9.3.7
Operation principle
M15331-3 v7
Two step residual overvoltage protection ROV2PTOV (59N) is used to detect high single-phase
voltage, such as high residual voltage, also called 3V
0
. The residual voltage can be measured
directly from a voltage transformer in the neutral of a power transformer or from a three-phase
voltage transformer, where the secondary windings are connected in an open delta. Another
possibility is to measure the three-phase voltages and internally in the IED calculate the
corresponding residual voltage and connect this calculated residual voltage to ROV2PTOV (59N).
ROV2PTOV (59N) has two steps with separate time delays. If the single-phase (residual) voltage
remains above the set value for a time period corresponding to the chosen time delay, the
corresponding TRIP signal is issued.
The time delay characteristic is individually chosen for the two steps and can be either, definite
time delay or inverse time delay.
The voltage related settings are made in percent of the base voltage, which is set in kV, phase-
phase.
9.3.7.1
Measurement principle
M15331-6 v5
The residual voltage is measured continuously, and compared with the set values,
Pickup1 and
Pickup2.
To avoid oscillations of the output PICKUP signal, a hysteresis has been included.
9.3.7.2
Time delay
M15331-10 v9
The time delay for the two steps can be either definite time delay (DT) or inverse time delay (TOV).
For the inverse time delay four different modes are available:
•
inverse curve A
•
inverse curve B
•
inverse curve C
•
customer programmable inverse curve
The type A curve is described as:
TD
t
V Vpickup
Vpickup
=
æ
ö
-
>
ç
÷
>
è
ø
ANSIEQUATION2422 V1 EN-US
(Equation 181)
where:
Vn>
Set value for step 1 and step 2
V
Measured voltage
The type B curve is described as:
1MRK 502 066-UUS B
Section 9
Voltage protection
629
Technical manual
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