Overcurrent protection relay with communications

In an overcurrent relay system for use in an electrical power system, the electrical power system having a transformer supplying electrical power having a current and a voltage of a fundamental frequency and a load connected through a circuit breaker, a relay for the relay system, said relay communicating with a master unit, said relay comprising:

• means for sensing both a current and a voltage of the electrical power of the fundamental frequency and for sensing at least two harmonics of both the current and the voltage of the transformer and for producing analog signals representative of the sensed current and the sensed voltage;
• means for periodically sampling the analog signals a predetermined number of times during a preset period of time and for converting the analog signals into a series of digital values;
• means for separately processing each of the digital values to determine a processed current value which is a function of the sensed current and the preset period and a processed voltage value which is a function of the sensed voltage and the preset period;
• means, responsive to the processing means, for actuating the circuit breaker to disconnect the transformer from the electrical power system in the event that at least one of the processed current value or the processed voltage value is not within preset limits;
• means for generating a relay signal representative of the processed values;
• and
• means, responsive to the relay signal, for communicating the processed values to the master unit.

In an overcurrent relay system for protecting an electrical power system supplying electrical power having a current of a fundamental frequency to an electrical load, a relay for the system, said relay communicating with a master unit, said relay comprising:

• means for sensing the current of the fundamental frequency and for sensing at least two harmonics of the current of the electrical power and for producing analog signals representative of the sensed current;
• means for periodically sampling the analog signals a predetermined number of times during a preset period of time and for converting the analog signals into a series of digital values;
• means for separately processing each of the digital values to determine a processed current value which is a function of the sensed current and the preset period, the processed current value corresponding to the period of time that the sensed current is above a preset current limit;
• means, responsive to the processing means, for disconnecting the power system from the load in the event that the processed current value is not within its preset limit;
• means for generating a relay signal representative of the processed value;
• and
• means, responsive to the relay signal, for communicating the processed current value to the master unit.