Different Types of Relay Connections

Different types of Relay wiring CT CONNECTIONS 1.Simple O/C wiring

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Here CT are connected in Star and relay is also connected in Star.No earth fault(Io) element in relay In this no provision for neutral current/voltage, hence cant be used for earth fault protection 3 o/c protections,over load protections etc

2. O/C and E/F element combined

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Here CT is in Star and relay is also Star connected.But there is additional earth fault coil made of CTs earthed star point. In the second case the earth fault element is directly connected to the Summation ring CT. Can be used for non directional O/C + E/F

3. Differential Protection CT Connections

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In Differential protection we have to connect the CT secondary in current circulating mode In old practice in Star side CTs are connected in Delta and vice versa to avoid phase displacwmwnt problems.But in modern numerical relays it is possible to provide comprnsation in software.

4. REF Protection

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In REF the sum of all phase CTs are connected across N.CT as current in current circulating mode There will be metrosils,stabilizing resistors etc. Before connecting to relay

5. Differential + REF

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Genaral Note   

CTs can be connected either in delta or in star.Only important thing is that we have to take are of extra arrangments like aux. Ct etc. for getting desired o/p. We can also reverse the primary polarity of CTs but we have to reverse secondary also. In differential,REF and similar protections the CTs must be connected in current circulating mode.So we have to change the polarity accordingly.

VT CONNECTIONS 1.

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Here no provision for neutral voltage Can be used for 29,59,81 etc

For Neutral voltage