6kV vs 6.6kV
6kV vs 6.6kV
(OP)
Recently a contractor installed three conveyor motors for my company. The motors are 230kW, 160kW & 150kW all 4 pole,three phase, 50Hz but the motor voltage is 6.6kV whilst our generated supply is 6kV with a power factor of 0.8 lagging. What will be the effect on the motors? Extra current draw, more heat generated in the windings, any effect on the motor output?
Remedies anyone? We cannot replace the motors easily as the lead time from Toshiba is more thsn 6 months.
Remedies anyone? We cannot replace the motors easily as the lead time from Toshiba is more thsn 6 months.





RE: 6kV vs 6.6kV
More important though, you are looking at a new installation that is not correct. I would look to the organization responsible for the discrepancy, whether it be motor manufacturer, contractor, or both to explain the reason for the discrepancy and the remedy that they propose.
Responsibility aside, the motor manufacturer should be able to provide detailed design data for motor performance at reduced voltages that would help you assess the effects on the motor.
RE: 6kV vs 6.6kV
RE: 6kV vs 6.6kV
In addition to the 6 KV generated, there is also a system voltage drop to the motor, making a bad situation worse.
I assume you mean 0.8 PF as a rating of the generator?
I guess you should derate the motor's output (shaft) capability by more than 10%. Hopefully your load (process) does not need all the power?
RE: 6kV vs 6.6kV
Motor torque will drop with the squared ratio of voltages.
The full load current will increase at least with the inverse proportion of voltage drop. The power factor could have a slight increase but the efficiency will be lower.
IFL = HPout*0.754/( 1.73 * VLL * Eff * PF)
The core losses will decrease due to lower flux densities in the magnetic circuit.
The winding losses will increase due to the current increase CUloss= R* I^2
Overall efficiency will be probably lower with the same load as compared to that operating at 6.6 kV.
Your motors will be in constant challenge, since you have no allowance for regular voltage drops or slight phase voltage unbalance.
A Olalde
RE: 6kV vs 6.6kV
RE: 6kV vs 6.6kV
1. The remedies may include an autotransformer increasing the voltage from the generated 6.0kV to the motor terminal voltage appropriate voltage such that the motor will receive 6.6kV across its terminals.
2. If possible, the motor with 6.0kV or lower terminal voltage should have had decreased its shaft load.
RE: 6kV vs 6.6kV
VOLTAGE 6% UP VOLTAGE 6% DOWN
Full load speed up to 0.5% down 0.75%
Starting torque up 12% down 11%
Starting current up to 6% down 5%
Full load current down 4% up 5%
Efficiency 1/2 FL down 1.5% up 2%
Efficiency 3/4 FL down 1.0% no change
Efficiency 1/1 FL no change down 1%
Power factor 1/2 FL down 4% up to 4%
Power factor 3/4 FL down 3% up to 2%
Power factor 1/1 FL down 2% up 1%
Temperature rise down 4% up 6%
In the context of Jeffer's problem (voltage down 10%), the danger is overheating of the windings - initially due to a slow start, and steady state due to increased current. If the steady state current doesn't exceed the FL nameplate value, and the starting isn't onerous, then no problem.