Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
438
3.3.17 Checking the 100 % Stator Earth Fault Protection
General
The 100% stator earth fault connection is tested together with the 90% stator earth fault protection.
Set the 100% stator earth fault protection (address 5301 100% SEF-PROT.) to Block relay (if not done so
already). Also, the accessories of the protection 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. Read out the rms current I SEF. The fault value
thus calculated should correspond at most to half the pickup value SEF I>> (address 5306), in order to
achieve the desired safety margin.
Shut down 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.
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 under U
N
/√3) until the 90% earth fault protection (Pickup thresh-
old U0>) has picked up.
With the earth fault bridge in place, the resistance stages of the 100% protection (warning and trip stage) must
pick up immediately on switching in the supply voltage of the 20 Hz generator.
To check the pickup behaviour of the current stage SEF I>>, read out the measured value I SEF from the
operational measured values at approx. 10 % to 20 % of the displacement voltage. The value thus obtained
should be about the same as the pickup value SEF I>> selected at address 5306. This ensures that the
current stage of the 100% stator earth fault protection covers a protection zone of about 80 % to 90 % of the
winding in addition to the 100 % resistance calculation.
Check Using Network Earth Fault
With the primary plant voltage-free and earthed, install a single-pole earth fault bridge on the high voltage side
of the unit transformer.
DANGER!
Primary measurements may only be carried out with the generator at stand–still on disconnected and grounded
equipment of the power system.
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