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Trip Circuit Supervision

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Dependability of protective system in electrical network is the ability to detect abnormal operating conditions and successfully isolate the fault by closing trip circuit through its trip contact. One of the major concern for isolation of fault by tripping of appropriate circuit breaker is the healthiness of whole trip circuit. To ensure the trip circuit remains intact and monitor the health of trip circuit, trip circuit supervision relays are installed in protection panels. Before understanding the internal circuitry of TCS (Trip Circuit Supervision) relay & how it works, let us see a basic trip circuit consisting of control voltages, trip coil, IED/relay trip contact and circuit breaker auxiliary contacts.  52a and 52b are Circuit Breaker NO and NC auxiliary contacts respectively. 52a follows the position of circuit breaker whereas 52b is opposite the position of circuit breaker. Trip Circuit Supervision Relay (Internal Circuit & Working) Basic inte...
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Understanding the Rated Characteristics of Medium Voltage and High Voltage Circuit Breakers

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Circuit Breakers are extensively used in power systems to make or break electrical circuit during normal operation as well as during fault conditions. Circuit Breaker must be able to withstand the thermal and electrodynamic stresses arise due to interruption of operating currents and short circuit currents during fault conditions. There are various types of circuit breakers (Air Blast CB, OCB, SF6 Breakers, VCBs), however the typical ratings that characterize the operation of circuit breaker in a power system remains the same. Rated Voltage It is the maximum RMS Voltage at which the breaker is designed to operate safely and satisfactorily. Rated Voltage is always greater than the operating voltage. For Example a breaker operating in a 132 kV Network may be rated at 145 kV or a medium voltage breaker in 11kV Network at 15kV or 17.5kV. Common Values of rated voltages are 15kV, 17.5 kV, 24kV, 36kV, 145kV, 245kV and so on. Rated Frequency 50 Hz and 60 Hz frequency systems are the...
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Understanding the Accuracy Class of Current Transformers (Protection Class)

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Current transformers and voltage transformers are extensively used in power system to scale down the operating current and voltage. The scaling down of the current and voltage is required chiefly for measuring, metering and protection purposes. The relays and other measuring instrument operates and tolerates much lower values of current and voltage for their safe operation. In terms of usage, CTs are broadly classified as Protection CT or Metering CT. This article shall focus on Protection Class Current Transformers. It is imperative here to mention the instrument transformers (CTs & VTs) may have multiple cores, in which case separate cores may be used for metering and protection purposes, all in one instrument transformer. Multi Core CTs and VTs may have different designated class for each core. Before dwelling into explaining accuracy class of Current Transformers let us first outline the following terms: Accuracy Limit Factor At the time of fault, heavy current...
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