Requirement of Separate Earthing System

W

Thread Starter

was00266

We are installing a Power Plant system of 4 machines of following denominations:

1. 2x24 MW, 60 Hz, 13.8KV (to supply our industrial power plant)

2. 1x10 MW, 60Hz, 13.8KV (to supply our industrial power plant)

3. 1x60MW, 50 Hz, 11KV (for Power Export to National Grid)

The 60 MW, 50Hz machine is being used to export power to national grid at 132 KV through a 11/132 kV 80 MVA transformer. The fault level of grid at 132 KV is 8KA (50hz) from the short circuit report.

Please note, all Generators are installed in a hall and grid is 250m away from the Generator hall/internal plant.

Whereas, the 3 remaining machines of 60 Hz are being used to supply internal plant having motors and Transformers of different ratings. The different levels of faults are as under at different voltage levels for the internal plant from the short circuit report are as follows:

13.8KV: 10 kA
6.6kV: 23kA
480V: 72kA

1) Please advice which fault current (8KA@132KV, [email protected], [email protected], [email protected]) to be used while calculating Step and Touch potential.

2) To calculate Touch potential do we have to consider system voltage or it is just related to highest available system fault current?

3)Should we need to have separate and isolated earthing system for our 60Hz & 50Hz power plant and 132KV Grid or we can keep them combine and interconnect our 50 & 60 Hz earthing system?

4) If we have two different grounding network for our 60MW (50hz) Machine and 132KV Grid station including Step up Transformer do thing it will create any problem in the operation of Protection and relay and coordination system?

5) Any reference available for IEC or IEEE.

regards
 
Was00266...

1) All can be evaluated, but there is more emphasis on the highest kV.

2) The calculation involves kV, kA, & fault-current duration.

3) No! Earthing-grids, Mats in USA, can be individualized, but all must be "bonded" together, with particular attention paid to any fenced-in area, if provided.

4) No

5) In USA: IEEE; US Fed CFR; and OSHA.

Regards,
Phil Corso
 
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