Large HP Motor

[Shaneyj]

I am looking to spec an electric driven pump for a wellhead application. The supply available is 600kW 3 phase, 480V.

Our pump can take up to 1000hp input to get max output. But 600kW converts to 804 hp ignoring losses.

I found the NEC stops at 500 hp so no help there.

Are there some general rules of thumb when designing for large hp motors?

I am in the process of getting some quotes for motors; I'd like to see some nameplate data on eff and pf, but are there safe values to use here for theoretical purposes in the design calculations?

This is outside my normal scope and the 1st design of its kind at my company.

Thanks for your input!

 

[Besoeker3]

I am looking to spec an electric driven pump for a wellhead application. The supply available is 600kW 3 phase, 480V.

Our pump can take up to 1000hp input to get max output. But 600kW converts to 804 hp ignoring losses.

I found the NEC stops at 500 hp so no help there.

Are there some general rules of thumb when designing for large hp motors?

I am in the process of getting some quotes for motors; I'd like to see some nameplate data on eff and pf, but are there safe values to use here for theoretical purposes in the design calculations?

This is outside my normal scope and the 1st design of its kind at my company.

Thanks for your input!

Wouldn't the motor name plate give you that? That's what I have found to be the case. I know I'm a Brit but the figures would still be the same.

 

[Rock86]

This question has been asked before... here is an old post.. https://forums.mikeholt.com/threads/700-hp-motor.1706/
Basically... you'll have to get the actual specs from the manufacturer.

 

[drcampbell]

You probably also need actual specs about the supply and engineering review.

 

[tom baker]

Impressive, a 15 year old link but its still good.
Whats the pumping capacity of this well? Line shaft or submersible?

 

[Shaneyj]

Wouldn't the motor name plate give you that? That's what I have found to be the case. I know I'm a Brit but the figures would still be the same.

Are there some general rules of thumb when designing for large hp motors?

 

[Shaneyj]

This question has been asked before... here is an old post.. https://forums.mikeholt.com/threads/700-hp-motor.1706/
Basically... you'll have to get the actual specs from the manufacturer.

Thank you, that answers my question.

 

[Shaneyj]

You probably also need actual specs about the supply and engineering review.

Supply is 3 600kW generators @ 480V. We are the OEM, so we are generating specs as customer supplies wish list.

 

[Shaneyj]

Impressive, a 15 year old link but its still good.
Whats the pumping capacity of this well? Line shaft or submersible?

Oil well. We give them a couple pump options and supply max hp available.

 

[drktmplr12]

Are there some general rules of thumb when designing for large hp motors?

some rules of thumb

1. don't start them across the line unless you absolutely have to.
2. generator will need enough starting kva to start the motor/pump assembly, otherwise, it can stall the engine. can lower the skva of the motor with mechanical means or type of starter.
3. depending on the power factor, you might consider improving with correction capacitors-this can save fuel costs. beware that the capacitors would need to be disconnected from the electrical system when the pump isn't operating. most industrially available correction capacitors will have this as an option with a contactor that closes when the pump operates, but it must be integrated into the motor controls.

 

[Besoeker3]

some rules of thumb

1. don't start them across the line unless you absolutely have to.
2. generator will need enough starting kva to start the motor/pump assembly, otherwise, it can stall the engine. can lower the skva of the motor with mechanical means or type of starter.
3. depending on the power factor, you might consider improving with correction capacitors-this can save fuel costs. beware that the capacitors would need to be disconnected from the electrical system when the pump isn't operating. most industrially available correction capacitors will have this as an option with a contactor that closes when the pump operates, but it must be integrated into the motor controls.

One possibility is Soft Starts for the original poster. We have used some of those.

 

[Jraef]

The supply available is 600kW 3 phase, 480V.

Supply is 3 600kW generators @ 480V.

Which one is it? 600kW or 1800kW? Makes a huge difference if your pump is 1,000HP...
You are not going to run a 1000HP pump from a single 600kW generator. But if you have 1800kW available, that could work. The Rule of Thumb though is that if you use a Soft Starter, you still need 2x the motor HP as generator kW, so you still come up a little short, unless this is a stand-alone power source (meaning only for THIS one pump) and you can design your controls to tolerate a voltage drop greater than 5%, meaning adding a UPS for control power, etc.. Alternatively you may need to use a VFD to be able to start this pump and there may be other good reasons to use a VFD as well.

 

[Shaneyj]

Which one is it? 600kW or 1800kW? Makes a huge difference if your pump is 1,000HP...
You are not going to run a 1000HP pump from a single 600kW generator. But if you have 1800kW available, that could work. The Rule of Thumb though is that if you use a Soft Starter, you still need 2x the motor HP as generator kW, so you still come up a little short, unless this is a stand-alone power source (meaning only for THIS one pump) and you can design your controls to tolerate a voltage drop greater than 5%, meaning adding a UPS for control power, etc.. Alternatively you may need to use a VFD to be able to start this pump and there may be other good reasons to use a VFD as well.

Speed control is required, so I anticipate using a VFD.
I am awaiting specs from the customer on site information. I don't know if the 3 generators are in parallel; whether the supply is 600kW x 3 or 1.8MW.
Does a soft start need to be used in tandem with a VFD, or does the VFD provide low current starting?

 

[Besoeker3]

.
Does a soft start need to be used in tandem with a VFD, or does the VFD provide low current starting?

Just the VFD. Not the soft start.

 

[drcampbell]

If it's a standalone, the engine speed may droop as starting current is imposed, reducing the "line" frequency and the motor starting current. Simulation and very detailed specs may be called for.

Of course, if it's a standalone -- one engine, one generator, one motor and one pump -- I wonder why electricity needs to be in the loop at all. Why not just drive the pump with the engine?

 

[Jraef]

A VFD is much better at controlling starting current than a soft starter. You can essentially start the motor without ever going over FLA if necessary, and you have all the time you need for acceleration. So if you need speed control, you are there.

 

[Besoeker3]

Oops - delete this........

 

[Besoeker3]

A VFD is much better at controlling starting current than a soft starter. You can essentially start the motor without ever going over FLA if necessary, and you have all the time you need for acceleration. So if you need speed control, you are there.

Having adjustable speed VFD could be of merit.

 

[zbang]

Especially at those sizes, is there anything special needed so the VFD doesn't argue with the generator and it's governor?

 

[Russs57]

A question I have not seen asked, and perhaps because I know nothing about oil well pumps, but is the pump positive displacement or centrifugal?