Equipment Protection, Such As For Motors, Generators, Reactors And Transformers; Equipment Protection, Capacitors; Power Supply Quality; High Impedance Grounded Systems - ABB Relion 670 Series Applications Manual

1MRK 511 358-UUS A
8.3.3.1 Equipment protection, such as for motors, generators, reactors and
transformers
High residual voltage indicates ground fault in the system, perhaps in the component to which
Two step residual overvoltage protection (ROV2PTOV, 59N) is connected. For selectivity reasons
to the primary protection for the faulted device ROV2PTOV (59N) 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
8.3.3.2

Equipment protection, capacitors

High voltage will deteriorate the dielectric and the insulation. Two step residual overvoltage
protection (ROV2PTOV, 59N) 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.
8.3.3.3

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.
8.3.3.4

High impedance grounded systems

In high impedance grounded systems, ground faults cause a neutral voltage in the feeding
transformer neutral. Two step residual overvoltage protection ROV2PTOV (59N) is used to trip the
transformer, as a backup protection for the feeder ground fault protection, and as a backup for
the transformer primary ground fault protection. The setting must be above the highest occurring
"normal" residual voltage, and below the lowest occurring residual voltage during the faults under
consideration. A metallic single-phase ground fault causes a transformer neutral to reach a
voltage equal to the nominal phase-to-ground voltage.
The voltage transformers measuring the phase-to-ground voltages measure zero voltage in the
faulty phase. The two healthy phases will measure full phase-to-phase voltage, as the faulty phase
will be connected to ground. The residual overvoltage will be three times the phase-to-ground
voltage. See figure 92.
Application manual
Section 8
Voltage protection
M13853-9 v7
M13853-12 v4
M13853-15 v3
M13853-18 v9
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