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3 Mounting and Commissioning
• The power measurement provides an initial indication as to whether the measured
• The measurements may have to be repeated after correcting the connections.
• The above described tests of the measured quantities also have to be performed at
• The protected object is now switched off, i.e. the circuit breakers are opened.
If the standard connection of the device is used whereby current input I
Polarity check for
the current measur-
in the starpoint of the set of current transformers (refer also to the connection circuit
ing input I
diagram in the Appendix A.3), then the correct polarity of the earth current path in
4
general automatically results.
If, however, the current I
rection check with this current is necessary.
The test is done with a disconnected trip circuit and primary load current. It must be
noted that during all simulations that do not exactly correspond with situations that
may occur in practice, the non-symmetry of measured values may cause the mea-
sured value monitoring to pickup. This must therefore be ignored during such tests.
DANGER!
Hazardous voltages during interruptions in secondary circuits of current trans-
formers
Non-observance of the following measure will result in death, severe personal injury
or substantial property damage.
Short-circuit the current transformer secondary circuits before current connections to
the device are opened.
312
values of one end have the correct polarity.
– If the direction of the reactive power is correct but the sign of the active power is
incorrect, cyclic phase swapping of the currents (right) or of the voltages (left)
might be the cause;
– If the direction of the active power is correct but the reactive power has an incor-
rect sign, cyclic phase swapping of the currents (left) or of the voltages (right)
might be the cause;
– if the signs of both active and reactive power are incorrect, the polarity in address
201 CT Starpoint has to be checked and corrected.
The phase angles between currents and voltages must also be conclusive. All three
phase angles ϕ (U
–I
) must be approximately the same and represent the oper-
Lx
Lx
ating status. In the event of power in the direction of the protected object, they cor-
respond to the current phase displacement (cos ϕ positive); in the event of power
in the direction of the busbar they are higher by 180° (cos ϕ negative). However,
charging currents might have to be considered (see above).
the other end of the tested current path. The current and voltage values as well as
the phase angles of the other end can also be read out locally as percentage values.
Please observe that currents flowing through the object (without charging currents)
ideally have opposite signs at both ends, i.e. they are turned by 180°. In the „WEB-
Monitor", the local and remote measured values can be shown graphically. An
example is shown in Figure 3-25.
is derived from a separate summation CT an additional di-
4
is connected
4
7SD610 Manual
C53000-G1176-C145-4
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