adding the input phase voltages. 3V
0
may also be input single phase by either
measuring directly from a voltage transformer in the neutral of a power transformer, or
from a secondary broken delta connection of a transformer with a wye-grounded
primary. ROV2PTOV (59N) has two steps with separate time delays. If the ground
overvoltage 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 setable for step 1 and can be either definite or inverse
time delayed. Step 2 is always definite time delayed.
The voltage related settings are made in percent of the global phase-to-phase base
voltage divided by √3.
8.3.7.1 Measurement principle
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.
8.3.7.2 Time delay
The time delay for step 1 can be either definite time delay (DT) or inverse time delay
(TOV). Step 2 is always definite time delay (DT). For the inverse time delay three
different modes are available:
• inverse curve A
• inverse curve B
• inverse curve C
The type A curve is described as:
EQUATION1625 V2 EN (Equation 34)
The type B curve is described as:
t
TD
V Vpickup
Vpickup
=
⋅
⋅
− >
>
−
−
480
32 0 5
0 035
.
.
ANSIEQUATION2287 V2 EN (Equation 35)
The type C curve is described as:
Section 8 1MRK 505 277-UUS C
Voltage protection
140
Technical Manual
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