[Chris]

I was wondering, what would the benefits be in implementing variable speed synchronous generators in a hydro generation scheme (not pumped storage), just the standard dam/river scheme?
I was wondering, what would the benefits be in implementing variable speed synchronous generators in a hydro generation scheme (not pumped storage), just the standard dam/river scheme? The reason behind this question is that i am conducting a feasibility on implementing these variable speed generators in a current power station, so i am just wondering what the advantages could be?
I would really appreciate in input

Thanks alot for your time

Chris

Topic

[Hamid]

Most hydropower plants employ conventional generators with one generator for each turbine. Generally both the turbines and the generators are designed for a specific site and the turbine and generator speeds are fixed. More recently variable-speed generators have also started to appear in hydropower applications. These allow an additional degree of flexibility by allowing the turbine speed to be varied in order to operate at the optimum efficiency under differing flow conditions. However variable-speed generators are generally more expensive than their fixed-speed equivalents. In a standard configuration when the hydraulic machine is coupled to a synchronous machine which is directly connected to the electric grid this speed variation is not possible at all. The use of a static frequency converter which is inserted between the grid and the stator is a well known solution to achieve an adjustable speed machine. Adjustable speed drive systems have already been applied in the past to hydro power plants. Up to now they have mainly been used for start -up purposes of pumps or pump -turbines. The used converters were therefore rather small in respect of converter power output (< 30 MVA). When a static frequency converter is used in the stator, this converter has to be sized for the full electrical machine power. The solution is therefore not applicable in an economical way to very big unit outputs (>250 MVA). In the last few years, considerable work has been done in order to develop a system which does not use a big converter and which presents considerable advantages also on the grid

[chris]

Thanks so much for your help/response, i really appreciate it. I was wondering could you possibly list your references? Thanks Chris

[Hamid]

You are welcome, the most important of my references is: Adjustable speed Asynchronous Machine in Hydro Power Plants and its Advantages for the Electric Grid Stability Daniel Schafer R&D Manager ABB Power Generation Ltd. Dept. KWHT 5242 Birr Prof. Jean-Jacques Simond Electrical Engineering Department Swiss Federal Institute of Technology DE-LEME 1015 Lausanne

[chris]

Sorry to be a pain, but i have one final question regarding variable speed generators? Is it possible to use an already installed, synchronous generator as a variable speed synchronous generator, if you were to connect the existing synchronous generator to a “mini grid” at the power station and do the frequency regulation before it connects to the Main grid. So basically, the generator used in the variable speed generator setup can be a standard synchronous generator. There are no special features on the generator itself? Thanks so much, in advance

[Jafarpour]

Dear chris, It is not any pain, indeed we appreciate you for new discussions issuance. Best Regards Site Manager Jafarpour

[Hamid]

Yes it is possible, as is said in my last reply,the use of a static frequency converter (SFC) which is inserted between the grid and the stator is a well known solution to achieve an adjustable speed machine (refer to type D in Figure below) . Adjustable speed drive systems have already been applied in the past to hydro power plants. Up to now they have mainly been used for start -up purposes of pumps or pump -turbines. The used converters were therefore rather small in respect of converter power output (< 30 MVA).

[Valentini Agostino]

dear Chris, I confirm you the possibility to drive a syn generator with a static converter. we already did that with synchronous wound salient rotor poles, and with permanent magnet generators in both cases the range of rotation of the turbine is 20-30% (ex. 180-230 rpm, 500-600 rpm, …) Agostino

[Author]

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