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Description

The relay comprises of two elements: 27UV (Undervoltage protection) and 59OV (Overvoltage protection) elements. The overvoltage (59) element operates when the voltage it monitors exceeds a threshold value whereas undervoltage (27) element operates when the monitored voltage falls below a set threshold value.

There are five levels of settings available for each element. Each level corresponds to a predefined overvoltage or undervoltage level and a tripping delay time.

The model works for 50 Hz or 60 Hz system.

Table of Contents

Model Overview

27 Undervoltage Relay

The undervoltage element picks up whenever the line or phase voltage drops below the selected settings. A timer is normally used to enable it to ride through momentary sags and thus prevent nuisance tripping.

The five-level undervoltage relay characteristic is presented in Figure 1.

For instance, if level 1 voltage is 0.8 pu and tripping time is 1 sec. It means that when the input voltage is lower than 0.8 pu and continues to be lower than 0.8 pu for more than 1 second, the undervoltage relay will be asserted. If the voltage is lower than 0.8 pu for less than 1 second, its timer will reset and will not restart until the voltage amplitude violates the level 1 voltage threshold again. All voltage levels and delay times are tunable parameters.

59 Overvoltage Relay

The overvoltage element trips electrical equipment under its protection whenever the line or phase voltage exceeds the selected setting. A time-delay is normally used to enable it to ride through momentary spikes and thus prevent nuisance tripping.

The five-level overvoltage relay characteristics is presented in Figure 2.

For instance, if Level 1 voltage is 1.05 pu and tripping time is 2 sec. It means that when the input voltage is higher than 1.05 pu and continues to be higher than 1.05 pu for more than 2 seconds, the overvoltage relay will be asserted. If the voltage is higher than 1.05 pu for any time that is less than 2 seconds, its timer will be reset and will not restart until the voltage violates the level 1 voltage threshold again. All voltage levels and delay times are tunable parameters.

Figure 1 Undervoltage relay characteristic

Figure 2 Overvoltage relay characteristic

Mask and Parameters

General parameters

NameUnitDescription

Enable

-

Enable and disable relay operation

Frequency

Hz

The frequency of the measured current signals. Both 50 and 60 Hz are supported within the model.

Base Voltage (L-L)

V

The base voltage (L-L) at the measurement location

Operating Quantity

N/A

Two types of operating quantity are provided in this model: 

Phase-Neutral Voltage or Phase-Phase Voltage among three phases.

Sample Time

s

Model time step

27 Undervoltage


NameUnitDescription

Enable 27UV

-

Enable and disable for 27UV element

27UV Level 1

pu

Undervoltage level 1.

27UV Level 2

pu

Undervoltage level 2.

27UV Level 3

pu

Undervoltage level 3.

27UV Level 4

pu

Undervoltage level 4.

27UV Level 5

pu

Undervoltage level 5.

Time for 27UV Level 1

s

Time delay associated with 27UV Level 1.

Time for 27UV Level 2

s

Time delay associated with 27UV Level 2.

Time for 27UV Level 3

s

Time delay associated with 27UV Level 3.

Time for 27UV Level 4

s

Time delay associated with 27UV Level 4.

Time for 27UV Level 5

s

Time delay associated with 27UV Level 5.

59 Overvoltage

NameUnitDescription

Enable 59OV

-

Enable and disable for 59OV element

59OV Level 1

pu

Overvoltage level 1.

59OV Level 2

pu

Overvoltage level 2.

59OV Level 3

pu

Overvoltage level 3.

59OV Level 4

pu

Overvoltage level 4.

59OV Level 5

pu

Overvoltage level 5.

Time for 59OV Level 1

s

Time delay associated with 59OV Level 1.

Time for 59OV Level 2

s

Time delay associated with 59OV Level 2.

Time for 59OV Level 3

s

Time delay associated with 59OV Level 3.

Time for 59OV Level 4

s

Time delay associated with 59OV Level 4.

Time for 59OV Level 5

s

Time delay associated with 59OV Level 5.

Inputs and Outputs

Inputs

NameDescription
VabcA 3-dimension voltage input for three-phase voltages, in the order of Va, Vb and Vc.
ResetThe reset signal for the relay. The relay will be reset when this signal becomes 1.

Outputs

NameDescription
Trip

The output of the relay. By default, it is 0, if an overvoltage/undervoltage scenario is detected, it becomes 1.

Available monitoring signals

NameDescription

Trip_59

Trip output of the 59OV element.

Trip_27

Trip output of the 27UV element.

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