Generalized frequency conversion system for steam turbine generator unit

Abstract

The present invention provides a generalized frequency conversion system for a steam turbine generator unit. The system comprises at least a steam turbine (T) with an adjustable rotating speed, a water feeding pump (BFP), a generator (G), a speed increasing gearbox (GB), a variable frequency bus (a, c) and an auxiliary machine connected thereto. With a change in load of the unit, parameters of steam entering the steam turbine (T) and an extracted steam amount are correspondingly adjusted (changed), so that the rotating speed of the steam turbine (T) changes correspondingly; and thus the rotating speed of the water feeding pump (BFP) is changed through the speed increasing gearbox (GB) on the one hand, and the frequency of an alternating current outputted by the generator (G) is changed on the other hand. Other types of frequency converters do not need to be additionally provided. The system is simple, reliable, low in cost, and high in efficiency.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the field of steam turbine generator units, and in particular to a generalized frequency conversion system for a steam turbine generator unit.DESCRIPTION OF THE PRIOR ART[0002]During production of power plants, water is heated into steam in the boiler; and then steam is used to drive the steam turbine to rotate, thereby driving the generator to rotate and finally converting the chemical energy of the fuel into electricity. In the process of power generation, a large number of rotating auxiliary machines such as pumps and fans provided in the power plants need to consume a large amount of electricity. At present, the general practice is to use a plant transformer to draw part of the generated electricity for the use of plant auxiliary machines.[0003]In engineering design of power plants, the capacity of auxiliary machines is usually selected according to a maximum demand plus a certain allowance, so the auxiliary machines i...

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Benefits of technology

[0010]In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a generalized frequency conversion system having the advantages of low cost, high reliability, high efficiency and simple operation.

Problems solved by technology

In the process of power generation, a large number of rotating auxiliary machines such as pumps and fans provided in the power plants need to consume a large amount of electricity.

However, when the auxiliary machines running at a fixed speed do not operate at full load, especially at low load, their working efficiency will drop sharply, which causes a serious waste of electricity.

Therefore, the energy saving effect of variable-speed operation is very considerable.

Magnetic coupling frequency conversion has high reliability and the highest cost, its efficiency is directly proportional to the square of the rotating speed, the efficiency is low when the rotating speed is low, and if a magnetic coupling device is additionally mounted, the mounting position of the motor or equipment needs to be changed and the original civil construction foundation needs to be removed.

In these three frequency conversion methods, the cost of silicon controlled rectifier frequency conversion is in the middle.

The biggest disadvantage of the silicon controlled rectifier technology is that the higher the voltage level is, the lower the reliability of the equipment is, the area occupied by the frequency conversion equipment is large, and its frequency conversion harmonic waves have influences on both the power grid and the motor.

Therefore, in the power plants, the promotion and application of the silicon controlled rectifier frequency conversion technology is relatively slow.

With the development of technology, some products have been able to better solve the above-mentioned problems at present, but the high price of these products hinders their further promotion.

Moreover, the manufacturing process ability of water feeding pump steam turbines is limited by factors such as cylinder structures and blade strength at present, especially by the high stress at the root of long blades caused by high centrifugal force under high-speed rotation, the length of the last-stage blades and the exhaust area of the steam turbine are limited, the exhaust pressure of the water feeding pump steam turbines under the rated working condition will be very high, and thus, not only the economy efficiency is poor, but also it is difficult to match the rotating speed of the water feeding pump.

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