How to calculate the Operating region for Directional over current relay ?
Relay characterstic Angle (RCA)
The Relay characterstic value is used to define the region to operate the relay in the
specified direction.
Example :-
Let RCA = 45 ͦ
In normal condition angles between Current & Voltages
IR IY IB
0 ͦ 120 ͦ 240 ͦ
VR VY VB
0 ͦ 120 ͦ 240 ͦ
VRY VYB VBR
120 ͦ 360 ͦ 240 ͦ
If any fualt occure in any phase the voltage will be drop and heavy current will flow.
So to see the direction of the current flow relay will take other helth phase voltages.
Operating region = ( Phase displaced + RCA) to ( Phase displaced + RCA +180 )
Let's take R phase grounded and relay will take VYB voltage value is referance
VYB displaced 0 or 360 ͦ from IR
Operating region = ( 0 + 45 ͦ to 45 ͦ + 180 ͦ)
= 45 ͦ to 225 ͦ
Let's take Y phase grounded and relay will take VBR voltage value is referance
VYB displaced 240 ͦ from IR
= (240 ͦ + 45 ͦ ) = 285 ͦ and
= 285 ͦ + 180 ͦ = 465
= 465 - 360 = 105 ͦ
Operating regien = 105 ͦ to 285 ͦ
Let's take B phase grounded and relay will take VBR voltage value is referance
VRY displaced 120 ͦ from IB
= (120 ͦ + 45 ͦ ) = 165 ͦ and
= 165 ͦ + 180 ͦ = 345 ͦ
Operating regien = 165 ͦ to 345 ͦ
