3 Installation and Commissioning
382
7UM62 Manual
C53000-G1176-C149-3
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.
Spill Current
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
EE2
. This measured values determines the
setting value of address
. Parameter
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
must be reduced.
Switch the stator earth fault protection to be operative: address
=
ON
.
3.4.7
Testing the 100–% Stator Earth Fault Protection
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
) 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.
Check without
Earth Fault
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
(address
) to allow for the desired safety margin.
Shut down the generator.
Check Performed
with an Earth Fault
in the Machine
Zone
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.
Start up the generator and excite it slowly (but to less than U
N
/
√
3) until the 90-% earth
fault protection (Pickup threshold U0>) has picked up (see also Section 3.4.6.1, side
title “Checking for Generator Earth Fault”).
DANGER!
Primary measurements may only be carried out with the generator at stand–still
on disconnected and grounded equipment of the power system.
