1 - What is the Master trip(Lockout) relay:

Master Trip is an auxiliary relay which works as intermediate between multiple protection relay and circuit breaker trip coil.It receives multiple tripping commands from protection relays and provides a single trip commands to the breaker trip coil. Master trip relay is not a monitoring relay. It is used as isolation of protection relay and breaker trip coil. it is used in HT panel for the safety of the protection relay. It is received multiple commands from the protection relay and then a single command is received by the breaker trip coil from the master trip coil.

2 - Working principle of master trip(Lockout) relay.

Master trip relay (MTR) is used for keeping safe conditions to the all protection relay.it is received tripping commands from auxiliary alarm and tripping relay, over current, and earth fault relay then it provides an own a single tripping command to the breaker trip circuit.

If by chance a fault occurs in the breaker trip circuit resultant a major fault current will pass towards the master trip relay from the trip circuit in this situation master trip relay will be affected but the protection relay will be safe.

master trip(Lockout) is not monitoring microprocessors so its cost is very low because it has only one coil for the closing circuit.

3 - Circuit diagram of master trip(Lockout) relay.

4 - Master trip relay Applications.

The Applications of master trip relay is so important in HT panel. Some important points is given below mentioned.

• All HT panel protection relay is isolated with breaker trip coil by using a master trip relay. If any problem creates in the tripping circuit then only the master trip relay will be affected and the protection relay will be safe.
• MTR is low cost in comparison of protection relay. So, we use MTR so that if there is a fault that occurred in the trip circuit, only MTR contact will burn and not the protection relay.
• If the Master trip Relay is not used in the HT panel then all protection relay outgoing wires will be connected to the trip coil, for this reason, a lot of wiring will have to connect to the breaker trip coil.so DC supply may be leakage and lose connection also will be increased wiring cost.
  On the other hand, if we use a master trip relay then only one wire will be connected into the tripping circuit.
• The Master trip Relay provides us with another parallel circuit for using other circuit breaker tripping, annunciator panel, interlocking, etc.

5 - Types of Master Trip Relays.

1. L & T master Trip Relays
2. ABB PQ Series Relays
3. Siemence 7PJ12 Mater Trip Relay
4. JVS master trip relay.
5. Alstom master trip relay
6. Avana Master trip realy
7. Ashida master trip relay

L & T master Trip Relays:

ABB PQ Series Relays:

ABB master trip relay is high speed tripping electromechenical relays.

• PQ8nCH2JMaster trip relay with 7 contacts, low burden
• PQ5nCH2JMaster trip relay with 4 contacts, low burden
• PQ8nC2JWMaster trip relay with 6 contacts, high burden

Siemence 7PJ12 Mater Trip Relay:

6 - What is the ANSI code of Master Trip Relay?

The Master Trip relay code of ANSI- American national standard institute is 86.

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