3 Installation and Commissioning
380
7UM62 Manual
C53000-G1176-C149-3
With Directional
Determination
The earth fault directional determination requires a check of the current and voltage
connections for correctness and correct polarity. The machine continues to be excited
to a voltage that corresponds to a displacement voltage above the pick-up value. If the
polarity is correct, the trip indication “
“ is output (LED 6 when delivered
from factory).
A cross check is then performed. After the generator has been de-excited and shut
down, the earth fault bridge is installed on the other side of the current transformers
(as viewed from the machine).
After restarting and exciting the generator above the pick-up value of the displacement
voltage, “
U0> picked up
” picks up (LED 2 for global indication of a device pick-up
when delivered from factory), however “
3I0 picked up
” does not pick up and
tripping does not occur. The measured value IEE should be negligible and on no
account should it be larger then half the setting value
Shut down and de-excite generator. Remove earth fault bridge.
Directional Check
with Toroidal CTs
without Loading
Resistor
If loading equipment is not available and if an earth fault test with the network is not
possible, then the following test can be performed with secondary measures, however
with the symmetrical primary load current:
With current supplied from a toroidal residual current transformer, a voltage
transformer (e.g. L1) is by-passed which simulates the formation of a neutral
displacement voltage (Figure 3-35). From the same phase, a test current is fed via a
current-limiting impedance Z through the toroidal transformer. The connection and
direction of the current conductor through the toroidal transformer is to be closely
checked. If the current is too small for the relay to pick-up, then its effect can be
increased by feeding the conductor several times through the toroidal transformer.
For Z either a resistor (30 to 500
Ω
) or a capacitor (10 to 100 µF) in series with an
inrush-current-limiting resistor (approximately 50 to 100
Ω
) is used. With correct
connections, the described circuit results in the alarms: “
U0 > picked up
”, “
3I0>
picked up
” and finally “
S/E/F Trip
” (LED 6).
DANGER!
Primary measurements must only be carried out with the generator at stand–
still on disconnected and grounded equipment of the power system.
