Documentation Home Page HYPERSIM Home Page
Pour la documentation en FRANÇAIS, utilisez l'outil de traduction de votre navigateur Chrome, Edge ou Safari. Voir un exemple.

27 - Undervoltage Relay (1-ph)


The under-voltage relay (27-UV) operates when the voltage it monitors falls below a set of threshold values. There are five threshold levels available with this relay. Each level corresponds
to a predefined under-voltage level and a tripping delay time. The operating quantity of the relay can be the RMS value of phase voltage, or the positive, negative or zero sequence of a three-phase voltage signals. The operating quantity can be either in per unit or actual value. 

Icons and diagrams

Model overview

The under voltage relay 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 under-voltage relay characteristics is presented in below figure. For instance, if we use the default values as mentioned above, 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 under voltage 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 reaches the level 1 voltage threshold again. All voltage levels and delay times are tunable parameters.


The below figure shows the control panel of the 27-UV relay

The following gives a brief description about the parameters of 27-UV relay

Parameter tab of 27-UV Relay

NameDescriptionUnitSample value
Level 1pu or VUndervoltage level 10.8 
Level 2pu or VUndervoltage level 20.7
Level 3pu or VUndervoltage level 30.6
Level 4 pu or VUndervoltage level 40.5
Level 5pu or VUndervoltage level 50.4
Time 1secTime delay associated with level 11.0
Time 2secTime delay associated with level 20.5
Time 3secTime delay associated with level 30.4
Time 4 secTime delay associated with level 40.3
Time 5secTime delay associated with level 50.2

Input and output signals

The module has 1 input and 1 output. 

27-UV Relay I/O

I/O NameType (Unit)Description

 pu or V

A single dimensional signal,  it should be the RMS value of phase voltage, or the positive, negative or zero sequence of a three-phase voltage signals.


The output of under-voltage relay. By default it is 0, if an under-voltage scenario is detected, it becomes 1

OPAL-RT TECHNOLOGIES, Inc. | 1751, rue Richardson, bureau 1060 | Montréal, Québec Canada H3K 1G6 | | +1 514-935-2323