Overvoltage in a Mains

During the day when the load is high you utility voltage is normal. At other time the voltage is high because the load is low. The utility voltage regulation is lacking. Also the capacitors will cause a voltage rise when they are on line. You may want to measure the voltage with the cap off line and see it it helps.

pls mention about your loads (what type of loads are you loading 1 phase or 3 phase). in case if single phase loads more than three phase loads this type of problem may happen. as you mentioned that magnetic netural contactor burning frequently. this type of problem happening because of temperature increasing on that contactor(core, coil etc., i think contactor coil slowly getting weak and making problem). check the return current as well as contactor rating suitable for return current.

dear,

contactor coil rating is 240v ac. proper.

LOAD ON SYSTEM : < 100 kva , transformer rating 200kva

nature of load : welding machines 15kva * 10 nos. , 20kva * 4 nos. , 8kva * ^ NOS>

Check the load on each phase & balance the load.

Harry

You have the answer to your question. Measure the voltage at peak loads, light loads and light loads with the capacitors off line. Then we can discuss the problem.