Quick review of steam turbine manufacturing technology development

Steam turbine generator unit manufacturing technology development

1. Cooling system

The stator winding is indirectly cooled, and the heat flows through the slot wall and is transmitted from the winding insulation to the iron core. For generators with a medium length or more, the base is used as a stator ventilation duct, so that air not only passes through the air gap but also enters each section of the iron core through the outer circle of the iron core, so that the axial temperature is evenly distributed. The rotor winding adopts the direct cooling method, the winding wire is a hollow wire, and the cooling air directly enters the wire for cooling. The cooling system has two sets of symmetrical circuits, corresponding to the fans at both ends of the rotor body, regardless of the position of the cooler. The rotor cooling air enters the end area of the rotor coil from the air duct between the guard ring and the rotating shaft, and enters the hollow copper wire through the copper wire tuyere at the notch, and then divides into two airflows. One air flow passes through the hollow copper wire in the slot to reach the middle of the rotor, and then is discharged through the copper wire and the radial ventilation holes on the slot wedge. The other air flow cools the coil at the end of the stator and enters the second chamber of the machine base along the axial air duct, enters the air gap through the iron core lamination, and divides it again. One half is folded back to the first air chamber in the forward direction; the other half is combined with the rotor cooling air from the middle of the unit, and then returns to the fan along the laminations through the third air chamber and the second cooler. The make-up air filter is installed at the lowest point of static pressure.

2. Structural characteristics of stator

The stator frame adopts the upper and lower horizontal split half structure welded by thin steel plate. Since there is no special airtight requirement for air cooling, all surfaces of the machine base are not processed after welding to save costs. Therefore, the requirements for the welding process of the machine base and the control of welding deformation are strict. Each layer of stator punching sheets consists of 6 sheets. The stator iron core is press-fitted outside, the outer circle of the punching piece is polygonal, and each stack of iron cores is 500mm, and it is pressed once with 6 hydraulic pressures. After the punching sheets are stacked, the punching sheets are welded with the 12 positioning ribs on the back under pressure. The external pressure fitting makes it very intuitive to observe the lamination situation. The adjustment is also very convenient, so that the lamination of each part of the core can be the same, the parallelism of the two end faces is kept within 1mm, and the bending of the whole length does not exceed 0.4mm, which ensures the high quality of lamination of the core. The stator core pressure ring is made of non-magnetic aluminum alloy. In addition to good mechanical properties, the pressure ring forms a good shield at the end of the core, reducing the end loss of the generator. In addition, the stator press ring has a certain slope, so that the iron core has a self-locking effect after being press-fitted. A special suspension device is used to mechanically isolate the iron core from the machine base. Figure + shows the structure used on this type of air-cooled generator. A set of rings are welded on the outer periphery of the iron core. There is a connecting plate on both sides of the ring, and its function is equivalent to a spring plate. After the iron core is installed in the lower half of the frame, the spring plate is connected with the frame by a short tube. The vibration of the iron core is weakened by the base plate and then transmitted to the foundation, and the vibration isolation effect is obvious. Another advantage of using an external press-fitted iron core is that the size of the stator iron core is small, which is convenient for full immersion, and the stator iron core and the machine base can be operated in parallel, which shortens the production cycle and is suitable for mass production.

3. Brushless excitation system

The suspended coaxial exciter has a small axial size, adopts a single rectifier ring full-wave rectification, and the diode of the rotating rectifier adopts resistance-capacitance protection. A diode magnetic field relay is installed in the exciter magnetic field circuit, which indirectly monitors the rectifier bridge, so that in the event of a diode blocking or breakdown, the generator can be quickly tripped to protect other diode automatic voltage regulation systems. AVR has dual channels, and its performance can meet the high demands of generator independent operation and grid-connected operation in various working conditions. Its dual-channel excitation system consists of two independent channel systems. One channel is usually running, which completes the voltage regulation of the generator, and is called the main channel. The other channel is also fully input except the output pole is blocked, which is called the spare channel. The backup channel is equipped with a control and tracking system. During the excitation process, the work of the main channel is always monitored, and the backup channel is automatically tracked and adjusted with the working point of the main channel to ensure that the main channel fails from measurement to output. It can switch to the standby channel smoothly and without disturbance, and the whole system not only has a high level of automation, but also has good reliability.

4. Insulation material

At the beginning of the 21st century, when we manufacture large-scale steam turbine generator stator bars, we need to wrap them with mica tapes with good bonding strength and less rubber powder, and then manufacture them by vacuum solvent-free impregnation (VPI). The peak-to-valley difference of power consumption in the power grid is very large, and the insulation of the stator and rotor windings of the generator is required to be verified by 10,000 cold and heat cycle tests. Air and hydrogen-cooled surface-cooled turbo-generators also require a substantial increase in the thermal conductivity of insulation, which requires improving the thermal conductivity of paints composed of mica tape materials. Large-scale steam turbine generator stator winding ends are fixed, and a large cone ring made of glass fibers with mechanical strength and thermal expansion coefficient that meets the design requirements, a support made of high-strength flame-retardant laminate without air gap, and in addition Various films and tape insulation products with high temperature resistance, good mechanical strength and electrical strength are also required. The use of nanoparticles of metal oxides to improve and modify the properties of synthetic coatings, fibers and films has been reported and applied. The KaplonCR film newly developed by a company is a polyimide film containing nano-inorganic powder, which greatly improves the corona resistance of PI film, and can be used for corona-resistant film wrapping wire to manufacture high-power frequency conversion motor. Using nanotechnology, nano-ceramics with precise texture and remarkable superplasticity can be produced at low temperature and low pressure, and it is expected to be possible to manufacture ceramic insulated wires. In short, the improvement of insulation materials and insulation technology is an important aspect for the development of turbo-generators in the 21st century.