การคํานวณกระแสล ัดวงจร ํ ั (Short Circuit Calculation)

1 ( short Circuit calculation ). ( short Circuit ) . ** Co ordination **. ( short Circuit ) . ( short Circuit ) . ** Interrupting Rating **. ( short Circuit ) .. Line to Ground Fault Line to Neutral Fault Line to Line Fault Double Line to Ground Fault Three Phase Fault !! . Line to Ground Fault = 70 %. Line to Line Fault = 15 %. Double Line to Ground Fault = 10 %. Three Phase Fault = 5%.. (Panel Board). MDB (Main Distribution Board).. + . - . - .. - . - ( ) .. - / . - .. (> 1,000 A) .. (fuse & Circuit Breaker) .. - . - .. - . - . / . - Fuse - Circuit Breaker . 1.. 2.. 3.. 4.. (Symmetrical).. (Unsymmetrical).. IEC 60909 2 .. 1.. ( MDB) .. IC .. 1.. : (IU). IU.

2 (IM).. A B. IU IM IM. M. (IU).. IU = 100 * IFL,Tr % Zk IU . IFL,Tr . % Zk (Impedance Voltage) .. (IFL). I FL,Tr =. S. 3VL. S (VA). VL . (V). ( . = 400 V ; . = 416 V). Impedance Voltage (Zk). short Circuit Test . Uk Zk P sh_s Xp Rp Xs Rs W I. Ish_s V. Vsh_s Zk . Vs / c ( meter ). %Z k 100. Vrate 22 kV / 416-240 V . Voltmeter 850 V.. 850. %Z k 100 %. 22000. Impedance Voltage (Zk).. Italy France 1.. 1600 kVA 24 kV/416-240 V. S. MEA 24 kV I FL,Tr =. 3VL. CEI Std IU 1600 kVA 1600 103. 24 kV / 416-240 V =. 3 416. = 2,221 A. ( ) . I FL ,Tr 100. IU =. %Z k CEI Zk = %. 2,221 100. IU =. = 35,536 A. 36 kA. CB IC > 36 kA 35 kA 42 kA. (3 ) (1 ). (IM).. (Asynchronous Motor).

3 4 .. I M = 4 I FL ,M.. IM (A). IFL,M (A). 2. A Bus Bar MDB. (IU). S I FL ,Tr 100. I FL,Tr = IU =. 3 VL %Z k 1, 443 100. 1, 000 103 =. = 3 400. = 24,050 A. = 1, 443 A. = kA. (IM). S 500 103. I FL,M = =. 3 VL 3 400. = 722 A. I M = 4 I FL,M = 4 722. = 2,888 A. = kA. A . I SC = IU + I M. I SC = + = kA. 2.. (Interupting Capacity, IC).. 3 .. 1. (Impedance Diagram). 2.. (Impedance Diagram).. ZN ZTr ZM ZF ZSf . VL. I SC =. 3 Zt ISC 3 . VL . ( . = 400 V ; . = 416 V). Zt . (ZN). IEC 60909 ZN . cV 2 1. ZN = 2. MVASC tr ZN . c (Voltage Factor). V ( ). MVASC . tr (Turn Ratio). c (Voltage Factor) IEC 60909 . (MVASC).. 1. 24 kV. - MVASC = 500 MVA. 2. 24 kV. - MVASC = 1,000 MVA.

4 Std. IEC & CEI. ( .). 24 kV / 416-240 V MVASC = 500 MVA. cV 2 1. ZN = 2. MVASC tr 2. (24 10 3 ) 416 . 2. ZN = . 500 106 24 103 . = mW. ( .). 22 kV / 400-230 V MVASC = 500 MVA. cV 2 1. ZN = 2. MVASC tr 2. (22 103 ) 400 2. ZN = . 500 106 22 103 . = mW. RN XN . Z N = RN + jX N. X N = Z N. RN = X N.. ZN XN RN. (MVASC) (mW) (mW) (mW). 22 kV / 400-230 V 500 24 kV / 416-240 V 500 (ZTr). : % Z k VL 2. ZTr =. STr 100.. Pcu ,loss RTr = 2. 3 ( I FL,Tr ). X Tr = ZTr 2 - RTr 2. : ZTr . RTr . XTr . VL . Pcu,loss . Pcu,loss UNEL 21001-74 [I] DIN 42500. STr [kVA] Pcu,loss [W]. 25 700. 50 1100. 100 1750. 160 2350. 250 3250. 400 4600. 630 6500. Pcu,loss NFC 15-105[P].

5 Pcu ,loss [W ] = 3 (% Z k ) (STr [ kVA]). 3. NFC. 1,600 kVA 22 kV/400-230 V.. S 1600 103. I FL,Tr = =. 3VL 3 400. = 2,309 A. %Zk 1,600 kVA %ZK = %. Pcu,loss . Pcu ,loss [W ] = 3 (% Z k ) ( STr [ kVA]). Pcu ,loss = 3 1600. = 28,800 W. = kW.. % Z k VL 2. ZTr =. STr 100. 2. 6 (400). =. (1600 103 ) 100. = mW.. Pcu ,loss 28,800. RTr = 2 = = mW. 3 ( I FL,Tr ). 2. 3 (2,309 ).. 2 2. X Tr = ZTr 2 - RTr 2 = ( ) -( ) mW. = mW. (ZM , ZF , ZSf ). R X . 40 oC. THW. 40 oC. R X (Bus Way). 4.. 24 kV/416-240 V. 500 MVA. MDB 4. set of (3x300 mm2, 1x240 mm2(N) THW) IMC 30 . MDB 3x185 mm2, 1x95. mm2 (N) THW IMC 50 .. A ( MDB). B ( ). 1 A. ( A). MDB.. ZN ZTr ZM ZF. (ZN).

6 ZN XN RN. (MVASC). 22 kV / 400-230 V 500 24 kV / 416-240 V 500 . 24 kV/416-240 V ZN . Z N = + j (ZTr). Pcu,loss Pcu,loss . Pcu ,loss [W ] = 3 (% Z k ) (STr [ kVA]). Pcu ,loss = 3 1000. = 18,000 W. = kW.. % Z k VL 2. ZTr =. STr 100. 2. 6 (416). =. (1000 103 ) 100. = mW.. Pcu ,loss S. RTr = 2 I FL,Tr =. 3 ( I FL,Tr ) 3VL. 18, 000 1000 103. = 2 =. 3 (1,388) 3 416. = mW = 1,388 A.. X Tr = ZTr 2 - RTr 2. 2 2. = ( ) - ( ) mW. = mW.. ZTr = + j mW.. 4 set of (3x300 mm2, 1x240 mm2(N) THW) . IMC MDB .11-2531. 4 4 . 4 (A, B, C) . 300 mm2 3 240 mm2 1 . 16 . ** 300 mm2 4.. ( ) . Z = Z1 = Z 2 = Z3 = Z 4. : Z. Z M = Z // Z // Z // Z =. Z1 Z2 Z3 Z4 4. R X . = + j L.

7 4 4 . 300 mm2. R= mW/m XL = mW/m 30 4 . R = 30 X L = 30. = mW = mW. (ZM) . 1. Z M = ( + j ). 4. = + j mW. A. Zt = Z N + ZTr + Z M. = ( + j ) + ( + j ) + ( + j ). = + . 2 2. Zt = ( ) + ( ) = mW.. VL. I SC =. 3 Zt 416. =. 3 ( 10-3 ). = kA.. - 200 kVA. S. I M = 4 I FL,M I FL,M =. 3 VL. = 4 200 103. =. 3 380. = kA. = A. A. A = I SC + I M. = + = kA. IC 25 kA (480 V). 2 B. ( B). MDB.. ZN ZTr ZM ZF. 1 . 1. 24 kV/416-240 V 500 MVA. Z N = + j mW. 2. 1000 kVA. ZTr = + j mW. 3. 4 set of (3x300mm2, 1x240mm2 THW) in IMC. Z M = + j mW. (Feeder). 3x185 mm2, 1x95 mm2 THW IMC. R X THW 185 mm2. 185 mm2. R = mW/m XL = mW/m 50 . R = 50 X L = 50. = mW = mW. (ZF) . Z F = + j m.

8 Zt = Z N + ZTr + Z M + Z F. = ( + j ) + ( + j ) + .. + ( + j ) + ( + j ). = + m .. 2. Zt = ( ) + ( ). 2. = mW. (ISC). VL 416. I SC = =. 3 Zt 3 ( 10-3 ). = kA.. - 200 kVA. S. I M = 4 I FL,M I FL,M =. 3 VL. = 4 200 103. =. = kA 3 380. = A. B. B = I SC + I M. = + = kA. IC 14 kA (480 V). 5.. ZF4 ZF5. ZF3. ZF2. ZF1.. ZN ZTr ZM ZF.