NER used for what?

[bejoyeleengineer]

I am a bit confused on the topics below
1. What is the difference between a Neutral earth resistor and Neutral earth reactors?
2. Why isn?t it that any of the one of them is used to connect between the star point and neutral of a transformer ?
3. If a fault occurs ? the fault current tries to take the low path resistance ? which is the ground itself , so then why is the NER placed?

Kindly do reply

 

[topgone]

Resistors are used to limit the ground fault to manageable levels, and as reference ground.

Reactors are used only if the ground fault current is at least 60% of the possible three phase current to prevent transient over voltage. The amount of grounding reactance can be chosen such that the inductive reactance of the lines to which the generator is connected to gets cancelled by the reactance of the neutral grounding reactor. You are going to relieve the system of damaging TOV's and prevent damages to the switchgear. Sometimes both methods are used at the same time, a surge protection and limiter of ground fault current.

 

[bejoyeleengineer]

Thanks for the reply

Are these NER connected at the LV side of a transformer or HV side or does it depend on the connection i.e, if HV side is star and LV side is delta, then the NER will be connected to the HV side as the neutral is connected to the ground and vice versa..

 

[T.M.Haja Sahib]

Thanks for the reply

Are these NER connected at the LV side of a transformer or HV side or does it depend on the connection i.e, if HV side is star and LV side is delta, then the NER will be connected to the HV side as the neutral is connected to the ground and vice versa..

Neutral resistance earthing on the secondary side only makes sense.Also,I think in star-star transformers resistance earthing can not be used due to resulting unbalanced voltages on the secondary side.