Neutral To Ground Voltage

You have the voltages and the currents and so you can calculate the resistances, and also how much you need to lower the resistance to meet specs. E=IR.

sir actually that 600A is full load I.this is happening when we just on the machne breaker and without starting machine.so servo also not in running mode .and this is new machine and just taking trial run on the machine

noturordinaryjoe sir,

thank u for ur answer but again i want to ask u 1 thing,is that distortion do trouble in system communication? because we r facing prob in in that also

The power distortion is not likely to be the cause of communication problems. Generally the communication issues come from the power lines being too close to the communication lines. This is a very common problem that people learn to appreciate once they solve it. If you are seeing the communication noise when the big drives are connected, it is probably due to magnetic linkage between cables.

Sometimes you can solve communication problems by using shielded cables or wires. If, however, you connect the shield at both ends of the cable then you have more noise instead of less. This makes for a condition called a ground loop. Always only connect only one end of a shield wire.

Remember that currents produce magnetic fields which can then be absorbed by communication lines and converted back to a current of the same frequency as the source. That magnetic field falls off at the rate of 1/r*r where r is the radial distance between conductors. Generally you should keep communication wires at least 25 cm from communication lines if they are running in parallel. If they must cross or come close, try to minimize the overlap.

GA to NotUR...

As to the "distortion"...

Shielding bonded at each end should work for a high frequency (>300kHz) control circuit. Try adding a shunt capacitor at one end (if it's bi-directional you can experiment). You can also try using multipoint (equipotential) shielding along the entire length (but that may be cost-prohibitive). Using a toroid in conjunction with the shunt cap may increase the efficiency as well.

Measure your shield with your test equipment (spectrum analyzer) on a dedicated isolated ground circuit (to see the actual interference with harmonics). Your control circuits may have an isolated SMPS which is common for some control devices (VME is one). The combination of an isolated (from line) SMPS and improper shielding (for the application) may be causing your issues.

1)check the winding resistance of motor for each individual phase - it should be same .

2)check the voltage of each phase which has been feeded to the motor-it should be same .

If in case of changes , due to unbalance , there might be a flow of voltage in neutral circuit .

this may be the reason why you are getting the 8-9 volt .

Certainly there will be electric current flow when you switch on ground breaker of the motor, this causes increase in voltage. What is the permissible neutral to ground voltage in your system? Possibly you should use bigger grounding cables and reduce resistance of ground cable to earth. Check also grounding current of each motor for possible excessive grounding current.