1. Due to such connection, ROV2PTOV (59N) measures the 3Vo voltage at generator
HV terminals. Maximum 3Vo voltage is present for a single phase-to-ground fault
at the HV terminal of the generator and it has the primary maximum value 3V
o
Max
:
3 3 3 11 19 05Vo V kV kV
Max Ph Ph
= ⋅ = ⋅ =
−
.
ANSIEQUATION2395 V1 EN-US (Equation 239)
2. One VT input is to be used in the IED. The VT ratio is to be set according to the
open delta winding ratio. For this application correct primary and secondary rating
values are 19.05 kV and 110 V respectively
.
3. For the base value, a generator-rated phase-to-phase voltage is to be set. Thus for
this application VBase=11 kV.This base voltage value is not set directly under the
function but it is instead selected by the Global Base Value parameter.
4. ROV2PTOV (59N) internally divides the set voltage base value with √3. Thus, the
internally used base voltage value is 6.35 kV. This is three times smaller than
maximum 3Uo voltage. Therefore, if the wanted pickup is 5 percent from the
neutral point the ROV2PTOV (59N) pickup value is set to Pickup1=3·5%=15%
(that is, three times the desired coverage).
5. The definite time delay is set to 0.5 seconds.
10.3.3.4 Power supply quality
M13853-15 v3
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.
10.3.3.5 High impedance grounded systems
M13853-18 v10
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
206.
Section 10 1MRK 502 071-UUS A
Voltage protection
450 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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