3.4 Primary Commissioning Tests with the Generator
377
7UM62 Manual
C53000-G1176-C149-3
Figure 3-33
Neutral displacement voltage during earth faults
Checking for
Generator Earth
Fault
Switch stator earth fault protection
(address
) to
Block relay
.
If the sensitive earth fault protection is used for stator earth fault protection, it must be
set to
Block relay
as well under address
With the primary plant voltage-free and earthed, install a single-pole earth fault in the
proximity of the generator terminals.
Start up generator and slowly excite (however, not above U
N
/
√
3) until the stator earth
fault protection picks-up.
Read out U
E
from the operational measured values and check for plausibility. If the
connections are correct, this value corresponds with the machine terminal voltage in
percent, referred to rated machine voltage (if applicable, deviating rated primary
voltage of earthing transformer or neutral earthing transformer must be taken into
account). This value also corresponds with the setting value
under address
If the plant comprises more voltage transformers with broken delta windings, the
voltage U
E
must be measured on them as well.
For protection zone Z the following applies:
Example:
Machine voltage at pick-up
0.1 x U
sec N
Measured value
U
E
= 10 V
Setting value
U0>
= 10 V
Protected zone
Z
= 90 %
Read out the indication “
Uearth Lx
” in the fault annunciations. The “Lx” indicates the
faulted phase provided voltages are connected to the voltage protection inputs of
7UM62.
Shut down generator. Remove earth fault bridge.
Pick–up value
0,5
1,0
10 %
40 %
100 %
corresponds to 90 % protected zone
Earth fault on machine side
Earth fault on
upper voltage side
Value extrapolated to
100 % U
Nmach
U
E
U
ERD>
U
U
N mach
DANGER!
Primary measurements must only be carried out with the generator at stand–
still on disconnected and grounded equipment of the power system.
Z
U
sec N
U0>
–
U
sec N
----------------------------------
100 %
⋅
=