Generator Stator Cooling Water System
The Stator Cooling Water (SCW) system is used to provide a source of de-mineralize water to generator winding for direct cooling of stator winding and associated component.
Strainer are to remove debris in the 20 to 50 microns or large and filter for 3 micron.
De-ionizing sub system is required to maintain low conductivity 0.1 μs/cm. High conductivity can cause a flashover to ground in the stator winding.
Many de-ionizing system use the mixed bed type, employing both a strongly acidic cation resin and a strongly basic anion resin.
De-ionizing sub system is required to maintain low conductivity 0.1 μs/cm. High conductivity can cause a flashover to ground in the stator winding.
Many de-ionizing system use the mixed bed type, employing both a strongly acidic cation resin and a strongly basic anion resin.
The content of copper and iron in the SCW is normally less than 20 ppb. High concentration of either could cause conductivity problem.
When no leaks are present in the system, hydrogen content is s minimum. High hydrogen content into SCW can cause gas locking and conductivity problem.
When no leaks are present in the system, hydrogen content is s minimum. High hydrogen content into SCW can cause gas locking and conductivity problem.
The dissolved oxygen content of the SCW is controlled to prevent corrosion of the hollow copper strand. Corrosion product can build up and block the cooling water flow. Oxygen at 200 to 300 μg/l produces at highest corrosion rate. The content pf oxygen in the SCW is normally maintained at less than 50 ppb in hydrogen saturated and low oxygen type system, and without limit for open vented or high oxygen type system.
High Oxygen refer to air-saturated water with dissolved oxygen present in the SCW in the range of grater than 2000 μg/l (ppb) at STP. The high oxygen system is based on supposition that the surface of pure copper forms a corrosion resistance and adherent cupric oxide layer (CuO) that becomes stable in the high oxygen environment.
Low oxygen refer SCW with a dissolved oxygen content less than 50 μg/l (ppb). The low oxygen system is based on the supposition that pure copper does not react with pure water in the absence of dissolved oxygen. The upper limit is set by the corrosion rate that the water cleansing system can handle. The lower limit is set to the level where copper will not deposit on any insulating surface in the water circuit such as hose. This is to avoid electrical tracking path to ground. It has better heat transfer properties at copper/water interface and a lower copper ion release rate.
pH value is manufacturer specific. Generally, there are two modes of operation, Neutral and Alkaline.
Neutral pH (7) with low oxygen content less than 50 μg/l is work best. Oxygen at 200 to 300 μg/l produces the highest corrosion rate, but high oxygen over than 2000 μg/l will also work.
Alkaline pH refer to high pH value around 8.5. Again, low oxygen work is best. However high oxygen will also work. This method requires an alkalizing subsystem to keep the pH at the proper level.
The SCW inlet temperature is maintain below 50C and outlet limit is 90C. The pressure set to 5 psi below hydrogen pressure to minimize the possibility water leakage into the generator. The flow velocities are design specific and are based on such thing as heat carrying capacity of water, cross sectional flow area in each bar and corrosion effect on the copper.
Neutral pH (7) with low oxygen content less than 50 μg/l is work best. Oxygen at 200 to 300 μg/l produces the highest corrosion rate, but high oxygen over than 2000 μg/l will also work.
Alkaline pH refer to high pH value around 8.5. Again, low oxygen work is best. However high oxygen will also work. This method requires an alkalizing subsystem to keep the pH at the proper level.
The SCW inlet temperature is maintain below 50C and outlet limit is 90C. The pressure set to 5 psi below hydrogen pressure to minimize the possibility water leakage into the generator. The flow velocities are design specific and are based on such thing as heat carrying capacity of water, cross sectional flow area in each bar and corrosion effect on the copper.
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