Setting Guideline - ABB REB670 Applications Manual

1MRK 505 337-UUS -
7.5.3
Application manual
If the heat content of the protected transformer reaches a set alarm level a signal can be
given to the operator. Two alarm levels are available. This enables preventive actions in
the power system to be taken before dangerous temperatures are reached. If the
temperature continues to increase to the trip value, the protection initiates a trip of the
protected transformer.
After tripping by the thermal overload protection, the transformer will cool down over
time. There will be a time gap before the heat content (temperature) reaches such a level
so that the transformer can be taken into service again. Therefore, the function will
continue to estimate the heat content using a set cooling time constant. Energizing of the
transformer can be blocked until the heat content has reached a set level.

Setting guideline

The parameters for the thermal overload protection, two time constants (TRPTTR, 49) are
set via the local HMI or Protection and Control IED Manager (PCM600).
The following settings can be done for the thermal overload protection:
Operation: Disabled/Enabled
Operation: Sets the mode of operation. Disabled switches off the complete function.
GlobalBaseSel: Selects the global base value group used by the function to define (IBase),
(UBase) and (SBase).
IRef: Reference level of the current given in % of IBase. When the current is equal to IRef
the final (steady state) heat content is equal to 1. It is suggested to give a setting
corresponding to the rated current of the transformer winding.
IRefMult: If a binary input ENMULT is activated the reference current value can be
multiplied by the factor IRefMult. The activation could be used in case of deviating
ambient temperature from the reference value. In the standard for loading of a transformer
an ambient temperature of 20°C is used. For lower ambient temperatures the load ability
is increased and vice versa. IRefMult can be set within a range: 0.01 - 10.00.
IBase1: Base current for setting given as percentage of IBase. This setting shall be related
to the status with no COOLING input. It is suggested to give a setting corresponding to the
rated current of the transformer with natural cooling (OA).
IBase2: Base current for setting given as percentage of IBase. This setting shall be related
to the status with activated COOLING input. It is suggested to give a setting
corresponding to the rated current of the transformer with forced cooling (FOA). If the
transformer has no forced cooling IBase2 can be set equal to IBase1.
Section 7
Current protection
199