SOFT START ON GENERATOR USED AS TURNING GEAR
SOFT START ON GENERATOR USED AS TURNING GEAR
(OP)
Some vendors now offer a variable speed drive to use for acceleration and turning gear for Gas Turbines instead of starter motors.. Since synchronous motors are not inherently self starting, use an embedded squirrel cage, does any one have an explanation how this is applied to use the generator as a synchronous motor.






RE: SOFT START ON GENERATOR USED AS TURNING GEAR
As you may know, the gas turbine requires a rolling start. Often it is run at 20% speed for extended time before it is lit off to purge the unit. The variable speed drive allows you to maintain this speed without needing the starter. Since you are not trying to get the machine up to synchronous speed, you need the variable speed drive.
So basically, the amortissuer windings make the unit a large induction motor driven by the variable speed drive until the unit is lit off. Then the varibale speed drive is taken off line and the unit is acceleratedd by the gas turbine up to synchronous speed where it is synchronized to the grid and driven as a generator.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
Does your generator have amortissuer windings? If it doesn't, then you would apply the field. The variable speed drive would then start this up as a brushless DC motor rather than an inductive motor. If your varibale controller has a feedback path for sensing rotor position (it could even use feedback voltage) then you would need the field to be applied and the amortissuer windngs are unneccessary.
What make is the generator?
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
A small turning gear motor rolls the generator and turbine at slow speed (12 rpm?) when it is off line. During a start the VFD runs the unit at 30% speed for a few minutes to purge the system of any unspent fuel. The speed is then reduced to keep from blowing out the ignition pilot flame and fuel is injected. After successful ignition, the VFD goes to full power (5-11 MW) and accelerates up to 90% speed where the turbine takes over and the VFD and the excitation shuts down.
The VFD operates at about 4.16 kV on an 18 kV generator winding and is connected to the generator terminals via a motor-operated switch. It is isolated before excitation is applied. Also, the generator neutral ground is automatically disconnected during the starting sequence to prevent circulating current problems. The generator excitation is interlocked to prevent normal energization unless the starting and neutral disconnect switches are in the correct position.
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
All the static starts I'm aware of use an LCI connected to the generator IPB via a disconnector and require the field to be energised. The machines which do not use an LCI usually have a torque converter or something similar.
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If we learn from our mistakes I'm getting a great education!
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
I only mentioned turning gear because the LCI doesn't have to start the machine from a dead stop. That said, there's not much difference between dead stop and turning gear speed!
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
It was the use of 'turning gear' in the title of the thread I'd picked up on rather than your mention. In answer to the original post, the LCI does start the machine from a couple of rpm and it can be a bit 'lumpy' at very low speed. As the unit accelerates it becomes very smooth.
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If we learn from our mistakes I'm getting a great education!
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
The normal use for the drive is to bring the unit up to 90% speed to start.
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
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If we learn from our mistakes I'm getting a great education!
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
and the VFD matches the speed frequency and applies the field. Then it becomes a synchronous motor.
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
"Read page 16. A sychronous motor can not start from standstill"
It actually says that in a GE Brochure? Point it out to me please. What line?
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
I'm pretty sure the LCI would move the rotor from standstill, it just happens to be rotating at a couple of RPM for other reasons when the LCI is energised. The same situation applies to the torque converter systems: the rotor is already on barring before the torque converter kicks in.
Why do you think the rotor needs to be rotating prior to the LCI being able to operate?
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If we learn from our mistakes I'm getting a great education!
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
Our problem was to keep pole angle stable during acceleration (no rotor position feedback). Solved by going from vector to torque operation.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
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If we learn from our mistakes I'm getting a great education!
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
Yes, excitation must be on so that the stator field has something to 'pull'. Then start rotating the three-phase system (equals increasing frequency from zero) and take it from there. No sweat - if you can keep pole angle stable.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
RE: SOFT START ON GENERATOR USED AS TURNING GEAR
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...