3.3 Commissioning
273
7UM61 Manual
C53000-G1176-C127-3
Calibrate the Im-
pedance Protection
Switch impedance protection (address
3301
) to
IMPEDANCE PROT.
=
Block
relay
.
With the primary system voltage-free and earthed, install a three-pole short-circuit
bridge which is capable of carrying rated current (e.g. earthing isolator) to the primary
side of the unit transformer.
DANGER!
Energized equipment of the power system ! Capacitive coupled voltages at discon-
nected equipment of the power system !
Non-observance of the following measure will result in death, severe personal injury
or substantial property damage.
Primary measurements must only be carried out on disconnected and grounded
equipment of the power system !
Start up machine slowly and excite to 20 % of rated machine current.
Test Instruction
A test with about 20 % of the rated generator current is sufficient for checking the
transformer connections and the operational measured values. If the relative short-
circuit voltage of the transformer is small, the voltage values measured are very low,
so that it may be necessary to increase the generator current somewhat. A test with
rated generator current is only required for the quantitative calibration of the imped-
ance protection (e.g. if it is necessary to calibrate the transformer uK).
The protection device calculates from the currents and voltages the impedance
between the point of installation of the voltage transformer set and the short-circuit po-
sition, which is mainly established by the short-circuit impedance of the unit transform-
er. Reactance and resistance values can be read out under operational measured
values. For this the protection device automatically considers the rated device current
1 A or 5 A. In the present case for transformer impedance, the following results:
Primary transformer impedance:
with
u
K
- relative transformer short-circuit voltage
U
N
- Rated transformer voltage
S
N
- Rated transformer power
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