3 Installation and Commissioning
378
7UM62 Manual
C53000-G1176-C149-3
Check Using
Network Earth Fault
With the primary plant voltage-free and earthed, install a single-pole earth fault bridge
on the primary side of the unit transformer.
Start up machine and slowly excite to 30 % of rated machine voltage.
Read out U
E
in the
OPERATIONAL MEASURED VALUES
. This value is extrapolated to
rated machine voltage (Figure 3-33). The fault value thus calculated should
correspond, at the most, to half the pick-up value
(address
), in order to
achieve the desired safety margin.
Shut down generator. Remove earth fault bridge.
If the starpoint of the high-voltage side of the unit transformer is to be earthed during
normal operation, re-establish starpoint earthing.
Switch stator earth fault protection to be operative: address
=
ON
. If the sensitive earth fault detection is used for stator earth fault protection, switch
it to be operative as well: address
=
ON
.
3.4.6.2
Busbar Connection
Firstly, the correct functioning of the loading equipment must be checked: sequencing,
time limit, etc., as well as the plant data, the earthing transformer and the value of the
load resistor (tapping).
Switch stator earth fault protection (address
) to
Block relay
. If the sensitive
earth fault detection is used for stator earth fault protection, switch it to
Block relay
as well under address
With the primary plant earthed and voltage-free, install earth fault bridge between
generator terminals and toroidal current transformer (Fig. 3-34).
DANGER!
Primary measurements must only be carried out with the generator at stand–
still on disconnected and grounded equipment of the power system.
Caution!
The starpoints of the unit transformer must not be connected to earth during this test!
DANGER!
Primary measurements must only be carried out with the generator at stand–
still on disconnected and grounded equipment of the power system.
