Over correction

[ptonsparky]

We installed a PP with PFC, for a 40 HP submersible as requested. The pump installer informed us the installed was 30HP as my guys were setting the overloads.

Is it worth the effort to change the PFC? I'm inclined to adjust the overloads lower & forget it. Open discharge on the pump if it means anything.

PFC is required by the POCO and in the past it was a visual confirmation if it was installed, working or not.

 

[Tony S]

If there are other drives running at the same time I’d leave it as it is. Although be careful with the O/L settings.

Normally for PFC I’d connect between the contactor and motor O/L unit. Saves all the messing about with O/L settings as they can be set at the motor FLC.

 

[luckylerado]

If it runs a lot, it might be worth running the numbers. Over the life of the unit there could be a substantial cost benefit. Should only be a few Kvar off.

Sounds like you should be paid to do it no? They told you one thing and installed another.

 

[Tony S]

Sounds like you should be paid to do it no? They told you one thing and installed another.

I’m not known for my sweet temper. I would have gone ballistic if someone dropped that on me.

 

[Phil Corso]

PtonSparky...

While PFC can result in economic benefit, over-correction can jeopardize safety. Can you reveal:

1) How much correction (in MFD) is being installed?

2) What is the motor's nameplate data?

3) What is the typical current-draw compared to its rated FLA?

4) How deep is the well?

Regards, Phil Corso

 

[ptonsparky]

PtonSparky...

While PFC can result in economic benefit, over-correction can jeopardize safety. Can you reveal:

1) How much correction (in MFD) is being installed?12.5 kvar... 144mfd. Should be 7.5 kvar ...86 mfd. According to wholesaler. I used online conversion calc so I hope that is correct.

2) What is the motor's nameplate data? 3ph 460v 36.8 amp, ?? rpm. I did not see the motor and a label with the full details was not left there.

3) What is the typical current-draw compared to its rated FLA? About 28 vs the 36.8 from conversation with help.

4) How deep is the well? Pump is at 180. Draw down is 140 to 150 @ 600gpm

Regards, Phil Corso

IDK the tfmr kva. 480/277.

 

[kingpb]

In order to provide any insight, I think additional information is needed such as NEMA Motor Design, rpm, power factor.

If it is too large, self-excitation can occur causing motor damage when disconnected from line and also if you try to reconnect while motor is still rotating.

 

[Bugman1400]

I don't think extra PFC matters much. I'm surprised you have PFC for that size of motor. The only reason I would think of using PFC is for voltage support because of a weak source. Since induction motors are already self-excited, I don't think there is an issue there.

 

[Phil Corso]

PtonSparky...

The maximum PFC for a fully loaded induction-motor should not exceed its no-load kVAr! If this limit is ignored, and PFC is switched with the motor, two dangerous conditions could arise:

1) Over-voltage
This condition occurs because excess capacitance will increase the motor’s a magnetizing-current above nominal, thus causing self-excitation, that is, turn the motor into a generator!

2) Transient-torque.
This occurs if the motor has a feature to automatically reaccelerate following a brief power interruption! It is especially a problem for motors having load-factors below 80%.

Let me know if additional info, such as optimum PFC-location, Cap-Voltage, Cap-CB rating, and OL setting, is required!

Regards, Phil Corso

 

[ptonsparky]

No nameplate yet. Written on the door by pump installer: FLA 39.5. Max amp 45.2. (Assuming SF amps)

My measurements today
Motor amps before PFC 39.9
With PFC 32.6.

Fluke 43B says PF of about 97 with cap, 78 without. Assuming I connected it correctly, it's been awhile.

 

[Phil Corso]

PtonSparky...

1) Since you have line-current and PF measurements, do you have V and kW measurments?

2) Have you confirmed PFC location, i.e., is it switched with the Motor?


Bugman...

"Since induction motors are already self-excited, I don't think there is an issue there."

Have you confused an Induction-Generator with an Induction-Motor?

Phil

 

[ptonsparky]

PtonSparky...

1) Since you have line-current and PF measurements, do you have V and kW measurments?

2) Have you confirmed PFC location, i.e., is it switched with the Motor?


Bugman...

"Since induction motors are already self-excited, I don't think there is an issue there."

Have you confused an Induction-Generator with an Induction-Motor?

Phil

1. 286.5 L-N 26.3kw. 27.2kva 6.93 Kvar .97dpf All with amp clamp including capacitor
26.1 kW, 33.2kva, 20.4 Kvar .79dpf. Excluding capacitor

2. PFC is switched with motor.

 

[ptonsparky]

View attachment 13266 View attachment 13267

IF. I did it correctly.

 

[templdl]

PtonSparky...

The maximum PFC for a fully loaded induction-motor should not exceed its no-load kVAr! If this limit is ignored, and PFC is switched with the motor, two dangerous conditions could arise:

1) Over-voltage
This condition occurs because excess capacitance will increase the motor’s a magnetizing-current above nominal, thus causing self-excitation, that is, turn the motor into a generator!

2) Transient-torque.
This occurs if the motor has a feature to automatically reaccelerate following a brief power interruption! It is especially a problem for motors having load-factors below 80%.

Let me know if additional info, such as optimum PFC-location, Cap-Voltage, Cap-CB rating, and OL setting, is required!

Regards, Phil Corso

Finslly, a reply that cuncurs with my thiughts. I was going to suggest that over voltage would be an issue with a leading PF but I didn't want to reply because I couldn't substantiate it. Thus, Leading PFs are a no no.

 

[Besoeker]

Normally for PFC I’d connect between the contactor and motor O/L unit.

There can be a problem with that. A cage motor can self excite if the PFC is permanently connected. That's why we always fit a separate PFC contactor.
Some years ago, I did some tests on a submersible pump set with capacitors with a view to offering affordable generation for remote locations with a decent head of water to power the pumps.
It needed a bit of power electronics to control voltage and frequency but it worked quite well.

 

[Phil Corso]

Tom, I've moved your measured values around a bit:

Before PFC:
286.5VLN, 34.9A, 33.2kVA, 26.2kW, 20.4kVAr, 079pf

After PFC:
286.5VLN, 36.2A, 27.2kVA, 26.3kW, 6.93kVAr, 0.97pf

1) If VLN is 286.5, then 3-ph, supply ph-ph voltage is ~496 Volts, Is this correct?

2) Assuming a NEMA-Premium motor, and using generic data, i.e., 460V, 4-Pole, Eff ~94%, then output is 24.6kW => 33Hp.
Thus if motor it operating above rating! I know Submersibles are unusual... and water, in this case, is the coolant, but...?

3) The PFC Cap factor, Q = [kVAr(b)-kVAr(a)]/kW = 0.511kVAr/kW, which is too high (using generic data)!
Can you get No-load current from Motor Mfg?

Phil

 

[Phil Corso]

Besoeker...

Reur: "Some years ago, I did some tests on a submersible pump set with capacitors..."

Some years ago, I too was involved with submersible pumps in the FL Everglades! Some 10 kft deep. Your app to use the pump-motor as an Ind'n-Gen'r intrigues me!

How did you overcome the check-valve(s)?

Regards, Phil

 

[Besoeker]

Besoeker...

Reur: "Some years ago, I did some tests on a submersible pump set with capacitors..."

Some years ago, I too was involved with submersible pumps in the FL Everglades! Some 10 kft deep. Your app to use the pump-motor as an Ind'n-Gen'r intrigues me!

How did you overcome the check-valve(s)?

Regards, Phil

The mechanical design was someone else's responsibility.
All I needed was a pump running as a turbine.

 

[Bugman1400]

PtonSparky...

1) Since you have line-current and PF measurements, do you have V and kW measurments?

2) Have you confirmed PFC location, i.e., is it switched with the Motor?


Bugman...

"Since induction motors are already self-excited, I don't think there is an issue there."

Have you confused an Induction-Generator with an Induction-Motor?

Phil

No, I haven't. How do you think the poles (field) of an induction motor are established. It is self-excited by the rotating magnetic field. Come on Phil, I know you know this. The induction generator does the same thing but, in reverse when the prime mover drives the shaft (generation) instead of the shaft driving the load (motor). High voltage on the leads to the induction motor will NOT cause the induction motor to turn into a generator if the shaft is not being driven by an external force. As most folks already know, a motor is instantly turned into a generator when the supply (breaker) to the motor is tripped. The mechanical inertia is now the external force and thus, keeps the voltage leads of the motor (generator) elevated for some time until the shaft spins down.

 

[Phil Corso]

Bugman,

I strongly disagree! The magnetic-structure of an induction-motor is energized, hence excited, by the source its connected to.

Self-excited** is a condition in which an induction motor, operating as an induction-generator, in an isolated power system derives its excitation from shunt-capacitors or the natural capacitance of its connected power-line, if any!

** IEEE Std 100 "Standard Dictionary of Electrical and Electronic Terms"

Phil