How to design the earth grid for lightning protection in an
industry
Answer Posted / vishal ingle
lighteining protection can be achieved by using lightening
arrestors at the highest points in an industry if its area
is less. but for larger area to be covered, several
lightening areestors are to be used. or
in the EHV substations, continuous earth wire mesh is
formed covering entire area.
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DEAR SIR/MADAM,CLEARLY EXPLAIN ABOUT CRAWLING AND COGGING EFFECTS IN INDUCTION MOTOR.
We have drive feeding an output contactor for a 5000 hp motor @ 5kV application. The motor FLA is 629amps x 1.25% service factor = 786.25 amps The cable that we current have in place between the drive and the output contactor is 350kcmil- MV-105 (parallel cables). Per the NEC table 310.60 (C) (69). This show the cable ampacity is at 615 amps per cable for a rating of 1230 amps. We have derated the cable for the cable tray and the multiple cables application and our calculations show that after the correction factor factor we are at 922amps. 1230 amps x .75% correction factor factor = 922.5 amps. The customer is driving us to then use another safety factor of .25% off of the already derated cable. Can you please provide a longhand calculation for your solution on this application?
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