Tank Leakage Protection - Siemens siprotec SJ62 User Manual

2 Functions
2.5.3

Tank Leakage Protection

Application
Example
127
For protection against overvoltages it is also important that the device is directly con-
nected to the grounded side of the current transformers so that the high voltage at the
resistor can be kept away from the device.
For generators, motors and shunt reactors high-impedance protection can be used
analogously. All current transformers at the overvoltage side, the undervoltage side
and the current transformer at the starpoint have to be connected in parallel when
using auto-transformers.
In principle, this scheme can be applied to every protected object. When applied as
busbar protection, for example, the device is connected to the parallel connection of
all feeder current transformers via the resistor.
The tank leakage protection has the task to detect ground leakage — even high-resis-
tive — between a phase and the frame of a power transformer. The tank must be iso-
lated from ground. A conductor links the tank to ground, and the current through this
conductor is fed to a current input of the relay. When a tank leakage occurs, a fault
current (tank leakage current) will flow through the grounding conductor to ground.
This tank leakage current is detected by the single-phase overcurrent protection as an
overcurrent; an instantaneous or delayed trip command is issued in order to discon-
nect all sides of the transformer
A high-sensitivity single-phase current input is normally used for tank leakage protec-
tion.
Figure 2-40 Principle of tank-leakage protection
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015