DESCRIPTION
GEK-105597C
DBT Digital Trip Coil Supervision Relay
3
1. DESCRIPTION
The DBT is a digital trip coil supervision relay. This supervision includes:
•
Integrity of coils (monitoring continuously their resistance). In case coils are in a good condition, the output COIL
OK will be activated.
•
Control voltage (supervision of low voltage). If voltage is correct, the output BREAKER VOLTAGE OK will be
activated.
•
Checks the breaker control circuit. If both control voltage AND coils integrity are correct, then the output
BREAKER CIRCUIT OK will be activated.
Note:
The activation of a NO (Normally Open) output means contacts will be closed, whereas the activation of a NC
(Normally Closed) output means contacts will be opened.
In its single-coil version, the DBT monitors coil continuity whether the breaker is open or closed. It also has a timing
device to avoid indicating failure signals during opening to closing transitions.
The three-coils version of the DBT can monitor three coils at a time, regardless of the position of the breaker, and
with timer delay for transitions.
In addition to coil monitoring, both versions (single- and three-coil) have a continuous DC undervoltage function to
monitor the battery’s power supply.
The supervised coils can be either the tripping or the closing ones, futhermore, in the three-phase version coils can
be coming from different breakers. Instead of measuring the continuity of the circuit (like other relays), the DBT
measures real resistance. It injects a current of 5 mA, limited to a maximum of 24 V. By measuring the voltage drop
in the coil the DBT calculates the resistance.
Figure 3 shows a typical three-coil DBT connection to a coil. In this way the relay can measure the coil resistance at
any time (in reality, the association of the breaker coil with any other auxiliary coils), either by the 52/a type contact, if
the breaker is closed, or the 52/b type if it is open. The relay also measures the breaker power supply at terminals B1
and B2.
The advantage of measuring real resistance is in selectivity, as failures in trip circuits can be detected apart, even in
cases where auxiliary circuit coils are connected in parallel. In these situations a break or interruption of the breaker
coil would not be detected by a continuity measurement because the auxiliary coils would create an alternative path
to the current flow. On the other hand, a resistance measurement like that made by the DBT is a valid procedure
because the resistance will rise when the breaker coil fails.
An extra advantage of the DBT is in its limitation of current sources to a maximum of 24 V, which avoids the DBT
operating other high impedance auxiliary circuits. This kind of circuits run the risk of being enabled by the low level of
milliamperes injected by conventional monitoring relays.
When maintenance work is carried out on the breaker, a disable switch available on the front of the relay should be
operated in order to deactivate all the outputs. The effect produced is similar to a lack of continuous auxiliary voltage
as shown in figures 2 and 3.
This inhibition can also be done by energizing a digital input. The three-coil model has four inputs and the single-coil
model just one.
Summary of Contents for DBT
Page 5: ...DESCRIPTION 4 DBT Digital Trip Coil Supervision Relay GEK 105597C ...
Page 9: ...MODEL LIST 8 DBT Digital Trip Coil Supervision Relay GEK 105597C ...
Page 15: ...TECHNICAL CHARACTERISTICS 14 DBT Digital Trip Coil Supervision Relay GEK 105597C ...
Page 24: ...FIGURES GEK 105597C DBT Digital Trip Coil Supervision Relay 23 FIGURE 1 NAMEPLATE 226B1298H3 ...
Page 30: ...FIGURES GEK 105597C DBT Digital Trip Coil Supervision Relay 29 FIGURE 7 BLOCK DIAGRAM ...