Large HP Motor

[Shaneyj]

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?

Positive displacement

 

[Shaneyj]

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?

Something about paying taxes on gallons of diesel and inefficiency of tier 4 engines, etc. The oil companies are incentivized to go electric.

 

[zbang]

So they buy diesel for the generators instead (unless they're burning heavy oil)? That said, electric controls are much easier than mechanical controls (ref things like railroad locomotives and ships' propulsion).

"Clients wants it painted purple, we paint it purple."

 

[Jraef]

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

Good thing to bring up with the generator supplier and the VFD supplier. As a generalization, most modern generator suppliers have fixed most of the early issues with AVRs being affected by harmonics from VFDs, and most VFDs for motors that side will likely be inclusive of some form or harmonic mitigation. But you are right, it's not something you want to leave to chance.

Shaneyj,
You say this is a PD pump, so not an ESP, right? If this is a rod pump (a type of Positive Displacement pump used in oil wells), there is another potential issue to consider; braking the motor when you stop. If it is a rod pump, let me know and I'll explain, otherwise it's a lot of typing for nothing...

 

[Jraef]

So they buy diesel for the generators instead (unless they're burning heavy oil)? That said, electric controls are much easier than mechanical controls (ref things like railroad locomotives and ships' propulsion).

"Clients wants it painted purple, we paint it purple."

It's really only about the cost of running xx miles of high voltage transmission lines, building a unit substation and transformer to run one load for a few years, vs renting diesel gensets that are pulled out and moved somewhere else when the well stops producing enough.

Oh wait, you were probably referring to just running the pump with a diesel engine directly weren't you? Yeah then, it's about the speed controls. Diesels run best when they are run at constant speeds, like with a generator. That's why diesel locomotives and ships do it that way; diesel engines are running generators, then the wheel or propeller motors are electric.

 

[zbang]

If this is a rod pump

I remember reading somewhere, quite a long time ago, that the motors driving "horsehead" pumps were built for a very high slip (<7-8%) because of the mechanical inertia of the rod. That also could be a faulty memory.

(Yes- I was referring to mechanical vs electrical coupling of prime mover to the actual load.)

 

[texie]

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.

I fail to see how correcting PF will save fuel. The engine sees KW not KVA.

 

[Shaneyj]

Good thing to bring up with the generator supplier and the VFD supplier. As a generalization, most modern generator suppliers have fixed most of the early issues with AVRs being affected by harmonics from VFDs, and most VFDs for motors that side will likely be inclusive of some form or harmonic mitigation. But you are right, it's not something you want to leave to chance.

Shaneyj,
You say this is a PD pump, so not an ESP, right? If this is a rod pump (a type of Positive Displacement pump used in oil wells), there is another potential issue to consider; braking the motor when you stop. If it is a rod pump, let me know and I'll explain, otherwise it's a lot of typing for nothing...

This is a piston style pump.
I asked if the pump was capable of spinning the motor and turning it into a generator and the response from our application engineer was that it is a non issue. He also said the pump is pumping against enough pressure (he said averages are 5k to 7k psi) that when not energized, the back pressure would cause the pump to stop spinning immediately, eliminating the need for braking.

Sent from my SM-G965U using Tapatalk

 

[drktmplr12]

I fail to see how correcting PF will save fuel. The engine sees KW not KVA.

I was mistaken, thank you

 

[Russs57]

In the interest of throwing all possible ideas out there and seeing what sticks....

How about a fluid coupling? Might let the motor start unloaded and the once at full rpm you can stage the pump in at whatever RPM you need.

 

[Shaneyj]

In the interest of throwing all possible ideas out there and seeing what sticks....

How about a fluid coupling? Might let the motor start unloaded and the once at full rpm you can stage the pump in at whatever RPM you need.

Good idea, but the operators have control over the load so they can uncouple from the high pressure side via valving before the motor is started. Which is SOP.

 

[Besoeker3]

Good idea, but the operators have control over the load so they can uncouple from the high pressure side via valving before the motor is started. Which is SOP.

SOP?
Ignorant Brit here...............

 

[drcampbell]

Standard Operating Procedure
(apologies for the language barrier)