Ct Calculation P541

PROJECT:

SUBSTATION: BAY NAME:

TENDER NO

: KKLW.T2/2011

DEPARTMENT DOCUMENT

CONTRACT NO

:

PAGE

BEKALAN ELEKTRIK LUAR BANDAR (BELB) SAMBUNGAN GRID ZON DUA (4) NEGERI SABAH TAHUN 2012-2013 SECARA REKA DAN BINA TUNGKU STATION

ENGINEERING 2

Prepared

Checked

SAHARIN

MAZLAN

OF

5

Verified

Date: 18/10/2012 Date: 18/10/2012 Date :

33KV INCOMER

CURRENT TRANSFOMER CALCULATION CT Core Duty COP Relay Designation

: Current Differential Protection : 87CD

Relay Manufacturer Relay Model

: Schneider : MiCOM P541

Core CT Ratio Class

: 1 : 600/1A : X

According to manufacturer Schneider manual P54x/EN AP/H53 page 118/138, required knee point voltage:

Vk

≥

K.In (Rct + 2RL)

...………………………………………(1)

where, In Rct RL K

= = = =

rated line CT secondary current (1A or 5A) resistance of line CT secondary wiring resistance of singlelead from line CT to relay Dimensioning factor

K is dependent on: If = maximum value of through fault current for stability =25000A/600=41.67A X/R = Primary system X/R ratio = 10 (TNB CT Application Guide) If x X/R = 41.67A x 10 = 416.7A K is determined as follow: For relay set at Is1 = 20%, Is2 = 2In, k1=30%, k2=150% (manufacturer recommended setting for two terminal application) K

≥ 40 + (0.07 x (If x X/R)) ≥ 40 + (0.07 x (416.7)) ≥ 69.17 ≥ 69

Calculation of Lead burden : ( Multicore cable resistance per km for 4mm sq conductor ) Cable Length, L C = Cable Resistance (per km), RL = RL =

50 m 4.61 ohm/km 0.2305 Ohm

=

0.05

km

RCT = The secondary winding resistance of The CT = 2.4 Ohm @ 600/1A (0.4Ohm per 100 turns as per TNB standard)

for CT ratio 1000/1A, Vk

≥

K. In (Rct + 2Rl)

≥ ≥

69 x 1 x (2.4+ (2x0.2305)) 197.4 V

Therefore proposed CT as below is sufficient: 600/1A, Vk≥

197.4V, Rct≤2.4 Ohm

REV NO : PAGES

1

Approved

Date :