OpModeU<: Under voltage seal-in feature is enabled using this setting and can be
selected as Off or Z2Start or Z3Start. If the under voltage seal-in has to be triggered
with zone 2 start, Z2Start enumeration has to be selected . If zone 3 select Z3Start
enumeration.
U<: The start value of the under voltage seal-in feature can be set using U<. This is
provided in percentage of UBase. Recommended setting is 70%.
tU<: The operate time delay in seconds for the under voltage seal-in. The
recommended time delay is to provide the same operate delay setting as the selected
zone that is, either zone 2 or zone 3.
8.10 Rotor earth fault protection using CVGAPC
The field winding, including the rotor winding and the non-rotating excitation
equipment, is always insulated from the metallic parts of the rotor. The insulation
resistance is high if the rotor is cooled by air or by hydrogen. The insulation resistance
is much lower if the rotor winding is cooled by water. This is true even if the insulation
is intact. A fault in the insulation of the field circuit will result in a conducting path
from the field winding to earth. This means that the fault has caused a field earth fault.
The field circuit of a synchronous generator is normally unearthed. Therefore, a single
earth fault on the field winding will cause only a very small fault current. Thus the
earth fault does not produce any damage in the generator. Furthermore, it will not
affect the operation of a generating unit in any way. However, the existence of a single
earth fault increases the electric stress at other points in the field circuit. This means
that the risk for a second earth fault at another point on the field winding has increased
considerably. A second earth fault will cause a field short-circuit with severe
consequences.
The rotor earth fault protection is based on injection of an AC voltage to the isolated
field circuit. In non-faulted conditions there will be no current flow associated to this
injected voltage. If a rotor earth fault occurs, this condition will be detected by the
rotor earth fault protection. Depending on the generator owner philosophy this
operational state will be alarmed and/or the generator will be tripped. An injection unit
RXTTE4 and an optional protective resistor on plate are required for correct rotor
earth fault protection operation.
Rotor earth fault protection can be integrated in the IED among all
other protection functions typically required for generator protection.
How this is achieved by using COMBIFLEX injection unit RXTTE4
is described in Instruction 1MRG001910.
1MRK 502 071-UEN - Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 317
Application manual
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