Static Start of Combustion Turbine Generator 5

[jliu1]

For Combustion Turbine Generator like GE's machine, we use static start system to start the machine. There is something which I am not sure here. First the machine is running like a Variable Frequency Drive, powered by the static start system. Then the machine is driven by the Turbine, as a Generator. The question is when do we need to start the excitation system?

 

[migs52]

This is an interesting topic, since practice seems to vary among operator experience. First, is your static-start system involing more than one T/G? I've provided circuit design and equipment for systems that have unequal numbers of static-start equipment and T/G's whereby there are numerous factors involved in the safe and orderly startup of the units. Please describe your system in a little more detail and include types of protection on the system, especially if you have redundant volts/hertz relaying and first level relay(diff's, etc.) disabling capability.

 

[jbartos]

Suggestion: Visit

http://www.traction-ganztrans.hu/en/download/powerelectronics/sfc_paper.pdf

etc. for more info

 

[mazlan]

Intereseting question, just like to state that we are operating a single shaft 9FA ge machine here. Of course we have to drive the generator as "Electrical Motor" from Turning Gear speed, up to about 2500 rpm. At about 2200 rpm the Gas Turbine engine combustor will start to fire, once the Combustor and its dynamics play its role, the Load Commutated Inverter (Static Frequency Converter) has to be switched off. After that the Gas Turbine Engine will works as the main prime mover, by virtue that the air was compressed in the compressor stage, and a fuel (natural gas) is ignited in the combustor to produce the mechanical energy to drive the machine at the Turbine Stage. This mechanical rotating energy will drive the machine up to the rated speed i.e. 3000 rpm (50Hz). Hope this simple explaination helps.

 

[neps3]

jliu1

I did a static start project to convert four staal laval GTs to operate as synchronous condensers for voltage support. (prevent voltage collapse)

The principle is fundamental. In a three phase motor we know about Ferrare's principle of rotating vector. In a static start system, the rotor is excited (about 10% I think of full excitation) and the stator is supplied with a supply. This supply is actually switched via thyristors to the three phase windings to create a rotating vector. ie. Initially the switching is slow, so that the rotor follows the stator vector. The switching frequency is increased slowly until the rotor attains speed. In the case of GTs, the static starter should be pulled out after the second critical speed, I think, before firing the GT. But in the case of a synchronous motor (converted GT generator) the speed is taken above 3000 rpm to 3150 rpm and then the SFC is switched off with the excitation to full voltage and the synchronisation is done while running down.

In your case the excitation should be to full excitation when the speed is around 2850 rpm. The manufacturers should provide all details. Do you have an automatic synchronising system and an AVR. The excitation should be set to come in in a sequence. Is your starting system a speedtronic system or a plc.

 

[jliu1]

Kantor - Thanks.
Yes. We do have an automatic synchronising system and an AVR. Our starting system is a GE MArk VI speedtronic system.
The GT system is GE 9FA Machine.

 

[DougMSOE]

As a former operator of this type of system;
1. Start the turbine rolling with the VFD system.
2. Once the fire is put to the GT and the energy into the GT is > the VFD starter, the VFD masy be shut down.
3. Bring the GT up to 0.9p/u (90%)of sync RPM.
4. Apply the excitation keeping within the volts per hertz limit on the gen.
5. Bring gen volts up linear with RPM
6. Sync... you know the rest

 

[bigamp]

Kantor,

May I ask which power station you installed the static start project on and also how big a generator can these systems be used on.

Regards

 

[peterb]

To bigamp -
I also worked on a SFC start project - this was for a 120MW steam unit that doubled as a synchronous condenser when de-coupled from the turbine. This was in the early/mid 80's & I am sure that the unit size today will be larger than that.
We used the unit static excitation system, with a separate power source and at lower levels, for the SFC startup process. The system accelerated the unit above synchronous speed and we caught the synch on the coastdown after the SFC was shut down and the regular static exciter switched in.

 

[neps3]

bigamp

The units were 4 x 55MVA GT units (1967 vintage). ASEA generators and Staal Laval GTs. The design has only one SFC with the individual unit selected via a motorised Isolator (11kV). The entire system was on an Alan Bradley PLC master controlled. Project completed in 1990 (one year milestone).

The latest unit that had a SFC for starting is a 400MW combined cycle generating plant.

Thanks

kantor

 

[bigamp]

Kantor and Peterb,

Thanks guys, very much, for the information. SFC looks to be a great way to go.

Regards