Setting Guideline - ABB REC670 Applications Manual

Section 8
Current protection
8.8.3
192
• OA: The air is naturally circulated to the coolers without fans and the oil is
naturally circulated without pumps.
• FOA: The coolers have fans to force air for cooling and pumps to force the
circulation of the transformer oil.
The protection can have two sets of parameters, one for non-forced cooling and one
for forced cooling. Both the permissive steady state loading level as well as the
thermal time constant is influenced by the cooling system of the transformer. The
two parameters sets can be activated by the binary input signal COOLING. This
can be used for transformers where forced cooling can be taken out of operation,
for example at fan or pump faults.
The thermal overload protection estimates the internal heat content of the
transformer (temperature) continuously. This estimation is made by using a thermal
model of the transformer which is based on current measurement.
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)
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: Off/On
Operation: Sets the mode of operation. Off 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
1MRK 511 401-UEN A
M13250-3 v8
Bay control REC670 2.2 IEC
Application manual