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Turbine & Generator Fundamentals

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#1 chinmaay


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Posted 24 May 2010 - 05:32 AM

Dear All,
I am a process engineers from India & studying Steam Power Plant operations for my project work.
I am having very crude fundamental understanding about the power plant. I have some doubts regarding the same

1. What is the direct relation between the POWER & Hz?

2. How the grid controls the Hz of steam turbine after synchronization with it. As per my understanding generator can produce power which is proportional to its RPM. But for a power plant the speed of turbine has to be constant in order to maintain Hzs constant, which is 3000RPM for 50Hz. Then how the generator can produce different power (say 12 MW & 200 MW) of power on same speed but the different steam input?

Thank You all in advance.

#2 Iarik


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Posted 19 February 2011 - 02:26 PM

it seems, that the question was asked a while ago, but anyway, maybe my answer still can be useful for somebody.

You're right about relation between a turbine RPM's and a network frequency. 3000 RPM for 50 Hz, 3600 RPM for 60 Hz.
There's no relation between power and Hz.

To answer your question regarding a relationship between power load of a generator and turbine steam flow, let's look at generator principles.
As all electrical machinery, generator works on a principle of difference of magnetic fields between rotor and stator. Magnetic field is created on a stator of the generator (through applying of a current on the drive winding), and to generate electrical energy, rotor has to overcome resistance of the magnetic field of the stator. Therefore, by regulating the stator magnetic field (current, that excites the field), it is possible to regulate the load of the generator. In other words, higher current load on the stator - more steam is required for turbine to overcome it - and more MW's is generated.
But, control of magnetic field on the drive windings of the generator is related with dealing with high currents, and that causes problems with a precise control of loads of the generator. Therefore, there is another mini-generator (exciter) is used, to provide generator with required current, and to precisely control a current load on the drive winding. Exciter is placed on the same shaft as the generator is, but requires much less current on its' drive winding.
So, to sum up. To regulate generator load we need a network current for regulation of magnetic field on the exciter, which generates current to control load on the generator.

Hope it helps.

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