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P!E" S#STEM P"TE$T%N &EE'(2)*

Samiya Zafar Assistant Professor, EED NEDUET M.Engg Fall Semester 2017

Application of Inverse Definite Minimum Time Relay on a Distribution Feeder Consider

the same feeder with two buses A and B

where IDMT OC relays are to be used. The

purpose of R B is to provide primary protection to

line BC and The purpose of R A  is to provide primary protection to line AB and bac!up to line BC. "e

start settin# process from tail end of the system.

$a% Decidin# the CT ratios and plu# settin#s for Relay A and Relay B&

$i% At relay B' the ma(imum load current' assumin# )*+ overload is&

,- A  $-.)* ( ,- A% / 0-- A

Assumin# 0 A relay to be used' the CT ratio can be selected to be 0-- & 0. The plu# settin# 12 can be done at 0oo+' i.e. 12 / 0.- A. $ii% At relay A the ma(imum load current' assumin# )*+ overload is&  $03-,-%  -.)* $03-,-% / 4-- A Assumin# 0 A relay to be used' the CT ratio can be selected to be 4-- & 0. The plu# settin# can be done at 0oo+' i.e. 12 / 0.- A.

$b% Decidin# the time!multiplier settin#s& 2tartin# from the most remote relay RB $i% 2ince RB  does not have to maintain selectivity with any other relay' it can be made to operate the fastest. Thus the TM2 of RB can be selected as -.0. $ii% 5ow' to maintain selectivity between R A and RB' the followin# constraint must be met&

The operatin# time of RB for ma(imum fault 6ust beyond bus B can be found from

7or ma(imum fault at B' fault current / 4--- A on primary

side

which

becomes

$4---80--%

/

4-

A

secondary. 2ince plu# settin# is done at 0.- A' The TM2 of RB has already been set at -.0. 2ubstitutin# these values' we #et& 9et TCB'B/ -.* 2. Then' TR'B  TCB'B / -.: s This value of -.: s is the desired operatin# time of RA. Assumin# overshoot time of RA to be 0-+ of -.: s' i.e. TO2'A / -.-: s.

Thus' we #et the reeren*al protec*on. It provies efnite/*me an inverse/ *me over current protec*on. T"e nominal ,T currents applie to t"e IROTE, ?@+(1 can 9e 1 A or ' A.

T"e microprocessor controlle! mul*#unc*onal over current/ *me protec*on evice AE PS 8(1 is suita9le #or efnite *me or inverse/*me over current protec*on o# V motors! trans#ormers! an po0er lines. arameters may 9e set eit"er #rom t"e local control panel or t"rou&" t"e , inter#ace! as esire.

P+A$EMENT AND SETT%N F 9E" $ U " " E N T " E + A# S  N ETAP