Earthing of Transformers 2

[paulcolesec]

On a standard 11kV/415v distribution transformer, what is the minimum size of earthing conductor required ?<br>Should it be bare tape, insulated tape, bare stranded conductor or covered stranded conductor ?

 

[gmazumder]

the KVA or MVA rating of the transformer will determine the conducter size required for the neutral earthing. Also what is the expected fault level and the neutral i hope is on the LV side. Regarding the conductor type if it is insulated type&nbsp;&nbsp;it is better, if for some reason the joint or some thing in the earthing is defective and also if for some reson the fault does occur and the heating of any particular region occurrs then the deformation of the insulation will give an idea regarding the same. The insulation also helps in minimising the atmospheric oxidation. Also it is important that the location of the transformer be taken into account wether indoor or out door.<br>Also from the transformer neutral take out two parallel strips as if there is a fault in one then atleast there is one to take care of the earthing. Also with parallel conductors the effective resisitance is always low.<br><br>hope you find this usefull if you give further details then other data can also be given.<br><br>regards<br>gautam<br>&nbsp;

 

[jbartos]

May I suggest that you also follow electrical safety codes complying with local, state and federal laws and regulations. National Electrical Code NFPA 70-1999 Table 250-122 gives &quot;Minimum Size Equipment Grounding Conductors for Grounding Raceways and Equipment.&quot; The size of equipment grounding conductor (not for system grounding) is related to the setting of automatic overcurrent device which is ahead of equipment, conduit, etc. The system grounding conductor depends on a type of system grounding, e.g. high-resistance, solidly grounded neutral, medium resistance grounding, etc.

 

[SooryaShrestha]

In my experience, whatever may be the size of the transformer, it shall never be less than 50 mm^2 cu equivalent in order to take care of the fault current, mechanical strength and of course good earth.