GB2182464A

GB2182464A - Vertical hydro-electric unit with floating rotor

Info

Publication number: GB2182464A
Application number: GB08527147A
Authority: GB
Inventors: Chang-Tong Choy
Original assignee: CHOY CHANG TONG
Current assignee: CHOY CHANG TONG
Priority date: 1985-11-04
Filing date: 1985-11-04
Publication date: 1987-05-13
Also published as: GB8527147D0

Abstract

The magnetic pull in an axial-field generator is utilized to support the rotating body of a vertical-shafted hydro-electric generating unit. The thrust bearing in the unit is eliminated and smooth starting and stopping are achieved. While the total excitation of the generator is kept constant in order to maintain the total e.m.f. generated unchanged, the magnetic flux densities in the generator's upper and lower airgaps are controlled by adjusting the currents in its two field windings. A feed-back system may be used to control automatically the output of generator exciter in response to the rotor's vertical displacement, generator armature current and output voltage.

Description

SPECIFICATION Vertical hydro-electric unit with floating rotor This invention relates to the method of controlling and utilizing the magnetic attraction in a vertically-mounted axial-field water wheel generator.

The thrust bearing in a vertical hydro-electrical generating unit supports the weight of the rotating bodies and withstands the hydraulic thrusts. In pumping storage stations where starting and stopping are frequent, the practice of establishing an oil film by mechanical methods before starting has been introduced to a number of thrust bearings. This further complicates the design, installation and opera ation of the bearings and their auxiliary systems.

A vertical water wheel generator with axialfield configuration has a magnetic attraction between its stator and rotor, which can be used to counteract the downward force of the hydro-electric unit and eliminate the thrust bearing.

A specific embodiment of the invention will now be described with reference to the accompanying drawing in which: Figure 1 shows the steel cores of a doublestator axial-field generator; Figure 2 illustrates the floating rotor principle; Figure 3 shows the block diagram of a feedback levitation control system; Figure 4 shows the layout of the generator having a limiting supporter.

In an axial-field generator, the stator and rotor are in the form of coaxial discs located side by side, unlike the conventional machines in which the stator and rotor are concentric cylinders one placed inside the other. Fig. 1 shows the arrangement with one rotor sandwiched between two stators. The stator cores 1 and 2 are made of laminated magnetic straps wound to form a ring. In both upper and lower stators, there is a complete threephase symmetrical double-layer winding accommodated in radially-cut slots on one face of the core. The rotor body is built up from a thick disc 3 shrunk or pressed on to the shaft. Laminated poles 4 comprising steel plates are secured onto the disc. Field coils are wound on the rotor poles for producing the magnetic flux 5 and exciting the machine.

The stator windings and field coils are not shown in Fig. 1 for the sake of clarity.

The flattening out of the airgap introduces considerable magnetic force normal to the stator and rotor surfaces. In the double airgap machine as shown in Fig. 1, the magnitude and direction of the magnetic pull are controllable by adjustment of the field excitations.

The whole rotating body can be lifted and floating and get rid of the support of a thrust bearing.

The operational principle is illustrated in Fig.

2. On each side of the rotor, all field coils are connected with each other to form a field circuit and supplied by an exciter 1. The currents of two field circuits 2 and 3 are independently controllable and excite the upper and lower halves of the machine separately (see Fig. 1).

The stator windings 4 and 5 of the same phase on the upper and lower stators are connected in series. Their polarities are so arranged that the e.m.f. generated in upper and lower windings are additive. When the rotor is to be raised during normal running at a certain voltage output, the field current in upper pole coils will be increased with a corresponding decrease in the field current of the lower pole coils. The generator output voltage, power and power factor etc. can thus remain unchanged. In the same way, the rotor can be lowered.

An automatic feedback control system, which takes over the function of the upper and lower field rheostats 6 and 7 in Fig. 2, should be used. This system, like any other close-loop control system, has three parts: the controller, the detectors and the actuator. The actuator here is a field exciter supplying currents to the upper and lower field windings on the rotor. The detectors measure the vertical displacement of the rotor, the armature phase currents and the output voltages and provide signals to the controller which regulates the output voltages of the field exciter. The relationship among the three parts of the control system and the generator is shown in the block diagram in Fig. 3.

Thrust bearing can be eliminated from a vertical hydro-electrical unit with the above-described axial-field generator and is replaced by a limiting supporter 1 filled with oil 2 as shown in Fig. 4. The cylindrical bracket 3 limits the vertical movement of the shaft 4 and also serves as a guide bearing. In normal running, thick oil film is maintained between the runner 5 and the inner surface of the bracket.

In case of a fault occurring in the control system or the field circuits of the generator, the rotor tends to fall down or shoot up but there will be no calamitous results as the viscosty of the oil will resist extrusion. The load carrying oil film will be maintained for an appreciable length of time and any shocking effects onto the building of the power house will be absorbed. When the unit is not in operation, the runner rests on the bracket which supports the rotors of the turbine and generator.

The axial-field configuration is ideal for a short-core large-diameter machine. An umbrella type arrangement where the limiting supporter is placed below the rotor 6 and inside the central space of the lower stator ring core 7 as shown in Fig. 4, is more suitable than the suspension type arrangement where the limiting supporter is placed above the rotor because the building cost of the former is smaller. In this layout the bottom frame 8 only spans the pit 9 and is carried on the concrete foundation. Top frame 10 is light because it supports only the stationary part of auxiliary equipment such as main exciter and pilot exicter etc., which are accommodated inside the central space 11 of the upper stator ring core 12. 13 is the guide bearing and 14 are air coolers in Fig. 4.

Claims

1. A vertically-mounted, low-speed hydroelectric generating unit with its rotating body floating during operation, wherein the vertical position and displacement of the rotating body are controllable, the performance of the generator in a power system will not be affected by the adjustment of the floating action and thrust bearing is not needed.

2. A large-diameter and short-core synchronous generator assembly according to Claim 1 wherein one rotor comprising salient electromagnets is sandwiched between two stators, each comprising an annular laminated wound core of magnetic material and a symmetrical three-phase winding and whereby two independently adjustable magnetic fields are produced and extend axially through the upper and lower airgaps in two opposite directions.

3. A method of controlling the vertical position of the rotating body of the hydro-electric unit according to Claims 1 and 2, wherein the electromagnet coils on each side of the rotor are connected with each other to form a field circuit and the field currents in two circuits are separately controlled and the stator windings of the same phase on the upper and lower stators are connected in series so that the e.m.f. generated in them are additive and whereby the increase in the field excitation on one side of the rotor will be compensated by a corresponding decrease in that on the other side in case the rotor is to be displaced vertically and the total e.m.f. induced of the generator is to be kept constant.

4. An automatic feedback control system according to Claim 3 comprising a controller to regulate the output voltages of the field exciter of the generator and detectors to measure the vertical displacement of the rotor, the armature phase currents and the output voltages and provide signals to the controller.

5. A limiting supporter according to Claims 1 and 2 comprising a runner secured on the shaft of the hydro-electric unit and limited and supported by a cylindrical bracket immersed in oil.