Starting Methods for Motors in Oil and Gas Industry 6

[NickParker]

Why are autotransformers, reactor starters no longer used in the oil and gas industry?
VFDs and soft starters are all I see. What significant advantages does the VFD and soft starters bring that older reduced voltage starting is no longer used in oil and gas industry?

Any references to IEEE papers for cost benefit analysis!

 

[jraef]

No papers that I’m aware of. But electro-mechanical reduced voltage starters are now more expensive than solid state, they are not as flexible in terms of starting parameters, and offer no other benefits, such as soft STOPPING to reduce the effects of water hammer when there are check valves involved. So since most of the large motors are going to be pumps, that has value in the selection process. Then because RVAT and Reactor Starters have become less common, the cost and availability has become worse in comparison. I recently tried to replace a 600HP RVAT starter, it was 52 weeks delivery, I got a soft starter in 8 weeks. Lastly, RVAT are larger and heavier to deal with.

As to the choice to use VFDs, that’s all about flow control by changing the pump off fan speed, as opposed to using throttling valves or dampers and wasting a bunch of energy. A VFD on a centrifugal pump or fan will typically pay for itself in under 2 years.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[edison123]

Pace of progress with greater versatility in speed and current control. No moving parts, much less complicated wiring and smaller footprint. Fewer switching sparks, which matters in Ex world. Power saving based on your operation cycle.

Muthu

http://www.edison.co.in

 

[panter]

On the other hand, after 10 years initial failure of the device start to occurs and you run into a problem because there are no spare parts or original VFD , softstarter to replace. In some countries, there is a lack of technical support, so you should think carefully if someone suggests modernizing the way to start large motors.

 

[LittleInch]

Without hijacking the thread,

"A VFD on a centrifugal pump or fan will typically pay for itself in under 2 years.".

I don't agree with this. In many cases the savings are small or negative as less flow via a valve means less power. Add on the VFD losses (8-10%), plus the need for a cabin which then need A/C to get rid of the VFD heat.

In the right circumstances where pumps or fans operate under a wide range of flows and low flows for long periods then maybe, but in many cases VFDs don't really do anything for you.

Soft starters on the other hand are good and have replaced the auto transformer market virtually completely.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ashtree]

Little Inch is spot on. Unless there is a requirement for flexibility in operation in terms of flow then the overall savings are marginal. But because no one can select pumps properly anymore a VFD is typically installed because you can normally get the output you want at some speed. Maybe that is round the wrong way. No one can select pumps anymore because you can just stick on a VFD to get the output required......
VFDs and soft starters are great. But from a service continuity/ reliability, get your self out of trouble scenario, an auto transformer, wye delta or primary resistance starter was much less complex to maintain and repair. If you blow a VFD or soft starter , unless you have another one you are out of business. If you blow a contactor on an auto tranny , even if you don't have one on the shelf it might be much easier(particularly in a smaller hp) to scrounge or purchase a contactor and get it installed with a low level of skill than to get a VFD repaired or replaced.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[edison123]

There is a reason that VFD market is a growing multi billion dollars industry. Old eletromechanical type motor controllers and their servicing is a dead / dying industry. I used to service, repair & rewind such starters but my clients have now replaced them with VFD's.

More than the power saving, less starting stresses and dynamic torque & speed control are the reasons almost all industries I service have moved on to VFD's, whose increasing reliability, higher MTBF and lower costs have become their selling points now. I am now converting large slipring motors for VFD duty operation for steel mills, who are very conservative when it comes to tech change.

Muthu

http://www.edison.co.in

 

[LionelHutz]

I would tend to agree about VFDs. Great for process control but the energy savings thing is so over-hyped it's ridiculous. The automatic energy savings is so believed that you can get energy savings grants in certain places by just installing a VFD, regardless of how it is operated. It's complete stupidity.

 

[LittleInch]

I think the thing to a lot of people and engineers us that it sounds so obvious - running the pump at 50% of flow using a control valve MUST waste energy and therefore using a fancy electronic box MUST save you money.

It's only when you start to look at the specifics, especially power and pump curves and the system curve do you find out that it doesn't really save anything. The VFD sellers also tend to neglect to tell you how much heat these things put out / efficiency of electrical power in to power out. Or the power / cost you need to upgrade and run your A/C unit in the switchboard room to stop everything overheating. To be fair, some vendors do now make units which use the outside air for cooling of the main thyristors, but many still place them inside the room.

However by the time yo find out that a fixed speed motor with a soft start unit is all you need, the VFD is on order.....



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LionelHutz]

I see the classic simplified energy savings explanation ignoring head pressure.

 

[TugboatEng]

This is a supply and demand issue. VFD's can do what soft starers do and do it better. There is demand for VFDs, there is demand for soft starers. If you can convince your customers that the VFD can perform soft start duties then you increase the demand for your VFD which reduces cost. As a comparison, I recently replaced a 10hp 2016 vintage soft starter with a VFD. The soft starter was $4k and the VFD was $1500.

If efficiency is a concern I believe some VFDs can be programmed to utilize a bypass relay to give the same efficiency as a soft starter.

I spent the early part of my career replacing the pneumatic time delay relays in autotransformer type soft starters because my industry believes if it's broken or needs to be removed or bypassed. I also used to replace a lot of contacts in motor starters.

 

[edison123]

All starters have losses unless they are bypassed at full speed.

All RVS (eletromechanical or electronics based) sacrifice torque by V[sup]2[/sup] while reducing the inrush current only by V.

VFD (MG set or electronics based) is the only one that provides the required torque while simultaneously keeping the starting current under FLC, which protects the motor against overheating and mechanical sudden load and prevents the voltage sags.

Speed control, whether power saving or not, is an excellent process control which other starters cannot offer.

Muthu

http://www.edison.co.in