How to do Relay settings

Relay Settings :

here we can see about what is relay and how to do relay settings. Relay is a device used to protect the equipment from damage during the abnormal or faulty conditions.

relay

usually relays having two coil supply A1 and A2, two NO and NC contacts, and common supply contacts.

working:

whenever the coil in the relay get energized, the relay transfer the voltage from common to NO contacts. at normal condition it transfer voltage from  common to NC contacts. usually coil supply will be DC voltage.

Types of Relay:

based on protection it’s classified into different types,

under voltage relay

over voltage relay

under frequency relay

over current relay

earth fault relay

fault trip send relay

fault trip receive relay

logout relay

negative phase sequence relay

reverse power forward relay

Relay Settings:

as per relay settings we need to find base current IE first,

IE = IN x 1/CT

IE- base current

IN – rated full load current

CT- current transformer ratio

for example we calculate relay setting for motor 50 HP , IN=61A, CT = 75/1A

so IE= 61*1/ (75/1)

IE = 0.813

so based on IE value the relay settings are below,

I2 – Negative phase sequence= 30% x IE

Io – Earth fault = 20% x IE

I> – short circuit = 35-40% x IE

I>> – Excessive starting time = 10-20 times x IE

^I – over load = 150%

 

 

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