motor starting devices 4

[tinashe8]

why are starting devices used extensively on large a.c machines in most industrial establishments but to a much lesser degree in power stations? thanx

 

[ScottyUK]

You need to define 'starting devices' a bit more clearly. All power station motors have some means of starting them, whether it be contactor, circuit breaker, VFD, etc.

 

[tinashe8]

scotty, other industrial large a.c motors use a star delta starter whereas a motor of the same size is connected direct online in a power station.

 

[hooverdale]

Industrial sites uses reduce voltage starting because their power supply is somehow limited and they want to lessen electrical stresses as much as possible. While in power station/generating stations, ironically they have all the power supply they need

Otherwise, its just a matter of choice.

 

[jraef]

So true.
I just got back from doing a proposal to add VFDs to some 4,000HP 5KV cooling water pump motors at a gas fired power plant that have been running Across-the-Line for 25 years. The pumps never shut down, but they do throttle the output a little with valves to control flow. Normally this would be a perfect application for a VFD to replace the throttling valve control and save on energy consumption. But I asked the reason they were considering adding VFDs anyway, because I know that usually a power generating company doesn't often care about energy consumption. I was right, they said it was because of impending environmental regulations on the water use, they didn't give a hoot about energy costs. The throttling valves were not designed to restirct flow enough to make a difference, so they were considering trimming the impellers. But that created a situation where they would lose the peak flow capability, so the VFds are being considered. Everyone else from my company that was with me that day was shocked to find out they didn't care about the energy consumption, but I had been down that road before with power companies.


"Will work for salami"

 

[dpc]

Also - often in large power plants, large motors are controlled directly by the circuit breaker - no starter at all. This is because the motors generally are not started very frequently and use of circuit breaker makes sense. For motors subject to frequent start/stop service, using a circuit breaker for direct control of the motor may not be as cost-effective as a starter.

 

[Bronzeado]

Hi folks,

In my case I have two synchronous motors (13 MW, 6,9 kV) at the same busbar fed by just one transformer 230/6,9 kV, 14% impedance).

It has been recommended to use soft starters with thyristors. this device will ramp up the voltage at the motor starting, keeping the motor current to values for not giving voltage drop to trip the other motor in operation.

I wonder if anybody in this forum have experience on this kind of operation.

Best Regards,

Herivelto S. Bronzeado
Brasília, Brazil

http://www.linkedin.com/profile/view?id=46319837&trk=tab_pro

 

[jraef]

Lots of additional questions need to be addressed. Do these need to start and stop often? Are you already having the problem with voltage drop and you are looking for a solution? Or did the recommendation come from a salesman for soft starters who was wandering through your facility? If it is working fine electrically now, is there a mechanical justification to use soft starting?

If this is a new upcoming installation (or even if it is existing), you can perform a Transient Motor Starting analysis with someting like ETAP or SKM software to see if it is going to be a problem first. At 6.9kV, the soft starters will be a major investment, better to know in advance that you really need them. Often times salesmen see big motors and try hard to convince you that you must have a soft starter, but never ask the type of questions that might expose that it is possibly unnecessary.

Please don't ask me why I know this...


"Will work for salami"

 

[Bronzeado]

Thanks jraef for your reply.

This is a new upcoming installation. The soft starter solution was given in the past and 12 device were already bought. As I am now in charge on this Project, I am trying to be convinced that this solution was the best.
If YES, I have to buy similar device to start the new motors that will be installed. Electrical studies are in progress, using ATP like software.

Regarding to your other questions:

jraef - Do these need to start and stop often?
HB - Yes, the motors will start once a day.

jraef - Are you already having the problem with voltage drop and you are looking for a solution?
HB - A quick calculation of direct motor starter (without soft starter) will give arround 20-25% of voltage drop, which may trip the other motor running in the same busbar.

jraef - Is there a mechanical justification to use soft starting?
HB - No. The problem maybe the voltage drop at the busbar.

I know that soft starters at 6.9 kV is a major investment. The Project has bought soft starters for use in the previous stage. Now, by default, it is necessary to buy new devices to start new motors. My question is to basically certify me if this is the better solution or necessary.


Best Regards,

Herivelto S. Bronzeado
Brasília, Brazil

http://www.linkedin.com/profile/view?id=46319837&trk=tab_pro

 

[electricpete]

why are starting devices used extensively on large a.c machines in most industrial establishments but to a much lesser degree in power stations? thanx

You need to define 'starting devices' a bit more clearly. All power station motors have some means of starting them, whether it be contactor, circuit breaker, VFD, etc.

scotty, other industrial large a.c motors use a star delta starter whereas a motor of the same size is connected direct online in a power station.

To recap one big reason why reduced voltage start is not often used at power plants: the power plants tend to have a stiff power system where it is not likely that motor start will cause enough voltage drop on buses to affect any other loads significantly.

I apologize if it was already stated... the conversation wandered and I just wanted to reinforce it what I saw as an important point.

Jeff - you weren't ever involved in marketing soft starters by any chance?


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(2B)+(2B)' ?

 

[waross]

Fair comment Pete;
Jeff has posted several disclaimers from time to time concerning his employment in the drive industry. I understand that his role was more support than direct sales.

Often times salesmen see big motors and try hard to convince you that you must have a soft starter, but never ask the type of questions that might expose that it is possibly unnecessary.

This is a fairly good illustration of Jeff's interaction with marketing, and his ethic in giving the customer what he needs rather than what he can sell him.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

Thanks Bill. My comments were definitely no intended as an attack. I don't know Jeff's exact experience but I know he's extremely technically knowledgable in these areas. I was picking up on the "Please don't ask me why I know this..." ... thought it might be a funny story. In retrospect perhaps I should have taken it at face value and not asked.

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(2B)+(2B)' ?

 

[jraef]

I was being funny, or at least trying to, given that I was (and am) employed by companies that make and sell soft starters and drives. My role is no longer directly sales, I am now a Technical Consultant so I am given free rein to say what I think is best since I don't get paid on commission. But I have been in that role in years past and confess that when times were tough, I would chase motor applications by conduit size; i.e. any motor using 2" conduit and larger must therefore need a soft starter

HB,
If you have a known 20-25% VD on DOL starting, and you already know that a soft starter works to fix that, then there is no controversy in my opinion, it sounds like a good solution. You might be able to use other types of electro-mechanical reduced voltage starting technology, but at 6.6kV they will not be as flexible, will likely be significantly larger than solid state and may end up costing more.


"Will work for salami"

 

[automatic2]

why are starting devices used extensively on large a.c machines in most industrial establishments but to a much lesser degree in power stations? thanx

the primary reason is distance from source, and the potential voltage drops induced. When you are the source, you have much less influence on voltage regulation, as your 'hands are on the controls' sort of speak. Local high drawing consumers can signal starts with part winding schemes, or co ordinate starts with provider. Distant consumers are left to their own devices, guided by code. What happens when max code fuses won't allow a motor to start?, you go to alternate starting schemes.