1 2 3 4 A - SIPROTEC

Functions
2.9 Thermal Overload Protection
Output of Results
232
The hot-spot temperature is calculated for the winding which corresponds to the side of the protected object
configured for overload protection (Subsection 2.1.4, margin heading „Further 3-phase Protection Functions“,
address 442). The calculation includes the current of that side and the cooling temperature measured at a
certain measuring point. The phase information is taken from the concerned phase in case of generators,
motors, etc., or wye- or zigzag-connected transformer windings; in case of delta-connected transformer
windings the phase-difference currents are decisive which correspond to the current flowing in the winding.
There are two thresholds which can be set. They output a warning (Stage 1) and an alarm (Stage 2) signal.
When the alarm signal is assigned to a trip output, it can also be used for tripping the circuit breaker(s).
For the middle ageing rate, there is also a threshold for each of the warning and the alarm signal.
The status can be read out from the operational measured values at any time. The information includes:
• hot-spot temperature for each winding in °C or °F (as configured),
• relative ageing rate expressed in per unit,
• load backup up to warning signal (Stage 1) expressed in per cent,
• load backup up to alarm signal (Stage 2) expressed in per cent.
Further limit values can be set on the thermobox itself, as in Section „RTD-Boxes for Overload Recognition“
2.9.5 Setting Notes
General
Note
The first thermal overload protection is described in the setting instructions. The parameter addresses and
message numbers of the second thermal overload protection are described at the end of the setting instructions
under „Additional Thermal Overload Protection Functions“.
The overload protection can be assigned to any desired side of the protected object. Since the cause of the
overload current is outside the protected object, the overload current is a through-flowing current, the overload
protection may be assigned to a feeding or a non-feeding side. When setting the assignment of the protection
functions to the sides of the protected object according to Subsection 2.1.4, margin heading „Further 3-Phase
Protection functions“, you have performed this assignment under address 442 THERM. O/L AT. Respective
notes are given here.
Three methods are available for overload detection, as set out above. During configuration of the functional
scope (section 2.1.3.1) it was set under address 142 THERM. OVERLOAD whether the overload protection must
function according to the thermal replica (THERM. OVERLOAD = th rep w.o. sen), if necessary, under
inclusion of the environmental or coolant temperature (THERM. OVERLOAD = th repl w. sens) or whether
the hot-spot calculation according to IEC 60354 must be executed (THERM. OVERLOAD = IEC354). In the
latter two cases, at least one RTD-box 7XV5662-xAD must be connected to the device in order to digitally
inform the device about the coolant temperature. The required data for the RTD-box were set under address
191 RTD CONNECTION (section 2.1.3.1).
Under address 4201 THERM. OVERLOAD overload protection ON or OFF can be set. If address 142 THERM.
OVERLOAD has been set to th rep w.o. sen during configuration of the functional scope, the setting Alarm
Only is also possible. With that latter setting the protection function is active but only outputs an alarm when
the tripping temperature rise is reached, i.e. the output function is not active. The option Block relay allows
to operate the protection but the trip output relay is blocked.
SIPROTEC, 7UT6x, Manual
C53000-G1176-C230-2, Release date 06.2012