To implement the above concept, a separate injection box is required. The injection
box generates a square wave voltage signal which for example, can be fed into the
secondary winding of the generator neutral point voltage transformer or the grounding
transformer. This signal is propagated through the transformer into the stator circuit.
Thus, any connection or interference into the existing stator primary circuit or re-
arrangement of the primary resistor is not required.
The magnitude of the injected voltage signal is measuredat the injection point. In
addition, the resulting injected current is measured through a resistive shunt located
within the injection device. These two measurements are fed to the IED. Based on
these two measured quantities, the protection IED determines the stator winding
resistance to ground. The resistance value is then compared with the preset fault
resistance alarm or trip levels.
When the synchronous machine is at standstill, the protection function can not only
detect the earth fault at the generator star point, but also along the stator windings and
at the generator terminals, including the connected components such as voltage
transformers, circuit breakers, excitation transformer and so on. The protection
function is fully operative in all operating conditions when stable measurements are
achieved. Both functions STTIPHIZ and ROV2PTOV shall be configured and shall
operate in parallel in the same REG670 in order to perform the 100% stator earth-fault
protection function. STTIPHIZ performs the earth-fault protection based on the
injection principle to protect the section of the stator windings close to the generator
neutral point; the function ROV2PTOV performs the standard 95% stator earth-fault
protection based on the neutral point fundamental frequency voltage displacement.
For a detailed description of 100% stator earth fault protection STTIPHIZ and
sensitive rotor earth fault protection, see document no
1MRG005030 "Application
example for injection based 100% Stator EF and Sensitive Rotor EF protection."
8.8.2.1
100% Stator earth fault protection function
The injection to the stator is schematically shown in figure
. It should be observed
that in this figure injection equivalent circuit is also shown with all impedances and
injection generator related to the primary side of the neutral point voltage transformer.
Points a & b indicate connection terminals for the injection equipment. Similar
equivalent circuit can be drawn for all other types of generator stator earthing shown
in latter figures.
Section 8
1MRK 502 071-UEN -
Impedance protection
300
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Содержание Relion REG670
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