Installation and Connection
Voltage Transformers
Check the installation direction of the VTs.
It is imperative that the secondary sides of measuring transformers be
grounded.
For current and voltage sensing function external wired and appropriate
current and voltage transformer shall be used, based on the required input
measurement ratings. Those devices provide the necessary insulation
functionality.
Check of the Voltage Measuring Values
Connect a three-phase measuring voltage equal to the rated voltage to the relay.
Take connection of the measuring transformers (star connection/open delta
connection) duly into account.
Now adjust voltage values in the nominal voltage range with the corresponding nominal frequency which are not
likely to cause overvoltage- or undervoltage trips.
Compare the values shown in the device display with the readings of the measuring instruments. The deviation
must be according to the technical data.
When r.m.s. value measuring instruments are used, higher deviations can
arise if the fed voltage has a very high harmonic content. Since the device
is provided with a filter for the harmonics, only the fundamental oscillation
is evaluated (exception: thermal protection functions). If, however, a r.m.s.
value forming measuring instrument is used, the harmonics are also
measured.
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EN MRU4 10/09
