Output of Results
The hot-spot temperature is calculated for the winding which corresponds to the side of the protected object
configured for overload protection (Section 2.1.4.3 Assignment of Protection Functions to Measuring Loca-
tions / Sides, 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 infor-
mation 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 deci-
sive 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”
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 over-
load 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 Section 2.1.4.3 Assignment of Protection
Functions to Measuring Locations / Sides, 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 Setting Notes) 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 Setting Notes).
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
ThOverload TRIP
is not
active. The option Block relay allows to operate the protection but the trip output relay is blocked.
k-Factor
The rated current of the side of the main protected object which is assigned to the overload protection is taken
as the base current for detecting an overload. The setting factor k is set in address 4202 K-FACTOR. It is deter-
mined by the relation between the permissible thermal continuous current and this rated current:
2.9.5
Functions
2.9 Thermal Overload Protection
SIPROTEC 4, 7UT6x, Manual 205
C53000-G1176-C230-5, Edition 09.2016
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