Overload on starter motor of GE MS 5001 (Turbine Generator).

[Kaadm]

Gents,

What are the causes of having overload on starter motor (driven a torque convertor voith turbo E 6 WAT) of GE MS 5001 turbine model when the machine is hot.
Please note that this happen only when the turbine wheel space is hot, however the overload on the starter motor doesn't occur when the machine is cool as the the machine starts normally without overload alarm.

Thank you,

 

[ScottyUK]

Increased mechanical load is the simple answer. Where from though? Have you checked the IGV position, and compressor bleed valves? Is the control logic executing a slightly different sequence because of the higher temperatures detected elsewhere on the machine?

 

[Kaadm]

During the machine starting phase, The IGVs were in the required position and bleed valves of the axial compressors were fully open.
The overload occurred at 6% of the required speed.
The logic not executing different sequence except when the temperatures achieve the alarm or trip conditions and this was not the case.
My suspect was on the torque convertor hydraulic circuit, but after checking no issue were found.

Your help is appreciated.

 

[NCTHAI]

Starting devices on GE machines are designed to get overloaded. Have seen this on all frames - up to Frame 6F where starting motors are also used. This design is intentional and is balance of not have to big motor (economical and site lay out considerations) for short service duration (During start up only). If you look at motor thermal characteristics, they allow short term overloading and i is this capability used while designing the system and selecting the motor. The maximum overload occurs due to acceleration. Compressor does not offer much load as its bleed valves are open to atmosphere - so it is developing the pressure but not the rated one and with IGV closed, the flow is reduced.