GENERATOR AUXILIARIES (PRIMARY WATER SYSTEM ) PART-II ABC OF THERMAL POWER PLANT

We are breifly discussing the important auxiliary system of Generator . In part-i

we discussed about the seal oil system of generator. Now i will describe briefly

about primary water system used in power house of 500 MW above rating sets.

The treated water used for cooling the stator winding, phase connectors and 

bushings is referred to as primary water in order to distinguish it from the 

secondary coolant (raw water, or condensate). The primary water is circulated in 

a closed system and dissipates the absorbed heat to the secondary cooling water

The pump is supplied with hot primary water from the primary water tank, and delivers the water to the generator via the coolers. 

Primary water system comes as a skid only pipelines and cabling connections are to be made after erection. Skid erection gives front for piping erection and this job can be done  independently . However the total piping job including impulse

piping of instruments to be done by SS material. Stator purity is challenge to erection and commissioning engineer therefore system should be leakproof . O2

measured in the stator water in p.p.b. ( parts per billion).

The skid contains 2x100% pumps , 2x100% coolers , filters , primary water tanks ,necessary valves and insrtumentations. A typical PID is given below.

Flow path I of primary water is used for cooling the stator winding.

This flow path routes the water to the manifold at the exciter end and from there to the stator bars via insulating hoses. Each stator bar is connected to the manifold by a separate hose. The cooling water flows through hollow conductors towards the turbine end of the generator. After exiting the stator bars, the water flows through insulating hoses to a water manifold from where it is rerouted to the primary water tank.

The other flow path is for cooling the phase connector and bushings.

The bushings and phase connectors are made of thick-walled copper tubes carrying the cooling water. The 6 bushings and the phase connectors, which are arranged in circular fashion around the stator-end winding, are interconnected in such a manner that 3 parallel flow paths are established. The cooling water is admitted from outside the generator through 3 bushings and exits through the other 3 bushings.

The secondary water flow through the primary water cooler is automatically controlled to ensure that the generator temperature is maintained at a constant level under different load conditions. 

continued to part-iii

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