My system is 22kv/3.3kv transformer. client is asking to use
NGR, but as we have dedicated Neutral Earthing systems which
has a value less than 1 Ohm. So i want solid comparision.
Why i should not use NGR as my system is already
protected.Can any one help me to get out of this.how should
i reply on basis of some great comparision and calculations.
Please help
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Answer Posted / k.prakashchandra
NGR is provided to limit the earth fault current
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When we use air circuit breaker, it has O/L protection ,time delay SC protection, Instataneous SC protection & ground fault protection. They all have some setting range. But what is the suitable/allowable setting for the above protection which will be safe for the equipment? For example-O/L protection setting have a range of (0.4,0.45,0.5,0.55,0.6,0.65,0.7,0.8,0.9,1.0)xIn Time delay SC protection have a range of (1.25,1.5,2,3,4,6,8,10,12)xIn Time delay setting is 0.02,0.1,0.2,0.3,0.4 Instataneous setting is fixed to 20xIn Gound fault setting is given 100A,300A,600A,900A,1200A This setting are for 2500A ACB. So what will be the basic allowable setting for the above protection? is there any formulae to calculate this<
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