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3 Installation and Commissioning
Spill Current
3.4.7
Testing the 100–% Stator Earth Fault Protection
Check without
Earth Fault
Check Performed
with an Earth Fault
in the Machine
Zone
382
If, in an isolated network, the voltage connections for the reactive current
measurement should be maintained for testing, then it should be noted that with a
power flow with inductive component in forwards direction results in a backwards
direction for the earth fault relay (contrary to an earth fault in this direction).
Shut down generator after completion of the directional tests. Correct connections
must be re-established and re-checked.
For calibration to the spill current, a three-pole short-circuit bridge that is able to
withstand rated current is installed at the circuit breaker. Start up generator and slowly
excite until the rated machine current is reached.
Read out the operational measured value I
setting value of address 5003 3I0>. Parameter 3I0> should be about twice that
measured value to ensure a sufficient security distance between the earth fault current
used for directional determination and the spill current. Next, check whether the
protection zone determined by the setting value U0> must be reduced.
Switch the stator earth fault protection to be operative: address 5001 S/E/F PROT.
= ON.
The 100-% stator earth fault connection is tested together with the 90-% stator earth
fault protection (see Section 3.4.6.1, Unit Connection).
Set the 100-% stator earth fault connection (address 5301 100% SEF-PROT.) to
Block relay (if you have not done so already). Also, the accessories of the protec-
tion device must be operational.
The tests to be performed are described in more detail below.
Start up the generator and excite it to maximum generator voltage. The protection
does not pick up.
The operational measured values need to be checked as well (see also Section 3.3.8).
Read out the r.m.s. current I SEF. The fault value thus obtained should not exceed half
the pickup value SEF I>> (address 5306) to allow for the desired safety margin.
Shut down the generator.
Connect the 20 Hz generator 7XT33 to the DC voltage or to an external three-phase
voltage source.
With the primary equipment disconnected and earthed, insert a single-pole earth fault
bridge in the generator terminal circuit.
DANGER!
Primary measurements may only be carried out with the generator at stand–still
on disconnected and grounded equipment of the power system.
Start up the generator and excite it slowly (but to less than U
fault protection (Pickup threshold U0>) has picked up (see also Section 3.4.6.1, side
title "Checking for Generator Earth Fault").
. This measured values determines the
EE2
/√3) until the 90-% earth
N
7UM62 Manual
C53000-G1176-C149-3
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