Feeder Protection Relay

  • Technical Articles
  • Mar 01,18
The relay showcased by JVS results in faster response time due to mini-core digital signal processing.
Feeder Protection Relay

The relay showcased by JVS results in faster response time due to mini-core digital signal processing

JVS Electronics has been providing solutions in the electrical protection industry for over two decades by conceptualising new designs, developing new products, making products more user friendly and adding value to the businesses. The protection relay developed by the company provides time graded phase and earth fault (2 stage)protection, (high impedance) restricted earth fault/sensitive earth fault protection with communication facility. It has multi short auto re-closer facility for breaker operation, monitoring breaker status and gives indication about the trip coil healthiness. It also has IEC61850 compatibility port, to interface to SCADA system.

Principle of operation

The relay measures the line current from each of the line CTs and if the current exceeds the set threshold, then relay extends a trip signal after an operating time. The relays ‘operating time’ is determined by selecting ‘definite time’ or one of the six ‘inverse time’ characteristics. Input to sensitive earth fault can be derived in two ways: Residual current, derived from three phase current transformers can be used as an input and output of core balance current transformer (CBCT) having appropriate characteristics can be used as an input.

Input to high impedance restricted earth fault protection will be derived from neutral CT output with an external stabilising resistor. Phase over current, earth fault, sensitive earth fault/restricted earth fault protections features can be made active or inhibit independently. Inhibition of all protection is not possible.

TCSR

TCSR monitors trip coil continuously. If the trip circuit (or any coil) that is being supervised develops a snag, then the supervision relay extends an alarm without a delay. The relay monitors the trip coil under all the states of a breaker viz. close, open and during the transition. The underlying mechanism of supervision is to perform hi-impedance measurement across two input circuits appropriately wired along with trip coil, 52A and 52B auxiliary contacts. 2 NO and 1 NC contacts have been provided for the purpose of alarm and SCADA. The current rating of these contacts is 5A at 24VDC/230VAC.

Auto re-close facility

Relay has a multi shot auto re-closer that facilitates automation for breaker operation. Auto re-closer can be programmed to provide a maximum of five shots. ‘Dead time’ starts when a trip signal is provided due to the occurrence of a fault involving L-L or L-G or L-L-G or L-L-L or L-L-L-G. After an elapse of a time interval equal to ‘dead time'’, closing command will be extended. The ‘reclaim time’ timer starts at the instant when the ‘dead time’ timer expires. If after extending the ‘breaker close’ signal an over current fault was detected before the ‘reclaim time’ timer reached its terminal count, then the relay understands that the fault in the system is still persisting and the over current relay will issue a trip signal. The relay tries to close the breaker for a maximum of the programmed number of shots before it chooses to lockout. The relay can be configured for independant trip sequence as IDMT or Definite time.

Stuck breaker protection/Local breaker back-up protection

The relay monitors line current even after the trip condition to ensure breaker operation. Even if small current exist in the line the relay sends trip command to adjacent or backup breaker after definite operating time. The current threshold and definite time required to detect breaker failure are programmable.

Programmable digital inputs-outputs

The relay has 4 programmable digital inputs (PDI) and 4 programmable digital outputs, which can he used to synthesize logic along with some internal digital inputs. Together, this feature can be effectively used to reduce the number of auxiliary tripping relays in a protection scheme.

Trip test facility

The trip test will facilitate testing of relay operation without applying the input current. The trip test is useful to test the panel wiring and operation of breaker without any current. The trip contact will operate instantaneously. The phase and earth fault alarm contact will not operate during the trip test.

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