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Tandem

Tandem

(OP)
Hi,

We have on site a steam turbine 500 kW driving a high inertia load.
The people on site a did major moficication on the load that the turbine is no longer sufficient in capacity to drive the load. We are thinking of the possibilty to drive the steam turbine in tandem with an electric motor.
By setting the speed droop on the turbine to a value identical to the full load slip of the motor, the load will be shared equally by the two. My concern is the reverse power protection on the turbine. I am looking for possible hiccups for the turbine. I would appreciate comments from members of this forum as well as comments from turbine gurus.
Thks.

Guardiano  

RE: Tandem

What is the load? It may make a difference.
You may consider sizing the electric motor to handle the entire load. Then the turbine may assist the motor.
Any energy supplied by the turbine based on your in house steam will be energy that you don't have to buy from the utility. The motor will be able to safely carry over turbine "hickups"
Set the turbine speed slightly above the motor speed. The turbine will supply as much of the load as it is able. As increasing load tends to slow the turbine the motor will pick up the slack.
I don't see a need for an even division of the load between the prime movers.
If the motor is driven over-speed, it will regenerate. You may increase or decrease the regeneration by tweaking the no load and droop settings of the turbine governor, depending on your wishes. If electricity is more costly than steam, you may want regeneration during light loading.  

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

RE: Tandem

(OP)
Thanks waross for your pertinent comment. My concern is the protection to prevent motoring of the turbine.

Guardiano

RE: Tandem

Guardiano, it would seem to me that the speed-torque characteristics of a steam turbine would be much different than an electric motor. In addition to matching the speed torque characteristic at full load (near the synchronous speed of the motor), you would also have to figure out how to match it during starting (the acceleration curve of the motor versus the turbine).

This is not impossible, but it is also not an obvious solution. Perhaps the use of a VF drive could allow this(?).
 

RE: Tandem

Are you expecting the steam flow to drop to zero? As long as the turbine has enough steam flow to run at rated speed with no load it will not be driven. (Motoring refers to a generator over-driving a turbine, you have a similar situation but the drive is mechanical.)
With a generator, motoring is interupted by tripping the breaker open. To prevent being driven by the motor under low steam flow conditions you will have to trip the motor feed.
What do you do now under low load conditions?
Can you consider a clutch on the steam turbine?
Given that you are anticipating a loss of steam, you may want to rethink the motor size.
What is the load? It often makes a difference to control and protection issues.

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

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