Undervoltage definition 2

Could you please advise me about the meaning of the protection function 27i. ( I Know that the ANSI Code for undervoltage protection is [27] but i did never hear about 27i. Also what is 27R ( somebody said:residual undervoltage). Does this function exist? if so whatis its application?
Thanks in advance.

 

[ElecDar]

ANSI 27i : Instantaneous Undervoltage relay.
ANSI 27r : Residual Undervoltage relay.

Suggestion: Visit

http://www.orionitalia.com/products/Vmpr.htm

 

[hemajaybittu]

Residual Voltage or Unbalanced Voltage protection is normally included in an ungrounded system where under single to ground fault leads to 1.732X VL increase to healthy lines. S-L-G fault leads unbalanced condition in a balanced system. So its better to include Unbalanced protection as it is faster & relates insulation co-ordination.

Generalised setting for 27R may be assigned as >20% with 5Sec & >50% instantaneous.

This also reduces the arcing ground under S-L-G fault.

(A Singh)
IOCL, India

 

dear 27 i is instataneous under voltage and 27 r is residual under voltage.