Equipment Protection, Such As For Motors, Generators, Reactors And Transformersequipment Protection For Transformers; Equipment Protection, Capacitors; Power Supply Quality; High Impedance Earthed Systems - ABB RED650 Applications Manual

Section 9
Voltage protection
9.3.3.1
9.3.3.2
9.3.3.3
9.3.3.4
198
situations, where the residual 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.
Equipment protection, such as for motors, generators, reactors and
transformersEquipment protection for 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.

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.

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.

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 occurring "normal" residual voltage, and below
the lowest occurring residual voltage during the faults under consideration. A
metallic single-phase earth fault causes a transformer neutral to reach a voltage
equal to the nominal phase-to-earth voltage.
The voltage transformers measuring the phase-to-earth 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 earth. The residual
overvoltage will be three times the phase-to-earth voltage. See figure 92.
1MRK 505 393-UEN B
Line differential protection RED650 2.2 IEC
Application manual
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