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Reference to thread 238-161221

Reference to thread 238-161221

Reference to thread 238-161221

(OP)
In this thread it was discussed that

The IEC designation for cable voltage rating is :Uo/U (Um),
Where:
Uo = max phase-to-ground voltage
U   = max. Line—to-line-voltage
Um = maximum system voltage.

And an example was given for one cable where
'Designation:      
Uo = 18kV    
U =  30 kV    
Um = 36 kV      

If I have a 33kV nominal voltage system can I use this cable? or should I be using a 36/50kV cable.

The network is high resistance ground with NER rated for 10secs, with 67 relay for earth fault trip.



 

RE: Reference to thread 238-161221

Theoretically yes, but I prefer for 7.2 kV 6/10 kV and for 33 kV 26/45 kV [manufactured according to IEC 60502 of course!]even for low resistance grounded system..
Compared with US [UL, AIEC] the thickness of insulation of 18/30 Kv cable is only 8 mm [315 mils]
and 35 KV US cable [for 100%-grounded- insulation] will be 345 mils [8.8 mm]. 26/45 kV it is provided with 10.5 minimum insulation thickness [413 mils]. For ungrounded 35 kV US cable [133% insulation] the thickness is 420 mils [10.66 mm].

 

RE: Reference to thread 238-161221

jimmy2times,

I donot know how did you get 36/ 50 kV. It should be either 36/ 60kV, 36/ 66kV or 36/ 69kV. It is suitable for systems with nominal system voltages 60, 66 and 69 kV.

Therefore, using a 36/ 60kV cable is in overkill.

In my opinion, it should be decided as follows.

If the NOMINAL system voltage is 33 kV, then the HIGHEST system voltage shall be 36 kV per IEC 60038.

Then based on above you have to select a cable designated as 19/ 33kV (36 kV)per IEC 60183,where

19 kV = U0 between phase and ground r.m.s voltage
33 kV = U nominal system voltage r.m.s.
36 kV = Um maximum possible voltage between any two phases excluding temporary overvoltage conditions.

Also, it seems that your HRG system allows an earth fault upto 10 seconds only. Therfore, 19/ 33kV(36kV) cable of Category A design (equivalent to 100% insulation in ANSI world) is sufficient for your application.

Hope this helps.

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