柴油發(fā)電機組是常用的備用電源,由于它以柴油發(fā)動機燃燒柴油為動力,帶動發(fā)電機發(fā)出與市電同樣性質(zhì)的電力,所以用在市電斷電后需要后備電源供電幾小時以上的場合。從性能價格比、對工作環(huán)境的要求、帶非線性負載能力方面考慮,采用柴油發(fā)電機組比使用很多大容量蓄電池的長延時UPS往往具有一定的優(yōu)勢。但是柴油發(fā)電機組在市電斷電后需要十秒鐘左右才能發(fā)出穩(wěn)定的電力,這就大不如UPS可不間斷供電的特點。因此,柴油發(fā)電機組和UPS通常是取其各自的優(yōu)勢構成一個完善的、可靠的電源系統(tǒng),以確保重要設備的不間斷供電。 

　　柴油發(fā)電機組一般是采用同步發(fā)電機(也俗稱電球)將柴油發(fā)動機的旋轉機械能轉為電能。各種用電設備要依靠它發(fā)出的電力工作,因此對同步發(fā)電機的工作性能要求是很高的。

　　1 同步發(fā)電機的工作原理

　　同步發(fā)電機是根據(jù)電磁感應原理制造的。主要組成部分如圖1?，F(xiàn)代交流發(fā)電機通常由兩部分線圈構成;為了提高磁場的強度,一部分線圈繞在一個導磁性能良好的金屬片疊成的圓筒內(nèi)壁的凹槽內(nèi),這個圓筒固定在機座上稱為定子。定子內(nèi)的線圈可輸出感應電動勢和感應電流,所以又稱其為電樞。發(fā)電機的另一部分線圈則繞在定子圓筒內(nèi)的一導磁率強的金屬片疊成的圓柱體的凹槽內(nèi),稱為轉子。一根軸穿過轉子中心并將其緊固在一起,軸兩端與機座構成軸承支撐。轉子與定子內(nèi)壁之間保持小而均勻的間隙且可靈活轉動。這叫做旋轉磁場式結構的無刷同步發(fā)電機。 

　　工作時,轉子線圈通以直流電形成直流恒定磁場,在柴油機的帶動下轉子快速旋轉,恒定磁場也隨之旋轉,定子的線圈被磁場磁力線切割產(chǎn)生感應電動勢,發(fā)電機就發(fā)出電來?！　?

　　1—前端蓋;2—出風蓋板;3—軸承;4—定子;5—端子箱側板;6—電壓調(diào)節(jié)器;7—調(diào)節(jié)器支架;8—端子箱頂蓋;9—端子箱前后板;10—接線板;11—接線板支架;12—端子箱側板;13—吊攀;14—軸承蓋;15—進風蓋板;16—后端蓋;17—勵磁定子;18—勵磁定子固定螺栓;19—軸承;20—旋轉整流器;21—勵磁電樞;22—接地牌;23—轉子;24—風扇;25—永磁機機殼;26—永磁機轉軸;27—永磁機轉子;28—永磁機定子;29—永磁機定子固定螺栓;30—永磁機轉子固定螺栓;31—墊圈;32—永磁機蓋板

圖1 雙軸承發(fā)電機剖視圖

　　轉子及其恒定磁場被柴油機帶動快速旋轉時,在轉子與定子之間小而均勻的間隙中形成一個旋轉的磁場,稱為轉子磁場或主磁場。平常工作時發(fā)電機的定子線圈即電樞都接有負載,定子線圈被磁場磁力線切割后產(chǎn)生的感應電動勢通過負載形成感應電流,此電流流過定子線圈也會在間隙中產(chǎn)生一個磁場,稱為定子磁場或電樞磁場。這樣在轉子、定子之間小而均勻的間隙中出現(xiàn)了轉子磁場和定子磁場,這兩個磁場相互作用構成一個合成磁場。發(fā)電機就是由合成磁場的磁力線切割定子線圈而發(fā)電的。由于定子磁場是由轉子磁場引起的,且它們之間總是保持著一先一后并且同速的同步關系,所以稱這種發(fā)電機為同步發(fā)電機。同步發(fā)電機在機械結構和電器性能上都具有許多優(yōu)點。

　　2 同步發(fā)電機的調(diào)控

　　同步發(fā)電機在其額定負載范圍內(nèi)允許帶各種用電負荷。這些負荷的輸入特性會直接影響發(fā)電機的輸出電壓;當負載為純電阻性時,因為同步發(fā)電機的定子端電壓——電樞端電壓與負載電流是同相的,所以使得轉子磁場的前一半被定子磁場削弱,而后一半又被定子磁場加強,一周內(nèi)合成磁場平均值不變,發(fā)電機輸出電壓不變。負載呈現(xiàn)為純電感性時,則因負載電流滯后電樞端電壓90°而使得定子磁場削弱了轉子磁場,合成磁場降低,造成發(fā)電機輸出電壓下降。若負載是純電容性的,負載電流就會超前電樞端電壓90°,從而使定子磁場加強了轉子磁場,合成磁場增大,發(fā)電機輸出電壓上升?？梢?合成磁場是使發(fā)電機性能變化的一個重要因素。而合成磁場中起主要作用的是轉子磁場即主磁場,因此,調(diào)控轉子磁場就可以調(diào)節(jié)同步發(fā)電機的輸出電壓改善其帶負載能力,從而達到在額定負荷范圍內(nèi)穩(wěn)住發(fā)電機輸出電壓的目的。

　　(1)同步發(fā)電機轉子的勵磁

　　所謂勵磁即是向同步發(fā)電機轉子提供直流電使其產(chǎn)生直流電磁場的過程。同步發(fā)電機轉子凹槽內(nèi)的線圈就是由稱做勵磁機的一個專門的設備為其供以直流電形成直流磁場的。早期的發(fā)電機是采用單獨的勵磁機給轉子線圈提供直流電的,系統(tǒng)龐大而復雜。隨著技術的進步,現(xiàn)代同步發(fā)電機都是將發(fā)電機與勵磁機組裝在一起構成一個完整的發(fā)電機。

　　勵磁機其實就是個小發(fā)電機,它的工作原理與同步發(fā)電機一樣。所不同的是它的定子線圈和轉子線圈所起的作用與同步發(fā)電機——主發(fā)電機正好相反;固定在主發(fā)電機定子旁的勵磁機的定子線圈通以直流電形成直流磁場,而安裝在主發(fā)電機轉子軸上的勵磁機的轉子線圈成為輸出電動勢的電樞。勵磁機的轉子與定子內(nèi)壁之間也是保持著小而均勻的間隙。這也稱為旋轉電樞式結構的無刷同步發(fā)電機。安裝在主發(fā)電機定子旁的勵磁機定子線圈的直流電,是由主發(fā)電機定子線圈即電樞的部分輸出電壓經(jīng)整流后而得到的。與主發(fā)電機轉子同軸安裝的勵磁機轉子線圈在其定子線圈產(chǎn)生的磁場內(nèi)旋轉、切割磁力線所產(chǎn)生的感應電動勢,經(jīng)同軸安裝在它旁邊的整流器也就是旋轉整流器變成直流電流,輸?shù)街靼l(fā)電機的轉子線圈使其產(chǎn)生直流轉子磁場。從而達到了對主發(fā)電機轉子線圈勵磁的要求。

　　(2)同步發(fā)電機輸出電壓的調(diào)控

　　調(diào)控的目的就是實現(xiàn)在同步發(fā)電機額定負荷范圍內(nèi)穩(wěn)住輸出電壓。調(diào)控技術的理念是實時地從主發(fā)電機電樞取得電壓和電流,經(jīng)整流和負反饋調(diào)理后供給勵磁機的定子線圈,使其產(chǎn)生變化規(guī)律與主發(fā)電機輸出電壓變化規(guī)律相反的直流電磁場,這個磁場也必然使勵磁機轉子電樞的輸出電壓及旋轉整流器供給主發(fā)電機轉子線圈的直流電流按同樣的規(guī)律而變化。從而起到實時調(diào)節(jié)主發(fā)電機轉子磁場大小,使主發(fā)電機在額定負荷范圍內(nèi)保持良好輸出特性的作用。

　　Three phase synchronous generator working principle and maintenance of control principle

Diesel generating sets are commonly used in standby power supply, because it to diesel engines burning diesel as power, drive the generator to generate electricity and the city of the same nature power, so in the electric power need backup power supply for several hours or more occasions. From the ratio of performance to price, the requirements on the working environment, with nonlinear load capacity is taken into consideration, the use of diesel generators than the use of a lot of large capacity storage battery long time delay UPS often has certain advantages. But the diesel generating set in the city of electric power needs about ten seconds to make a stable power, which is much larger than the UPS uninterruptible power supply characteristics. Therefore, diesel generating sets and UPS is usually take their advantages to form a perfect, reliable power supply system, to ensure the important equipment of uninterrupted power supply.

Diesel generator set is generally adopted in synchronous generator ( also known as electric ball ) diesel engine rotating mechanical energy into electric energy. A variety of electrical equipment to rely on it sends the electrical work, so the synchronous generator performance requirements are very high.

1the principle of a synchronous generator

Synchronous generator is based on the electromagnetic induction principle manufacturing. The main part of figure 1. Modern AC generator typically consists of two portions of the coil form; in order to improve the strength of the magnetic field, a portion of the coil wound on a magnetic properties of good metal lamination of the cylinder inner wall of the groove, the cylinder is fixed on the frame referred to stator. Stator coil can output the induced electromotive force and induced current, so also known as the armature. Generator and another part of the coil is wound on the stator cylinder of a permeability strong metal sheet laminated cylindrical groove, called rotor. A shaft extends through the center of the rotor and fasten together, both ends of the shaft and the base form bearing support. The rotor and stator inner wall between remain small and uniform gap and can rotate flexibly. This is called a rotary magnetic field type structure of brushless synchronous generator.

When working, the rotor coil with DC DC magnetic field is formed, in the diesel engine driven rotor spun, constant magnetic field is rotated, the stator coil by the magnetic field lines cutting to produce induced electromotive force, the generator can generate electricity.

1 - front cover;2, a wind cover plate;3 - bearing;4 - stator;5 - terminal box side plate;6, voltage regulator;7 - regulator bracket;8 - terminal box cover;9 - terminal box front plate;10 - terminal plate;11 - wiring board bracket;12 - terminal the side box;13, a lifting;14 - bearing cap;15 - air inlet cover;16 - rear cover;17, the stator of the exciter;18, the stator of the exciter fixing bolt;19 - bearing;20 - rotating rectifier;21, the exciter armature;22 - Grounding card;23, the rotor;24 - fan;25 - permanent magnet machine;26 - permanent magnet machine rotating shaft;27 - permanent magnet machine rotor;28 - permanent magnet machine stator;29 - permanent magnet machine stator fixing bolt;30 - permanent magnet machine rotor retaining bolt;31 - washer;32 - permanent magnet machine cover

Fig 1 the double bearing generator section view

The rotor and the magnetic field is a diesel engine to drive a fast rotation, between the rotor and the stator are small and uniform gap in the form of a rotating magnetic field, known as the rotor magnetic field or magnetic field. The normal work when the generator stator whereby the armature is connected with a load, the stator coil is the magnetic field lines after cutting the induced electromotive force generated by the load currents induced in the formation, the current flowing through the stator coils can generate a magnetic field in the gap, known as the stator magnetic field and armature magnetic field. When the rotor, stator between small and uniform gap has emerged in the rotor magnetic field and stator magnetic field, the two magnetic field interactions constitute a composite magnetic field. The generator is composed of synthetic magnetic field of the magnetic lines cutting stator coil and power. Due to the magnetic field of the stator is composed of rotor magnetic field is induced, and they always keep one after the other and the same speed synchronization relationship, so that the generator for synchronous generator. Synchronous generator in the mechanical structure and electrical properties has many advantages.

2synchronous generator control

Synchronous generator at its rated load range allowed a variety of electric load. These load input characteristics will directly affect the output voltage of the generator; when the load is purely resistive, for synchronous generator stator terminal voltage -- the armature terminal voltage and the load current are in phase, so that the magnetic field of the rotor stator magnetic field weakening before the half, and the second half was the stator magnetic field strengthening, within a week of the resultant magnetic field average constant value, the output voltage of the generator. Load show pure inductive, is due to the load current hysteresis armature voltage90 °and the weakening of the magnetic field of the rotor magnetic field decreases, synthesis, resulting in the generator output voltage drop. If the load is purely capacitive, load current will lead the armature voltage90 degrees, so that the stator magnetic field enhanced rotor field, resultant magnetic field increases, the output voltage of the generator to rise. Synthesis of magnetic field is visible; make generator performance change is one of the important factors. Synthesis of magnetic fields and played a major role in the magnetic field of the rotor is the main magnetic field, therefore, regulation of rotor magnetic field can adjust the synchronous generator output voltage to improve the load capacity, so as to achieve the rated load range to stabilize the output voltage of the generator to.

(1) the excitation of synchronous generator rotor

The excitation of synchronous generator rotor is to provide DC power to the DC electromagnetic process. Synchronous generator rotor groove is called exciter coil by a specialized equipment for its formation for DC DC magnetic field. Early generator is used to separate the exciter rotor coil to provide DC power to the system is large and complex. With the development of technology, modern synchronous generator is the generator and exciter assembled together constitute a complete generator.

The exciter is actually a small generator, its working principle and the synchronous generator. The difference is that the stator coil and the rotor coil the role of main generator and synchronous generator -- just the opposite; fixed in the main generator stator adjacent to the stator of the exciter coil with DC DC magnetic field is formed, and is mounted on the main rotor shaft of generator 's exciter rotor coil becomes the output electromotive force of the armature. Exciter rotor and stator inner wall is also maintained a small and uniform gap. This is also known as the revolving armature type structure of brushless synchronous generator. Mounted on the main generator stator side exciter stator coil DC, is composed of a main generator stator coil or armature portion of the output voltage is rectified obtained after the. With the main generator rotor coaxially mounted exciter rotor winding in the stator coil to generate a magnetic field in rotating, cutting the lines of magnetic force produced by the induction electromotive force, the coaxially mounted beside it is rotating rectifier rectifier into DC current, input to the main generator rotor coil of the DC magnetic field of the rotor. We can reach the main generator rotor coil excitation requirement.

(2) output of a synchronous generator voltage regulation

The purpose of regulation is to realize the synchronous generator rated load range to stabilize the output voltage. Regulation of technical philosophy is in real time from the main generator armature voltage and current by the rectifier to obtain, and the negative feedback adjust supply a stator of the exciter coil, make its produce variation and main generator output voltage variation instead of DC electromagnetic field, the magnetic field will also make the exciter rotor armature voltage and rotating rectifier supply main generator rotor coil DC current according to the same rule changes. In order to adjust the main generator rotor magnetic field, so that the main generators in the rated load range to maintain good output characteristic function.

The generator output voltage regulating process, can use the following process representation;

As the load increases the main generator armature voltage. (down ) to the negative feedback after conditioning exciter stator currents and magnetic fields up to the exciter rotor armature voltage up to rotating rectifier output current up to the main generator rotor magnetic field to make up of main generator armature voltage.

If the main generator voltage increases, the feedback control to the above each link function reduces, causes the voltage to rated value.

Visible through the exciter real-time regulation of main generator rotor magnetic field size, can stabilize the output voltage. Which play an important role in the negative feedback regulation unit, usually called constant-voltage excitation device and automatic voltage regulator.

(3) the automatic voltage regulator

Modern AC synchronous generator automatic voltage regulator AVR commonly used the electronic component regulating exciter stator magnetic field intensity. Although the AVR type are many, but the performance is similar; real-time sampling of the main generator output voltage value and the predetermined value are compared, with comparable results to the regulating pulse width modulator PWM; the output voltage value is high, narrow pulse width modulator output, whereas the width. Then these pulses to control high power switching devices such as a transistor or FET controls into the exciter stator coil current time. So that the magnetic field strength as the main generator output voltage change the opposite changes; i.e. the output voltage wave exciter stator magnetic field decreases, lowering the output voltage exciter stator magnetic field enhancement. So as to achieve the purpose of negative feedback regulation.

Figure 2 automatic voltage regulator circuit principle of Fang Kuangtu

Figure 2is a commonly used type AVR. Sampling independent generator output voltage signal from the8,9 ends and input to a voltage measuring unit of comparison, and internal predetermined voltage value ( for example380V ) phase comparison. And compare the results with the output voltage of UA into pulse width modulation unit PWM, output voltage UC into low frequency protection unit. Voltage measurement comparison unit L, S, H is connected to the main generator output voltage amplitude adjusting potentiometer three terminals.

Pulse width modulator by the regulator output DC voltage of UCC as a working power supply, in order to ensure its stable performance. Its output voltage UB control modulation tube VT3. If the voltage measurement comparison unit sent UA, shows that the output voltage of the generator is increased, the UA will enable pulse width modulator output pulse width of UB. Narrow pulse will make VT3conduction time is short, the current through the less. Conversely, the main generator voltage to reduce the UA smaller, pulse width modulator output pulse width of UB become wide, so that VT3turn-on time is long, the current increase.

Exciter stator coil end of the terminal X1, the other end of the XX1terminal. The main generator armature. EA, EB, Ec three-phase voltage, through the three diode VD10, VD11, VD12rectifier, current from the X1 end into a stator of the exciter coil, by XX1outflow, and after modulated tube VT3and XN terminals to the main generator armature, forming the exciter stator coil excitation current path. VT3 is the channel switch, conduction time is long, the stator coil current flowing through a long time, the stator magnetic field strength; VT3conduction time is short, the stator coil current, stator magnetic field intensity.

This is the AVR regulation of main generator voltage due to the load causes; main generator output voltage increases, voltage measurement comparison unit output UA increasing, UA control of the pulse width modulator output UB pulse width becomes narrower, the switch tube VT3conduction time is short, the exciter stator field weakens, the rotor armature voltage and rotating rectifier output electric current. Decrease, bring about supply main generator rotor excitation current is small, then the main generator because of its rotor magnetic field decreases so that the output voltage is reduced. Conversely, negative feedback regulation of AVR function will make the main generator output voltage rise.

The main generator for the load exceeds a rated value and output maximum current, diesel engine also subsequently output power that led to its rotational speed is lower than the rated value. Low frequency protection unit is the role of condition limiting exciter stator coil current excess increases. It composed of resistor and capacitance charge and discharge circuit set a low frequency protection, when the main generator load normal, from a voltage measuring unit of UC less than low frequency protection points, then low frequency protection unit output voltage of Ud, diode VD8is off, Ud reach the pulse width modulator, having no effect. If the main generator overload Ud becomes lower, VD8conduction, Ud and UA can simultaneously act on the pulse width modulator, the output pulse of UB with Ud decline narrowed, modulation tube VT3turn-on time become short, excitation current decreases the exciter stator magnetic field become weak, which leads to the main generator rotor magnetic field decreases. Generator output voltage, current decrease decline. Low frequency protection unit to protect the exciter and generator effect.

3synchronous generator maintenance

The synchronous generator is the key part of diesel generating set. For the diesel generator set to establish a suitable working environment, make daily maintenance is very necessary.

Generator room inside the high temperature, humidity and air pollutants are the most common factors caused by fault of generator. Dust, dirt and other air pollutants accumulation will cause the bad performance of the insulating layer, not only easy to form the conductive pathways, may also make the rotor bearing part of the friction increases heating. Moisture and air pollutants in the moisture easily in the generator of the leakage path, cause the fault of generator. Room temperature is too high will make the generator generates heat when not out, causing the output power decreases, unit overheated. So the room dust prevention, damp, ventilation cooling must cause enough attention.

Either a single or double bearing generator bearing generator, the rotor shaft and the diesel engine spindle is connected between the high requirement of coaxiality. Long period running of units sometimes coaxial may reduce, lead generator noise increases, high temperature. Should be checked regularly, in order to maintain concentricity good maintenance.