Differential protection is a power system relay method that compares current entering and leaving a protected zone. Principle of Operation: These relays activate based on discrepancies in electrical quantities. The aim of this technical article is to cover the most important principles of four fundamental relay protections: overcurrent, directional overcurrent, distance and differential for transmission lines, power transformers and busbars.
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The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current,, reverse flow, over-frequency, and under-frequency.
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Protective relays work in conjunction with various electrical protection and control devices, such as Miniature Circuit Breakers (MCBs) and Molded Case Circuit Breakers (MCCBs), to maintain system stability and prevent damage during fault conditions. Protective relays and devices have been developed over 100 years ago to provide "last line" of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system continue to run under normal conditions.
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There is a code of practice that sets out safety distances and that must be followed: New Zealand Electrical Code of Practice for Electrical Safe Distances. This Electrical Code of Practice (Code) sets minimum safe electrical distance requirements for overhead electric line installations and other works associated with the supply of electricity from generating stations to end users. Distance relaying is used to detect faults on long-distance lines, pinpointing not only the fault condition but also measuring the distance between the current sensing mechanism and the fault location in the wire. Our advanced distance protection relays offer field-proven experience with sophisticated algorithms and protection characteristics such as quadrilateral, polygon or mho which are well known for their high performance in complex applications. 'Direct contact' and 'indirect contact' are now designated 'basic protection' and 'fault protection'.
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This part of IEC 60255 specifies common rules and requirements applicable to measuring relays and protection equipment, including any combination of equipment to form a distributed protection scheme for power system protection such as control, monitoring and process. Measuring, protecting, controlling and maintaining electricity power networks in a smart grid world requires intelligent electronic devices (IED), such as smart energy meters, measuring relays, protection systems, control and automation devices. Protective relays and devices have been developed over 100 years ago to provide "lastline"of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system continue to run under normal conditions. The basic functions are to receive input signals, monitor and determine them, and output an alarm signal if a set.
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