Tank Leakage Protection - Siemens 7SC80 Manual

High-impedance Protection
With 7SC80, the sensitive measuring input Ι
the protection detects current through the resistor instead of the voltage across the resistor R.
The following figure shows the connection diagram. The protection device is connected in series to resistor R
and measures its current.
Varistor B limits the voltage when internal faults occur. High voltage peaks emerging with transformer satura-
tion are cut by the varistor. At the same time, voltage is smoothed without reduction of the mean value.
[sj6x-ueb-einph-hochimpedanz3-141103, 1, en_US]
Figure 2-44
For protection against overvoltages, it is also important that the device is directly connected to the grounded
side of the current transformers so that the high voltage at the resistor can be kept away from the device.
The high-impedance differential protection can be used analogously for generators and parallel reactors. All
current transformers at the overvoltage side, undervoltage side, and the neutral point current transformer
have to be connected in parallel when using auto transformers.
In principle, this procedure 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.

Tank Leakage Protection

2.5.3
Application Example
The tank leakage protection has the task to detect ground leakage — even high-ohmic — between a phase
and the frame of a power transformer. The tank must be isolated 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 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 disconnect all sides of the transformer.
A high-sensitivity single-phase current input is used for tank leakage protection.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Connection diagram of the ground fault differential protection according to the high-impe-
dance principle
is used for high-impedance protection. As this is a current input,
Ns
2.5 Single-Phase Overcurrent Protection
Functions
169