Electricity: electrical systems and devices – Safety and protection of systems and devices – Capacitor protection
Patent
1976-11-24
1978-08-01
Salce, Patrick R.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Capacitor protection
361 15, 361 88, H02H 716
Patent
active
041046870
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.
REFERENCES:
patent: 2933652 (1960-04-01), Cuttino
patent: 3859564 (1975-01-01), Zulaski
S&C Electric Company
Salce Patrick R.
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