US 5,134,356 A · Reactive power compensator

Abstract

A system and method for determining and providing reactive power compensation for an inductive load. A reactive power compensator (50,50') monitors the voltage and current flowing through each of three distribution lines (52a, 52b, 52c), which are supplying three-phase power to one or more inductive loads. Using signals indicative of the current on each of these lines when the voltage waveform on the line crosses zero, the reactive power compensator determines a reactive power compensator capacitance that must be connected to the lines to maintain a desired VAR level, power factor, or line voltage. Alternatively, an operator can manually select a specific capacitance for connection to each line, or the capacitance can be selected based on a time schedule. The reactive power compensator produces control signals, which are coupled through optical fibers (102/106) to a switch driver (110, 110') to select specific compensation capacitors (112) for connections to each line. The switch driver develops triggering signals that are supplied to a plurality of series-connected solid state switches (350), which control charge current in one direction in respect to ground for each compensation capacitor. During each cycle, current flows from ground to charge the capacitors as the voltage on the line begins to go negative from its positive peak value. The triggering signals are applied to gate the solid state switches into a conducting state when the potential on the lines and on the capacitors reaches a negative peak value, thereby minimizing both the potential difference and across the charge current through the switches when they begin to conduct. Any harmonic distortion on the potential and current carried by the lines is filtered out from the current and potential signals used by the reactive power compensator so that it does not affect the determination of the required reactive compensation.

Claims60

Dependent claims

A reactive power compensating system, comprising:

a. an electrical current sensor that produces a current signal corresponding to an instantaneous value of an electrical current supplied through a line to an inductive load, the electrical current generally varying periodically at a fundamental frequency;
b. a voltage sensor that produces a potential signal corresponding to an instantaneous voltage on the line, the potential signal varying according to a generally periodic cycle at the fundamental frequency;
c. filter means, connected to receive the current signal, for producing a filtered current signal from which any harmonics of the fundamental frequency that are present in the current signal are substantially filtered out;
d. processor means, connected to receive the potential signal and the filtered current signal, for determining a reactive power compensation for the inductive load as a function of the filtered current signal when the potential signal is at a predefined point in its periodic cycle and operative to produce a switching signal to select that reactive power compensation;
e. a plurality of capacitors, each selectively connectable to compensates reactance on the line;
and
f. switching means, connected to the plurality of capacitors and connected to receive the switching signal from the processor means, for selectively connecting the capacitors to provide the reactive power compensation determined by the processor means in response to the switching signal, the reactive power compensation being substantially free of errors that would otherwise be caused by the harmonics of the fundamental frequency present in the electrical current in the line.

4 more elements

A reactive power compensating system for compensating a reactive load drawing power from multiple phases of a supply, comprising:

a. a plurality of electrical current sensors, each of which is connected to sense a generally periodically varying electrical current supplied to the reactive load on a different one of the phases, producing a current signal corresponding to said electrical current;
b. a voltage sensor connected to sense a generally periodically varying voltage on each of the phases, producing a plurality of potential signals, each potential signal corresponding to the voltage on one of the phases;
c. reactive power sensing means, connected to receive the current signal and the potential signal for each phase, for determining a separate reactive power compensation for each phase, each of which can be different, as required to compensate each phase for the reactive load connected to that phase, and further operative to produce switching signals to select the reactive power compensation for each phase;
d. a plurality of capacitors assembled in arrays, each array being associated with one of the phases, each of the capacitors in the arrays being selectively connectable to provide at least a portion of the reactive power compensation required for one of the phases;
and
e. switching means, electrically connected to the plurality of capacitors and connected to receive the switching signals for the reactive power sensing means, for selectively connecting the capacitors to provide the separate reactive power compensation independently determined for each phase by the reactive power sensing means, in response to the switching signals.

3 more elements

An adaptive reactive power compensation system for compensating reactive power loads in an alternating current power system having at least one phase, comprising:

a. monitoring means for monitoring the voltage in each phase of the power system;
b. synchronization means for synchronizing to the voltage on each phase in the power system, producing a synchronization signal in respect to each of the phases;
c. current monitoring means for monitoring the current in each phase of the power system;
d. triggering means for producing a triggering signal for each phase;
e. processor means, connected to the voltage monitoring means, the current monitoring means, and the synchronization means for:
i. determining a reactive current in each phase when the voltage on that phase is at a predetermined synchronization level;
ii. determining a desired reactive power compensation for each phase a function of the reactive current;
and
ii. controlling production of the triggering signal by the triggering means to effect the desired reactive power compensation;
f. a plurality of capacitors, each selectively connected to provide reactive power compensation to one of the phases;
and
g. a plurality of switching blocks, each of which is associated with one of the phases, each switching block being connected to the triggering means and responsive to the triggering signal so that an appropriate capacitance can be connected by the switching block to each phase to provide the desired reactive power compensation determined by the processor means, the triggering signal enabling said capacitance to be connected at an appropriate time, each capacitor including means for sampling a charge current flowing to the capacitor and producing a closed loop feedback signal indicative thereof, the processor means using the closed loop feedback signal to verify that the appropriate reactive power compensation is being supplied to each phase.

9 more elements

A method of compensating for a reactive load that draws power from a multi-phase supply, comprising the steps of:

a. sensing a generally periodically varying electrical current on each of the phases, producing a plurality of current signals corresponding thereto;
b. sensing a generally periodically varying voltage on each of the phases, producing a plurality of potential signals corresponding thereto;
c. in a manner unaffected by any harmonic distortion that may be present on the phases, separately determining a reactive power compensation required for each phase to compensate each phase for the reactive load connected to that phase, wherein the reactive power compensation for each phase may be different;
d. assembling a plurality of capacitors in arrays, each array being associated with one of the phases, each of the capacitors in the arrays being selectively connectable to provide at least a portion of the reactive power compensation required for one of the phases;
and
3. selectively connecting the capacitors to provide the reactive power compensation determined for each phase.

3 more elements

Dependencies are inferred from the claim text.

Reactive power compensator

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Reactive power compensator

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Abstract

Claims60