Siemens SIPROTEC 4 7UT6 Series Manual page 34

Functions
2.1 General
tion you may select one of the characteristic types, the same way as for the phase time overcurrent protec-
tion, no matter which characteristic has been selected for the latter.
Time overcurrent protection 2 for earth current (starpoint current)
For the detection of earth current, 7UT613/63x has another earth-current time overcurrent protection avail-
able with which you can realize another single-phase time overcurrent protection. If, for example, you have
earthed a transformer YNyn0 at both starpoints, you can monitor the inflowing earth current in each star-
point. Of course, you can also use the two earth-current time overcurrent protection funtions at completely
different locations of your system for the detection of single-phase currents. For DMT/IDMT Earth2, you
may independently select under address 138 from the same options as for the other time overcurrent protec-
tion functions .
Single-phase Overcurrent Protection
A single-phase definite-time overcurrent protection DMT 1PHASE for different user requirements is available
in address 127. This protection function is very well suited e.g. for highly sensitive tank leakage protection or
high-impedance unit protection. A high-sensitivity current input can be used for this purpose.
Unbalanced Load Protection
The unbalanced load protection monitors the asymmetrical current (negative sequence system) in threephase
protected objects. In address 140 UNBALANCE LOAD the trip time characteristics can be set to definite time
(Definite Time), additionally operate according to an IEC–characteristic (TOC IEC) or to an ANSI–charac-
teristic (TOC ANSI). It can also be supplemented by a thermal stage (DT/thermal). The unbalanced load
protection is normally not possible in single-phase applications (address 105 PROT. OBJECT = 1 phase
transf. or 1ph Busbar).
Thermal Overload Protection
In address 142 THERM. OVERLOAD the user can additionally choose one of the two methods of overload
detection. Note that the overload protection for single-phase busbar protection (address 105 PROT. OBJECT
= 1ph Busbar) is not possible. If the overload protection is not required, set to Disabled. Furthermore, the
following is available:
•
Overload protection with a thermal replica according to IEC 60255-8,
•
Overload protection with calculation of hot-spot temperature and the aging rate according to IEC 60354
•
Overload protection using a thermal replica with ambient temperature influence
In the first case it can still be selected whether only the overtemperature in the thermal replica, resulting from
the ohmic losses in the windings of the protected object must be detected, or whether the total temperature
under consideration of the coolant or environmental temperature must be calculated.
If the coolant or environmental temperature must be taken into consideration, a RTD-box must be connected
to the device (see below), via which the coolant or environmental temperature is entered into the device. In
this case set address 142 THERM. OVERLOAD = th repl w. sens (thermal replica with temperature meas-
urement).
If there is no possibility to measure the coolant or environmental temperature and to pass to the device,
address 142 THERM. OVERLOAD = th rep w.o. sen (thermal replica without temperature measurement)
can be set. In this case the device calculates the overtemperature in the protected object from the flowing
current, with reference to the permissible temperature. This method is characterised by its easy handling and
a low number of setting values.
Detailed knowledge about the protected object, the environment and cooling is required for overcurrent
protection with hot-spot calculation in accordance with IEC 60354; it is advisable in case of transformers with
integrated temperature detectors. For this method, set address to 142 THERM. OVERLOAD = IEC354. For
further details see Section
Thermal overload protection 2
With 7UT613/63x you have the option to use another overload protection. It allows you, for example in a
transformer, to detect the overtemperature of two windings by current measurement, or, in addition to a
34
2.9 Thermal Overload Protection.
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016