ABB Relion REQ650, Applications Manual

Page: 167 / 340

to prevent damages to the protected object. The speed might be important for example
in case of protection of transformer that might be overexcited. The time delay must be
co-ordinated with other automated actions in the system.
t1Min : Minimum operating time for inverse time characteristic for step 1, given in s.
For very high voltages the overvoltage function, using inverse time characteristic, can
give very short operation time. This might lead to unselective trip. By setting
t1Min
longer than the operation time for other protections such unselective tripping can be
avoided.
k1 : Time multiplier for inverse time characteristic. This parameter is used for co-
ordination between different inverse time delayed undervoltage protections.
7.3 Two step residual overvoltage protection
ROV2PTOV
7.3.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Two step residual overvoltage
protection
ROV2PTOV
3U0>
IEC10000168 V1 EN
59N
7.3.2 Application
Two step residual overvoltage protection ROV2PTOV is primarily used in high
impedance earthed distribution networks, mainly as a backup for the primary earth-
fault protection of the feeders and the transformer. To increase the security for
different earth-fault related functions, the residual overvoltage signal can be used as
a release signal. The residual voltage can be measured either at the transformer neutral
or from a voltage transformer open delta connection. The residual voltage can also be
calculated internally, based on measurement of the three-phase voltages.
In high impedance earthed systems the residual voltage will increase in case of any
fault connected to earth. Depending on the type of fault and fault resistance the
residual voltage will reach different values. The highest residual voltage, equal to
three times the phase-to-earth voltage, is achieved for a single phase-to-earth fault.
The residual voltage increases approximately to the same level in the whole system
and does not provide any guidance in finding the faulted component. Therefore,
ROV2PTOV is often used as a backup protection or as a release signal for the feeder
earth-fault protection.
1MRK 505 291-UEN A
Section 7
Voltage protection
161
Application manual