Electronic reactive power regulator

A reactive power regulator for controlling a bank of power factor correction capacitors or reactors having different values capable of being connected to a three-line electrical power network to thereby control the amount of the reactive power comprising:

• a measuring circuit to measure the reactive power comprising at least one multiplier circuit which receives at least two input signals from said network, one of said two input signals being in phase with the voltage between two lines of said three-line electrical power network and the other input signal being in phase with the current in the third line of said three-line electrical power network to thereby provide an initial phase shift value of 90 degrees between said signals when the reactive power is zero, and producing in response to the received signals an output signal having a DC component indicative of the reactive power;
• a filtering circuit which extracts the DC component of the output signal and which produces a filtered output signal proportional to the DC component;
• a control signal generating circuit which compares the filtered output signal to lower and upper reference limits and which produces an increase control signal when said upper limit is exceeded and a decrease control signal when said lower limit is exceeded;
• a logic circuit which is responsive to said control signals and which selectively disconnects, in response to a decrease control signal, the lowest value capacitor or reactor available in said network, and which selectively connects, in response to an increase control signal, the lowest value capacitor or reactor available from said bank, to thereby regulate the reactive power and keep the filtered output signal between said lower and upper reference limits.

A reactive power regulator system for an electrical power network which includes:

• an array of unequal value correction capacitors or reactors for connection to said network;
• measuring means for measuring the reactive power in the power network comprising at least one multiplier circuit means for receiving from said network at least two input signals having an initial relative phase shift value of 90 degrees when the reactive power is zero but which changes in response to a change in reactive power and for producing in response to the received input signals an output signal having a characteristic indicative of the existing reactive power;
• control signal generating means for comparing said characteristic to reference limits and for producing an increase control signal if one limit is exceeded and for producing a decrease control signal if a different limit is exceeded;
• and
• logic means, response to said control signals, for selectively incrementally adjusting the number of correction capacitors or reactors in the electrical power network in response to said control signals by disconnecting the lowest value capacitor or reactor from the network in response to a decrease control signal, and by connecting the lowest value unconnected capacitor or reactor into the network in response to an increase control signal, to thereby regulate the amount of reactive power.

A method for controlling the level of reactive power in an electrical network comprising the steps of

• providing an array of correction capacitors or reactors having unequal graded values, wherein the connection of each capacitor or reactor is responsive to the state of a switching device and associated therewith;
• comparing the actual reactive power to a predetermined level of reactive power;
• generating a control signal representative of the difference between said levels;
• and
• sequentially applying the control signal to said switching devices in the order of increasing capacitor or reactor values associated therewith, until a switching device changes state.