US 4,104,687 A · Device for detecting unbalanced conditions in a polyphase equipment bank

Abstract

A sensing device is connected to an intermediate tap point on each phase leg of a polyphase system such as a grounded wye-connected capacitor bank to detect faulted capacitor units and thereby control a switching device to isolate the capacitor bank. The intermediate tap point is selected in each phase leg such that the number of series units (such as parallel capacitor groups) above the tap point equals (or exceeds by one) the number of series units below the tap point. The outputs of these sensing devices are coupled through a calibration network to a summing amplifier which operates to add the three signals vectorily to produce on AC output signal that is filtered by a 60 Hz band pass filter to attenuate unwanted harmonics and noise which might introduce error into the measurement. Initial balance is achieved by adjusting the magnitude of each phase to ground signal to equalize those signals from each of the intermediate tap points. By this adjustment, the output signal of the summing amplifier and filter is then proportional to the percent unbalance among the three intermediate tap point voltages. The percent unbalance output signal is directly related to the change in voltage occurring at the tap point due to faulted capacitor units. When the unbalance persists for a preselected time period, an alarm or a switching device is actuated to isolate and protect the capacitor bank.

Claims25

Dependent claims

A device for detecting voltage unbalances in a polyphase equipment bank, each phase of the bank being energized by a respective line of an electrical power system, the unbalances resulting from failure or inadvertent change of one or more components of the polyphase equipment bank comprising:

voltage sensing means for providing a voltage signal for each phase of the equipment bank representative of the voltage between ground and an electrically similar tap point located within each phase of the equipment bank;
summing means for vectorily adding the voltage signals for each phase and producing an output AC signal representative of the summation of the voltage signals for all phases;
calibration means for adjusting said voltage signal for each phase of the equipment bank to nullify any manufacturing tolerance errors of components of the equipment bank;
signal processing means for producing a first output signal indicative of component failure or change when the output AC signal exceeds a predetermined magnitude.

1 more element

A device for detecting capacitor unit failures in a multi-phase grounded wye-connected capacitor bank in a high voltage electrical power system comprising:

a plurality of potential devices, one potential device for each phase of the power system being connected between ground and an intermediate tap point for each phase, said tap point located approximately an equal number of capacitors between ground and a transmission line for that phase of the power system, and said potential devices providing a voltage signal for each phase representative of the voltage at each tap point;
a summing amplifier connected with each potential device and vectorily adding the voltage signals for each phase and producing an AC signal representative of the summation of the voltage signals for all phases;
a rectifier means for converting the AC signal from said summing amplifier into a corresponding DC voltage signal;
a first voltage comparator receiving said DC voltage signal and comparing said DC voltage signal with a first predetermined reference voltage representative of the failure of a preselected number of capacitors and providing a first output signal when said DC voltage signal is equal to or exceeds the first reference voltage;
a first timing circuit that measures the time duration of said first output signal of said first voltage comparator and provides a first control signal when the duration of said first output signal exceeds a first predetermined time interval;
a lockout control circuit receiving said first control signal and causing the capacitor bank to be disconnected from the power system in response to receipt of said first control signal.

3 more elements

Dependencies are inferred from the claim text.

Device for detecting unbalanced conditions in a polyphase equipment bank

Life of this patent

Device for detecting unbalanced conditions in a polyphase equipment bank

Life of this patent

Abstract

Claims25