ABB Relion 670 Series Applications Manual page 211

1MRK 511 407-UUS Rev. J
magnitudes during islanding situations and frequency instability. Further, uncontrolled frequency
represents a high risk for drives and other machines.
Islanding can occur as a consequence of :
• a fault in the network
• circuit-breaker maloperation
• circuit-breaker opening during maintenance
If the distributed generator continues its operation after the utility supply is disconnected, faults
do not clear under certain conditions as the arc is charged by the distributed generators.
Moreover, the distributed generators are incompatible with the current reclosing practices. During
the reclosing sequence dead time, the generators in the network usually tend to drift out of
synchronism with the grid and, reconnecting them without synchronizing may damage the
generators introducing high currents and voltages in the neighbouring network.
Due to the technical difficulties mentioned above, protection should be provided, which
disconnects the distributed generation once it is electrically isolated from the main grid supply.
Various techniques are used for detecting Loss of Mains. However, the present feature of voltage
supervision focuses on voltage vector shift.
For islanding based on vector shift protection, the logic shown in Figure
the breaker. With this logic, reliable tripping can be ensured as angle shift has been detected in all
the three phase voltages.
V3P*
BLOCK
ANSI18000903 V1 EN-US
Figure 79: DELVSPVC connection diagram
The vector shift detection guarantees fast and reliable detection of mains failure in almost all
operational conditions when a distributed generation unit is running in parallel with the mains
supply, but in certain cases this may fail.
If the active and reactive power generated by the distributed generation units is nearly balanced
(for example, if the power mismatch or unbalance is less than 5...10%) with the active and reactive
power consumed by loads, a large enough voltage phase shift may not occur which can be
detected by the vector shift algorithm. This means that the vector shift algorithm has a small non-
detection zone (NDZ) which is also dependent on the type of generators, loads, network and start
or operate value of the vector shift algorithm.
Other network events like capacitor switching, switching of very large loads in weak network or
connection of parallel transformer at HV/MV substation, in which the voltage magnitude is not
changed considerably (unlike in faults) can potentially cause maloperation of vector shift
algorithm, if very sensitive settings are used.
Phasor measurement unit RES670
Application manual
DELVSPVC (78V)
BFI_3P
PICKUP_A
PICKUP_B
PICKUP_C
STRISE
STRISE_A
STRISE_B
STRISEL3
STLOW
STLOW_A
STLOW_B
STLOWL3
DELMAG_A
DELMAG_B
DELMAGL3
© Copyright 2017 Hitachi Power Grids. All rights reserved
78V Pickup
AND
ANSI18000903‐1‐en.vsdx
Section 13
Secondary system supervision
79 should be used to trip
205