GE DBT, Instruction Manual

APPLICATION

6 

DBT Digital Trip Coil Supervision Relay 

GEK-105597C

2.4  RECOMMENDED SETTINGS 

 
This section is only included for customer information, given the importance of the right choice of settings to ensure 
good protection and a range of possible applications. 
 

Resistance 

 
Because the coil is made of copper its resistance varies considerably with temperature. The temperature coefficient 
of copper is approximately 0.43%/ºC (see UNE 20-003 “Annealed and industrial copper for electrical applications”). 
This means that, at an ambient temperature of 0ºC, resistance is 8.6% lower than that measured at an ambient 
temperature of 20ºC. 
 
Furthermore, the resistance of cables connected to resistance measurement inputs of the relay can vary the 
resistance measured by the DBT (as a result of common mode impedance effect). 
 
It is also sometimes difficult to measure the resistance of a coil, or perhaps this information does not appear in the 
technical data on the coil. 
 
A practical way of adjusting the DBT is to vary the resistance setting, starting from the minimum value (50 

Ω

) until the 

relay disables its resistance monitoring output. It is advisable to increase this setting to approximately 20% to reduce 
the impact of temperature and ground impedance. 
 
If the setting cannot be made in this manner, apply the maximum setting (200 

Ω

) to avoid unwanted operation. 

Voltage 

 
The recommended setting is al 10% less than the lowest expected voltage from the battery. 
 

Time 

 
The recommended time varies depending on the application. 
 
In any case, the time set must be greater than the maximum time during which both auxiliary breaker contacts (52a 
and 52b) are open simultaneously. The reason for this requirement is that during that time, the resistance measured 
by the DBT protection is infinite for both inputs (52a and 52b) indicating a fault. This fault could produce a COIL alarm 
if this situation is maintained over the time set in the relay. 
 
If other auxiliary contacts are connected in series with 52a or 52b contacts (i.e. springs, etc.) their response time 
should be included in the calculation of the total time of coincidence of 52a and 52b open.