Grounding

[pithpal]

Hi Everybody,
Today I happened to have a word with a utility director and he gave me the value of 3 phase fault of 1000 A on 8.3 Kv line and 700 A ground fault. It surprised me, after finishing my engineering degree and since I have stepped in this engineering field( 1 yr exp.) and from what I have read, I have always read stories of ground fault current being limited to couple of amperes and those big issues of transformer grounding and to my surprise he tol me that their 230 KV/44 kV substation is solidly grounded. If this happenes, so where do we ground a transformer. I have these IEEE standards just providing exhaustive information about transformer grounding, where do we use it then. I dont work in this area but just casually came acroos while related to one of projects. Could you help me with this.
Thanks

 

[dpc]

Utility distribution and transmission systems are generally solidly grounded, for a variety of reasons. One concern on long lines is making sure a grounded conductor can even be detected.

Industrial systems are often impedance-grounded to limit fault current damage and hazards from ground faults.

The grounding method depends on the type of system, equipment involved and local custom.

 

[RalphChristie]

Regarding the 230/44kV transformer:

What is the arrangement of the transformer, thus the vector-group of the transformer? Yd or Yy? If the secondary side is delta, how do you ground it? And if you say the substation is solidly grounded, to which side do you refer? Normally the primary side will be solidly grounded on that voltage range (230kV) This is because non-uniform insulation (insulation degraded towards neutral point) is used for a saving in cost - this is for 132kV and above. For the secondary side it depends - many older installation is still solidly grounded.

As a side note: Regulation (British) state that any low voltage system (between 50V and 1000V) must be solidly grounded.

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[mnnc]

The transformer might be equipment grounded. You can ground the transformer by placing ground rods connected to a bare copper wire with ground clamp, and connect it to the body of the transformer. I hope this helps.

 

[Max9999]

The fault current levels typically depend on the tranformer that is feeding your system and your geographical location. For example, if your facility lies a distance from a well populated area; don't be surprize if the fault currents are low. In regardss, to the ground fault current; IEEE Red book states that ground fault can be up to 115% of the 3-phase fault.

I hope this helps,