Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
275
• The power measurement provides an initial indication as to whether the measured values of one end have
the correct polarity.
– If the reactive power is correct but the active power has the wrong sign, cyclic phase swapping of the
currents (right) or of the voltages (left) might be the cause.
– If the active power direction is correct but the reactive power has the wrong sign, cyclic phase swapping
of the currents (left) or of the voltages (right) might be the cause.
– If both the real power as well as the reactive power have the wrong sign, the polarity in address
201
CT
Starpoint
must be checked and rectified.
The phase angles between currents and voltages must also be conclusive. All three phase angles
ϕ
(V
Lx
–
I
Lx
) must be approximately the same and represent the operating status. In the event of power in the direc-
tion of the protected object, they correspond 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 taken into consideration (see above).
• The measurements may have to be repeated after correcting the connections.
• The above described tests of the measured values also have to be performed at 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°.
• The protected object is now switched off, i.e. the circuit breakers are opened.
Polarity Check for the Current Measuring Input I
4
If the standard connection of the device is used whereby current input
I
4
is connected in the neutral of the set
of current transformers (refer also to the connection circuit diagram in the Appendix A.3), then the correct po-
larity of the ground current path in general automatically results.
If, however, the current
I
4
is derived from a separate summation CT an additional direction check with this
current is necessary.
Otherwise 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 measured value monitoring to pick up. This must therefore be ignored during
such tests.
DANGER!
Hazardous voltages during interruptions in secondary circuits of current transformers
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.
