System and method for rms overcurrent backup function
AssigneeABB Power T&D Company Inc.
InventorsMichael Egolf, David G. Hart, James D. Stoupis
Life of this patent
Estimating the term…
Abstract
A method and apparatus for over current backup protection is provided. The method generates a set of root mean square (rms) values from samples that are taken from the system current. Several rms current values are averaged to generate an estimated rms over current value. The estimated over current value is compared with a predetermined threshold value. If the estimated current is above the predetermined threshold value, a fault protection mechanism, such as opening a circuit breaker, is activated. A generator protection unit having digital signal processing capabilities executes the inventive method to provide protection from over current episodes.
Claims14
A method of over current backup for a system having a current signal, comprising the steps of:
- (a) obtaining a current measurement;
- (b) determining whether frequency tracking is available;
- (c) if frequency tracking is available, employing said frequency tracking to provide fault protection;
- and
- (d) if frequency tracking is not available, providing fault protection by performing the following steps:
- (e) obtaining additional current measurements until a sufficient number of current measurements have been obtained to calculate a root mean square (rms) current value;
- (f) generating a rms current value from said sufficient number of current measurements;
- (g) repeating steps (e) and (f) to generate a plurality of rms current values;
- (h) generating a current estimate from said plurality of rms current values;
- and
- (i) activating a fault protection mechanism if said current estimate is above a predetermined threshold.
A method for over current backup protection in a generator protection unit (GPU), wherein the GPU receives a plurality of current signals from a generator, the method comprising the steps:
- (a) obtaining a current measurement;
- (b) determining whether frequency tracking is available;
- (c) if frequency tracking is available, employing said frequency tracking to provide fault protection;
- and
- (d) if frequency tracking is not available, providing fault protection by performing the following steps:
- (e) obtaining additional current measurements until a sufficient number of current measurements have been obtained to calculate a root mean square (rms) current value;
- (f) generating a rms current value from said sufficient number of current measurements;
- (g) repeating steps (e) and (f) to generate a plurality of rms current values;
- (h) generating a current estimate from said plurality of rms current values;
- and
- (i) activating a fault protection mechanism if said current estimate is above a predetermined threshold.
An apparatus for over current backup protection in a system transmitting current, comprising:
- a current sensor for sensing the current being transmitted;
- an A/D converter operably coupled to said current sensor for sampling the sensed current at a fixed sampling interval;
- a digital signal processor (DSP) operably coupled to said A/D converter for generating rms current values from the sensed current;
- and
- a microprocessor operably coupled to said DSP, having code therein for performing the following steps:
- (a) obtaining a current measurement;
- (b) determining whether frequency tracking is available;
- (c) if frequency tracking is available, employing said frequency tracking to provide fault protection;
- and
- (d) if frequency tracking is not available, providing fault protection by performing the following steps:
- (e) obtaining additional current measurements until a sufficient number of current measurements have been obtained to calculate a root mean square (rms) current value;
- (f) generating a rms current value from said sufficient number of current measurements;
- (g) repeating steps (e) and (f) to generate a plurality of rms current values;
- (h) generating a current estimate from said plurality of rms current values;
- and
- (i) activating a fault protection mechanism if said current estimate is above a predetermined threshold.
A generator protection system for analyzing current signals output from a generator wherein the current signals are monitored by current sensors to produce a plurality of signals representative of the current of the generator, the generator protection system comprising:
- sampling means for receiving an input of the plurality of current signals and sampling the plurality of current signals at a predetermined fixed rate to provide an output of sampled current signals;
- and
- a processing means coupled to the sampling means and receiving an input of the sampled current signals, the processing means being operable to perform the following steps:
- (a) obtaining a current measurement;
- (b) determining whether frequency tracking is available;
- (c) if frequency tracking is available, employing said frequency tracking to provide fault protection;
- and
- (d) if frequency tracking is not available, providing fault protection by performing the following steps:
- (e) obtaining additional current measurements until a sufficient number of current measurements have been obtained to calculate a root mean square (rms) current value;
- (f) generating a rms current value from said sufficient number of current measurements;
- (g) repeating steps (e) and (f) to generate a plurality of rms current values;
- (h) generating a current estimate from said plurality of rms current values;
- and
- (i) activating a fault protection mechanism if said current estimate is above a predetermined threshold.
Dependencies are inferred from the claim text.