Dear Friends;

A 55Mw Steam turbine has problem with Diff. expansion. After turbo generator connected to electrical network and power start to increase. This parameter goes to negative value and the turbine will be tripped at -1mm (as it defined). so the width of turbine insulation was controlled, it is according installation instruction. the inlet steam temp. was controlled, the steam is super heated. the measuring instrument was be checked. it hasn't any problem. Normally the expansion of rotor must be greater than cylinder expansion, but at this unit it isn't happen. Please help me. Thanks

 

Was the turbine recently removed from service, i.e. was this a "hot start". If so, the admission temperature of the steam will be lower than main steam due to the throttling losses of the control valves. for a hot start, the loading rate needs to be increased so that the throttled steam at low load does not cool the rotor. there may be other methods for hot start, like full verses partial arc control. even reduced main pressure can be beneficial.

 

I think Byrdj and I are wondering if you are experiencing what is known as "ROTOR SHORT" in which your rotor is essentially quenched by low incoming steam temperature. You mentioned that the inlet steam was superheated, but was the incoming main steam temperature greater then the steam turbine 1st stage metal temperature?

Can you provide us with some more information?

What kind of unit are you operating (Combined Cycle, Conventional)?

What this a hot, warm, or cold start?

What were the incoming main steam temperatures? What were the Steam turbine first stage metal Temperatures (degrees F rather then degrees SH)?

Steam Pressure?