Camille Bauer CAM mobile, Руководство пользователя

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Zero displacement voltage U
NE
Starting from the generating system with star point E
(which is normally earthed), the star point (N) on load
side is shifted in case of unbalanced load. The zero
displacement voltage between E und N may be
determined by a vectorial addition of the voltage vectors
of the three phases:
U
NE
= - (U
1N
+ U
2N
+ U
3N
) / 3
A displacement voltage may also occur due to
harmonics of order 3, 9, 15, 21 etc., because the
dedicated currents add in the neutral wire.
Earth fault monitoring in IT systems
Via the determination of the zero displacement voltage it's possible to detect a first earth fault in an
unearthed IT system. To do so, the device is configured for measurement in a 4-wire system with
unbalanced load and the neutral connector is connected to earth. In case of a single phase earth fault
there is a resulting zero displacement voltage of U
LL
/ √3. The alarming may be done e.g. by means of a
relay output.
Transformer, secondary side Load
Because in case of a fault the voltage triangle formed by the three phases does not change the voltage
and current measurements as well as the system power values will be still measured and displayed
correctly. Also the meters carry on to work as expected.
The method is suited to detect a fault condition during normal operation. A declination of the isolation
resistance may not be detected this way.