Earthing strip matrix for transformer

Earthing strip size for transformer.

Cross Section Area of Earthing Conductor As per IS 3043

A = (I_f x√t) / K  

Where:

t = Fault current Time (Second)., 1 sec or 3 sec

K = Material Constant, Material Constant, For GI=80, copper K=206, Aluminium K=126).

Part-A: Typical Protective conductor size required for Transformer Ratings (100-500KVA)

Sr.	A	B	C	D	E	F
1	Transformer Rating ( KVA)	100	160	250	315	500
2	Secondary Voltage (V)	433	433	433	433	433
3	Full Load current	133	213	333	420	667
4	Percentage Impedance Z%	5	5	5	5	5
5	Short Circuit Current (SC) in A =FLC*(100/Impedance)	2660	4260	6600	8400	13340
6	Area of Protective conductor Reqd in sq.mm = SC *√t/k
7	t = 1 Sec
8	Copper k = 206	12.9	20.7	32.0	40.8	64.8
9	Recommended strip size	25 x 3 mm	25 x 3 mm	25 x 3 mm	25 x 3 mm	25 x 3 mm
10	Alluminium k = 126	21.1	33.8	52.4	66.67	105.9
11	Recommended strip size	25 x 3 mm	25 x 3 mm	25 x 3 mm	25 x 3 mm	25 x 6 mm
12	Steel, k= 80	33.3	53.3	82.5	105	166.8
13	Recommended strip size	25 x 3 mm	25 x 3 mm	25 x 6 mm	25 x 6 mm	40 x 6 mm
14	t =3 Sec
15	Copper k = 206	22.34	35.85	56.42	70.67	112.23
16	Recommended strip size	25 x 3 mm	25 x 3 mm	25 x 3 mm	25 x 3 mm	25 x 6 mm
17	Alluminium k = 126	36.55	58.54	90.76	115.47	183.42
18	Recommended strip size	25 x 3 mm	25 x 3 mm	25 x 6 mm	25 x 6 mm	40 x 6 mm
19	Steel , k= 80	57.68	92.32	142.89	181.86	288.9
20	Recommended strip size	25 x 3 mm	25 x 6 mm	25 x 6 mm	40 x 6 mm	50 x 6 mm

PART-B: Typical Protective conductor size required for Transformer Ratings (630-2000KVA)

Sr.	A	G	H	I	J	K	L
1	Transformer Rating ( KVA)	630	750	1000	1250	1600	2000
2	Secondary Voltage (V)	433	433	433	433	433	433
3	Full Load current	840	1000	1333	1667	2133	2667
4	Percentage Impedance Z%	5	5	5	6	6	6
5	Short Circuit Current (SC) in A	16801	20001	26668	27779	35558	44447
6	Area of Protective conductor Reqd in sq.mm = SC *√t/k
7	t = 1Sec
8	Copper k = 206	81.96	97.57	130.09	135.51	173.45	216.81
9	Recommended strip size	25 x 6 mm	25 x 6 mm	25 x 6 mm	25 x 6 mm	40 x 6 mm	40 x 6 mm
10	Alluminium k = 126	133.34	158.74	211.65	220.47	282.2	352.75
11	Recommended strip size	25 x 6 mm	40 x 6 mm	40 x 6 mm	40 x 6 mm	50 x 6 mm	75 x 6 mm
12	Steel, k= 80	210.01	250.01	333.35	347.24	444.47	555.59
13	Recommended strip size	40 x 6 mm	50 x 6 mm	75 x 6 mm	75 x 6 mm	75 x 6 mm	75 x10 mm
14	t =3 Sec
15	Copper k = 206	141.26	168.17	224.22	233.56	298.96	373.7
16	Recommended strip size	25 x 6 mm	40 x 6 mm	40 x 6 mm	40 x 6 mm	50 x 6 mm	75 x 6 mm
17	Alluminium k = 126	230.95	274.94	366.58	381.86	488.78	610.97
18	Recommended strip size	40 x 6 mm	50 x 6 mm	75 x 6 mm	75 x 6 mm	75 x 10 mm	75 x 10 mm
19	Steel , k= 80	363.74	433.03	577.37	601.42	769.82	962.28
20	Recommended strip size	75 x 6 mm	75 x 6 mm	75 x10 mm	75 x10 mm	100 x 10 mm	100 x 10 mm

Reader can choose safely factor as 1.5.

Suppose calculated strip size is 40x6 sqmm = 240sqmm

Considering safety factor , strip size = 240x1.5 = 360 sqmm.

Electrode always should be installed in 2 and opposte side of equipment. The distance between electrode is not less than height of one electrode.