Pure water, with its high heat capacity, good non-conductivity and easy availability is widely used in large capacity generators as a cooling medium for generators. The copper wire stator coils of turbine generators are cooled by passing water through hollow wires, which is one of the most traditional methods used for a long time. cooling, which is one of the most traditional methods used for a long time. In power plants, the cooling water for the generator comes from the power plant's demineralised water or condensate. plant's demineralised water or condensate. This cooling water achieves a low conductivity, but its PH value is barely around 7, and most of the time it is below 7. The PH value of this cooling water can reach a low conductivity, but its PH value can only barely reach about 7, and most of the time it is lower than 7, which makes the generator stator copper hollow conductor always in the region of high weak acid corrosion rate. The copper hollow conductor of generator stator is always in the weak acidic corrosion rate high area, which has certain erosion to the system. With the gradual increase of single generator capacity, especially When the generator capacity is above 600MW, due to the rise of stator coil voltage to ground and the increase of coil current density, it is gradually found that the stator coil water circuit is not as strong as the stator coil water circuit. gradually found that the stator coil water circuit copper wire hollow conductor internal scaling phenomenon is also more and more frequent, cooling water on the copper wire corrosion is also more and more obvious, especially water water The corrosion of cooling water on copper wire is also more and more obvious, especially when the water quality is not well controlled, this phenomenon is more obvious.
The results of corrosion：
⑴Generation of sediment clogging generator hollow wire rods.
⑵Affects the flow of cooling water.
⑶Downtime for unblocking, affecting normal generator operation.
⑷Shorten the service life of the generator.
Analysis of the causes of water quality corrosion on copper wire.
1.Relationship between cooling water quality and corrosion of copper wires
⑴Cooling water quality on the corrosion of copper wire although there are many factors, but the cooling water PH is low is a major factor
⑵Cooling water PH between 7.0 ~ 7.5, the most obvious corrosion of copper wire
⑶PH in the 8.5-9.0 region of the alkaline cooling water and oxygen content in the 10-30ppb operation, the cooling water corrosion of copper windings is almost negligible
Solutions to reduce copper corrosion
⑴Adding corrosion inhibitors to water systems：
Early way, side effects, long-term use of deterioration of water quality, no longer used.
⑵Adopt small mixed-bed technology + intermittent water exchange operation to control water quality：
Conductivity can meet the standard, but PH is still low, copper ion concentration exceeds the standard, to solve the rod corrosion effect is not obvious
⑶Adopting special type of resin and special structure of internal cold water special ultra-purification treatment device：
PH can be controlled between 7.78-7.85, still does not meet the GB/T 7064 standard PH8-9, slowing down corrosion, not a fundamental solution.
⑷Use vacuum method + ion exchange method：
Can remove O2 in the supplementary water, control copper ions and conductivity to reach the standard, but the PH is only 7.0-7.3. This method of water system requires a high degree of airtightness, it is actually more difficult to do!
⑸Directly adopt PH signal to control the addition of alkali to the cooling water system：
Pure water PH instrumentation is unstable, causing unstable alkali control, and then the water quality is also unstable, the corrosion of the copper wire is still a potential problem
Currently the most effective solution for copper corrosion - NaOH injection
At present, foreign generator manufacturing companies have been gradually in the use of copper wire as a cooling tube in the water system of large generators using the addition of NaOH to control the PH value of the cooling water, so as to control the corrosion of the cooling water on the copper wire.
The size of the conductivity of the stator cooling water is determined by the role of anions and cations respectively on the conductivity. In the ultra-pure water, conductivity and PH value there is a certain relationship, this relationship is consistent with the above figure conductivity and PH relationship curve
Generator cooling water ultra-purification microprocessor theory of adding alkali is based on the above pure water PH and conductivity of the corresponding relationship between the PH and the corrosion rate of the copper wire relationship to conductivity as a control parameter, increase the PH, so that the generator is in the PH in the 8.5-9.0 region of the alkaline cooling water and the oxygen content of 10-30ppb operating conditions, the basic elimination of water corrosion on the copper rods.
Generator cooling water ultra-purification microprocessor working principle
⑴A set of sodium hydroxide dosing device is set up at the outlet of the ion exchanger to improve the pH value of the effluent water. Sodium hydroxide solution is dosed through a syringe pump.
⑵The PH of the cooling water is indirectly controlled by controlling the conductivity of the alkaline solution with the corresponding relationship between conductivity and PH in pure water.
⑶Ion exchanger outlet water is treated pure water, the conductivity of the mixed lye solution depends only on the concentration of sodium hydroxide solution, using the ratio between the conductivity of the mixed lye solution with alkali and the set value of the conductivity (1.5 μm/cm) as a control signal to implement the control of the injection rate of the syringe pump for the addition of the dosage injection rate.
⑷The conductivity of the main water circuit is controlled by controlling the conductivity of the small loop of the softened water treatment circuit, increasing the reliability of the generator water system operation.
2. Generator cooling water system with ultra-purification microprocessor control flow chart
Composition of Generator Cooling Water Alkaline Addition Device
Technical parameters
Supply voltage/power: 220VAC/500W
Volume of treated stator cooling water: (4-10)m3
Piping design pressure: 1.0MPa
Cooling water conductivity control range: (0.7-2.0)µs/cm
Corresponding PH control range： 8.0-9.0(18℃)
Rated control setting of cooling water conductivity: 1.5µs/cm
Medium temperature:<50℃
Lye tank volume: 200L
Control of copper ion content: ≤20 µg/L
Normal softened water flow rate: (2.0-4.0)m3/h
Piping material of overflow part: stainless steel
Structural Outline Drawing
Characteristics of the device
⑴Collective structure design, easy to install and easy to maintain.
⑵Easy on-site modification, small workload for modification.
⑶Reliable quality, small workload for daily operation and maintenance.
⑷The device is first simulated by the laboratory operation, and then through the generator cooling water system device online to do the type test, after a long time test assessment proved that the overall operation is stable.
⑸The data control is precise, and the PH value of cooling water is controlled between 8.5-9.0, which is better than the requirement of the national standard (GB/T 7064-2008 requires 8-9). It can sufficiently reduce the degree of corrosion of the cooling water on the copper hollow wire, which can greatly improve the safe operation of the generator.
⑹The device completely realises fully automatic control and has a series of control and protection measures to ensure the safe operation of the device.
⑺The strong formula resin is better adapted to the working conditions of the water system operating in a strong alkaline environment, and the resin has a long life.
Safety Protection Functions
This alkali dosing unit has the following switching and analogue signals involved in the protection and control of the metering pump:
⑴Low and high conductivity alarm protection for main water circuit.
⑵Ion exchanger outlet water conductivity high alarm protection.
⑶Alarm protection for low and high conductivity of mixed alkali solution.
⑷Mixed filter differential pressure high alarm protection.
⑸Water treatment circuit flow rate low alarm protection.
⑹Alarm protection for low level of lye tank.
Once the above signals are issued, the injection pump will be forced to stop running to protect the lye filling device, which effectively prevents the expansion of the water system from abnormal working conditions and improves the reliability of the generator's safe operation.
