3 Mounting and Commissioning
398
7UT613/63x Manual
C53000-G1176-C160-2
DANGER!
Operations in the primary area must be performed only with plant sections
voltage-free and earthed! Perilous voltages may occur even on voltage-free
plant sections due to capacitive influence caused by other live sections!
On network power transformers and asynchronous machines a low-voltage test is
preferably used. A low-voltage current source is used to energise the protected object,
which is completely disconnected from the network. A short-circuit bridge, which is
capable of carrying the test current, is installed outside the protected zone and allows
the symmetrical test current to flow. On transformers, the test source is normally con-
nected at the primary side, and the short-circuit bridges are on the lower voltage side.
Figure 3-25 Test installation with low-voltage source — example for transformer and motor
On power station unit transformers and synchronous machines, the checks are per-
formed during the current tests, with the generator itself supplying the test current. The
current is produced by a short-circuit bridge which is installed outside the protected
zone and is capable of carrying generator rated current for a short time.
Figure 3-26 Test installation at power station with generator as voltage source — example
On busbars and short lines a low-voltage test source can be used or alternatively one
can test with load current. In the latter case the above hints about backup protection
must be observed!
With the single-phase differential protection for busbars
with more than 2 feeders,
symmetrical current test is not necessary (but permissible, of course). The test can be
carried out using a single-phase current source. However, current tests must be per-
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