Siemens SIPROTEC 7UT613 series Manual page 40

2 Functions
Time Overcurrent
Protection for Earth
Current
Overcurrent Pro-
tection for Earth
Current 2 (Starpoint
Current)
Single-phase Over-
current Protection
Asymmetrical Load
Protection
Thermal Overload
Protection
40
There is another earth current time overcurrent protection which is independent from
the before-described zero sequence time overcurrent protection. This protection, to be
configured in address 124 DMT/IDMT Earth, acquires the current connected to a
single-phase current measuring input. In most cases, it is the starpoint current of an
earthed starpoint (for transformers, generators, motors or shunt reactors). For this pro-
tection you may select one of the characteristic types, the same way as for the phase
time overcurrent protection, no matter which characteristic has been selected for the
latter.
For earth current detection in 7UT613/63x a second earth current overcurrent protec-
tion is available with which a further single-phase overcurrent protection can be rea-
lised. If, for example, a transformer YNyn0 is earthed at both starpoints, the in-flowing
earth current can be monitored in each starpoint. Naturally, both earth current over-
current protection functions can be used completely independently at different points
of your system for the detection of single-phase currents. For DMT/IDMT Earth2
under address 138 a selection can be made from the same options independently for
the other overcurrent protection functions.
A single-phase definite-time overcurrent protection DMT 1PHASE for different user re-
quirements 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.
The asymmetrical load protection monitors the asymmetrical current (negative se-
quence system) in three-phase 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–characteristic
(TOC ANSI). It can also be supplemented by a thermal stage (DT/thermal). The
asymmetrical load protection is normally not possible in single-phase applications
(address 105 PROT. OBJECT = 1 phase transf. or 1ph Busbar).
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 ac-
cording 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 en-
vironmental 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 environ-
mental temperature is entered into the device. In this case set address 142 THERM.
OVERLOAD = th repl w. sens (thermal replica with temperature measurement).
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 calcu-
7UT613/63x Manual
C53000-G1176-C160-2