What Happens to AC Electric induction Motor Parameters Beyond Service Factor HP & Amps 1

[HydraulicsGuy]

These questions are specifically for AC Electric Induction Motors that we might spec to run an HPU. The questions are about what happens as we go beyond Service Factor HP & Amps.

One example of the kind of motor I'm referring to:

https://www.worldwideelectric.net/p...premium-efficiency-severe-duty-motors-c-face/

Parameters for questions below:

230 V 3-phase
SF = 1.15
FLA (full load amps) = 6.14
SFA (service factor amps) = 7.06
Full-load Eff = 87%
Full-load PF = 69%
Full-load Torque (FLT) = 8.98 lb-ft
Breakdown Torque (BDT) = 275% FLT

1. Let's say motor is drawing 8.5 Amps. What has happened mathematically to efficiency and power factor? What do you think their values would be?

2. Let's now say current continues to climb to 2 x FLA = 12.28 Amps. What has happened mathematically to efficiency and power factor? What do you think their values would be?

3. Is current directly proportional to torque demand? So as the torque demand goes beyond full-load torque toward breakdown torque, does the current follow proportionally? If current = 2 x FLA, is the torque that's being demanded = 2 x FLT? If not, what do you think torque would be?

4. If BDT = 275% FLT, is breakdown current = 275% full-load current? If not, what do you think current would be?

5. What happens to voltage through all this? Is voltage only dependent on the power source, or does it degrade as motor goes beyond service factor HP & amps?

6. I assume that through all this, the motor power equation still applies: P = V x A x Eff x PF (x 1.73 if 3-phase)?

 

[HydraulicsGuy]

The smaller units are very price sensitive and the vendors will always "big up" the performance whilst constantly trying to reduce costs. Result is a performance figure rarely achieved in practice (think miles per gallon of cars - how often does anyone actually get that performance in real life???). Applies equally to pumps. e.g. from your example if your pumps actually needs 20% more power (now 2.2 HP), but your motor is only giving you 1.6HP, you're now ~30% over FLA. But everything is within its accuracy range.

They also tend not to comply with any known standards as they are too small, but if you press them hard enough they will often only give you a performance guarantee of 20-25%. The "testing" also leaves a lot to be desired and the word "typical" turns up more than once.

You would think their published performance data would be conservative, for CYA purposes.

 

[HydraulicsGuy]

Google "Cowern Papers"

This is an awesome document. I'm about halfway through.