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7.2.7 Operation principle

Two step overvoltage protection OV2PTOV is used to detect high power system

voltage. OV2PTOV has two steps with separate time delays. If one-, two- or three-

phase voltages increase above the set value, a corresponding START signal is issued.

OV2PTOV can be set to START/TRIP, based on 1 out of 3, 2 out of 3 or 3 out of 3 of

the measured voltages, being above the set point. If the 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 settable 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 set base voltage UBase,

which is set in kV, phase-to-phase.

OV2PTOV can be set to measure phase-to-earth fundamental value, phase-to-phase

fundamental value, phase-to-earth RMS value or phase-to-phase RMS value. The

choice of measuring is done by the parameter ConnType.

The voltage related settings are made in percent of base voltage which is set in kV

phase-to-phase voltage. OV2PTOV will operate if the voltage gets higher than the set

percentage of the set global base voltage UBase. This means operation for phase-to-

earth voltage over:

(%) ( )

U UBase kV> ×

EQUATION1434 V1 EN

(Equation 35)

and operation for phase-to-phase voltage over:

U (%) UBase(kV)> ×

EQUATION1993 V1 EN (Equation 36)

When phase-to-earth 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,

U1> for Step 1 and U2> for Step 2. The parameters OpMode1 and OpMode2

influence the requirements to activate the START 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 START signal.

To avoid oscillations of the output START signal, a hysteresis is included.

Section 7 1MRK 511 287-UEN A

Voltage protection

166

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