Analysis on the Fast Excitation System of Composite Magnetic Controllable Reacto
开篇：润墨网以专业的文秘视角，为您筛选了一篇Analysis on the Fast Excitation System of Composite Magnetic Controllable Reacto范文，如需获取更多写作素材，在线客服老师一对一协助。欢迎您的阅读与分享！
Abstract. The fast excitation system of a composite magnetic controllable reactor is introduced. In this excitation system， a bidirectional function （i.e. fast forward excitation and backward forcible demagnetization） is available， which can significantly improve the response speed， performances， and application scope of magnetic controllable reactor.
Key words： Composite； Fast； Excitation； Magnetic Control； Reactor
1. Introduction
Improving the response speed of the magnetic controllable reactor through great efforts is an urgent need of the development of the magnetic control technology. In recent years， a variety of different excitation plans have been offered successively by many magnetic controllable reactor manufacturers， scientific research departments， and the institutions of higher learning， but all of them have different advantages and disadvantages. In this paper， the fast excitation system of a composite magnetic controllable reactor is introduced. In this excitation system， a bidirectional function （i.e. fast forward excitation and backward compulsive demagnetization） is available， which can shorten the response time of the magnetic controllable reactor from a few hundred milliseconds to tens of milliseconds.
2. Overview of the fast excitation system of magnetic controllable reactor
In the working winding or exciting winding of magnetic controllable reactor， a certain amount of DC current is passed for changing the reactance value or volume of magnetic controllable reactor. This DC current is called as the exciting current of magnetic controllable reactor. The impedance of the magnetic controllable reactor is smaller， and then thecurrent passing the magnetic controllable reactor is greater， and also the capacity of the magnetic controllable reactor is larger if the excitation current is greater.
The basic function of magnetic controllable reactor is to compensate system reactive power. The size of system reactive power is in instantaneous changes， requiring the magnetic controllable reactor to follow the change of system reactive power， timely adjust its own reactance value， and implement real-time compensation.
In the application fields such as steel rolling， electric arc furnace， and wind power generation， the magnetic controllable reactor is required to possess a fast response speed： the response time to the capacity jumping from 5% to 95% or from 95% to 5% should be controlled within 30 ～ 60ms. Thus， a very high requirement is proposed for the response speed of the magnetic controllable reactor. The basic methods for implementing the fast excitation are the same， namely the application of forcible excitation technology.
Forcible excitation technology owns two meanings： （1） fast magnetization， for making iron core inductance saturated quickly in a short time： this process is to make the magnetic controllable reactor reactance value decreased rapidly and the reactive current increased rapidly； （2） rapid demagnetization， for making iron core inductance exit quickly in a short time： this process is to make the magnetic controllable reactor reactance value increased rapidly and the reactive current decreased rapidly. There are multiple excitation methods in magnetic controllable reactor.
2.1 Self-excitation
Self-excitation is divided into ordinary self-excitation and fast self-excitation.
1.1.1 Ordinary self-excitation
The ordinary self-excitation way is as shown in figure 1. Excitation voltage sources from the working winding of magnetic controllable reactor and a high suspended voltage exists between it and the system ground， so it is also known as high-pressure self-excitation. This way of excitation features simple circuit and easy control， and its disadvantages are as follows： slow excitation speed； long magnetic control reactor response time （up to 1s or even longer）； it can be applied to the sites having low requirements on response speed， but cannot meet the needs of the fast response.
1.1.2 Fast self-excitation
There are many ways for implementing fast self-excitation， and the way shown in figure is one of them. If magnetic controllable reactor runs stably， thyristors V1 and V2 are alternatively conducted and cut-off， so as to provide the magnetic controllable reactor with exciting current. During the working period of V1 and V2， V3 has been always in an on state and provides follow current； if magnetic controllable reactor needs to jump toward capacity increase （hereinafter referred to as forward excitation）， thyristors V1 and V2 are cut off， and V3 and V4 are conducted to provide greater excitation current and implement fast jump under the action of high voltage； if magnetic controllable reactor needs to jump toward capacity decrease （hereinafter referred to as backward excitation）， V4 is cut off and provides magnetic controllable reactor with backward excitation current when V1， V2， and V3 are cut off， so as to implement fast demagnetization.
With this way of excitation， the response speed of magnetic controllable reactor is improved to about 100ms. Limited by thyristor reverse voltage， the backward voltage undertaken by V3 should be not too high， so the speed of forward excitation is limited. Also， the backward excitation has high requirements on the control accuracy of the control system because it is implemented relying on V4 cut-off and has strict requirements on V4 shut-off time.
2.2 Fast external excitation
The way of external excitation generally consists of exciting transformer， controllable rectifier circuit， and control system. The excitation voltage of external excitation sources from the secondary winding of the self-excitation transformer， so its electrical isolation is very good， the response speed of the magnetic controllable reactor can be controlled within 60ms if different excitation combinations and control modes are applied， and also its superior excitation performances will be displayed if it is applied to extra-high voltage and large-capacity magnetic controllable reactor.
2.3 Composite fast excitation
Compound excitation is a way of excitation combining self-excitation with external excitation. Generally， the fast forward excitation is implemented relying on self-excitation， and the fast demagnetization is implemented relying on external excitation. In a complete excitation system， excitation executing system and excitation control system are included. The excitation system introduced here specifically refers to the execution part of excitation.
3. The circuit structure of the composite fast excitation system
Composite fast excitation circuit is shown in figure 3： N1， N1'， N2 and N2' are the working winding of magnetic controllable reactor， and N3 and N3' are fast demagnetization windings. Thyristors V1～V6 constitute a composite single-phase bridge rectifier circuit， in which the AC rectifier voltage is provided by the windings 30V and 600V of magnetic controllable reactor， and the rectification circuit outputs forward DC voltage as the stable excitation source and forward over-excitation power supply of magnetic controllable reactor； V7 and V8 constitute a single-phase full wave controlled rectifier circuit， in which the AC rectifier voltage is provided by the 90V double windings of magnetic controllable reactor， and the rectification circuit outputs negative DC voltage as the backward forcible demagnetization excitation power supply of magnetic controllable reactor.
4. Compound fast excitation principle analysis
4.1 The basic principle of implementing inductance fast excitation and fast demagnetization
Inductance is an energy storage element， which is a basic physical property of inductance. This property of inductance is the fundamental reason affecting the fast response of magnetic controllable reactor. When current flows through inductor coil， part of the electrical energy is converted by coil to magnetic energy and stored in it. This is the excitation of inductance， as shown in figure 4（a）. At the instant that the external circuit is interrupted， the self-induced emf generated by inductance is backward， and the magnetic energy stored in inductance is converted to electrical energy and then released through follow current components. This is known as the demagnetization of inductance， as shown in figure 4（b）. Theory and practice prove that the backward demagnetization process of inductance is longer than forward demagnetization process.
Fig.4.The excitation and demagnetization of inductance
From the above mentioned， it is known that the speed of inductance forward excitation should be improved， and the forward excitation current can be increased， so that inductance is in a state of forward over-excitation. To increase the speed of inductance backward demagnetization， backward excitation current can be provided so that inductance energy storage is quickly released under the action of backward excitation current. This excitation method is proposed based on this principle.
From figure 3， the working way of external excitation is used in circuit. Thyristors V1～V6 constitute a composite single-phase bridge rectifier circuit and can implement forward fast excitation； the negative single-phase full wave controlled rectifier circuit constituted by V7 and V8 can implement fast demagnetization.
4.2 The implementation process of fast excitation
If magnetic controllable reactor steadily works， thyristors V1 and V4 in figure 3 are cut off under the action of control circuit， and V2， V3， V5， and V6 are conducted to output certain forward DC current， and the capacity of magnetic controllable reactor is maintained at a stable value.
When the capacity of magnetic controllable reactor is required by the system to rapidly increase， control circuit makes thyristors V3 and V6 cut off， and V1， V2， V4 and V5 are conducted， and the rectifier circuit outputs greater forward DC current under the action of high input voltage so that magnetic controllable reactor is in an excitation state， and subsequently the forward excitation speed of magnetic controllable reactor is improved. When the current of the reactor is stable， thyristors V1 and V4 are cut off， and V2， V3， V5， and V6 are conducted in the reduced control angle so that magnetic controllable reactor enters a new steady state.
4.3 The implementation process of fast demagnetization
The fast demagnetization is implemented by the backward excitation circuit consisting of thyristors V7 and V8. When the capacity of magnetic controllable reactor is quickly required by the system， control circuit makes thyristors V7 and V8 conducted and V2， V3， V5， and V6 cut off to output certain backward DC current， so that magnetic controllable reactor is fast demagnetized； when the current of the reactor is stable， V7 and V8 are cut off， and V2， V3， V5， and V6 are conducted in the increased control angle， so that magnetic controllable reactor enters a stable state of small capacity. The above mentioned sequential process is implemented by excitation control system.
5. Analysis on response time
Under the condition that rectifier components and control system self-delay are not considered， the conversion time of the rectifier circuit should be half to one cycle of power frequency voltage （i.e.10～20ms）， which is deemed to be 20ms generally. Considering the response time of the control system and the delay time of the rectifier circuit， the total response time of excitation system should be in the range of 30～40ms.
6. Requirements on control circuit
and executive components
According to the above analysis， it is known that all conversion instructions are sent by the control system when the instantaneous conversion working process of the rectifier circuit exists in the compound excitation system， so the accuracy and reliability of timing sequence control instructions are the keys to a successful compound excitation， and a control system appropriate for the requirements of compound excitation is required. In timing sequence conversion， rectifier components may be impacted by certain current. This requires a greater safety margin and complete protection measures to be available.
7. Experimental result
In table 1， a comparison between conventional self-excitation way and composite fast excitation way is shown.
From table 1， it is seen that the excitation speed of the composite fast excitation way is only 1/10 of the conventional excitation speed， so the response speed of magnetic controllable reactor is significantly improved.
8. Conclusion
The bidirectional excitation function of the fast excitation system of composite magnetic controllable reactor significantly improves the response speed of the magnetic controllable reactor， so it is a very practical and powerful fast excitation way. The popularization and application of this excitation technology provides a technical support for improving the performances and application range of magnetic controllable reactor.
References
[1] Zhongdong Yin， Hong Liu， et al. Research on the Magnetic Valve Controlled Reactor [J]. Transformer， 1998， 35 （7）.
[2] Bochao Chen. The Theory and Application of New Controllable Saturable Reactor [J]. Wuhan： Wuhan University of Hydraulic and Electric Engineering Press， 1999.
[3] Weixian Chen， et al. The Controlled Regulation of Electric Reactor [Journal Article]. High Voltage Engineering， 2000 （05）.
[4] Ziqiang Song， et al. The Principles and Applications of Magnetic Control Reactor [J]. Journal of Jiangxi Vocational and Technical College of Electricity， 2006， 19 （2）.