse this process
and
charge a battery the current inverter acts like a buck converter, transferring
energy
from a high DC voltage source to a lower voltage. Again, the negative battery
terminal
3.0 is attached to point 359. To charge a battery, power from the DC Link
Capacitor 363
and buses 358 and 359 the upper switch 364 is turned on until a voltage at
terminal
366 is reach which is suitable for charging the battery attached. This also
builds a
current up within the inductor 368 and is the charging current for the
battery. Then the
upper switch is turned off, this current continues to charge the battery
through the fly
back diode of the lower switch 365, inductor 368, until the voltage/current
drops to a
point, where again the upper switch is turned on, repeating the cycle. The
current
inverter now functions as a buck converter, reducing the voltage of the DC
Link
capacitor to a level needed for the attached battery. Both the boost and buck
conversion cycles are well known in the industry as a way to transfer energy
between
two DC voltages, a DC converter.
Using the current inverters as the compensation element dramatically
improves the flexibility and stability of the arrangement. With the current
inverter or
CA 03059517 2019-10-09
Universal compensator any passive element or combination of (capacitor,
resistor,
inductor, and negative resistor) can be implemented with software using this
structure. Current injection feedback control avoids any resonant interaction
with
external system components highlighting its inherent stable characteristic.
Structures
5 are built from half bridges 364, 365 which interface DC link buses 358,
359 with the
AC systems or renewable energy sources 351 to 354. The current Inverters are
constructed with half bridges to interface to any number of AC phases or
renewable
energy sources. At a minimum only one half bridge is required to interface a
renewable energy source such as solar, wind or battery with a DC link bus.
This
1.0 structure has a natural modular design topology, where additions to the
compensator
can be made as needed. Multiple half bridges can be assembled in parallel as
shown
in Figure 4 to service an AC phase or energy source to increase current
transfer
capability and reduce operation noise through interleaving techniques.
As shown in Figures 1 and 3, the current Injection compensation uses
15 a two meter structure 22, 23 with the compensation injected in-between
these two
meters points. When power flows from the system to the service side,
compensation
action is determined by the service meter 23. Injection of correction
currents, enables
the entire service side to appear from the systems side (meter 22) as a
resistive load
(PF=1). The harmonic cleansing and power factor correction has a great benefit
to
20 the system. Stability margin is dramatically increased and systems with
older relaying
equipment benefit by removing undetectable harmonics. As local renewable
energy
sources 351 to 354 are added to the service side, energy will flow both to the
system
CA 03059517 2019-10-09
36
and service loads 14. With the present two meter structure and injecting the
renewable energy again in-between these two metering points at the power
correction
circuit 20 as shown in Figure 4, the flow of this energy can be metered and
conditioned
using the current injection inverter used for compensation.
The system acts as a universal compensator in that the dual meter
structure is particularly useful in this instance to enable reverse flow of
power.
Connecting a renewable source such as solar panels, wind generators, and
batteries
at the point of compensation between the two meter structure using a generic
half
bridge. This enables the inverter to not only compensate for VARs but inject
real
power from these renewable sources and add the required VAR compensation to
these sources before they are injected into the system. The dual meter 22, 23
enables
the tracking of this real power, the quantity and where it is delivered
whether to the
system, service or both. This is an important distinction from current systems
available where power delivered is measured but without tracking and VAR
compensation. And if VAR compensation is provided, a communication network as
provided by the communication system 91 to the network 9 is necessary to
provide
the Power and VAR orders. However in the present invention communication
system
91 is not required for the device to provide VAR compensation and maintain
system
stability.
CA 03059517 2019-10-09
37
The arrangement shown in Figure 4 can also be used for generating
soft load changes. When a load is turned on and off it causes a discontinuous
change
to the power system as shown in Figure 8.
Referring to Figures 2, 4, 5 and 8, when a new load 710 (Figure 8) is
introduced, it is seen by the second meter 23 (Figure 1) and immediately power
is
drawn, as shown at 712 in Figure 8, from the battery 354 through half bridge
357 onto
DC bus 358, 359 (Figure 5) and charges DC link capacitor 363 (Figure 4) this
charge
is then immediately inverted out onto BUS A 30 and BUS B 31 via half bridges
361
and 362. In this way the system is spared the shock of the new load as it is
absorbed
by the local battery 354. Then, over a short period of time matching the
overall
systems natural time constant, this power supplied by the battery 354 is
diminished
as indicated at 713 in Figure 8. This power is replaced by the system but at a
rate
the system can naturally accommodate minimizing mechanical and electrical
stresses
throughout the system. In this way the battery power is no longer needed to
supplement the new loads power. Again, the system and loads are in equilibrium
and
no change is necessary, as indicated at 718 in figure 8. Upon removing a load
as
shown at 711 in Figure 8, power from the system continues in excess of the
attached
loads, this excess power is immediately drawn from the system via BUS A 30 and
BUS B 31 through half bridges 361 and 362 charging the DC link capacitor 363
via
DC BUS 358 and 359. This energy is then immediately used to recharge the
battery
354 via DC bus 358 and 359 and half bridge 357 as indicated at 717. Again in
this
way the system avoids the shock of this load' being removed, it is absorbed by
the
CA 03059517 2019-10-09
38
local battery. Again over a short period of time matching the overall system
natural
time constant, this power is returned to the battery as indicated at 716 in
Figure 8,
and the power requirement of the system is reduced in a gradual way minimizing
mechanical and electrical stresses throughout the system. It should be noted
that
using this gradual assertion and removal of load currents, as seen by the
system,
reduces (if not eliminates) the need for control communication, increasing
system
stability both mechanically and electrically, and minimizes mechanical and
electrical
stress. For the purpose of simplicity, simple linear ramps are used for the
transitions
713, 714, 715, and 716 shown in Figure 8. Where any transition shape may be
used
lo and is under the complete control of software, further the new load
assertion transition
shape may differ from the load removal transition shape. What shape is optimal
is
system dependent.
Thus the system uses the standard configuration shown and described
herein of half bridges or current inverters as shown in Figure 4. In this way,
when a
load is switched on, instead of the full load power being supplied by the
power system,
it is supplied by this battery 354 for a short time and this power supplied is
reduced
over a short period matching or greater than the natural time constant of the
power
systems response time. Similarly when a load is switched off, instead of the
full load
power being released, it is used to charge the battery for a short time and
this charging
is reduced over this period again matching or greater than the natural time
constant
of the power system. The profile of the load change as seen by the power
system can
be tailored in software of control unit 21.
CA 03059517 2019-10-09
39
Referring now to Figure 7, there is provided an arrangement for active
load balancing between the different phases at the consumer premises by which
loads between the various phases can be balanced. Thus two source phases BUS A
s 30 and BUS B 31 and a return phase BUS C 700 (more commonly known as
Neutral)
comprises a dual phase system as is commonly found in homes. Many loads within
a home are attached from one phase BUS A or BUS B to the return line BUS C.
When
the size, of loads attached to BUS A and BUS B do not equal this causes an
imbalance between the current or power delivered on the two BUSes A and B and
lo the difference between these currents is returned via BUS C. So, in
order to have
balanced loading on BUS A and BUS B the current in BUS C must be zero. This is
not typically true since loads are rarely balanced between BUS A and BUS B.
With
the present invention these imbalanced currents are balanced in the view of
the
system or utility side using the current inverter half bridges 361 and 362
connected to
15 BUSes A 30 and B 31.
When an imbalance is detected, the currents in BUS A and BUS B are
measured by the second meter 23 (Figure 3) and these currents are averaged.
The
average current minus the actual current of each BUS A 30 and BUS B 31 forms
the
current order for each respective half bridge 361 and 362. It should be noted
for this
20 example we are considering only balancing and not the general function
of the device
as it relates to balancing, harmonic mitigation, and VAR compensation. The
loads in
this case can be thought of being purely resistive but unequal between each
BUS or
CA 03059517 2019-10-09
phase A and B. This simplification has no effect on the process since each of
these
components can be treated separately and then combined at the end using the
superposition theorem. These current orders will have one BUS drawing current
from
the system side while the other BUS will deliver an equal and opposite current
to the
5 load side. As an example, if BUS A has a load current of 15 Amps while
BUS B has
a load current of 5 Amps:
-- the current inverter for BUS A 30, which is inverter 361, will have a
current order for delivering 5 Amps that is (5 + 15)/2 = 10 - 15 = -5 Amps.
--the current inverter for BUS B 31, which is current inverter 362, will
10 have a current order of absorbing 5 Amps (5 +15)/2 = 10 -5 = 5 Amps.
So, current is absorbed by BUS B 31 and is delivered to BUS A 30
hence balancing out the currents as viewed by the system or utility side.
This is accomplished in this example by current flowing via BUS B 31
through half bridge 362 charging DC link capacitor 363. This charge on DC link
15 capacitor 363 is discharged through half bridge 361 onto BUS A 30.
In general, with the present system given more than one phase, loads
between the various phases can be balanced. In software, the load currents
from the
different phases are added then divided by the number of phases to determine
the
load current needed in each to be balanced. The differences between this
average
20 and the actual current in each phase determines the balancing correction
current
order. It is important to note this function has little cost impact on the
system.
CA 03059517 2019-10-09
41
,
Using both of these systems, therefore, the system now can provide
total power quality control in other words every load appears to be a balanced
resistive load no matter its makeup.
Instead of using a battery in any location herein it is instead possible
to use a super capacitors as the storage medium. Since the system typically
only
need a small amount of power and is constantly charging and discharging such
supercapacitors are eminently suitable.
The present invention can be packaged into local outlet receptacles as
shown in Figure 6. Where each panel breaker 600 sources a wiring path with
multiple
lo outlet compensation modules 601 connected along the wiring path. This forms
a
distributed compensation arrangement. Each module can contain a communications
interface 691 to communicate with a panel mounted compensator via
communications interface 91 and/or with other like units. Again the dual meter
structure within in each module enables the need for compensation and results
of
compensation to be measured at each location along the path. With
communications
all units can share this information to enable the group to maximize
distributed
compensation efficiency. Without communications, a natural sharing mechanism
of
this information is provided by placement along the wiring path. If a serial
path is
assumed then the module furthest away from the breaker is isolated, where that
module can only see the loads attached to its local outlets 602. Each module
up from
the furthest one can see the effects and loads of every module further away
from the
panel than itself. This allows compensation to be added to loads further down
the
CA 03059517 2019-10-09
42
chain that could not be compensated by their local modules. While the
compensation
efficiency would not be as efficient as modules with communications the added
cost
and complexity may be unwarranted. This distributed compensation arrangement
can
increase the capability of the panel breaker and associated wiring by
generating a
loads VAR requirement locally. Then the break need only carry the real power
necessary for these loads. As opposed to previously the break had to carry the
real
and imaginary power needs of each load. This can be significant, increasing
power
transfer 20 to 30% or more. All without violating established electrical codes
for
current capacity of wiring. This can have a great impact on older
installations and
homes where minimal wiring was installed and a greater need of power was
unforeseen. Now, with the installation of compensation outlet modules more
useful
power can be carried by the same old cables installed many years ago,
breathing
new life into older structures.
Demand side management and prioritize load identification and
management functions require the communications interface of 691. Demand side
load commands are received by each module and the appropriate loads are either
attached or detached depending on the order. With a power network control
communications connection such as 9 finer power system demand management
schemes are possible where millions of loads maybe identified by importance,
class
(chargers, heating, cooling, etc), size, noise content, etc. This would enable
a greater
and finer control of load profiles to match availability of network power,
time of day,
and types of power, renewable or grid, etc. Upon a power outage all non-
priority loads
CA 03059517 2019-10-09
43
are removed. With the power returning loads can be reinitialized in priority
order to
match current power availability criteria. Demand side management and load
sequencing can make a big difference to system reliability and stability,
especially in
power grids with a high concentration of renewable energy sources.
