US 4,034,269 A · Protective relay circuits

Abstract

A protective relay circuit. An electrical system signal quantity is monitored and applied to a filter and to a bipolar threshold device in parallel with the filter. The bipolar threshold device has a zero output signal level as long as the magnitude of the monitored signal is less than some predetermined value. When the monitored signal exceeds the predetermined value, the output of the bipolar threshold device will be substantially equal to the monitored signal level minus the predetermined value. The output of the filter and the output of the bipolar threshold device are combined in a summing amplifier to provide a signal for controlling the trip coil of a circuit breaker. When the circuit is used in an overcurrent or overvoltage protective relay, the combined signal is rectified and applied to a level detector which provides the signal for controlling the trip coil of the circuit breaker. When the circuit is used in a distance or directional relay, the phase of the combined signal as compared to the phase of a second monitored signal determines the generation of the signal for controlling the trip coil of the circuit breaker.

Claims49

Dependent claims

A circuit for generating a signal for controlling the trip coil of a circuit breaker protecting an a-c power system comprising:

(a) a sensor adapted to be coupled to one a-c power line for generating a sensor signal proportional to an electrical quantity in the power system that is subject to variations;
(b) a filter responsive to the sensor signal for filtering the transient component from the sensor signal;
(c) first circuit means responsive to the sensor signal for generating a signal having a first output level when the sensor signal is less than a predetermined level and having a second output level when the sensor signal exceeds said predetermined level, said second output level being a function of the sensor signal level;
(d) second circuit means for combining the first generated signal and the filtered signal;
and
(e) third circuit means responsive to the combined signal for generating said trip coil control signal when the combined signal exceeds a fixed level.

3 more elements

A circuit for generating a signal for controlling the trip coil of a circuit breaker protecting an a-c power system comprising:

(a first circuit means adapted to be coupled to the power system for generating a signal proportional to the power system voltage;
(b) second circuit means adapted to be coupled to the power system for generating a signal proportional to the power system current;
(c) a first filter responsive to the first circuit means signal for filtering the transient component from the first circuit signal;
means (d) third circuit means responsive to the first circuit means signal for generating a signal having a first output level when the first circuit means signal is less than a predetermined level and having a second output level when the first circuit means signal exceeds said predetermined level, said second output level being a function of the first circuit means signal level;
(e) fourth circuit means for combining the third circuit means signal with the signal of the first filter;
(f) a second filter responsive to the second circuit means signal for filtering the transient component from the second circuit signal;
(g) fifth circuit means responsive to the second circuit means signal for generating a signal having a first output level when the second circuit means signal is less than a predetermined level and having a second output level when the second circuit signal exceeds said predetermined level, said second output level being a function of the second circuit means signal level;
(h) sixth circuit means for combining the fifth circuit means signal with the signal of the second filter;
and
(i) seventh circuit means responsive to the fourth and sixth circuit means signals for generating the trip coil control signal when a predetermined relationship exists between the fourth circuit means signal and the sixth circuit means signal.

7 more elements

Dependencies are inferred from the claim text.

Protective relay circuits

Life of this patent

Protective relay circuits

Life of this patent

Abstract

Claims49