3 OVERVOLTAGE PROTECTION
Overvoltage conditions are generally related to loss of load conditions, whereby the supply voltage increases in
magnitude. This situation would normally be rectified by voltage regulating equipment such as AVRs (Auto Voltage
Regulators) or On Load Tap Changers. However, failure of this equipment to bring the system voltage back within
permitted limits leaves the system with an overvoltage condition which must be cleared.
Note:
During earth fault conditions on a power system there may be an increase in the healthy phase voltages. Ideally, the system
should be designed to withstand such overvoltages for a defined period of time.
3.1
OVERVOLTAGE PROTECTION IMPLEMENTATION
Overvoltage Protection is implemented in the VOLT PROTECTION column of the relevant settings group. The
Overvoltage parameters are contained within the sub-heading OVERVOLTAGE.
The product provides two stages of overvoltage protection with independent time delay characteristics.
Stage 1 provides a choice of operate characteristics, where you can select between:
● An IDMT characteristic
● DT (Definite Time)
You set this using the V>1 Function setting.
The IDMT characteristic is defined by the following formula:
t = K/( M - 1)
where:
● K = Time multiplier setting
● t = Operating time in seconds
● M = Measured voltage setting voltage (V>(n) Voltage Set)
The overvoltage stages can be configured either as phase-to-neutral or phase-to-phase voltages in the V>
Measur't Mode cell.
There is no Timer Hold facility for Overvoltage.
Stage 2 can have definite time characteristics only. This is set in the V>2 Status cell.
Outputs are available for single or three-phase conditions via the V> Operate Mode cell for each stage.
P543i/P545i Chapter 14 - Voltage Protection Functions
P54x1i-TM-EN-1 401
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