Thermal Overload Protection, Two Time Constants Trpttr; Introduction; Principle Of Operation - ABB Relion 670 Series Technical Reference Manual

Section 6
Current protection
6.3
6.3.1
6.3.2
170
Thermal overload protection, two time constants
TRPTTR
Function description
Thermal overload protection, two time
constants

Introduction

If a power transformer or generator reaches very high temperatures the equipment
might be damaged. The insulation within the transformer/generator will have
forced ageing. As a consequence of this the risk of internal phase-to-phase or phase-
to-earth faults will increase. High temperature will degrade the quality of the
transformer/generator insulation.
The thermal overload protection estimates the internal heat content of the transformer/
generator (temperature) continuously. This estimation is made by using a thermal
model of the transformer/generator with two time constants, which is based on
current measurement.
Two warning levels are available. This enables actions in the power system to be
done before dangerous temperatures are reached. If the temperature continues to
increase to the trip value, the protection initiates a trip of the protected transformer/
generator.

Principle of operation

The sampled analogue phase currents are pre-processed and for each phase current
the true RMS value of each phase current is derived. These phase current values
are fed to the Thermal overload protection, two time constants (TRPTTR).
From the largest of the three phase currents a relative final temperature (heat
content) is calculated according to the expression:
IEC 61850 IEC 60617
identification identification
TRPTTR
SYMBOL-A V1 EN
1MRK 505 208-UEN B
ANSI/IEEE C37.2
device number
49
Technical reference manual