Answer Posted / bikash chandra pal

The following is in reference to Mr.S Bhattacharrya's
answer. The following I wish to point out for readers who
are learning.
1) It is correctly indicated that VOLTAGES 415VOLT SYSTEM
GENERALLY NEUTRAL IS DIRECTLY GROUNDED AND THIS IS CALLED
EARTHED SYSTEM. But, it is to note "33KV & above system" is
normally grounded solidly (not that "above 33kv system" is
grounded solidly as indicated in mr. Bhattacharrya's reply)

2) Midium voltage level 3.3kv to 11kv(not upto33 kv) are
normally grounded through Impedance or resistance to limit
earth fault current. there are so many terms to describe
such system e.g. "high resistance(or impedance)
earthed" / "low resistance (or impedance)
earthed / "effectively earthed" /"non effectively earthed"
etc. but not termed as " UNEARTHED SYSTEM" (as indicated in
Mr. Bhattachrrya's reply.)

3)For information,"high resistance(or impedance)
earthed" / "low resistance (or impedance)
earthed / "effectively earthed" /"non effectively earthed"
terms are defined based on "co-efficient of earthing". What
is co-efficient of earthing??---- go through some text book
like "sunil s Rao" it will be clear to you.

4) For information "unearthed system " is that system,
which is not earthed at all, ie.nither solidly or through
resistance.

5) Please note, Earthing through Resistance or impedance ,
limits the "Earth fault current" to desired value as per
system requirement, But it is having no effect or
connection with system's Short circuit current(STC) or
Fault level, as indicated in Mr. Bhattacharyya's reply.

6)"----CALLED UNEARTH SYSTEMS AND THIS SYSTEM IS VERY
STABLE COMPARED TO DIRECTLY GROUND SYSTEM "---- is not a
true statement again given by Mr. Bhattachryya in his
reply. Both the system is quite stable. System stability is
not depended on system grounding. To know about system
stability you may refer any TEXT book for example "NAGRATH
KOTHARI".
systems "earthed" , "resitance or impedance earthed"
or "unearthed", having their own advantage / disadvantage
already explained to some extent in my earlier reply no.1
above.

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