High and Low Gr. System
High and Low Gr. System
(OP)
Hi,
I am sure many have answered this before:
Is this thubm rule or there is a logic behind this assumption:
1. Low resistance grounded system: 0-25 A
2. High resistance grounded system-25-600 A
Will it be correct to say, if I limit my ground fault current to 50 A, it will be a High resistance grounded system.
Thanks
I am sure many have answered this before:
Is this thubm rule or there is a logic behind this assumption:
1. Low resistance grounded system: 0-25 A
2. High resistance grounded system-25-600 A
Will it be correct to say, if I limit my ground fault current to 50 A, it will be a High resistance grounded system.
Thanks






RE: High and Low Gr. System
Low resistance: 5 to 10% common of 3 phase fault current & trip.
High resistance: Less 0.1% of 3 phase fault & alarm no trip.
RE: High and Low Gr. System
The debate is some what related actually. selection of a L.A. based on high resistance or low resistance grounding system.
My system is 44 Kv/13.8 KV star grounded 159 ohms I(Gf)50A there is a pole line of approx. 1 km from the sec. of transformer 13.8 KV. what would be your suggestion for be the MCOV of lightning arrester for Line to ground application.
Could you please put a word here?
Thanks
RE: High and Low Gr. System
RE: High and Low Gr. System
I beleive rating of L.A is different from MCOV.
Thanks
RE: High and Low Gr. System
RE: High and Low Gr. System
RE: High and Low Gr. System
* For High Impedance/resistance grounded : MCOV ≥ VLL
* For solidly & low impedance grounded: 0.63.VLL ≤MCOV ≤ 0.80VLL
See an example in the following link: http://cuky2000.250free.com/SA1.jpg
If the sequence impedance parameters are known, more accurate results could be obtained determining the coefficient of grounding (COG). The COG take in consideration the overvoltage effect of the grounding impedance and the system parameters at the surge arrester location. The surge arrester MCOV, regarless the type of grounding impedance could be calculated as follow:
MCOV=1.05.COG.VLL