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Cooling water system

key word:Heat exchange element


Product description

Cooling water system of stator winding of QFSN-2 and THDF type water hydrogen cooled Turbogenerator

 

1. Introduction

1.1. Purpose

The stator winding cooling water system (Stator Water System) of water hydrogen cooled turbogenerator is an assembled closed cycle system. The main system equipment and monitoring instruments are assembled on a base plate, which is convenient for installation, operation and maintenance. The features and functions of the system are as follows:

1.1.1. cooling water is used to pass through the hollow conductor of stator winding to start the motor with heat generated by loss of stator winding.

1.1.2. water cooler takes away the heat absorbed by cooling water from stator winding.

1.1.3. the system is equipped with filters to remove impurities in water.

1.1.4. the cooling water is softened by ion exchanger to control its conductivity (QFSN generator).

1.1.5. set monitoring instruments and alarm devices to continuously monitor the conductivity, flow, pressure and temperature of cooling water.

1.1.6. it has the function of backwashing stator winding to improve the flushing effect of stator winding.

1.1.7 all pipes in the water system and components in contact with stator cooling water shall be made of corrosion resistant materials.

1.2. System composition

1.2.1. QFSN-2 stator water system of 300MW and 600MW class. The water conduit in the stator winding of type QFSN-2 of 300MW and 600MW is made of steel. The whole system consists of stator cooling water supply device, stator water backwash valve (Group), stator water tank exhaust monitoring instrument and field monitoring instrument. See Figure 21-1 for the schematic diagram of QFSN-2 stator water system.

1.2.2.THDF type 1000MW stator water system. The water conduit in the stator winding of THDF1000mw generator is made of stainless steel. The whole system consists of stator cooling water supply device, stator water backwash valve (Group), upper water tank of stator and field monitoring instrument. See figure 21-2 for schematic diagram of stator water system of THDF generator.

1.3. stator water system description

1.3.1.QFSN-2 stator water system. QFSN-2 stator water system is mainly composed of cooling water main water circuit, ion exchanger bypass water circuit and supplementary water circuit.

1.3.1.1. main cooling water circuit. The centrifugal water pump extracts the internal cold water from the stator water tank, and then enters the ring main water inlet pipe in the stator frame at the excitation end of the generator from the upper part of the generator through the stator water cooler, water filter and the external water inlet pipe between the special stator water supply and the generator. One of them flows into the hollow conductor in the stator bar through Teflon insulated water pipe, then flows into the annular outlet pipe through the insulated water diversion pipe from the steam end of the winding, and the other is through the insulated water diversion pipe to the parallel ring and main lead of the stator winding, and then the main lead is then connected to the outlet pipe installed in the outlet box through the insulated water diversion pipe, and then into the annular outlet pipe at the steam end through the outer pipe. The two-way water flows out of the generator from the upper part of the turbine base at the steam end and returns to the water tank through the main outlet pipe.

The top of the annular inlet pipe and the outlet pipe is connected with each other through an exhaust pipe, which is directly connected with the water tank to eliminate the gas in the stator winding. The exhaust pipe can also prevent siphon when water system is cut off. A series of pressure, pressure difference, temperature, flow and other measuring elements are installed between the external pipes and the main inlet and outlet pipes to monitor the working conditions of the stator water system.

The main water circuit of stator is also equipped with backwash valve, which can change the flow direction by switching the valve and backwashing the stator winding when the generator is shut down to achieve better flushing effect.

The internal cooling water from the generator returns to the stator water tank, which is a water storage vessel. Nitrogen (or hydrogen) is charged on the upper part of the water tank to isolate the air and prevent the corrosion of oxygen and carbon dioxide in the air on the copper guide pipe of stator winding. The gas in the return water is precipitated from the stator water tank. When the gas in the upper part of the water tank accumulates to a certain pressure, the safety valve in the exhaust pipe on the water tank opens, and the gas is discharged into the atmosphere through a gas flowmeter. Monitoring the flow rate of gas flowmeter can analyze whether there is leakage point in stator winding.

1.3.1.2. water circuit of ion exchanger. One of the functions of QFSN-2 generator stator water system is to keep the cooling water entering the stator winding at the appropriate low conductivity value, which is because the stator insulated water diversion pipe must bear the stator winding to ground voltage. When the water system is running, a small part of cooling water is bypassed from the cooling water circuit, which flows through a mixed bed ion exchanger to realize the low conductivity of cooling water. The cooling water flow through the ion exchanger is indicated by flow meter.

1.3.1.3. make up water road. The water supplement water of water system comes from the condensate system or desalted water system of boiler. The supplementary water is successively passed through the make-up filter, pressure reducing valve, solenoid valve (or manual bypass valve) and ion exchanger, and then enters the water tank. The opening and closing of the solenoid is controlled by a level controller located on the water tank. In order to prevent the high pressure of the feed water, the inlet pipe is equipped with safety valve downstream of the pressure reducing valve.

1.3.2 THDF type stator water system. THDF type stator water system is mainly composed of main cooling water circuit and supplementary water circuit. Because the water conduit in THDF stator winding is made of stainless steel pipe, copper ion scaling will not occur during operation. Therefore, the water quality is required in a wide range, and ion exchanger can not be set in the system.

1.3.2.1. main cooling water circuit. The cooling water circuit adopts high water tank, the whole system is full of water, which is a closed circulating water system. Centrifugal water pump is arranged after stator water cooler, the water from the water pump passes through water filter, external water inlet pipe between stator water supply device and generator, and annular main water inlet pipe entering into stator base of excitation end of generator from the upper part of generator. After flowing through stator winding, hot water flows into ring main outlet pipe through insulated water diversion pipe from steam end and then flows out from top of generator. The discharge pipe at the top of generator is equipped with flow and temperature monitoring instruments. There is a section of coarse degassing pipe at the inlet of stator water supply device, the flow velocity slows down in the degassing pipeline, a small amount of gas in water is released from the water, and the exhaust pipe at the upper part of the degassing pipe enters the water tank with the water tank water flow and discharges the system. The water after degassing is cooled by the cooler and then cooled by the water pump Draw out and enter recycling. A series of side measuring instruments such as pressure / pressure difference, temperature and conductivity are also set on the water supply pipeline of generator to monitor the operation condition of stator water system.

The main water circuit of stator can also be equipped with backwash valve. When the generator is shut down, the direction of water flow can be changed by switching the valve, and the stator winding can be backwashed to achieve better flushing effect.

The stator water tank in the system is connected with the main circuit through the water pipe on the degassing pipeline. The thermal expansion and contraction of the stator water tank causes the volume of water to change, discharge the excess water and play the role of degassing. During the process of generator put into operation, when water is injected into the system, it temporarily meets the needs of supplementary water.

1.3.2.2. make up water road. The system is designed to make up for the possible water leakage loss in the system and improve the quality of cooling water. The water used as the supplementary water is taken from the desalted water system, which has a small water conductivity and can meet the requirements of the stator water system. The makeup water enters the main water path through a fine filter and is fed upstream of the stator water pump. The water flow can be controlled manually by the regulating valve and can be indicated locally.

1.4. description of stator water system equipment

1.4.1. QFSN-2 stator water system. See figure 21-3 for QFSN2 type stator water supply device.

1.4.1.1. stator water pump. Two stainless steel centrifugal pumps are installed in the stator water system, and the two pumps are standby for each other. The pump adopts mechanical seal, and the pump body of the pump is fixed type, that is, when removing the impeller of the pump, it is unnecessary to move the pipe connected on the pump body. The outlet of the pump is equipped with a check valve to isolate the two pumps. Two pumps have linkage function, that is, when one pump exits operation, standby water pump can start automatically immediately, and it is realized by differential pressure switch connected on the inlet and outlet pipes of the pump. When a pump in operation fails and the pressure difference at both ends of the pump drops to set, the standby pump will be automatically started to maintain the normal operation of the water system while sending out alarm signal.

1.4.1.2. stator water tank. Water tank is a water storage vessel in closed-circuit circulating water system, and it absorbs the volume change of water in the system and contains the gas discharged from water. The water from stator winding enters the water tank first, and if there is trace hydrogen in the return water, it can be released in the water tank. Because a small amount of high pressure hydrogen can penetrate through the wall of Teflon insulated water diversion pipe, it enters into the stator water system and finally collects in the upper part of the water tank. Therefore, hydrogen accumulation in the upper part of the water tank is normal when the generator is running. When the air pressure in the water tank is higher than a certain value, the air can be automatically discharged through the safety valve on the water tank. The exhaust pipe of the stator water tank is equipped with a gas meter to monitor and record the quantity of gas discharged from the water tank. When the flow through the gas meter increases obviously and the hydrogen supplement of generator increases, it is suggested that the cooling water circuit in the stator may leak. The water tank is equipped with a level controller, which is used to automatically control the make-up water to keep the normal level of the tank and alarm the high or low level. The water tank is also equipped with a level gauge to visually observe the water tank level.

1.4.1.3. Water cooler. There are two parallel water coolers in the water system, each of which can bear 100% of the heat exchange power required by the generator. Under normal conditions, one is in operation and the other is in standby. The structural forms of coolers are plate type and shell type. The plates in the plate cooler are made of stainless steel. The plates are sealed with rubber and can be separated for cleaning during maintenance. The shell and heat transfer tube of shell and tube cooler are all made of stainless steel, and the heat transfer tube is spiral tube

1.4.1.4. Water filter. The stator water system is equipped with two parallel water filters with 100% capacity. Under normal conditions, one is in operation and the other is in standby. The filter element of the filter adopts high-precision fiber spray fusion or folding filter element. Two ends of the filter are connected with differential pressure switches. When the pressure difference at both ends of the filter increases to a certain value, the pressure difference switch will send an alarm signal. At this time, the standby filter should be put into operation in time to clean or replace the blocked filter element.

1.4.1.5. Ion exchanger. The function of the ion exchanger is to eliminate the copper ions in the water and keep the cooling water entering the stator winding at a suitable low conductivity value, because the stator insulated water pipe must bear the voltage of the stator winding to the ground. During the operation of the water system, a small part of the cooling water is bypassed from the main cooling water channel to flow through a mixed bed ion exchanger to realize the low conductivity of the cooling water. The upper and lower parts of the ion exchanger are equipped with high-precision water caps to prevent ions from escaping into the main waterway. The water flow through the ion exchanger is indicated by the flow meter and controlled by the manual valve. Under normal conditions, only a small amount of cooling water (which may not be reflected on the flowmeter) flows through the ion exchanger to ensure that the conductivity of cooling water in the main circulating water circuit is within the specified range.

1.4.1.6. Water tank inflation. The water system tank is closed. The space above the liquid level of the water tank should be filled with nitrogen under a certain pressure to isolate the adverse effect of air on water quality. Nitrogen comes from the nitrogen supply device, and the nitrogen pressure charged into the water tank is automatically stabilized by the nitrogen pressure reducer. When the generator is filled with pressure hydrogen, a small amount of hydrogen can penetrate into the cooling water through the PTFE insulated water pipe and release in the water tank. In order to prevent the pressure in the water tank from being too high, the water tank is equipped with an alarm pressure switch. In addition, the water tank is equipped with a safety valve and is discharged through a gas meter.

1.4.1.7. Backwash valve (Group). Because the water path of the generator stator winding is not a smooth path, the water flow of the stator flows from one direction for a long time, which may produce dirt deposition in some corners or parts with path change. When the forward and back flushing is repeated, the dirt can be easily washed out by the reverse water flow, which can effectively prevent the stator winding from blocking.

The working principle of backwashing is shown in figure 21-4. The backwashing device consists of four separate valves forming a backwashing valve group through pipes, as shown in Fig. 21-4 (a) and (b) or a special four-way valve for backwashing, as shown in Fig. 21-4 (c) and (d). The special four-way valve can simplify the installation and use. According to the design, the backwash filter can also be set in the backwash pipeline to prevent the impurities in the pipeline from being brought into the generator during the backwash. Backwashing can only be carried out when the generator is shut down.

1.4.2. THDF type stator water system.

1.4.2.1. Stator water tank. THDF type stator water tank is a small container. The water tank is connected with the main circuit through the water supply pipeline. The stator water tank can absorb the change of water volume caused by heat expansion and cold contraction, and discharge excess water, and play the role of air exchange and degassing. When the generator is put into operation, when water is injected into the system, it temporarily meets the need of make-up water. The flow through the water tank is very small, and its function is to bring the bubbles in the main circuit to the water tank. The water tank is equipped with a liquid level gauge to observe the water level in the tank. When the water level drops below the lowest water level, the alarm signal is triggered.

The U-shaped sealing pipe filled with water combines the water discharge with the exhaust. In this way, when the tank is overpressured, the gas is discharged to the exhaust port, so that the water can be discharged without pressure. The u-seal is always refilled from the make-up water in the tank. Water injection does not require maintenance and monitoring. During normal operation, the high pressure hydrogen in the generator penetrates into the stator water system through the insulated water diversion pipe or due to a small amount of leakage, and accumulates in the water tank to make the water column in the water tank overpressure, and the pressure presses the water column in the U-shaped pipe down to the point where the exhaust pipe can discharge. After entering the hydrogen through the degassing pipe discharge, will not cause pressure rise.

1.4.2.2. Ion exchanger. Because the water conduit in the stator winding of THDF generator is made of stainless steel, the ion exchanger is omitted in the system. If the quality of make-up water is unstable, a small ion exchanger can be set in the make-up water circuit.

1.4.2.3. Other equipment. The configuration and functions of other equipment in THDF can be described in QFSN-2 stator water system.

 

2. Main technical parameters (see table 21-1 ~ table 21-4)

Table 21-1 technical parameters of QFSN-2 300MW stator water system (see independent excel table)

No. Parameter Index
1 Cooling water flowm3/h 55
2 Cooling water conductivityμS/cm 1.520℃)
3 Design hydrogen pressure differenceKpa) 35
4 Inlet water temperature(℃) 85
5 Outlet water temperature(℃) 50
6 Water pump  
6.1 Model DFB100-80-230
6.2 Flowm3/h 70
6.3 Headm 70
6.4 Speedr/min 2900
6.5 Power 380V(AC)/30KW
7 Cooler  
7.1 Heat exchange powerKW 1188
7.2 Secondary water volumem3/h 61
7.3 Inlet temperature of secondary water(℃) 38
7.4 Secondary water inlet pressureKpa 300800
7.5 Secondary water pressure drop 50
8 Water tank  
8.1 Volumem3 2.3
8.2 Specification of liquid level gauge (mm) 800
8.3 Model of liquid level switch 668J8-X3X373
8.4 Liquid level switch power supply 220V(AC)/10W
9 Ion exchanger  
9.1 Exchange capacitym3/h 6
9.2 Inlet water temperature(℃) 60
9.3 Resin volume in cylinderL 130
10 Main waterway filter  
10.1 Filter accuracyμm 5
10.2 Design flowm3/h 65
10.3 Pressure drop (kPa) 50
11 Shape of water supply deviceL×W×H,mm×mm×mm) 4648×3000×3190
12 Mass of water supply device (kg) 7900

 

Table 21-2 technical parameters of QFSN-2 600MW stator water system (power factor is 0.9) (see independent excel table)

No. Parameter Index
1 Cooling water flowm3/h 105
2 Cooling water conductivityμS/cm 1.520℃)
3 Design hydrogen pressure differenceKpa) 35
4 Inlet water temperature(℃) 85
5 Outlet water temperature(℃) 50
6 Water pump  
6.1 Model DFB125-80-250
6.2 Flowm3/h 130
6.3 Headm 80
6.4 Speedr/min 2900
6.5 Power 380V(AC)/55KW
7 Cooler  
7.1 Heat exchange powerKW 2750
7.2 Secondary water volumem3/h 300
7.3 Inlet temperature of secondary water(℃) 38
7.4 Secondary water inlet pressureKpa 300800
7.5 Secondary water pressure drop 50
8 Water tank  
8.1 Volumem3 2.7
8.2 Specification of liquid level gauge (mm) 800
8.3 Model of liquid level switch 668J8-X3X373
8.4 Liquid level switch power supply 220V(AC)/10W
9 Ion exchanger  
9.1 Exchange capacitym3/h 8
9.2 Inlet water temperature(℃) 60
9.3 Resin volume in cylinderL 130
10 Main waterway filter  
10.1 Filter accuracyμm 5
10.2 Design flowm3/h 130
10.3 Pressure drop (kPa) 50
11 Shape of water supply deviceL×W×H,mm×mm×mm) 5550×3000×2962
12 Mass of water supply device (kg) 8400

 

Table 21-3 technical data of QFSN-2 600MW stator water system (power factor 0.85) and 660MW stator water system (power factor 0.9)

No. Parameter Index
1 Cooling water flowm3/h 116
2 Cooling water conductivityμS/cm 1.520℃)
3 Design hydrogen pressure differenceKpa) 35
4 Inlet water temperature(℃) 85
5 Outlet water temperature(℃) 50
6 Water pump  
6.1 Model DFB125-80-250
6.2 Flowm3/h 130
6.3 Headm 80
6.4 Speedr/min 2900
6.5 Power 380V(AC)/55KW
7 Cooler  
7.1 Heat exchange powerKW 3280
7.2 Secondary water volumem3/h 300
7.3 Inlet temperature of secondary water(℃) 38
7.4 Secondary water inlet pressureKpa 300800
7.5 Secondary water pressure drop 50
8 Water tank  
8.1 Volumem3 2.7
8.2 Specification of liquid level gauge (mm) 800
8.3 Model of liquid level switch 668J8-X3X373
8.4 Liquid level switch power supply 220V(AC)/10W
9 Ion exchanger  
9.1 Exchange capacitym3/h 8
9.2 Inlet water temperature(℃) 60
9.3 Resin volume in cylinderL 130
10 Main waterway filter  
10.1 Filter accuracyμm 5
10.2 Design flowm3/h 130
10.3 Pressure drop (kPa) 50

 

Table 21-4 technical data of THDF 1000MW stator water system (see independent excel table)

No. Parameter Index
1 Cooling water flowm3/h 120
2 Cooling water conductivityμS/cm 1.520℃)
3 Design hydrogen pressure differenceKpa) 35
4 Inlet water temperature(℃) 85
5 Outlet water temperature(℃) 50
6 Water pump  
6.1 Model DFB100-80-250
6.2 Flowm3/h 135
6.3 Headm 80
6.4 Speedr/min 2900
6.5 Power 380V(AC)/55KW
7 Cooler  
7.1 Heat exchange powerKW 3428
7.2 Secondary water volumem3/h 155
7.3 Inlet temperature of secondary water(℃) 38
7.4 Secondary water inlet pressureKpa 300800
7.5 Secondary water pressure drop 50
8 Water tank  
8.1 Volumem3 0.58
8.2 Specification of liquid level gauge (mm) 800
8.3 Model of liquid level switch 24(DC),220(AC)/1.3
8.4 Liquid level switch power supply  
9 Ion exchanger 1
9.1 Exchange capacitym3/h 60
9.2 Inlet water temperature(℃) 130
9.3 Resin volume in cylinderL  
10 Main waterway filter 5
10.1 Filter accuracyμm 130
10.2 Design flowm3/h 50
10.3 Pressure drop (kPa) 6960×2400×2860
11 Shape of water supply deviceL×W×H,mm×mm×mm)
12 Mass of water supply device (kg) 7800

 

3. Scope of supply (typical configuration)

3.1. Typical configuration of QFSN-2 300 and 600 MW stator water system (see table 21-5)

Table 21-5 typical configuration of QFSN-2 300 MW and 600 MW stator water system (see independent excel table)

No. Name Quantity (unit)
1 Stator cooling water supply device 1
2 Water tank gas meter 1
3 Backwash valve (Group) 1
4 Backwash filter 1
5 Field installation of instruments 1

 

3.2. Typical configuration of THDF 1000MW stator water system (see table 21-6)

Table 21-6 typical configuration of THDF 1000 stator water system (see independent excel table)

No. Name Quantity (unit)
1 Stator cooling water supply device 1
2 Backwash valve (Group) 1
3 Backwash filter 1
4 Field installation of instruments 1