Microprocessor-based digital protective relay for power transformers
OwnerAzizur M. Rahman, Ivi Hermanto +1inventors
InventorsAzizur M. Rahman, Ivi Hermanto, Yalla, V. V. S. Murty
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Abstract
A stand alone protective apparatus and method is provided for electrical power devices. Power devices can be damaged due to conditions for example of over current, magnetizing in rush-current, over exitation voltage, saturation, ground fault or internal faults. To protect power devices from the noted conditions, electrical current of the power device is sensed and sampled. Digital processing is used for analyzing the digitally coded sample current and based on one of the conditions that can cause damage, a signal is provided for selectively actuating, by tripping an electric/electronic circuit breaker.
Claims17
A stand alone protective relay apparatus for protecting an electrical power device from damage due to conditions of overcurrent, magnetizing in-rush current, over-excitation voltage, saturation, ground fault, internal faults, mismatched ratio error for external fault outside the device, current, internal fault and in-rush occurring both independently and simultaneous, said stand alone protective relay apparatus comprising:
- means for sensing electrical current;
- means for sampling and holding said electrical current;
- filtering apparatus, operatively connected to said means for sensing and said means for sampling and holding;
- analog-to-digital converter means for digitally encoding the sampled current;
- digital processing means for analyzing the digitally-encoded current to identify at least one of the said conditions;
- and
- digital output interruption signal-producing means for producing an actuation signal for a digital power switching device, upon the identification of at least one of the said conditions, to cause an interrupt of a flow of electrical current to said electrical power device.
A method for protecting an electrical power device having an electronic/electrical circuit breaker therein, said method comprising:
- (a) sensing electrical current flow in said power device;
- (b) periodically sampling current sensed in step (a);
- (c) digitally encoding the current sampled in step (b);
- (d) analyzing the digitally encoded current in a predetermined manner to determine instantaneous values of fundamental, second harmonic, and fifth harmonic components thereof;
- and
- (e) comparing said second and fifth harmonic components to said fundamental component in a predetermined manner to indicate
- (i) a fault condition, and, if said fault condition is indicated, then to initiate an output trip signal to said electronic/electrical circuit breaker tripping said circuit breaker;
- or
- (ii) an in-rush condition and, if said in-rush condition is indicated, then to initiate an output non-trip signal or restraint signal to said electronic/electrical circuit breaker so that said circuit breaker remains open;
- or
- (iii) at least one of an over-excitation voltage, saturation, and ratio-error condition and, fi said condition is indicated then to initiate a tripping signal, tripping said electronic/electrical circuit breaker;
- or
- (iv) at least one of an over-excitation voltage saturation and ratio conditions and, if said condition is indicated then to initiate an alarm signal actuating an alarm.
A stand alone protective relay apparatus for protecting an electrical power device from damage due to conditions of overcurrent, magnetizing in-rush current, over-excitation voltage, saturation, ground fault, internal faults, mismatched ratio error for external fault outside the device, current, internal fault and in-rush occurring both independently and simultaneous, said stand alone protective relay apparatus comprising:
- means for sensing electrical current;
- means for sampling and holding said electrical current;
- filtering apparatus, operatively connected to said means for sensing and said means for sampling and holding;
- analog-to-digital converter means for digitally encoding the sampled current;
- digital processing means for analyzing the digitally-encoded current to identify at least one of the said conditions;
- and
- digital output interruption signal-processing means for producing an actuation signal for a digital power switching device, upon the identification of at least one of the said conditions, to cause an interrupt of a flow of electric current to said electrical power device;
- wherein said signal trips an electric/electrical circuit breaker resulting in the interrupt of electrical current to said electrical power device.
A method of protecting an electrical power device with circuit breakers contained therein, said method comprising the steps of:
- (a) actuating the power device and closing the circuit breakers;
- (b) sensing and periodically sampling current in said power device a plurality of times;
- (c) calculating the differential of through and ground fault currents;
- (d) determining after step (c) is completed, if the circuit breakers should be tripped;
- and
- (e) tripping said circuit breakers by giving a tripping command to said circuit breakers.
A stand alone self contained protective relay apparatus relay for protecting a transformer from damage due to conditions of overcurrent, magnetizing in-rush current, over-excitation voltage saturation, ground fault, internal faults, mismatched ratio error for external fault said protective relay comprising:
- (a) data acquisition circuits for receiving and processing current from a plurality of transformers;
- (b) signal processing circuits connected to said data acquisition circuits said signal processing circuits processing signals from said data acquisition circuits for sending tripping signals;
- and
- (c) circuit breakers receiving said tripping signals so that current to said transformers are interrupted upon receipt of said tripping signals.
Dependencies are inferred from the claim text.