Detect faults and trip breakers selectively.
Relays sense current, voltage, impedance or differential current and trip breakers. Types: overcurrent, distance, differential, earth-fault, Buchholz. Selectivity, speed, sensitivity and reliability are the key criteria. Modern relays are digital IEDs with communication.
A transformer differential relay trips for internal faults only.
Protective relays detect abnormal conditions and trip only the faulty part of the system, which keeps the rest of the network in service.
Detect faults and trip breakers selectively.
Protective relays detect abnormal conditions and trip only the faulty part of the system, which keeps the rest of the network in service.
The ability of protection to isolate only the faulty section, leaving healthy parts running, which is achieved with coordinated settings and time grading.
A relay that compares the current entering and leaving a protected zone, and trips if the difference indicates an internal fault.
Typical applications include tripping a feeder breaker when the current exceeds a threshold, protecting a transformer with differential protection and setting time delays so downstream breakers clear faults first.
Study "Symmetrical components" first (topic 73 of 106 in Electrical Engineering). It covers the groundwork this topic builds on.
Time grading and curves. Zones of protection. Backup protection.
A transformer differential relay trips for internal faults only.
The next topic is "Circuit breaker types", which builds directly on this one.
It is classed as Advanced in Electrical Engineering (topic 74 of 106). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Electrical Engineering.
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