IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 35, NO. 4, AUGUST 2007 891

Delay Characteristics and Controller Designof a Triggered Vacuum Switch

Liao Min-fu, Duan Xiong-ying, and Zou Ji-yan

Abstract—Two types of triggered vacuum switches (TVSs)named TVS-1 and TVS-2 with different configuration in triggerunit were described for investigating the delay characteristics. Adesign circuit for controlling the TVS is proposed herein. Thetrigger energy of the controller can be adjusted conveniently. Bymeans of changing the trigger energy, the experimental data showthat the delay and jitter times decrease with increasing triggerenergy. The delay and jitter times decreases magnificently withthe increasing voltage in the main gap. By increasing the main-gapvoltage, the triggered probability increases. The TVS-2 has betterperformance in delay characteristics than TVS-1 because of theimprovement in the trigger structure. With a trigger energy of0.064 J, it is possible to fire both of the TVSs. For the TVS-2 case,the delay time decreases to 2.3 µs, and its jitter time decreases to1.2 µs when the trigger energy is 1.6 J.

Index Terms—Delay effects, jitter, triggered vacuum switch(TVS).

I. INTRODUCTION

THE SWITCH is the kennel component and the maintechnical obstruction of the pulsed power system (PPS),

which demands the right and reliable action of the sequentialenergy releasing. The closing switch is the main device tocontrol the power supply of an electromagnetic launcher (EML)system. It should isolate the launcher reliably during the powerstorage period, and then close the circuit at a set time. Itshould carry high current during the acceleration period andinterrupt the residual current quickly when the projectile leavesthe muzzle. In order to achieve an adequate electromagneticforce, the closing switch should transfer high enough power.

Various types of closing switches have the ability to conducthigh peak currents at high coulomb levels. The comparison offeatures and operational characteristics of these types of closingswitches are reviewed by Singh et al. [1]. It was concludedthat in solid state devices, a series–parallel arrangement ofSCR array was the best choice for tactic railgun. The movablecore transformer and gate turn-off thyristor (GTO) are potentialcandidates in some gun concepts under consideration requiringa switch that can interrupt significant currents [2], and a siliconcarbide thyristor is being developed currently [3]. For tacticalapplications, some limits are stressed to the choice of switches.In nonsolid state devices, the triggered vacuum switch (TVS)

Manuscript received May 10, 2006; revised January 11, 2007. This work wassupported by National Natural Science Foundation of China (50507001).

The authors are with the Department of Electrical and Electronic Engineer-ing, Dalian University of Technology, Dalian 116024, China (e-mail: mfliao@dlut.edu.cn).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPS.2007.895211

Fig. 1. Experimental circuit of TVS.

is well suited to EML applications due to its compact structure,convenient operation, high-reliability trigger, and high current-carrying and high charge-transferring capability [4]–[8].

Currently, the peak current of a typical EML system is largerthan 100 kA, and the pulsewidth is about 2 to 5 ms. In thissituation, the commonly used TVS must be paralleled in orderto transfer such high current. This paralleled operation modebrings some problems such as the synchronism of main currentconduction and the jitter time of trigger, the balance sharingof current in each individual TVS, and so on. To solve theseproblems, the delay and the jitter times of the TVS need to beminimized. Improvements on trigger features and its controllerare helpful to get better delay characteristics.

The objective of this paper is to give some contributionson handling the problem about delay characteristics of TVS,by means of reformative design for trigger configurations andcontroller of the TVS. An improved trigger structure as wellas the controller was developed based on the experience ofvacuum interrupter research. Two types of TVSs with differentconfiguration in trigger unit were prepared for experiments. Theresults are given to show the effect of trigger structure andmain-gap voltage on delay characteristics of the TVS.

II. EXPERIMENTAL SETUP

A. Test Circuit

In order to investigate the basic delay characteristics of theTVS, an LC resonant circuit was set up and connected with theTVS’s main electrodes, which is shown in Fig. 1. The test cir-cuit can generate a high current with a frequency of 26 539 Hz.Pulsed capacitor is used as the energy stored component in this

0093-3813/$25.00 © 2007 IEEE

892 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 35, NO. 4, AUGUST 2007

Fig. 2. Schematic structure and photo of TVS.

Fig. 3. Schematic structure of trigger unit. (a) TVS-1. (b) TVS-2.

circuit, with a capacitance of 9 µF. As the TVS is triggered,power supply provides high-powered pulsed energy to a coil,with an inductance of about 4 µH.

Delay characteristics of sealed-off TVSs were experimen-tally examined in the cathode mode of operation [9], [10]. Thetrigger pin is located in the cathode, and the polarity of the maingap is positive. High-voltage dividers and an oscillograph areused to measure the triggered voltage and the voltage betweenthe main electrodes of TVS simultaneously.

B. TVS’s Structure

The schematic structure of the type of TVS is shown inFig. 2. The electrode material is copper–chromium (50% wt)alloy with a diameter of 58 mm. The diameters of the littlehole in the middle of the cathode and the trigger pin are 4 and2 mm, respectively. The trigger pin is made out of thoriatedtungsten. The sealed-off vacuum pressure is maintained below1.33 × 10−5 Pa. Two devices with different configuration intrigger unit were prepared, which are numbered as TVS-1 andTVS-2. The schematic structure of trigger electrode is shownin Fig. 3. TVS-2 has the similar cathode shape and differentdesign of trigger pin with the TVS reported by Lafferty [4] andSidorov et al. [11]. The distance L between the main electrodesis 8 mm, and the parameter d is 0.5 mm, which is the distancebetween the upper surface of the triggered pin and the surface ofthe cathode. All the two devices have the same L and d values.

For TVS-1, the shape of the trigger pin is clubbed. The holein the middle of the cathode is columned, while for the TVS-2

case, the hole is ladderlike, and the trigger pin is speciallydesigned as I-shaped. Compared with TVS-1, the improvementin the trigger structure of TVS-2 leads to a more nonuniformelectric field with the same L and d values. The improvementmakes TVS-2 easier to be triggered.

III. CONTROLLER OF TVS

Fig. 4 shows the electrical arrangement of the controllingcircuit of TVS. A circuit capable of simultaneously producingboth a low current at a high voltage and a high current at a lowvoltage was developed. A diagram of the circuit is shown inFig. 4 (the upper part). At first, the computer gives a controllingsignal to trigger the SCR, and the C1 is discharged. An inducedhigh voltage ignites the trigger gap of the TVS, and low currentflows through it. If this current is capable of applying highenough energy, then the capacitance C2 will discharge throughthis conducting channel, and a high-current pulse will form.The generated pulse fires the spark gap G.

When the spark gap G was fired, the trigger capacitor C3could discharge through the spark gap and the trigger gap,which would lead to a rapid breakdown of the main gap in theTVS. The capacitor C (in Fig. 1) would then discharge throughthe main gap of the TVS.

By this way, a dense initial plasma ball will be generated, anda high reliability of trigger will be desired.

IV. RESULTS AND DISCUSSION

The improvement in the structure and controller of the TVSis a good way of decreasing the delay and jitter times as well.The time delay td to firing the TVS is defined as the elapsedtime between the application of the trigger voltage and thecomplete voltage collapse to its minimum value across the maingap. It is the same definition with Warren et al. [12]. A largenumber of shots (20–30) must be applied in order to determinethe jitter (i.e., the amount of scatter) in the time delay fromshot to shot. The photo of test circuit is shown in Fig. 5. Thetypical wave of trigger delay time is shown in Fig. 6. In Fig. 6,CH1 stands for the measured triggered voltage waveform andCH2 for the measured voltage waveform in the main gap ofTVS. The polarity of applied triggered voltage is positive, asthe charged voltage in capacitor C3 is a positive one.

The triggered energy of the controller can be adjusted conve-niently by changing the capacity of C3 in Fig. 4. The triggeredenergy is

W =12CU2 (1)

where W is the triggered energy, C is the capacity of C3, andU is the charge voltage of C3. The calculated results of triggerenergy are shown in Table I.

The effect of trigger energy on delay time is shown in Fig. 7,and the effect of trigger energy on jitter time is shown in Fig. 8.The voltage in main gap was maintained to 12.5 kV. As shownin Figs. 7 and 8, when the triggering energy is relatively low,the delay time is quite long. With the increase in the triggering

MIN-FU et al.: DELAY CHARACTERISTICS AND CONTROLLER DESIGN 893

Fig. 4. Controlling circuit of TVS.

Fig. 5. Photo of test circuit of TVS.

energy, the delay time is sharply decreasing. After the triggerenergy is over some value, the delay time trends a constant.Obviously, the higher triggered energy will lead to more initialplasma injected. When the initial plasma diffuses to the maingap, it will be speeded by the electric field force in main gapand lead to the TVS’s breakdown in the end [4]. More initialplasma makes the breakdown quicker and steadier. Comparedto TVS-1, TVS-2 has a lower delay time and jitter time withthe same trigger energy, possibly because of the improvementin the structure of the TVS-2. The I-shape trigger pin for

Fig. 6. Typical wave of trigger delay time.

TABLE ICALCULATED RESULTS OF TRIGGER ENERGY

TVS-2 leads to a more nonuniform electric field. It makesTVS-2 easier to be triggered. The ladderlike hole in cathodeof TVS-2 is helpful for the initial plasma to diffuse into themain gap.

894 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 35, NO. 4, AUGUST 2007

Fig. 7. Effect of trigger energy on delay time.

Fig. 8. Effect of trigger energy on jitter time.

When the capacitance of C3 was maintained with 32 000 pf,the effect of trigger voltage on minimum breakdown voltage inmain gap is shown in Fig. 9. In Fig. 9, as the trigger voltagein the trigger gap increases, the needed minimum breakdownvoltage in the main gap decreases. Because the higher triggervoltage means that there is much higher trigger energy injectedto the trigger gap, the needed minimum voltage in main gapcan be lower. Compared to TVS-1, TVS-2 has a slightly lowerminimum breakdown voltage in main gap with the same triggervoltage. It means that the improvement of the structure of trig-ger unit has little influence on the needed minimum breakdownvoltage.

The TVS’s delay characteristics are strongly affected by thevoltage in the main gap. Fig. 10 shows the effect of voltagein main gap on delay time, and Fig. 11 shows the effect ofvoltage in main gap on jitter time. The trigger energy wasmaintained to 1.6 J. It can be seen that the delay and jittertimes decrease magnificently with increasing the voltage inmain gap. As the TVS is triggered, the initial plasma will beinjected into the main gap, and quickly, a plasma sheath can

Fig. 9. Effect of trigger voltage on minimum breakdown voltage in main gap.

Fig. 10. Effect of voltage in main gap on delay time.

be formed, which is responsible for the enhancement of theelectric field near the electrode surface [10]. The sufficientlylarge electric field causes the explosive formation of cathodespots [5], which generate metal vapor, ions, and electrons toconduct the main discharge current. In this process, the diffusevelocity of the initial plasma is in direct proportion to themain discharge current [13], which is in direct proportion tothe voltage in main gap if the impedance of the test circuit isinvariable. In this case, the higher voltage in main gap will leadto quicker and steadier breakdown for the TVS. It can be seen inFigs. 10 and 11 that TVS-2 has better performance in delay andjitter times than TVS-1 when applying the same voltage in themain gap.

According to the well-established knowledge, the initiationof vacuum breakdown is due to different physical mechanisms[14]. In fact, the initiation and development of a vacuumbreakdown event is a wholly stochastic process, and it should beunderstood on the framework of probability [15]. The triggeredprobability is affected by various factors such as the triggerenergy, the main electrode conditions, the trigger conditions,

MIN-FU et al.: DELAY CHARACTERISTICS AND CONTROLLER DESIGN 895

Fig. 11. Effect of voltage in main gap on jitter time.

TABLE IIRELATIONSHIP BETWEEN MAIN-GAP VOLTAGE

AND MAKING PROBABILITY

the main-gap voltage, and so on. The relationship betweenmain-gap voltage and triggered probability is shown in Table IIherein. The trigger energy was maintained to 0.064 J. Table IIshows that triggered probability increases with increasingmain-gap voltage. The triggered probability is zero when themain-gap voltage is below 2 kV. The triggered probability is100% when the main-gap voltage is over 9 kV. As the triggerenergy significantly influences the process of initial plasma’sforming and expanding into the main gap [10], [13], the phe-nomena might be due to the small trigger energy which cannotproduce sufficient initial plasma to lead to the breakdown of themain gap.

V. CONCLUSION

Delay characteristics of two sealed-off TVSs named byTVS-1 and TVS-2 were experimentally examined in the cath-ode mode of operation. A novel design for controlling the TVSis proposed herein. The triggered power of the controller canbe adjusted conveniently. With a trigger energy of 0.064 J, itis possible to fire the main gap. By increasing the triggeringenergy, the delay and jitter times sharply decrease.

The experimental results show that the delay and jitter timesdecrease magnificently with increasing voltage in the main gap.By increasing the main-gap voltage, the triggered probabilityincreases. The improvement in the structure and controller of

the TVS is a good way of decreasing the delay and jitter times.It shows that TVS-2 has better performance in delay and jittertimes than TVS-1. Particularly, for the TVS-2 case, the delaytime is 2.3 µs, and its jitter time is 1.2 µs when the triggeredpower is 1.6 J.

The TVS has good closing characteristics without an explo-sion sound on discharge. It can be utilized as a quick crowbarswitch in EML or other applications for high-voltage high-current PPS.

REFERENCES

[1] H. Singh et al., “Comparison of switching technologies for a tactical EMLapplication,” IEEE Trans. Magn., vol. 33, no. 1, pp. 513–518, Jan. 1997.

[2] V. A. K. Temple, “MOS controlled thyristors—A new class of powerdevices,” IEEE Trans. Electron Devices, vol. ED-33, no. 10, pp. 1609–1618, Oct. 1986.

[3] E. Spahn et al., “The application of thyristor as main switches in railguns,”in Proc. IEEE 9th Pulse Power Symp., 1993, pp. 583–586.

[4] J. M. Lafferty, “Triggered vacuum gaps,” Proc. IEEE, vol. 54, no. 1,pp. 23–32, Jan. 1966.

[5] J. M. Lafferty, Vacuum Arcs: Theory and Application. New York: Wiley,1980.

[6] Y. G. Chen et al., “High-coulomb triggered vacuum switch,” in Proc.IEEE 9th Pulse Power Symp., 1993, pp. 983–991.

[7] G. A. Farrall, “Low voltage firing characteristics of a triggered vacuumgap,” IEEE Trans. Electron Devices, vol. ED-13, no. 4, pp. 432–438,Apr. 1966.

[8] S. Kamakshaiah and R. S. N. Rau, “Delay characteristics of a simpletriggered vacuum gap,” J. Phys. D, Appl. Phys., vol. 8, no. 12, pp. 1426–1429, Aug. 1975.

[9] G. R. Govinda Raju, R. Hackam, and F. A. Benson, “Breakdown mecha-nisms and electrical properties of triggered vacuum gaps,” J. Appl. Phys.,vol. 47, no. 4, pp. 1310–1317, Apr. 1976.

[10] R. L. Boxman, “Triggered mechanisms in triggered vacuum gaps,” IEEETrans. Electron Devices, vol. ED-24, no. 2, pp. 122–128, Feb. 1977.

[11] V. A. Sidorov and V. A. Vozdvijenskii, “Trigger gap configuration effecton triggered vacuum switch initiation characteristics,” in Proc. XVth Int.Symp. Dielectr. and Elect. Insul. Vacuum, 1992, pp. 513–517.

[12] F. T. Warren, J. M. Wilson, J .E. Thompson, and R. L. Boxman, “Vacuumswitch trigger delay characteristics,” IEEE Trans. Plasma Sci., vol. PS-10,no. 4, pp. 298–301, Dec. 1982.

[13] V. A. Vozdvijensky and V. A. Sidorov, “Initial stage of discharge currentgrowth in a triggered vacuum switch,” IEEE Trans. Plasma Sci., vol. 19,no. 5, pp. 778–781, 1991.

[14] R. V. Latham, High Voltage Vacuum Insulation: The Physical Basis.New York: Academic, 1981.

[15] H. Toya, T. Hayashi et al., “Statistical analysis of breakdown prop-erty between electrode and shield in high voltage vacuum interrupters,”etz Archiv, vol. 7, no. 11, pp. 363–369, 1985.

Liao Min-fu was born in Hunan, China, on Septem-ber 15, 1975. He received the B.S. and M.S. degreesfrom Huazhong University of Science and Technol-ogy, Wuhan, China, in 1996 and 1999, respectively.He received the Ph.D. degree from Dalian Universityof Technology, Dalian, China, in 1999.

He is presently an Associate Professor at DalianUniversity of Science and Technology, and is en-gaged in the study of vacuum circuit breakers withmultibreaks and triggered vacuum switch.

896 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 35, NO. 4, AUGUST 2007

Duan Xiong-ying was born in Hubei, China, onJanuary 7, 1974. She received the B.S. and Ph.D. de-grees in electrical power engineering from HuazhongUniversity of Science and Technology, Wuhan,China, in 1996 and 2001, respectively.

She is currently an Assistant Professor at DalianUniversity of Technology, Dalian, China. Her cur-rent research activities are concentrated on intelli-gent switching apparatus and electrical measurementtechnology.

Zou Ji-yan was born in Liaoning, China, in 1954. Hereceived the Ph.D. degree in electrical engineeringfrom Xi’an Jiaotong University, Xi’an, China.

He is currently a Professor at Dalian University ofTechnology, Dalian, China. He has been engaged inthe study of vacuum circuit breakers.