Setting Guidelines; Equipment Protection, Such As For Motors, Generators, Reactors And Transformers; Equipment Protection, Capacitors; Power Supply Quality - ABB RELION 670 Series Applications Manual

Section 9
Voltage protection
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.
9.3.3

Setting guidelines

All the voltage conditions in the system where ROV2PTOV performs its functions should be
considered. The same also applies to the associated equipment, its voltage and time
characteristic.
There is a very wide application area where general single input or residual overvoltage
functions are used. All voltage related settings are made as a percentage of a settable base
voltage, which can be set to the primary nominal voltage (phase-phase) level of the power
system or the high voltage equipment under consideration.
The time delay for ROV2PTOV is seldom critical, since residual voltage is related to earth-faults
in a high impedance earthed system, and enough time must normally be given for the primary
protection to clear the fault. In some more specific situations, where the single overvoltage
protection is used to protect some specific equipment, the time delay is shorter.
Some applications and related setting guidelines for the residual voltage level are given below.
9.3.3.1 Equipment protection, such as for motors, generators, reactors and
transformers
High residual voltage indicates earth-fault in the system, perhaps in the component to which
Two step residual overvoltage protection (ROV2PTOV) is connected. For selectivity reasons to
the primary protection for the faulted device ROV2PTOV must trip the component with some
time delay. The setting must be above the highest occurring "normal" residual voltage and
below the highest acceptable residual voltage for the equipment
9.3.3.2

Equipment protection, capacitors

High voltage will deteriorate the dielectric and the insulation. Two step residual overvoltage
protection (ROV2PTOV) has to be connected to a neutral or open delta winding. The setting
must be above the highest occurring "normal" residual voltage and below the highest
acceptable residual voltage for the capacitor.
9.3.3.3

Power supply quality

The setting must be above the highest occurring "normal" residual voltage and below the
highest acceptable residual voltage, due to regulation, good practice or other agreements.
9.3.3.4

High impedance earthed systems

In high impedance earthed systems, earth faults cause a neutral voltage in the feeding
transformer neutral. Two step residual overvoltage protection ROV2PTOV is used to trip the
transformer, as a backup protection for the feeder earth-fault protection, and as a backup for
the transformer primary earth-fault protection. The setting must be above the highest
472
1MRK 504 152-UEN B
M13853-3 v7
M13853-9 v7
M13853-12 v4
M13853-15 v3
M13853-18 v9
Application manual