Application; Direct Connection To Coil; Use As A Dc Undervoltage Relay; Different Connections For Independent Batteries - GE Multilin DBT Instruction Manual

Digital trip coil supervision relay

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APPLICATION

2. APPLICATION

The DBT has been designed to monitor the biggest possible number of elements in the tripping and closing circuits of

the breaker. The relay checks voltages, coil resistance and the integrity of the auxiliary contacts 52/a and 52/b, since

they are also part of the trip and close circuits of the breaker.

For safety reasons, in order to avoid signalling BREAKER CIRCUIT OK when auxiliary voltage is low, it is strongly

recommended using a NO output. When using a NO output the DBT protection will energize that relay and will

CLOSE that output contacts if both voltage and coil are correct. When auxiliary voltage is low (or null) or there is a

failure in the breaker coil circuit, that output will be OPENED, indicating breaker circuit failure.

Although there are two connections for each coil (one through 52/a and the other through 52/b) these cannot be used

for two different coils because the relay compares the resistance measured by each contact. A three-phase relay is

designed to monitor up to 3 coils and a single-phase relay just one.

If, for whatever reason, there is a need to make a direct connection to the coils without going through contacts 52/a

and 52/b (in this case monitoring of these would be lost), it can be done. The connection of the coil at the input of

52/a has to be wired and leave input 52/b unconnected.

If you only want to use the undervoltage unit this can be done by simply disabling the coil monitoring units.

This inhibition is done by connecting inputs 52/a (terminals B3, B5 and B7 on the three-phase model, terminal B3 on

the single-phase) to the negative of the breaker power supply (terminal B2), leaving inputs 52/b unconnected

(terminals B4, B6 and B8 of the three-phase, B4 of the single-phase).

Once the resistance monitoring is disabled, when undervoltage condition occurs the BREAKER VOLTAGE OK and

the BREAKER CIRCUIT OK contacts will become deactivated.

Although the installation has just one battery, voltage can be distributed through different circuits (each one protected

by a MCB). If you connect the auxiliary voltage (terminals B9-B10) to a different circuit from the breaker power supply

circuit (terminals B1-B2), in the event of an incident in the breaker power supply (where the MCB trips) the DBT

continues working and is fully operative. This gives us the necessary information regarding BREAKER VOLTAGE OK

and BREAKER CIRCUIT OK.

When the auxiliary voltage fails the DBT gives a warning through the ALARM contact.

GEK-105597C

DBT Digital Trip Coil Supervision Relay

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Dbt