Vpickup VBase kV> â‹…(%) ( ) / 3
EQUATION1610 V2 EN (Equation 35)
and operation for phase-to-phase voltage over:
Vpickup (%) VBase(kV)> ×
EQUATION1992 V1 EN (Equation 36)
When phase-to-ground voltage measurement is selected the function
automatically introduces division of the base value by the square root of
three.
7.2.7.1 Measurement principle
All the three voltages are measured continuously, and compared with the set values,
Pickup1 for Step 1 and Pickup2 for Step 2. The parameters OpMode1 and OpMode2
influence the requirements to activate the PICKUP outputs. Either 1 out of 3, 2 out of 3 or
3 out of 3 measured voltages have to be higher than the corresponding set point to issue the
corresponding PICKUP signal.
To avoid oscillations of the output PICKUP signal, a hysteresis is included.
7.2.7.2 Time delay
The time delay for step 1 can be either definite time delay (DT) or inverse time overvoltage
(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:
t
TD
V Vpickup
Vpickup
=
− >
>
EQUATION1625 V2 EN (Equation 37)
The type B curve is described as:
1MRK 511 287-UUS A Section 7
Voltage protection
177
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