SF vs FL current imbalance

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If it said 'surface factor load', then I believe that was a type-o for 'service factor load'.

For a motor, the 'rated load' is the power output that the motor was designed for, but which takes into account requirements such as starting torque, acceleration requirements, voltage tolerance range, etc.

'Service factor load' is the continuous power output that the motor can supply while remaining within design maximum limits for things such as temperature.

For example, a 10 Hp motor with a SF of 1.15 can be expected to accelerate and behave like a 10 Hp motor, but if you were to load it up to 11.5 Hp in steady operation with perfect supply voltage and perfect balance, then the motor would not overheat.

Because the SF load is higher, you can expect the motor to run hotter and to have less tolerance for other factors (such as voltage imbalance) which would also cause heating.

I expect that the same meaning for SF load is used for motor driven pumps as for motors.

-Jon
 
I don't know if that was a typo or auto correct.

winnie said:
If it said 'surface factor load', then I believe that was a type-o for 'service factor load'.

For a motor, the 'rated load' is the power output that the motor was designed for, but which takes into account requirements such as starting torque, acceleration requirements, voltage tolerance range, etc.

'Service factor load' is the continuous power output that the motor can supply while remaining within design maximum limits for things such as temperature.

For example, a 10 Hp motor with a SF of 1.15 can be expected to accelerate and behave like a 10 Hp motor, but if you were to load it up to 11.5 Hp in steady operation with perfect supply voltage and perfect balance, then the motor would not overheat.

Because the SF load is higher, you can expect the motor to run hotter and to have less tolerance for other factors (such as voltage imbalance) which would also cause heating.

I expect that the same meaning for SF load is used for motor driven pumps as for motors.

-Jon
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Should the level for voltage imbalance be reduced as well when at SF load? 1% vs 2%?
 
Voltage imbalance causes current imbalance, so I don't see how you could fix one without fixing the other. Similarly I don't see that you need to specify one as long as the other is specified.

But now we are outside of my certain knowledge. I work pretty exclusively with VFD driven motors. If there is an imbalance then something is broken.

-Jon
 
winnie said:
Voltage imbalance causes current imbalance, so I don't see how you could fix one without fixing the other. Similarly I don't see that you need to specify one as long as the other is specified.

But now we are outside of my certain knowledge. I work pretty exclusively with VFD driven motors. If there is an imbalance then something is broken.

-Jon
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Just an academic question. My meters are mostly decorations on the work bench nowadays.
 
Unbalanced voltage creates unbalanced current. Unbalanced current causes "negative sequence current" to flow in the rotor. This creates a magnetic field rotating in opposition to the rotating magnetic field created by the stator, so is essentially "fighting" the torque that you want out of the motor. But the load is demanding torque, so to overcome that the stator must produce MORE torque, which means more current and more heat for the same net amount of work. A gross rule of thumb is that every 1% voltage unbalance (Vi) creates 6-10% current imbalance, and that in turn causes a temperature increase that is 2* Vi2. So 1% Vi = 2% temp increase, but 2% Vi = 8% temp increase and 5% Vi = 50% temp increase.

So one way you can think of is that by having unbalanced voltage, you are already consuming SOME or all of your SF capability.
 
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