WO1993014561A1

WO1993014561A1 - Apparatus for electrical speed control of a water turbine in a small hydroelectric power plant

Info

Publication number: WO1993014561A1
Application number: PCT/CS1992/000001
Authority: WO
Inventors: Zdene^¿k LEDR
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-03-29
Filing date: 1992-01-14
Publication date: 1993-07-22
Anticipated expiration: 1994-07-14
Also published as: CS193789A3; CS276478B6

Abstract

The apparatus consists of an asynchronous machine (4) with dual squirrel cage of the Boucherot system, designed for the same synchronous speed as the generator (2). The stator winding of the asynchronous machine (4) is coupled to the winding of a synchronous machine (6), designed for the same rated frequency and the same rated voltage as the asynchronous machine (4). The shaft (8) of the synchronous machine (6) is coupled to the shaft (8) of the direct-current machine (7), to the armature of which is coupled the accumulator battery (9).

Description

Apparatus for electrical speed control of a water turbine in a small hydro - electric power plant

Background of the invention

The invention relates to an apparatus for electrical speed control of a water turbine in a small hydro - electric power plant, consisting of a simple water turbine with stationary blades, where the shaft of the water turbine is coupled to the shaft of the generator.

Known state of the art

In the small hydro - electric power plants of this type, where the speed control is achieved through a throttling of. the water inlet toward the runner of the water turbine and where the water turbine drives either a synchronous generator or an idependert asynchronous generator excited by a condenser and provided by two oversaturated chokes, delta and star connected as is known in the art, difficulties occur in that when there is a change in the generator load, i.e. when there is a change in the water turbine load, great changes in the speed of the water turbine - generator arrangement occur, ensued by big changes in frequency of a generated voltage, eventually in the value of said voltage itself.

The most unfavourable case is a switching off of the full load from the generator, when the full water flow speeds up the runner of the turbine up to 2 times till 2,5 times of the rated speed. The known solution of this problem is an automatic ■ connecting and disconnecting of an active resistance to the generator with the help of a complicated contact automatics, controlled by electronic circuits. Such a control is not very reliable and is susceptible to failures. Brief summary bf the invention

The disadvantages of the prior art are partly removed by an apparatus for electrical speed control of a water turbine in a small hydro - electric power plant, consisting of a simple water turbine with stationary blades, where the shaft of the water turbine is coupled to shaft of the generator. The invent¬ ive idea of this solution consistStnat the shaft of the generator is coupled to the shaft of the asynchronous machine with a dual squirrel cage of the Boucherot system, designed for the same synchronous speed as the generator, where stator winding of said asynchronous machine is coupled to the winding of a synchronous machine designed for the same rated frequen- cy and the same rated tension as said asynchronous machine, the shaft of said synchronous machine being coupled to the shaft of a direct - current machine, the armature of which is coupled to the accumulator battery.

The main advantage of the apparatus according to the invention is that it functions continuously and in a contactless manner, so that it ensures a no - failure operation.

Another advantage of this apparatus is that the synchro¬ nous machine and the direct - current machine can be designt for considerably higher rated speed than the generator and the asynchronous machine have at the same frequency, so that the set consisting of the synchronous machine and of the direct - current machine can have a considerably smaller dimensions.

Another advantage of this apparatus is that if a gearbox is inserted between the shafts of the generator and the asynchronous machine, the rated speed of the asynchronous machine can be higher then the rated speed of the generator, so that the asynchronous machine can be smaller than in case of fixed coupling of shafts of the generator and the asyπhronαs machine.

Brief description of the drawings

The apparatus will be more in detail explained according to enclosed drawings, where Fig. 1 shows an example of the invention and Fig 2 shows characteristics of the water turbine, of the asynchronous machine and of the set consisting of the water turbine and the asynchronous machine.

Description of preferred embodiment

A small hydro -electric power plant according to Fig.l consists of a simple water turbine _1. ^anα> of a generator 2_, which are arranged with a common shaft 3_, although in another embodiment thereof the shafts 3_ of said water turbine 1_ and said generator J2 could be coupled through a gearbox as well. Generator 2_ can be either synchronous generator or an independent asynchronous generator. The shaft 3_ is coupled to the shaft of an asynchronous machine _4, e.g. an asynchronous machine with a dual squirrel cage in the Boucherot system, designed for the same rated synchronous revolutions as said generator 2.. On a base plate 6_ a synchronous machine 6_ and a direct - current machine 1_ are arranged, the shafts 8. of which are coupled together. The winding of said asynchronous machine _ is coupled in series with the winding of said synchr nous machine 6. The winding of said direct - current machine 2. is coupled to an accumulator battery _. Said synchronous ma¬ chine _6 is designed for the same rated frequency and for the same rated voltage as the asynchronous machine k_. Exciter and control circuits of the generator, starter circuits for the accumulator battery 9. and other circuits known in the art and necessary for the work of different embodiments of the apparatus, but not directly connected with the inventive idea, are in this application not described.

During the full power of the water turbine l_ with the characteristics as shown in Fig. 2 by the first curve _1C and when the water turbine JL_ has synchronous speed n and rated moment M , is the asynchronous machine A_ magnetized by the synchronous machine j5, which operates as a generator driven by the direct - current machine T__t said direct - current machine ]_ operating as a motor,supplied from the accumulator battery _ .

With synchronous speed the asynchronous machine provide a turning moment which equals zero. In case of a relief of the - -

generator 2_, i.e. in case of relief of the water turbine J-_ as well, the synchronous speed of the generator 2_ as well as of the asynchronous machine 4_ became super - synchronous and _ the asynchronous machine _ begins._'work as an asynchronous

5 generator, which beginsto brake the water turbine _1 through its braking torque, the characteristics of which is shown in Fig. 2 as a second curve 2). At the same time the asynchro¬ nous, machine supplies the power output into the supply, from which it is magnetized, i.e. into the synchronous machine 6_^,

10 which begins to operate as a synchronous motor, driving a direct - current machine ]_, which begins to operate as a direct current generator loading the accumulator battery 9_,

The characteristics of the brake moment of the asynchro- nousmachine 4_^ adds up with the characteristics of the water

15 turbine 1_, the resulting characteristics of the set consisting of the asynchronous machine 4_^ and of the water turbine 1_^ being shown as the third curve 3_0_. From this curve it is clear that a big change of the torque moment, i.e. the big change of the load of the water turbine 1_^ or the generator

20 2_ causes only very small change of the speed of the generator J2 and therefore the frequency of the generator 2_ is only a little higher.

And analogically : Uhen on the other hand the generator 2_ is overloaded, the speed of the generator 2_ and of the 25 asynchronous machine A_ becomes lower and the asynchronous machine 4_^ begins to operate as an asynchronous motor driven by the sychronous machine j5, which begin s to operate as a synchronous generator, driven by the direct - current machine 7_, which is supplied from the accumulator battery 9_^.

„_ The adding up of the characteristics of the water turbine 1_^ and of the asynchronous machine _ gives again the characteristic^ of the whole set, which is shown for the state of overloading of the generator 2^ in the bottom part of Fig. 2 by the third curve 30.

35 T e characteristics of the said set must ensure only small change of generator speed when a big change of the water turbine or generator load occurs. To achieve this it is necessary to ensure that the asynchronous machine j^ will have a big brake, moment in its super - synchronous region and a big torque moment in its sub- synchronous region. These conditions are fulfilled by an asynchronous machine with a dual squirrel cage of the Boucherot system.

In one specific embodiment of the invention as a generator _2 an alternating - current generator with a power

P- ■» 100 kVA, rated speed 750 revolutions/ min, cosy- = 0,8 and efficiency ^ ^β 0,85 was used. Its power demand, i.e. p the expected power output of- the water turbine P,_*=τ2= 94 kW.

1 .

The brake moment of the asynchronous machine during the gene rator speed = 1,1 ns, where sis a synchronous speed, i.e. during the generator speed 750.1,1 «= 825 revolutions/min , must equal to a driving moment of the water turbine at this speed. The value of this moment is M = 975 _ P1_ -= 975 9-4r = n

«= 122 kpm. Because of the shape of the water turbine characteristics the brake power will be a little smaller and it could be assumed that the brake power P_R = 90 kW.

This value is achieved atthe transition point, the value of which is at least 2,2 times higher than the value of moment at the rated speed, i.e. Mmax ^ 2,2 Mn, so that the rated power of the asynchronous machine should be 90 : 2,2 - 41 kW or less.

If there is a gearbox between the generator and the asynchronous machine with the ratio 1500 : 750 = 2, it is possible to use a common asynchronous machine, the para¬ meters of which are P = 37 kW, speed 1500 revolutions/min, U = 380 V, f » 50 Hz, Mmax : Mn = 2,9 and In ^~= 70 A. The current is during the no - load operation only 40 % I , i.e.

I , = 28 A. Synchronous machine magnetizes at the synchronou speed of the water turbine the asynchronous machine with

_3 the power Pg_M1 ■ 3.380.28.10 έ 20 kVA, but it must transmit a power of 90 kW into the direct - current machine. Of the power 90 kW from the asynchronous machine comes into the shaft of the synchronous machine with an efficiency » 0,906 a power P_SM2 = 90 kW . 0,906 = 82 kW. When consi¬ dering the overload capacity of the synchronous machine, a machine with a contimrms rating of 50 kW will be sufficient The direct - current machine, working as a dynamo, will have ^• the power P_DCM - 82 kW . ^ - 82 kW . 0,85 - 70 kW.- When considering the overload capacity of the direct - current machine, a machine with the continous rating of 50 kW will be sufficient. The proposed voltage of the accumulator batte¬ ry being 120 V, the loading current into the batery will be I_I - 70 kW : 120 V = 580 A.

From what was here described follows that the apparatus for electrical speed control of a water turbine in a small hydro - electric power plant according to the invention is simple and ensures the braking of a water turbine through an asynchronous machine, where the energy gained by braking returns into the accumulator battery, from which it is consum ed when the asynchronous machine goes over into the motor region and helps the water turbine.

The apparatus according to the invention could be used especially at the so called small energy suppliers with a power, which is lower than 1MW and at the so called micro-energy suppliers with a power,which is lower than 100 kW, where the using of water turbines with adjustable blades would not be economical, as they need complicated and expensive electrohydraulic control devices.

Claims

C L A I M S

1. An apparatus for electrical speed control of a water turbine in a small hydro - electric power plant, consist¬ ing of a simple water turbine with stationary blades, where the shaft of the water turbine is coupled to the shaft of the generator, characterized in that the shaft of the generator (2) is coupled the shaft of the asynchro nous machine (4) with a dual squirrel cage of the Boucherot system, designed for the. same synchronous speed as the generator (2), where stator winding of said asynchronous machine (4) is coupled to the winding of a synchronous machine (6) designed for the same rated frequency and the same rated tension as said asynchronous machine (4),the shaft of said synchronous machine (6) being coupled to the shaft of a direct - current machine (7), the armature of which is coupled to the accumulator battery .

2. An apparatus according to claim 1_» characterized in that the coupling of shafts of said turbine and said generator is fixed.

3. An apparatus according to claim 1, characterized in that the coupling of shafts of said generator and said asynchronous machine is fixed.

4. An apparatus according to claim 1, characterized in that the coupling of shafts of said turbine and said generator is executed through a gearbox means.

5. An apparatus according to claim 1, characterized in that the coupling of shafts of said generator and said asynchronous machine is executed through a gearbox means.