A New Method for Detecting Spark in Electrostatic

International Conference on Information Science and Technology March 26-28, 2011 Nanjing, Jiangsu, China

A New Method for Detecting Spark in Electrostatic Precipitation Zhuohan Li, Cheng Shao, Chongquan Zhong, and Yi An Abstract— Spark detection is an important problem in electrostatic precipitation. This paper proposes a new method for detecting the spark based on the load voltage variety. In order to obtain this variety, the control model of the power supply is established, and then the mathematical expression of the load voltage can be formulated. By analyzing the features of the spark breakdown, it is observed that the load voltage variety during the spark breakdown is much larger than that of normal condition. Therefore, the maximum variety of the load voltage under normal condition can be considered as the detection threshold. In addition, the control method which tracks the dielectric strength recovery curve is also presented. The simulations and experiments demonstrate that the proposed method is effective.

I. I NTRODUCTION

E

LECTROSTATIC precipitation is an environmental automatic control technique which removes particles in the flue gas by using electrostatic force. It has been widely used in the industrial world due to its advantages of high efficiency and low pressure drop [1]. Electrostatic precipitator (ESP) includes the power supply and the mechanical main body. The mechanical main body mainly consists of discharge electrodes, collecting electrodes, and rapping unit. The power supply provides negative pulse high voltage for the main body. Then, the strong electric field is generated between the sharp discharge electrodes and the smooth collecting electrodes. When the corona discharge takes place, ions and electrons are produced and attached to dust particles. Due to the electrostatic force, the charged particles move towards the collecting electrodes, and are collected on the plat electrodes [2]. In a typical industry ESP, the distance between the discharge electrode and the collecting electrode is around 150∼250mm, the power supply may be the single-phase 50/60Hz power, the three-phase 50/60Hz power, and the high frequency inverter power [3]. This paper focuses on the spark detection and control of the single-phase power, which is mostly used in electrostatic precipitators. For the single-phase power, the time-average voltage between two electrodes is usually 60∼100KV, and the peak voltage is 90∼155KV [4]. When the peak voltage is higher than the corona starting voltage, the corona discharge takes place in the strong electric filed according to the discharge colliding theory [5], and generates corona current across two electrodes. As the peak voltage rises, the density of the space charges increases, and the corona current, which contributes Zhuohan Li, Cheng Shao, Chongquan Zhong, and Yi An are with the School of Control Science and Engineering, Dalian University of Technology, Dalian, Liaoning, PR China (email: {ladaola, cshao}@dlut.edu.cn). This work was supported by the National Natural Science Foundation of China (Grant No. 61074020).

978-1-4244-9442-2/11/$26.00 ©2011 IEEE

to collecting dust particles, also increases. However, since the distance between two electrodes is fixed for the specific precipitator the peak voltage can not rise infinitely. When the peak voltage exceeds the maximum insulating voltage of dust medium, the spark discharge instead of corona discharge is generated according to the stream discharge theory [6]. The spark discharge is invalid for collecting dust particles, and the spark breakdown or flashover phenomenon easily occurs. During the spark breakdown, the discharge electrodes and the collecting electrodes are similar to instantaneous short circuit, and the precipitator current across two electrodes rises rapidly up to 2∼3 times of the rated current. Thus, it is very important to detect the spark breakdown precisely and control the spark discharge in time. Conversely, if the spark is not detected as it occurs, the generated continuous high current will form the electrical arc discharge and destroy the power supply. This is called the miss detection. If the spark is detected when it dose not occur, the precipitator voltage will drop and reduce the efficiency of ESP, which is called the false detection [7]. Zheng [8] researched the phase relation between the primary voltage and the primary current in the transformer that are used in the power supply. He proposed that the spark breakdown could be detected through the phase difference between voltage and current because the impedance angle of corona discharge differed from that of spark discharge. Since precise measurement of the phase difference is complex in factual application, and the measurement sensibility is low for the strict electromagnetic interference, it is difficult to meet the requirement of spark control. Shi [9] observed that one or two waveforms of the load current would generate fine distortion ahead of the spark breakdown, while the width of the waveform and the average current would increase. Therefore, the spark breakdown could be detected by measuring the current distortion. To be specific, operations, such as the full waveforms sampling of current and voltage, the half-wave integrate, and pointto-point comparison, are necessary for the measurement. However, completing such complex hardware and software designs for these operations on the embedded system is not easy. In addition, some researchers pay attention to the measurement of the rise rate or the peak value of the load current for spark detection because the current rises rapidly up to 2∼3 times of the rated value when the spark occurs. These methods achieve better results [10]-[13]. However, the feedback precipitator current signal usually includes much higher harmonic generation at light loads; moreover, the instant turning on of silicon controlled rectifier (SCR) in power supply will generate spike current, and these conditions leads

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to the false detection easily. Lin [14] proposed using analog circuits to detect the spark such as the hardware adder. The regulated feedback load current signal adds together with the regulated feedback load voltage signal, and the output of the adder is small on the condition of no spark. Since the normal current signal is positive and the normal voltage signal is negative, two signals cancel out. During the spark breakdown, the current signal rises rapidly as the voltage signal drops quickly to zero, which consequently result the ladder to produce a much higher positive signal. This output signal is efficient enough to identify the occurrence of the spark. However, since the phase of the current differs from that of the voltage, so under normal condition, the current signal and the voltage signal do not cancel out entirely. Moreover, it is possible for the precipitator to run under the condition of high current and low voltage, such as back corona. Under this condition, the method often leads to false detection. In this paper, the spark breakdown is detected through a software based on the feedback load voltage signal, and the load current signal is auxiliary. Compared with the load current signal, the voltage signal is more stable with strong anti-jamming capability because of the capacitive precipitator load, which is important for the precise spark detection. In section II, the control model of the power supply is established, the new detection method which could be easily implemented is provided, and the theory criterion is formulated. In section III, the detailed process of the spark control is described [15]. In section IV, simulations and experiments are completed, which verify the validity of the detection and control methods. At last, conclusions are drawn in section V. II. S PARK D ETECTION A. Control Model of ESP Power Supply The schematic diagram of ESP single-phase power supply is shown as Fig. 1. The input single-phase AC voltage Ui is

Fig. 1.

SCR1 is triggered when Ui is negative. The input voltage Ui is usually expressed as Ui = UP sin (2πfi t)

(1)

where UP is the peak voltage (V), fi is the frequency (Hz), and t is the time (s). The waveform of the primary voltage U1 is shown as Fig. 2, α is the conduction angle of the SCR. The transformer

Fig. 2.

Waveform of the TR primary voltage U1

steps up the primary voltage U1 to the desired secondary side AC high voltage U20 , and then the rectifier outputs the negative pulse high voltage U2 in order to provide the voltage for the discharge electrode. The transformer and the rectifier are integrated in one set, and this set is called the rectifier transformer (TR). The collecting electrode is connected with the earth. UL is the load voltage between the discharge electrode and the collecting electrode. The load voltage is also called the precipitator voltage. Compared with the general power transformer, the high-impedance transformer is used in ESP for avoiding damage to the TR under frequent spark breakdown. Usually, the leakage reactance of TR is around 35∼40 percent of the total reactance. The waveforms of the negative pulse high voltage U2 and the load voltage UL are shown in Fig. 3. α is the conduction

Schematic diagram of ESP power setup Fig. 3.

transmitted to SCRs through air switch QF1. The SCR1 and SCR2 are connected back-to-back, and used for controlling the primary side AC voltage U1 of the transformer. The SCR2 is triggered when the input voltage Ui is positive, and the

Waveform of the secondary output voltage

angle of SCRs, tα is the triggering time, and Ts is the period of U2 . The theoretical waveform of U2 is described by curve a, and the waveform of the load voltage UL is

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described by curve b. When the SCRs are triggered, the voltage U2 rises instantaneously from zero to some value, and then varies along curve a. However, on the other hand, in order to be increased quickly from zero to some value UL needs to experience a short procedure and then varies along the curve b. The reason is that the conditions, such as the distributed parameters of the rectifier transformer and the load capacitance, influence the rising speed of UL . According to the above analysis, the secondary output of the ESP power supply can be modeled as Fig. 4.

of the input voltage Ui is equal to 10ms. And the triggering time tα is within 0∼10ms. The conduction angle α varies theoretically from zero to 180 degree; however, α is normally within 18∼162 degree in practical control for avoiding the false triggering to the SCRs. Usually, the inner resistance Rs ≤ 30Ω, and the damping resistance Rd is around 200∼800Ω. Compared with the load reactance ZCL //RL and the leakage reactance ZLS , the sum of ZRS and ZRd in Eq. (2) can be omitted [18]-[19]. When the load is resistive, ZCL in Eq. (3) can be also omitted, because the reactance ZCL far exceeds the reactance ZRL , and then Eq. (2) can be simplified as 0 0 ≤ t < tα UL = (6) ULP (ZRL ) sin (2πfi t) tα ≤ t ≤ T s where

Fig. 4.

ULP (ZRL ) = nUP

Control model of ESP power supply

In the model, the voltage source U2 is the negative pulse high voltage provided by the TR. The cathode of the voltage source is connected with the discharge electrode. The anode is first connected with the collecting electrode, and then connected with the earth. Rs is the equivalent inner resistance of the TR, and Ls is the equivalent leakage inductance of the TR. Since the magnetic permeability of the air medium is the constant, the reactance of Ls is usually the constant for the specific TR [21]. Rd is the damping resistance, CL is the equivalent load capacitance between two electrodes, and RL is the equivalent dust load resistance. UL is the load voltage, and IL is the load current across two electrodes [16]. According to the model, the load voltage UL can be expressed as UL = U2

ZCL //RL ZRS + ZLS + ZRd + ZCL //RL

where ZCL //RL =

Z C L Z RL . Z C L + Z RL

(2)

(3)

ZRS is the reactance of Rs . ZLS is the reactance of the leakage inductance Ls . ZRd is the reactance of Rd . ZCL is the reactance of CL . ZRL is the reactance of RL . ZCL //RL is the parallel load reactance of CL and RL . IL is the load current which is also called the precipitator current. The reactance of ZCL and ZRL is determined by many factors such as gas flow, dust characteristics, the distance between two electrodes, and the area of collecting electrode [17]. According to the Eq. (1) and Fig. 3, the theoretical secondary voltage U2 is calculated as 0 0 ≤ t < tα U2 = (4) nUP sin (2πfi t) tα ≤ t ≤ T s where tα = T s

180 − α 180 − α = . 180 360fi

(5)

n is the winding turns ratio of the TR. For the singlephase 50Hz power supply, Ts which is half of the period

Z RL . Z L S + Z RL

(7)

ULP (ZRL ) stands for the peak value of the load voltage, and it is the function of the ZRL load reactance. B. Criterion of Spark Breakdown During the spark breakdown, the load is similar to the instantaneous short circuit, which means that the load resistance RL is close to zero and the load capacitance CL discharges to the earth immediately. Therefore, at this point, the load voltage drops rapidly from normal voltage to zero, and the normal load voltage of the spark moment is called the spark breakdown voltage Uspark . In addition, the load current rises rapidly and far exceeds zero due to the short circuit. These spark features are used for detecting the spark breakdown in this paper. 1) Criterion of Spark for Resistive Load: According to the above spark features, it is clear that the load voltage variety ∆UL (t) of the spark moment is the voltage Uspark (t). For example, if the spark moment is t1 , ∆UL (t) of the spark can be expressed as follows according to Eq. (6) ∆UL (t1 ) = Uspark (t1 ) = ULP (ZRL ) sin (2πfi t1 ) .

(8)

Under normal condition, the spark breakdown does not occur at the time t1 , and the load voltage variety ∆UL (t) of no spark can be expressed as ∆UL (t1 ) =ULP (ZRL ) (9) × [sin (2πfi t1 ) − sin (2πfi (t1 + ∆t))] where tα ≤ t1 < Ts . ∆t is the interval of time. By comparing Eq. (8) with Eq. (9), it is clear that ∆UL (t) of the spark is always more than that of no spark whenever the spark occurs. Conversely, if the factual ∆UL (t) is more than the maximum load voltage variety of no spark, it is confirmed that the spark breakdown takes place. Therefore, this maximum voltage variety on no spark can be used as the threshold for detecting spark, and then the key is how to compute the calculation of the maximum load voltage variety of the normal condition.

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According to Eq. (6), the partial derivative of the load voltage UL is shown as follows ∂UL (t) = 2πfi ULP (ZRL ) cos (2πfi t) ∂t and ∆UL (t) = −

∂UL (t) ∆t, ∂t

tα ≤ t Mu . (16) IL (K) > 0 UL (K − 1) is the K − 1th sampled value of the load voltage during the period of Ts , UL (K) is the Kth sampled value, and IL (K) is the Kth sample value of the load current. If both conditions are satisfied at the same time, it is confirmed that the spark breakdown takes place.

Fig. 5.

Curve of spark control

In case Ulim is the maximum insulating voltage, the curve a shows Ulim recovering, and the curve b shows the spark control. At the time t0 when spark breakdown takes place, Ulim will drop from the breakdown voltage Uspark to zero, and then be gradually recovered to Uspark . The load voltage

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α2 =

αspark − mα1 . 60 fset Ts − (m + 1)

AND

A. Simulation Calculation For three loads, the load voltage varieties ∆UL (t) of normal condition are simulated according to Eq. (9). The simulation curves are shown in Fig. 6. Normal − Different Loads ∆U (t) Curves, Ts = 10ms Tc = 400µs L

25 a − 100% Load b − 33% Load c − Open Circuit Load

20

c b

15

a

10 5 0 −5 −10 −15 −20

t = Ts − Tc → −25

0

2

4

6

8

10

Time t (ms)

(17) Fig. 6.

With approaching the breakdown voltage, the load voltage can be increased continuously until to the rated load voltage if the spark does not occur again. Otherwise, steps (a)-(c) are repeated. IV. S IMULATION

TR is 324 according to Fig. 1 and Fig. 4. In addition, the sample interval Tc is set as 400µs.

Voltage Variety ∆U (KV)

should always track the recovery curve. The detailed control process can be classified into the following three periods: (a) The time interval from t0 to t1 : lock the SCRs in one period of Ts for the recovery of the dielectric strength after the spark breakdown takes place. (b) The time interval from t1 to t2 : rapidly increase the voltage. The conduction angle is increased by the fixed step, and the load voltage UL will reach 80 ∼ 90 percent of the breakdown voltage Uspark during 3 ∼ 5 periods of Ts , so that the higher average load voltage can be achieved after the lock of the SCRs. In case the fixed step of conduction angle is α1 , and then α1 is around 15 ∼ 20 degree in practical application. The voltage Ur indicates the value of load voltage UL at the time t2 . (c) The time interval from t2 to t3 : approach the Uspark . The conduction angle is increased by the fixed step α2 , and the load voltage UL approaches the breakdown voltage Uspark . The time cost is determined by the set value of the spark rate fset (times/minute). In case the conduction angle is αspark at the moment of the spark, and the load voltage UL experiences m periods of Ts to rise rapidly from zero to Ur during the period of t1 ∼ t2 , and then the fixed step α2 can be calculated as

E XPERIMENT

In this section, simulations and experiments are completed. Firstly, the simulation verifies that the load voltage variety ∆UL (t) of normal condition reaches the maximum at the time t = Ts − ∆T . Secondly, the simulation verifies that ML is increased with the increasing of the load reactance, and reaches its maximum Mu ; moreover, it calculates the AD value Mu0 used for the detection threshold in the subsequent experiment. Furthermore, the rationality of the detection method is verified by comparing the load voltage variety of spark with Mu of the normal condition. Finally, the laboratory experiment proves that the spark detection and control are valid. The preconditions of the following simulation are defined here. The effective value of Ui is 380V, and the frequency fi is 50Hz. The rated average load voltage is 72KV, and the rated average load current is 1.0A. The leakage reactance ZLS of TR is designed as 35 percent of the total reactance of the rated voltage and current, and ZLS is fixed because the magnetic permeability of the air medium is constant. It is easily proved that the load reactance under the rated voltage and current is the minimum, and the load reactance at this time is called the rated reactance. Moreover, it is calculated that the period Ts of U2 is 10ms, the value of ZLS is around 38.77KΩ, and the winding turns ratio n of

Variation of ∆UL (t) along the time t

The curves a, b, and c show the variation of ∆UL (t) along the time t when the load is 100% of the rated average load current, 33% of the rated current, and open circuit respectively. It should be noted that the smaller the load current is, the higher the load reactance will be. Obviously, the load voltage varieties ∆UL (t) reach the maximum ML (ZRL ) for all three loads at the time t = Ts − Tc , and the result is consistent with Eq. (12). For all loads, the simulation curves of ML (ZRL ) varying with the load reactance ZRL are shown in Fig. 7. In Fig. 7-1, with the increasing of the load reactance, ML (ZRL ) increases and approaches Mu . It is verified that Mu is the maximum load voltage variety of all loads. The value of Mu is 21.71KV, which can be calculated according to Eq. (13). In Fig. 7-2, VL is the regulated feedback signal of ML . Similarly, VL rises with the increasing of ZRL and approaches Vu . The value of Vu is 0.376V. In the simulation, the load voltage UL is feed back by resistance voltage-dividing, and the feedback signal is regulated to 0∼2V by differential amplifying. VL is in fact the maximum difference value of two adjoining feedback signals, and it is also the function about ZRL . In Fig. 7-3, ML0 is the analog to digital (AD) value of ML , and it approaches the Mu0 . In the simulation, 10 bits analog to digital converter (ADC) is used, and the relation between the regulated feedback signal and the AD value is described as follows [20]. U0 (18) NL = 1024 L . Vref

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2. Normal − Regulated signal VL Curve for ML 0.38

Mu = 21.71 KV

21

Regulated Voltage Variety VL (V)

Maximum Load Voltage Variety ML (KV)

1. Normal − Maximum Load Voltage Variety ML Curve 22

20 19 18 17 16 15 14

0

500

1000

1500 2000 2500 Load Reactance ZR (KΩ)

3000

3500

Vu = 0.376 V 0.36 0.34 0.32

0.26 0

500

1000

L


Mu′ = 154

c Load Voltage Variety ∆U (KV)

L

4000

200

150 AD Value M ′

3500

4. Spark − Different Load Voltage Variety∆U(t) Curves

L

160

140 130 N = VL x 1024 / 2.5

120

N is the AD value 110 100

3000

L

3. Normal − AD Value M ′ Curve for M L

7

Au = 3.333, is the amplifying times

0.28

0.24

4000

3

VL = ML x 10 x Au x 270 ÷ (5.2 x 10 + 270)

0.3

0

500

1000


3000

3500

150

a 100

50 Mu = 21.71 KV 0

4000

100% Load 33% Load Open Circuit

b

0

2

4

6

8

10

Time t (ms)

L

Fig. 7.

Variation of ML along load reactance ZRL

UL0 is the regulated feedback signal of the load voltage UL , Vref is the reference voltage of ADC, and NL is the AD value of UL . In the simulation, Vref is set as 2.5V while the range of NL is within 0∼1024 due to 10 bits ADC. According to Eq. (12) and Eq. (18), ML0 can be calculated as ML0 = 1024

−2πfiVL cos (2πfi (Ts − Tc )) Tc . Vref

obtained with air medium by changing the distance between the two terminals. The spark breakdown voltage Uspark will vary with the changing of the distance. The experimental data are shown in Table I. As shown above, d indicates TABLE I E XPERIMENT DATA OF SPARK BREAKDOWN

(19)

Similarly, the AD value Mu0 can be also calculated, and its value is 154. Mu0 is used for the detection threshold in the following experiment. In Fig. 7-4, the load voltage variety of the spark is compared with the normal maximum load voltage variety Mu . The curves a, b, and c indicate the load voltage variety of spark along the time t, when the load is 100% of the rated current, 33% of the rated current, and open circuit respectively. Obviously, all of the load voltage varieties of the spark are more than Mu , which proves that Mu can be used for the spark detection. B. Experimental Data The laboratory experiment has been completed under the similar conditions as the simulation. Two copper wires with cross-sectional area 4mm2 are installed terminal to terminal, and they functioned as the discharge electrode and the collecting electrode respectively. Different loads can be

d (mm) 63 81 94 122 145 161

−UL (KV) 12 16 21 30 48 68

IL (mA) 160 185 250 350 550 600

Z RL (KΩ) 75.0 82.1 84.0 85.7 87.7 113.3

0 ML

Na

Nm

112 117 121 126 128 131

120 120 120 120 120 120

2 0 0 0 0 0

Er (%) 1.6 0 0 0 0 0

the distance between the two electrodes, UL is the load voltage measured by the analog voltage meter, and IL is the load current measured by the analog current meter. ZRL is the load reactance (KΩ), and is calculated approximately as follows −UL Z RL = . (20) IL 10−3 ML0 stands for the AD value of the maximum load voltage variety of no spark, and it is calculated by the software based on continuous sampling AD values of the load voltage. Obviously, ML0 is increased with the load reactance ZRL , which is consistent with the simulation result. Na is the total

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number of times for the factual spark breakdown, Nm is the number of times for the miss detection, and Er is the error rate. In this experiment, the detection threshold of spark is set as 154, which is the same as the simulation. When the factual load voltage variety ∆UL exceeds the threshold, the controller confirms the spark breakdown, and then processes the spark control. Table I shows that the spark detection is mostly correct, and the false detection never occurs, yet two miss detections occured when the distance d is 63mm. The reasons of the miss detection are described as follows. The short distance between two electrodes leads to the small load reactance ZRL , and furthermore leads to the small load voltage variety ∆UL . In such case, it is possible that the factual ∆UL of the spark is smaller than the threshold, so the miss detection takes place. However, it is not a problem because the practical distance between two electrodes is 150∼250mm, and the distance is certain for the specific precipitator. Moreover, the longer the distance is, the higher the spark breakdown voltage Uspark becomes, and the easier the spark detection will be. It is demonstrated that the precise spark detection has been realized through applying the simulation detection threshold to the factual experiment, and the experiment proves that the detection method based on the load voltage variety is valid. In practical application, the threshold may be finely adjusted. The experiment result of spark detection and control is shown in Fig. 8, and it is recorded by the oscilloscope.

Fig. 8.

Process of spark control

The spark breakdown takes place at time t0 , and Uspark is the breakdown voltage. During the time interval from t0 to t1 , the controller locks the SCRs with the lock time interval of 10ms. The load voltage rises rapidly during the the time interval from t1 to t2 , reaches 80 percent of Uspark at the time t2 , and continues approaching Uspark according to the set fire rate. The time interval is 30ms from t1 to t2 . It is obvious that the load voltage UL is gradually recovered to the breakdown voltage through three time periods.

V. C ONCLUSION This paper establishes the control model for ESP power supply, and presents a new method of spark detection based on the load voltage variety and the auxiliary load current. At the same time, the detection threshold is formulated to provide the theoretical basis for ESP application. The results of the simulation and experiment are valid, and verify that the proposed method is effective and easy to realize. R EFERENCES [1] S.X. Du and T.J. Wu, “Environmental Automatic Control-Promising Applications of Control Theory,” Control and Instruments in Chemical Industry, vol. 30, no. 2, pp. 1-9, 2003. [2] H.J. White, Industrial Electrostatic Precipitation. C.H. Wang Translation, Metallurgical Industry Press, Beijing, 1984. [3] Y.W. Lin and W.P. Liu, “Development of Chinese Electrostatic Precipitator Technology,” in Proceedings of 11th International Conference on Electrostatic Precipitation, 2008, pp. 3-11. [4] K.J. Mclead, “Electrostatic precipitators,” Commissioned IEE Review, vol. 135, no. 6, pp. 347-361, 1987. [5] A. Mizuno, “Electrostatic Precipitation,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 7, no. 5, pp. 614-624, 2000. [6] S.H. Kim and K.W. Lee, “Experimental Study of Electrostatic Precipitator Performance and Comparison with Existing Theoretical Prediction Models,” Journal of Electrostatic, vol. 48, pp. 3-25, 1999. [7] K. Shi and B.L. Zhou, “Research on Performance and Stability of Control Equipments in Electrostatic Precipitator,” power environment protection, vol. 9, no. 3, pp. 44-54, 1993. [8] C.M. Zheng, “A New Multi-Functional Power Supply in Electrostatic Precipitator,” Electric Power, no. 9, pp. 19-23, 1987. [9] W.Y. Wei, “Improvement of Processing Flashover in Electrostatic Precipitator,” Thermal Power Generation, no. 44, pp. 58-60, 1991. [10] Q.W. Fu and Z.F. Lu, “Design of Control Equipment in Electrostatic Precipitation Based on Multiprocessors,” in Proceedings of 9th Conference of ESP and 1st Conference of DeSOx, 2001, pp. 231-233. [11] Y.H. Lai, “Development of AVC430 High Voltage Control System for Electrostatic Precipitation,” in Proceedings of 13th Conference of Electrostatic Precipitation, 2009, pp. 346-349. [12] C.F. Li and Y.H. Hu, “The Application of Computer-controlled High Voltage Rectification Equipment for Electrostatic Dust Removing,” Shandong Electronics, no. 2, pp. 14-16, 1996. [13] Y.J. Xie, “Equipment of High Voltage Power Supply in Electrostatic Precipitation Based on MCU,” power environment protection, vol. 9, no. 3, pp. 55-59, 1993. [14] C.Q, Lin, “T/R Set Spark Detection and Control under Small Load,” power environment protection, vol. 22, no. 1, pp. 50-53, 2006. [15] G. Norbert and H. Werner, “Application of Different Types of HighVoltage Supplies on Industrial Electrostatic Precipitators,” IEEE Transactions on Industry Application, vol. 40, no. 6, pp. 1513-1519, 2004. [16] N.V.P.R. Durga Prasad, T. Lakshminarayana, J.R.K. Narasimham, Thenmozhi M. Verman, and C.S.R. Krishnam Raju, “Automatic Control and Management of Electrostatic Precipitator,” IEEE Transactions on Industry Applications, vol. 35, no. 3, pp. 561-566, 1999. [17] Senichi Masuda and Akira Mizuno, “Flashover measurements of back discharge,” Journal of Electrostatics, vol. 4, no.3, pp. 215-231, 1978. [18] Kelly S. Robinson and John J. Coleman, “Spark Protection Circuit for Measuring Current in High-Voltage Circuits,” Journal of Electrostatics, vol. 63, pp. 285-296, 2005. [19] Users Manual of ESP High-Voltage Rectifying Equipment. Dalian Jiahe Industrial Control Technology Co., Ltd, 2008. [20] LPC21xx and LPC22xx User manual. Rev. 4, NXP Semiconductor Co., Ltd, 2008. [21] J. Tang, Motor and Drag. Higher Education Press, Beijing, 2003.

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