600MW water hydrogen cooled generator

600MW water hydrogen cooled generator

 

1. Introduction

1.1. Purpose

QFSN type 600-700MW water hydrogen turbine generator is one of the three main engines in large thermal power plant. It is arranged in the main turbine building. The generator is of horizontal structure, which is directly coupled and driven by the turbine, and converts mechanical energy into electrical energy and transmits it to the power grid as industrial and agricultural power and daily civil power. It can match with 600 ～ 700MW subcritical, supercritical, ultra supercritical and nuclear power steam turbines of various models, capacities and specifications

1.1.1. The normal working conditions for long-term continuous operation of generator are as follows:

1.. 1.1.1. The installation site is in general indoor places with an altitude of 1000m and below. The generator can also operate with rated capacity when the altitude exceeds 1000m. The condition is that the hydrogen as the primary cooling medium in the internal cooling system can maintain the rated absolute hydrogen pressure regardless of the altitude, but the seal, casing and auxiliary equipment shall reach an agreement with the manufacturer in advance during the contract negotiation.

1.1.1.2. The maximum inlet water temperature of hydrogen cooler, stator water cooler and air cooler of exciter shall not exceed 35 ℃ (38 ℃ is allowed when secondary circulating cooling water system is adopted).

1.1.2. Product characteristics. The generator is an optimized design product based on the introduction of Westinghouse technology in 1988. The stator winding of QFSN 600-700MW water hydrogen turbo generator adopts water internal cooling, and the stator core and rotor winding adopt hydrogen as cooling medium. The characteristics of hydrogen cooling and water internal cooling are as follows:

1.1.2.1. The stator winding of turbo generator is internally cooled by water, and the heat generated by the internal loss of stator winding is directly taken away by water, which has good heat conduction effect, low operating temperature and long insulation life, and improves the reliability of generator operation.

1.1.2.2. Hydrogen cooling of stator core and hydrogen internal cooling of rotor, namely, hydrogen internal cooling of rotor winding and hydrogen surface cooling of stator core. According to the characteristics of cooling medium, hydrogen has small density, high thermal conductivity and good heat absorption performance. According to calculation, under the same wind speed, the heat release coefficient of industrial hydrogen (96% hydrogen content) is about 1.3 times of that of air, and the heat release coefficient of hydrogen is 0.8 power of its air pressure Therefore, the pressure of hydrogen can be increased, the heat release coefficient can be increased, and the temperature of rotor winding and stator core can be reduced.

1.1.2.3. In hydrogen state, the corona inception voltage of stator winding is increased, and there is no ozone and nitrogen compound produced by corona, which will not cause chemical damage and corrosion of insulation. Therefore, hydrogen cooling is also beneficial to prolong insulation life.

1.1.2.4. Hydrogen cooling at the end of stator core and rotor surface can improve the operation performance of generator, such as bearing negative sequence current and leading phase operation.

1.1.2.5. Under the same cooling gas flow rate, the density of industrial hydrogen is 1 / 10 of that of air. Although the density of hydrogen increases with the increase of hydrogen pressure, the ventilation loss and friction loss of generator decrease greatly. The hydrogen cooling system is a closed cycle system, which can run clean and dust-free for a long time and reduce the maintenance workload.

1.1.2.6. Although hydrogen is neither spontaneous combustion nor combustion supporting, it is very easy to explode when mixed with air. The relationship between the intensity of explosion and the mixing ratio of two gases is close to a sine curve. When the hydrogen content is 5% and 70% respectively, the explosion intensity tends to zero, and reaches the strongest level when the ratio between the two is in the middle. The special requirements of explosion-proof structure, sealing and safety monitoring must be considered in the frame of generator cooled by hydrogen. At the same time, it must be equipped with corresponding sealing oil and hydrogen system and other auxiliary equipment.

1.2. Model composition and representative significance

Q F S N-600-2

Q -------- steam turbine

F----------generator

S -------- direct water cooling in stator winding

N----------direct hydrogen cooling of stator winding and stator core

600 ------- 600 MW capacity

2------------pole

For example, QFSN-600-2 stands for 600MW, 2-pole water hydrogen turbo generator, QFSN-660-2 stands for 660MW, 2-pole water hydrogen turbo generator.

1.3. Structural features

The main structural features of this type of water hydrogen turbo generator are as follows: ① welded frame structure is adopted. Welded end caps support bearings insulated from ground. The stepped gasket is set between the base foot and the bottom plate (platen), so that the load of the base is concentrated on both ends of the foundation and symmetrically distributed on both sides. The stress distribution of the generator base foot is tested on site and checked and adjusted to ensure the load distribution at both ends of the stator base, so as to improve the support stiffness of the end cover bearing connected with the stator base and reduce the vibration of the unit. ② Vertical high-strength spring plate vibration isolation device is used between stator frame and iron core to reduce the effect of double frequency vibration of iron core on foundation. ③ The stator core is cooled by multi-path to hydrogen surface, and the stator end pressure ring, pressure finger and other structural parts are also cooled by hydrogen surface. ④ Because the effect of water internal cooling is better than that of hydrogen internal cooling, water internal cooling is adopted in the stator winding, connecting wire, main lead and outgoing porcelain bushing of this type of generator, which reduces the temperature rise of these parts and reduces the transportation size and quality of the stator. ⑤ The rotating shaft is made of alloy steel integral forging. ⑥ The straight-line part of rotor winding adopts diagonal flow ventilation with air gap, and the end part adopts hydrogen internal cooling mode with axial two-way ventilation. The stator and rotor have multi-channel parallel wind zones, and the cold and hot air zones of the stator and rotor correspond to each other. The adjustable binding ring on the inner side of the winding end is provided with an air windproof ring, and the cold and hot air zone partition ring is set in the air gap, so as to form the cooling circuit of the cold and hot air zones of the stator and rotor and improve the cooling effect. ⑦ The diagonal flow ventilation with air gap is self ventilation, as shown in Figure 7-1. The hydrogen in the generator is formed by a single-stage axial-flow low-pressure fan symmetrically installed at both ends of the rotor, which forms a closed loop of hydrogen flow in the generator. ⑧ The hot hydrogen is cooled by hydrogen coolers at both ends. Except for the outlet box at excitation end, the two loops of hydrogen flow are almost symmetrical. In order not to make the frame and rotor too long, the hydrogen cooler is set on the upper part of the steam and excitation ends of the stator, and is horizontally assembled in the cooler housing, which also reduces the transportation quality and size of the stator and rotor.

In addition to the outlet box at the excitation end, the two loops of hydrogen flow are almost symmetrical. In order not to make the frame and rotor too long, the hydrogen cooler is set on the upper part of the steam and excitation ends of the stator, and is horizontally assembled in the cooler housing, which also reduces the transportation quality and size of the stator and rotor

See Figure 7-2 for overall structure and wind path. The generator is equipped with brushless exciter excitation system or self shunt static excitation system (including automatic voltage regulator), as well as auxiliary systems such as oxygen supply, sealing oil supply and stator cooling water supply.

The detailed structure is as follows:

1.3.1. Stator.

1.3.1.1. Stator frame and vibration isolation structure. The frame is made of high-quality medium and heavy steel plate by cold welding, and the air tightness welds have passed the examination of the weld air tightness test. Each stand is strictly checked by hydraulic test, stress relief treatment and 0.5MPa air tightness test, so the operation of hydrogen cooled generator is very safe. ① The vibration isolation device composed of vertical high-strength spring steel plate is used between the stator core assembly and the generator base of the generator to reduce the frequency doubling vibration transmitted by the iron core to the base and foundation. ② At the top of the engine base, a long peripheral rectangular flange joint surface for installing the cooler cover is set at both ends of the steam turbine and exciter, and a rectangular sealing groove is opened on the joint surface, which is filled with sealant to prevent hydrogen leakage; another long peripheral flange joint surface is set at the bottom of the exciter end to connect the outlet box. ③ The top of the base is also provided with manhole and inspection hole, which are sealed by cover plate; the bottom is provided with cleaning hole flange, pipeline interface flange for gas replacement, pipeline interface for measuring gas purity, gas analysis sampling, float type liquid level controller (leak detector) and hydrogen dryer, as well as sewage flange of stator water system at both ends. The main inlet and outlet pipe flange of the stator water system is arranged on the upper side of the frame. ④ The stator frame has two kinds of structural design: integral type and three section assembled type, which can be selected by users when ordering. The integral frame is easy to install. The net weight of the whole transport is 345t. It can be transported by special clamp car on railway and 325t by water. The advantage of the three-stage frame is that it has light transport weight, net transport weight is about 245t, and can be loaded by D25, D26 and above concave flat cars, which is more suitable for inland railway transportation.

1.3.1.2. Stator core. The iron core is made of 0.5mm thick fan-shaped cold-rolled silicon steel sheet with high permeability and low loss. Both sides of the fan-shaped silicon steel sheet are coated with class F epoxy insulating paint. The axial direction of stator core is made of support bar screw and ground insulated high-strength non-magnetic steel through core screw, which are screwed into a whole by pressing fingers, pressing rings and block pressing plates at both ends with nuts. After several times of cold state and hot state pressurization, and fastening nuts, a solid core is formed. The upper teeth of the silicon steel sheets at the two ends of the iron core are provided with small separation grooves, and the silicon steel sheets at the side end are glued together with adhesive. The inner circle is a ladder shaped magnetic shield formed by laminating and bonding silicon steel sheets between the two ends of the pressing ring and the non-magnetic block pressing plate. These measures effectively reduce the additional loss caused by the end magnetic leakage, so the end temperature rise is low, so that the generator has a good ability of leading phase operation. There are radial ventilation channels in the iron core, which are composed of more than 10 air zones with hydrogen surface cooling, multi-channel parallel ventilation and corresponding rotor air inlet and outlet separated from each other. In order to reduce cross ventilation and improve the efficiency of ventilation and heat dissipation, the air partition ring is installed between the air inlet and air outlet areas on the inner circle of the iron core and around the circumference of the upper 5 / 6 of the air gap.

1.3.1.3. Assembly of stator bar and stator winding. The stator bar of water internal cooling is composed of solid strand and hollow conductor. The ratio of the number of hollow and solid copper wires is 1:2, all of which are covered with glass fiber insulation layer. The conductive cross-sectional area of the upper bar is larger than that of the lower bar; the upper bar is composed of 4 rows of 5 groups of empty and solid strands, and the lower bar is composed of 4 rows of 4 groups, as shown in Figure 7-3. This design can be balance the total loss and temperature rise of upper and lower bars. The 540 ° Robel transposition between the strands in the slot can also reduce the additional loss of the winding. The end of stator bar is involute, and the unequal distance structure of nose end is adopted to reduce the in-phase distance and expand the discharge distance of out of phase nose end. The end pitch of upper and lower bar is different, there are 7 kinds of specifications. The hollow and solid strands of the bar are brazed in the water box of the joint copper at both ends by medium frequency heating, and the water box cover of the water box is welded with a non-magnetic stainless steel water joint, which is used as the interface of the cooling water in and out of the water branch in the bar. The formed insulating water pipe is used for the water connection.

Class F epoxy mica tape is used for insulation of stator winding to ground, and class B insulation is used to ensure service life. And the stator winding is effectively treated to prevent corona. The stator winding is fixed under the high-strength molded slot wedge in the slot, as shown in Fig. 7-4 and Fig. 7-5. The two ends of the iron core are locked on the spot by using the door closing slot wedge with inverted teeth and actual effect, so as to prevent the axial displacement caused by vibration during operation. A high strength elastic insulating corrugated plate is arranged under the wedge to compress the wire rod in the radial direction. Some slot wedges are provided with small holes so that the compressibility of the corrugated plate can be measured during maintenance to control the tightness of the slot wedges. A thermosetting conformal material is padded between the bottom of the slot and the upper and lower bars to keep good contact with each other. The expansion tube hot pressing process is adopted to make the bar firmly and reliably in place in the slot. In order to make the surface of the bar well grounded and prevent the electric corrosion in the slot, the semiconductor plate is used to plug the bar tightly on the side.

 

The end of stator winding adopts mature and reliable rigid flexible binding structure, as shown in Figure 7-6. It consists of rubber filled interlayer support hose, adjustable binding ring, radial support ring, insulating wedge, insulating screw and other structural parts, as well as binding band, conformal material, etc. to fix the winding end extending out of the iron core slot in the insulating large cone ring to form a solid whole. The ring body of the insulation big cone ring is fixed on the insulation support, and the lower part of the support is fixed on the block pressing plate at the end of the iron core through the spring plate, forming an elastic structure along the axial direction, so that the winding has good integrity and rigidity in the radial and tangential directions, and has a certain ability of expansion along the axial direction, which effectively reduces the different expansion of copper and iron due to the temperature change during operation The mechanical stress produced in the insulation can fully adapt to the peak load regulation mode and abnormal operation condition of the unit. The water-cooled stator winding connecting wire is fixed on the large cone ring and the insulation bracket. In order to run safely, all the fastening parts on the winding end are made of high-strength insulating materials.

1.3.1.4. Stator main outlet and outlet box. The generator stator insulating conducting rod is assembled in the insulating porcelain sleeve to form the outgoing bushing, as shown in Figure 7-7. The main outlet of the stator is connected with the outlet sleeve installed on the outlet box, and the outlet terminal of the stator winding is led out of the machine base, so as to ensure no hydrogen and water leakage. There are six outgoing porcelain bushing: three main outgoing terminals are led out through large connector, and the other three are inclined neutral outgoing terminals, which are connected by neutral point motherboard and braided copper bar to form neutral point. Both outgoing bushing and neutral point motherboard are water cooled. The outlet box is shaped like a long cylindrical pressure vessel. It is made of weak magnetic stainless steel plate by welding. It is explosion-resistant and has enough rigidity. It can safely support the stator outlet bushing and the current transformer sheathed outside the bushing. Each outlet box should also pass the strict examination of water pressure and air tightness test of the same level as the base, with good strength, stiffness and air tightness. Because the stainless steel plate is weak magnetic, it greatly reduces the eddy current loss caused by the large current on the main outgoing conductor pole on the steel plate around it. A T-shaped sealing groove is opened on the large plane of the outlet box and the base to inject liquid sealant under pressure, so as to prevent the possibility of hydrogen leakage from the gap on the joint surface.

 

1.3.1.5. Stator waterway. ① The main inlet and outlet manifold pipes are respectively installed in the base of excitation end and steam end, as shown in Figure 7-8. The main water inlet and outlet pipes are insulated from the ground and need to be grounded during operation. Their water inlet, outlet and exhaust pipe are respectively placed above the manifold, which is a measure to prevent the winding from losing water in case of water cut-off. But their flange is set on the upper side of the base, which is convenient to connect with the main water inlet and outlet pipe outside the base. The discharge pipe outlets are respectively placed under the two ends of the base, with a specially designed structure: it is sealed to the base, but can adapt to the deformation caused by temperature change, and has reliable insulation to the ground for the base and the connected external pipes. Temperature measuring elements are installed on the external main water inlet and outlet pipes. When the insulation resistance of stator winding is measured with the water-cooled special insulation resistance meter, it is required that the main inlet and outlet manifold have a certain insulation resistance to the ground, and when the winding withstand voltage test is carried out, it is also required to ground them. For the convenience of the test, the grounding terminals are set on the terminal board, which is specially used for changing the insulation or grounding of the main inlet and outlet manifold and the small outlet manifold in the outlet box. ② Stator winding water circuit. The cooling water flows into the stator bar from the main inlet manifold at the excitation end or collector ring end through the shaped insulated water diversion pipe, and then flows into the main outlet manifold through the insulated water diversion pipe from the outlet joint of the bar. Each upper or lower bar forms an independent water branch, and there are 84 parallel water branches. In addition, the main water inlet manifold at exciter end or collector ring end is provided with 6-way cooling water to enter the insulated water diversion pipe, flow through the connecting line at winding end, main lead and outlet bushing, or flow through the small manifold in outlet box, then flow into the main water outlet manifold at steam end through external pipe, and then lead out to the external main water outlet pipe together, and flow back to the stator water tank.

1.3.1.6. Hydrogen cooler and its enclosure. The hydrogen cooler of the generator is horizontally placed in the outer cover of the hydrogen cooler on the top of the frame, as shown in Fig. 7-9 and Fig. 7-10. There are one hydrogen cooler in the outer cover of the hydrogen cooler at both ends of the steam turbine and exciter, and each one is divided into two independent water branches. When a water branch is shut down, the cooler can operate with 80% load. The cooler shall be subject to hydrostatic test before delivery, and the working pressure or acceptance test pressure on site shall not be greater than 0.8MPa. In order to prevent the cooling water from leaking into the machine directly, labyrinth baffle plate is used between the cooler and the machine base, and Rcl / 2 screw holes are set at the bottom of the cooler cover at both ends of the front and rear water chambers, which can be connected to the discharge pipe of the float type liquid level controller (leakage alarm device) to detect whether there is water leakage in the cooler.

1.3.2. Rotor. The rotor consists of shaft, rotor winding, rotor winding electrical connector, retaining ring, center ring, fan, coupling and damping system.

1.3.2.1. Shaft. Generator shaft is made of alloy steel forgings with high mechanical properties and good magnetic conductivity. The rotating shaft body is provided with large and small teeth slots, the center of the large teeth of the main body is provided with a plurality of transverse crescent slots along the axial direction, and the center line of the small teeth of the exciting end shaft handle is provided with two equalizing slots to equalize the two pole lead slots at the center line of the magnetic pole. All these are for the purpose of unifying the stiffness of two orthogonal axes on the rotating shaft, so as to reduce the frequency doubling vibration. A damping slot is arranged on the big tooth, which can reduce the damping current at the edge of the transverse slot and the sharp temperature rise at the sharp corner when the generator is under unbalanced load, thus effectively improving the ability of the generator to bear negative sequence. In order to weaken the local saturation of the air gap flux near the pole center and the rotor choke flux, and improve the magnetic field waveform, the unequal spacing distribution is adopted in the two embedding slots near the big teeth, and the shallow slot is also adopted in the four embedding slots of coil I. In order to increase the cross-section of copper wire as much as possible, the open half trapezoidal groove is used in the embedding groove. The utility model is also provided with a small tooth air guide groove, a semicircle arc groove for flaw detection and a balance screw hole for balance. In addition, two crescent shaped slots for axial ventilation of winding end are opened at the big tooth ends of flaw detection slot.

1.3.2.2. Rotor winding. The rotor winding is made of cold drawn silver oxygen free copper wire, which is resistant to creep and hydrogen embrittlement. Each circle of conductor is composed of straight line, bending angle and end arc. There are many kinds of specifications for the linear part. These parts are made of tongue and tenon joints which are precision processed and spliced by medium frequency brazing. Before leaving the factory, the AC impedance of the rotor winding at different speeds should be measured to check whether there is inter turn short circuit in the rotor, so as to ensure the quality.

The rotor body adopts the air gap oblique flow ventilation mode, as shown in Fig. 7-11. The linear part of the winding in the slot is divided into more than 10 sections with alternating air inlet and outlet areas along the axial direction, and there are two rows of radial air holes with oblique flow in the opposite direction in the width direction, which are processed by milling cutter. The slot wedge of the rotor winding is machined to form an air scoop. There are two kinds of air scoops, the suction air scoop in the air inlet area and the air throw air scoop in the air outlet area. The hydrogen from the radial air duct of stator core is drawn into the rotor winding from the air gap by the air suction bucket in the air inlet area, and then enters the opposite diagonal air ducts on the left and right sides from the bottom of the winding, and enters the air outlet area. The hot air comes out from the two symmetrical diagonal air ducts on the left and right sides, meets with an air throw bucket, and is thrown out of the slot wedge and discharged into the air gap In this way, a diagonal flow ventilation system with air gap between the inlet and outlet areas corresponding to the stator is formed.

The end of the winding is axial hydrogen internal cooling, as shown in Fig. 7-12. It is made of two cold drawn and formed up and down by two pairs of П - shaped copper wires. A cooling air duct is formed in the middle, and an air inlet hole is opened on the windward side. In order to reduce the maximum temperature of the end winding, the method of shortening the air duct is adopted. After the cold hydrogen is sucked into the air duct from the windward side, it is divided into two routes: the The middle road flows along the axial direction to the inclined outlet duct of the slot, and then flows into the air gap of the side outlet area from the slot wedge through the air throwing bucket; the other road flows along the transverse arc duct of the end to the center of the magnetic pole, and then flows into the low-pressure hot air area of the end from the air outlet hole on the upper side of the arc section of the pole center, and then flows into the air gap of the side outlet area from the crescent shaped ventilation slot at both ends of the big tooth.

1.3.2.3. The insulation of rotor winding to ground in the slot is the slot lining formed by hot pressing of high-strength composite foil, and the turn to turn insulation is a special ribbon glass cloth plate, which is pasted at the bottom of each turn of conductor. The insulation under the retaining ring is made of insulating glass cloth cylinder rolled by insulating varnish impregnated glass cloth. PTFE sliding layers are pressed and adhered between the rotor copper wire and slot insulation, retaining ring insulation and wedge underlay strip, so that the copper wire can expand and contract freely under centrifugal force and high pressure, avoiding permanent residual deformation, so as to meet the needs of peak load operation.

1.3.2.4. Electrical connection of rotor winding. The inter pole connecting wire of rotor winding is composed of two semicircle buckled concave wires, as shown in Figure 7-13. The flexible connection between the two poles is made up of high-strength silver containing thin copper strip. This structure is conducive to the balance of mass between the two poles of the rotor, and has good deformation ability, so as to reduce the stress.

The rotor pole lead consists of two half J-shaped conductors with grooves and Ω - shaped flexible connecting wires. One end of the pole lead is connected with the bottom turn of the No.1 winding at the excitation end of the rotor through a Ω type flexible connecting line composed of silver copper sheet, and the other end is connected with the radial guide electric screw. The lead is placed in the lead slot under the end of the winding and fixed with slot wedge and pressing plate. The flexible connection of lead wire makes it have good thermal deformation ability and bending resistance.

The axial guide pole and radial guide screw are made of high strength zirconium copper alloy material, which can bear the stress produced by the centrifugal force of the structure. The outer surface of the conductive screw is insulated with epoxy glass cloth, and the seal between the conductive screw and the shaft adopts the compression nut structure of herringbone special rubber seal ring, which is subjected to air tightness test. The shaft guide pole forms an L-shaped flexible connecting plate at the excitation end shaft end, which is brazed by silver copper sheet, and forms an electrical connection with the L-shaped lead wire of brushless exciter rotor or collector ring shaft. The flexible connection structure is also adopted in the middle part of the conductive rod to absorb the deformation caused by temperature change and protect the seal. The stainless steel ring is set in the connecting screw hole of the L-shaped end face to prevent damage to the shaft.

Rotor slot wedge, retaining ring, center ring, fan ring, coupling, fan blade, the strength and life of these parts are designed according to the requirements of 10000 times of start-up and shut-down, so they have enough reliability and peak shaving capacity during the life.

The rotor slot wedge is made of aluminum alloy. The air bucket on the slot wedge is combined with the special type of air hole in the wedge underlay strip to form a bucket and two channels, which has the function of air gap intake and outlet air bucket, and makes the flow of the two channels evenly distributed. The slot wedge at the lower end of the retaining ring is made of copper alloy with excellent conductivity.

The retaining ring for protecting the end winding of rotor is made of 18mn18cr high strength non-magnetic alloy steel, which has good stress corrosion resistance. The retaining ring is a suspended structure, which is hot jacketed on the mating surface at the end of rotor body.

The center ring, fan ring and coupling are alloy steel forgings, and the fan blade is aluminum alloy forgings. The single-stage axial fan is symmetrically arranged at both ends of the rotor to supply air to the back of the stator core and inside the rotor retaining ring.

1.3.2.5. Damping system of rotor

Damping on the big teeth: three damping slots are opened on each pole of the big teeth part of the generator rotor body. The copper alloy wedge with high conductivity and high strength can shunt more negative sequence current. If the connection between the wedges is not good, the current will flow from one wedge through the teeth to the other, resulting in the current concentration and local overheating at the teeth where the wedges are connected. Therefore, a silver plated copper alloy lapping block should be set at the joint of the two damping slot wedges, and two springs should be placed in the groove at the bottom of the lapping block to make the tower block support the slot wedges, so as to ensure a good electrical connection between the lapping block and the two slot wedges.

Damping in embedded slot: the slot wedge material of generator rotor front slot is LY12 high strength aluminum alloy (except that the slot wedge material beside big tooth is high temperature resistant copper alloy). Silver plated lapping block is also set at the joint of each two slot wedges to ensure good electrical connection between slot wedges.

1.3.3. End cover, bearing and oil seal. This type of generator adopts end cover bearing structure, that is, the bearing and sealing support are installed on the end cover. The structure has the characteristics of short axial span and good support stiffness, and the bearing center line is close to the end face of the machine base, so that the deformation of the end cover is minimum when supporting the shaft mass and bearing the internal hydrogen pressure, and the reliable air tightness of the unit is ensured.

As a part of the pressure vessel, the end cover is designed as a tailor welded structure of thick steel plate. The airtight weld is used. After welding, the airtight test and annealing treatment of the weld are carried out, and the hydrostatic test is carried out. Air tightness test shall be conducted for each end cover, various pipes and defoaming box to ensure the air tightness of the whole generator. The sealing of the joint surface of the upper and lower half end covers and the joint surface of the end cover and the base adopt the structure of sealing groove filled with sealant. In order to improve the connection stiffness of the end cover joint surface, the double row connection screw structure is adopted at the end cover joint surface.

A defoaming box is arranged under the bearing cavity of the lower half end cover. The hydrogen side return oil from the sealing pad collects under the bearing of the sealing pad and flows into the defoaming box. The hydrogen foam released from the oil flowing into the defoaming box is isolated in the box, and the hydrogen is returned to the machine. The hydrogen side oil flows back to the hydrogen side fuel tank of the sealing oil supply device, and then enters the hydrogen side oil path through the hydrogen side oil pump and the cold oil filter and the filter. The return oil from the air side of the shaft flows into the bearing seat and returns to the main oil tank together with the return oil. On the way, it first flows through the air side oil return tank, where the trace hydrogen contained in the oil is blocked by the U-shaped oil seal pipe and discharged to the oil tank by the range hood fan, so that the bearing oil returned to the main oil tank does not contain hydrogen, which ensures the operation safety of the main oil tank. The air side oil pump draws part of the return oil from the air side oil tank and returns it to the sealing pad through the oil cooler and filter. The sealing oil system is the air side sealing oil with three standby oil sources to ensure the supply of sealing oil and operation safety.

Overflow control is adopted for the oil level in the defoaming tank. Attention must be paid not to let the oil level be too high and pour back into the machine. The height of the oil return pipe in the tank extending out of the bottom of the tank ensures the minimum oil level in the tank, while the maximum oil level is controlled by the liquid level alarm, which will give an alarm when the oil level is too high, so that the operators can deal with it in time.

During oil flushing, the following precautions must be taken to avoid oil leakage into the base: fill the temporary oil retaining seal between the inner ring of the sealing pad support and the rotating shaft, do not move the rotor, the liquid level alarm should be in place, etc.

The bearings of the generator are equipped with high-pressure oil jacking system. The high-pressure oil jacking shaft forms lubricating oil film between the bearing bush surface and the journal to reduce the friction of the bearing during the start-up and shutdown stages of the turbine generator unit.

The temperature of the bearing bush is monitored by a temperature measuring element located at the maximum oil film pressure. The probe of the temperature measuring element extends close to the Babbitt layer. A sensor interface for measuring shaft vibration is set near the bearing block (the sensor is provided by the user or the turbine manufacturer). The oil seal ring on the outer oil shield cover is made of ultra-high molecular weight polyethylene, which can avoid grinding grooves on the shaft, and also has insulation performance.

The sealing pad is located in the groove of the sealing support, and the support is installed on the end cover, which is insulated and sealed with the end cover.

1.3.4. The oil seal structure is divided into double flow double ring structure and single flow single ring structure. The bearing bush and sealing bush of the two oil seal structures are different. For the specific structure of oil seal, users can refer to the technical agreement.

1.3.4.1. Double flow double ring oil seal structure. The structure of double flow and double ring oil seal is the same as that of water hydrogen cooled 300MW Generator. The generator bearing with oil seal structure is a combined tilting pad bearing. The upper half of the bearing is a cylindrical pad, and the lower half of the bearing is two tilting pads with pure copper matrix with good thermal conductivity. It has strong anti oil film disturbance ability and good operation stability. An insulating lower half bearing seat is arranged between the lower half bearing bush and the end cover, and an insulating top block is also arranged between the upper half bearing bush and the end cover, so that the whole bearing is insulated from the end cover. In the cold state, there is a gap of 0.127-0.381mm between the upper half bearing bush and the insulating top block, which is used for the thermal expansion of the bearing bush.

In order to prevent the shaft current, in addition to the insulation of the bearing bush to the end cover, the insulation is set between the sealing support and the end cover, and between the end cover and the outer oil baffle cover of the bearing. The end cover of excitation end, bearing and oil seal of this generator are double insulated, that is, the top block of insulated bearing at the top of upper half bearing bush and the insulating bearing block at the bottom half bearing block are double insulated structure, and an insulating middle ring to ground is added between the sealing support and end cover, so as to ensure the insulation of excitation end shaft to the end cover of base, and facilitate the insulation of rotating shaft and shaft during operation. The insulation resistance of bearing and oil seal is monitored to prevent the shaft, bearing and sealing pad from being damaged by shaft current.

The function of double flow double ring oil seal structure is to prevent hydrogen from overflowing through the oil flow between the inner diameter of journal and ring seal Bush and between the hydrogen side and air side of seal bush. Double flow means that the hydrogen side and the air side of the sealing pad have independent oil circuits. The double ring divides the axial direction of the sealing pad into two parts, keeps a certain radial clearance between the sealing pad and the journal, and can float more freely on the journal, so as to reduce the disturbance to the shaft diameter.

In order to prevent the sealing pad from rotating with the shaft, a rotation stop key is installed on the outer diameter of the sealing pad and positioned in the sealing support. Because the assembly clearance of the sealing pad is very small, the sealing pad should be carefully installed during installation, so it can not be used as the source of collision and friction, causing vibration drift. In the air side oil inlet system of the sealing pad, the differential pressure valve tracks the internal hydrogen pressure, thus controlling the air side oil pressure, ensuring that the oil pressure is greater than the hydrogen pressure, and strictly maintaining the oil hydrogen pressure difference of 0.084mpa. As mentioned above, in the hydrogen side oil inlet system, the balance valve tracks the air side oil pressure and controls the hydrogen side oil pressure, so as to maintain the balance between the two.

1.3.4.2. Single flow single ring oil seal structure. The single flow single ring oil seal structure and generator bearing bush are imported from Siemens technology, and the bearing bush is oval bush with simple structure and small bearing loss.

There is an oil groove on the outer spherical surface of the lower half bearing bush, and the bearing bush can be installed at the steam end or excitation end according to the actual situation. The lower half bearing bush is installed on the bearing bush seat, and its contact surface is a self-aligning outer spherical surface. The bearing bush seat is installed on the end cover and insulated from the end cover. The insulation here is double-layer insulation, which can prevent the shaft current from passing through and is convenient for monitoring during operation. The radial positioning block is fixed on the upper half of the bearing bush through bolt connection, which is used for circumferential positioning of the bearing bush to prevent the reverse rotation of the bearing bush.

Single flow in single flow single ring oil seal structure means that there is only one oil flow for sealing. The seal oil slightly higher than the hydrogen pressure keeps a continuous oil film between the rotating shaft and the non rotating floating seal Bush to prevent hydrogen leakage between the rotating shaft and the casing. In addition, the air side of the sealing pad is supplied with floating oil to ensure its free axial movement.

The two half seal Bush cast with Babbitt alloy floats on the journal with a small gap, and the axial position is controlled by an axial separation seal Bush support to prevent the deformation and bending of the seal bush. The sealing pad can float relatively freely in the radial direction, but there is a locating pin in the circumferential direction, so that it will not rotate. The sealing pad support is fixed on the end cover with bolts in the circumferential direction, and is insulated from the end cover to prevent the shaft current from passing through. The seal oil pump provides seal oil through a differential pressure valve at a pressure of 0.07-0.1mpa higher than the hydrogen pressure at the shaft seal.

1.3.5. Structural parts for alignment and positioning. The whole mass of the generator is supported on the base plate of the base and is located on the base plate of the foundation, and the base plate and the foundation are fixed with foundation bolts. There are many jack bolts on the foot plate for vertical alignment. After grouting, the final vertical alignment can be carried out by changing the number of gaskets between the foot plate and the bottom plate. In the formal alignment, the gaskets at both ends are changed into stepped gaskets. After adjusting the gaskets according to the measured results of stress distribution on the base foot, the load distribution of the generator on the foundation is more reasonable.

After alignment of the generator and the steam turbine, the axial and transverse positions are fixed so that they are not affected by thermal expansion and cold contraction. The generator relies on the anchor plate (positioning block) inserted on the end cover but fixed on the foundation to maintain its transverse positioning, and its axial positioning depends on the axial positioning blocks on the bottom foot plate and the bottom plate, as well as the bottom plate and the foundation. The adjustment of horizontal and axial alignment can be solved by repairing the size of the fixed key between the positioning block and the positioning groove. In addition, in order to make the foot expand freely on the bottom plate, the nut of the foundation screw presses the bottom plate through the sleeve of the screw on the one hand, and on the other hand, when processing the sleeve, it is slightly higher than the foot, so there is a gap between the nut and the foot.

1.3.6. Monitoring system of generator. Generator monitoring includes temperature measurement, shafting vibration monitoring, leakage measurement, hydrogen humidity measurement, internal partial discharge RF monitoring and generator partial overheating monitoring.

1.3.6.1. Monitor the internal temperature of generator

① Copper constantan t indexing thermocouple or Pt100 platinum resistance are set on the tooth top, yoke center, pressure finger and magnetic shield of generator stator side section iron core. See factory document "layout of generator temperature measuring elements" for specific quantity and location.

② A total of 84 single Pt100 platinum resistance temperature measuring elements are embedded between the upper and lower bars of the stator slot near the steam end, with two for each slot (one for standby).

③ A copper constantan t-scale thermocouple or a single Pt100 platinum resistance is installed on the upper and lower outlet joints of the main outlet manifold at the steam end, and a total of 84 temperature measuring elements are installed to monitor the return water temperature.

④ A copper constantan t-scale thermocouple or a single Pt100 platinum resistor is installed on the water joint of the outlet manifold in the outlet box. A total of six temperature measuring elements are used to monitor the return water temperature of the main lead and six outlet sleeve terminals.

1.3.6.2. Monitor the water temperature of the main inlet and outlet pipes of the stator winding cooling water. The main water inlet pipe at excitation end and the main water outlet pipe at steam end are respectively equipped with a double branch nickel chromium constantan e indexing thermocouple or two Pt100 platinum resistance elements (2 in total), one of which is connected to the computer system.

1.3.6.3. Monitor the hydrogen temperature of hydrogen cooler. One double platinum resistance temperature measuring element is set on the cold air side and hot air side of the steam end and excitation end cooler respectively. One display and the other can be connected to the computer system. There are four three wire double platinum resistance temperature measuring elements at both ends. There are two temperature controllers in the cold hydrogen air inlet area on the upper half end covers of both ends, which are used to alarm when the cold hydrogen temperature is higher than the upper limit. The temperature controller has a group of contacts which can be directly connected to the computer system,

1.3.6.4. Monitor the bearing temperature. A double thermocouple or a double Pt100 thermal resistor (the component graduation is selected according to the user's needs) is set in the lower half bearing bush at both ends of the steam excitation, one of which is connected to the computer system. There are two double support temperature measuring elements for the bearings at both ends. One double thermocouple or thermal resistance is set on the oil return pipe of bearing at both ends of steam turbine and exciter and the oil return pipe of brushless exciter bearing (or sliding ring end bearing) respectively to monitor the oil return temperature, and one of them is connected to the computer system (the component graduation is selected according to the user's needs).

1.3.6.5. Monitor shafting vibration. A non-contact vibration detector is set at both ends of the steam excitation and on the outer oil baffle cover of the bearing of the exciter to measure the vibration of the rotor journal. Three of them are connected to the computer system. Monitor the insulation resistance of bearing pedestal, bearing stop pin, insulating pad of upper half bearing bush, insulating pad of lower half bearing bush, sealing support, intermediate ring, high pressure oil inlet pipe and outer oil baffle cover to ground.

Double insulation is set at the exciting end bearing pedestal, bearing stop pin, upper half bearing bush insulating pad, lower half bearing bush insulating pad, sealing support, intermediate ring, high-pressure oil inlet pipe and outer oil baffle cover of the generator. These parts are connected with measuring leads leading out of the generator for monitoring the insulation resistance during the operation of the generator. These measuring leads are first connected to the terminal board on the lower half outer oil baffle cover of the excitation end. At the site, try to pass through the decorative enclosure and connect them to a suitable place, so as to monitor the insulation resistance regularly.

1.3.6.6. Leakage monitoring of generator. Flange or screw hole is installed at outlet box of generator, middle and lower part of base, bottom of cooler cover on top of base and neutral point cover. Pipeline is used to connect with float type liquid level controller (water leakage detector of generator) installed outside the unit, so as to detect leakage and discharge water from there.

1.3.6.7. Monitor internal discharge. A monitoring point is set on the neutral grounding wire of the generator or at the temperature measuring element or enclosed bus to monitor the internal partial arc discharge accident of the generator winding or other live parts.

1.3.6.8. Monitor the hydrogen content in the aircraft. A set of on-line hydrogen thermometer is added to the generator, which can directly reflect the hydrogen content in the generator, so it can effectively control the hydrogen humidity in the generator.

 

2. Main technical parameters of 2.600 MW water hydrogen cooled generator

2.1. Basic parameters of 2.1.600MW water hydrogen cooled generator (table 7-1)

Table 7-1 basic parameters of 600MW water hydrogen cooled generator (see independent excel table)

Specification and models	QFSN-600-2	QFSN-650-2	QFSN-660-2	QFSN-660-2	QFSN-700-2
Rated capacity SN(MVA)	667	722.2	733.3	776.5	823.5
Rated power PN(MW)	600	650	660	660	700
Rated power factor cosφN	0.9	0.9	0.9	0.85	0.85
Rated voltage of stator UN(KV)	20	20	20	22	22
Stator rated current IN(A)	19245	20849	21170	20377	21612
Rated frequency fN(Hz)	50	50	50	50	50
Rated speed nN（r/min)	3000	3000	3000	3000	3000
Rated hydrogen pressure（MPa)	0.41	0.5	0.5	0.45	0.5
Rated excitation voltage UN90℃(V)	407	435	441	494	520
Rated excitation current IfN(A)	4145	4377	4493	4690	4939
Connection mode of stator winding	YY	YY	YY	YY	YY
Direct axis transient reactance X′du/X′d(%)	30.1/26.5	32.6/28.7	33.1/29.1	31.3/27.5	33.2/29.2
Direct axis ultra transient reactance X″du/X″d(%)	22.3/20.5	24.1/22.2	24.5/22.6	23.2/21.4	24.6/22.7
Short circuit ratio SCR	0.54	0.5	0.5	0.518	0.5
Steady state negative sequence current I2 (standard unit,%)	10	10	10	10	10
Transient negative sequence current I22t(s)	10	10	10	10	10
Full load effect ŋ（%）	98.94	98.93	98.94	98.9	98.93
Insulation grade of stator winding	F	F	F	F	F
Insulation grade of rotor winding	F	F	F	F	F
Insulation grade of stator winding	F	F	F	F	F
Noise (1m away from the base)	90	90	90	90	90
Excitation mode	Brushless excitation or static excitation	Brushless excitation or static excitation	Brushless excitation or static excitation	Brushless excitation or static excitation	Brushless excitation or static excitation

 

2.2. Special parameters

Quality and dimension table of main components of generator (table 7-2)

Table 7-2 quality and dimension table of main components of generator (see independent excel table)

Specification and models	QFSN-600-2	QFSN-650-2	QFSN-660-2	QFSN-660-2	QFSN-700-2
Rated capacity SN (MVA)	667	722.2	733.3	776.5	823.5
Rated power (MW)	600	650	660	660	700
Total mass of stator（t)	374	374	374	391	391
Stator transport mass（t)	345	345	345	362	362
Stator transport dimension L×W×H (mm×mm×mm)	10520×4020×4350			11070×4020×4350	11070×4020×4350
Transport length of rotor L（mm）	12420	12420	12420	12970	12970
Total mass of rotor（t)	66	66	66	71	71
Total mass of rotor transportation（t)	77	77	77	82	82

 

3. Equipment outline and structural dimensions (see Fig. 7-14 and Fig. 7-15)

 

4. Selection method

4.1. Excitation mode

The excitation modes of the generator are brushless excitation and self shunt excitation system for users to choose.

4.2. Ordering requirements

Large turbo generator is an important electrical equipment with high voltage and high current. When ordering, it is necessary to formulate ordering technical specifications according to the generator capacity, output, network conditions and environmental conditions determined by the power station, so as to serve as the basis for product bidding.

The technical specifications include the following contents:

4.2.1. Overview, description of general requirements for generators,

4.2.2. Operation conditions of the equipment.

4.2.3. Main parameters of the equipment.

4.2.4. Technical performance requirements.

4.2.5. Structural design requirements.

4.2.6. Excitation system.

4.2.7. Cooling water system.

4.2.8. Requirements for temperature measurement and supporting instruments.

4.2.9. Technical standards.

4.2.10. Guaranteed value.

4.2.11. Technical data sheet,

4.2.12. Scope of supply. Including: spare parts and special tools, special monitoring device requirements, imported parts requirements, special requirements for kit suppliers.

 

5. Supply scope and instructions

5.1. Generator

The supply scope of single generator is shown in table 7-3

Table 7-3 supply scope of single generator (see independent excel table)

No.	Item	Quantity
1	Generator body, including:	1 unit
(1)	Rotor (coupling shaft with generator side, extended key, fastening nut, stop nut
(2)	Stator unit	1 unit
1)	Stator
2)	End shield
3)	Outlet box
4)	End cap
5)	Bearing assembly
6)	Oil seal assembly
3	Collector ring and sound insulation cover
4	Base plate, pad iron, anchor bolt (including matching nut and washer)
5	Temperature measuring device: Measure the stator core temperature, water outlet temperature of stator winding, air temperature, stator winding temperature, water outlet temperature of stator outlet, hydrogen temperature of hydrogen cooler inlet and outlet, bearing metal temperature, bearing oil return temperature, pressing ring and pressing finger temperature
6	Hydrogen cooler	1 set
7	Outgoing sleeve	6 pieces
8	Bushing current transformer	24 pieces
9	Harvard fittings for connecting outgoing and neutral enclosed bus	1 unit

 

5.2 spare parts supplied with generator (see table 7-4)

Table 7-4 spare parts supplied with generator (see independent excel table)

No.	Item	(Each generator)
1	Generator bearing bush	1 piece
2	Insulating parts for bearing oil seal	1 unit
3	Sealing pad	1 unit（steam, excitation）
4	Hydrogen cooler	1/2 for one unit
5	Outlet bushing assembly	2 pieces
6	Outgoing bushing TA (each specification)	each 1 piece
7	Sealing seat, intermediate ring gasket (including sealant)	1 unit for 1 set
8	Flange manhole seal	1 unit for 1 set
9	Seal of hydrogen cooler	1 unit for 1 set
10	Stator insulated water pipe (including pipe clamp)	6 pieces for each specification
11	Stator water joint temperature measuring element	10 pieces
12	Two blades are supplied at both ends of the propeller fan	4 pieces
13	Two generator brush boxes and one electric brush (only for self shunt excitation)	1 unit

 

5.3. Generator special tools (see table 7-5)

Table 7-5 generator special tools (2 generators for each of the following serial numbers)

No.	Item
1	Generator shaft rotor installation tool (including lifting tool)
2	Bearing disassembly tool
3	Assembly and disassembly tool of sealing seat
4	Wind guide ring assembly and disassembly tool
5	Cooler assembly and disassembly tool
6	Installation and removal tools for outgoing bushing
7	Assembly and disassembly tool of retaining ring
8	Hydraulic glue injection gun
9	End cover bolt heater
10	Disassembly tool for intermediate ring
11	Bolt measuring device for rotor ventilation hole
12	Water cooled stator insulation side tester
13	Portable hydrogen detector (halogen leak detector)
14	Corrugated plate measuring tool
15	Stator air gap measuring instrument