XXVth Int. Symp. on Discharges and Electrical Insulation in Vacuum - Tomsk – 2012

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Triggering Characteristic of TVS and Its Application Research in Synthetic Making Test

for High Voltage Circuit-breakers Zhang Xin1, Fan Xing-ming1,2,Huang Zhi-chao1,Zou Qi-tao2, Liang Cong3, Shi Wei-jian2

1Dept. of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin, China 2SUNRISE GROUP , 315700 , Zhejiang , China

3Guilin Power Capacitor Co.,Ltd，541004，Guilin，China

Abstract- Triggered vacuum switches (TVS), have found fast growing applications in the field of power system and pulse power. The key to perform synthetic making test at full rated voltage for high voltage switches is the making device of current source, so the chief aim of this research is to investigate the triggering feature of TVS, a series experiments have been carried out on the sample TVS especially with AC load between the main electrodes. The triggering and delay characteristics were emphatically expounded. An elaborated circuit for controlling the TVS is proposed herein. The triggering energy of the controller can be adjusted conveniently. By means of changing the triggering energy, the experimental results show that the delay and jitter times decrease with increasing trigger energy. The delay and jitter times decreases magnificently with the increasing voltage in the main gap. By increasing the main-gap voltage, the triggered probability increases. At last, theoretically and experimental research has been carried out of TVS used for high voltage circuit breakers synthetic making test equipment. The analyzing and test results are presented also, and which indicate TVS was suitable for high voltage circuit breakers synthetic making test.

I. INTRODUCTION

During synthetic making test a high speed making device is necessary to connect the switching device under test immediately after pre-strike during closing operation under applied voltage. A closing switch is the necessary controlling device of power supply of synthetic making test of high-voltage circuit breakers for short-circuit current introduce, which should have the ability to quick connect the circuit and precisely controlling the moment of connection. It also should isolate the high power storage, and then close the circuit at a set time.

A new kind of fast making device is emphatically expounded in this research, which is composed of triggered vacuum switch (TVS) and a fast vacuum circuit breaker (FVCB) with permanent magnetic actuator. Parallel-connected TVS and FVCB make up the basic optic-controlled module. And basic modules arranging in series can be increase the hold-off

(withstand) voltage. When the closing command is triggered, TVS acts in several microseconds and carries the high making current first. FVCB acts as the parallel protecting device for TVS, its closing command is sent simultaneously with TVS'. Once FVCB closed the making current will shift to this branch, the erosion in TVS can be remarkably decreased[1].

II. SYNTHE MAKING TEST CIRCUIT SETUP AND

CURRENT SOURCE INTRODUCE SWITCH (TVS)

Compared with high power laboratories abroad, high voltage test level in China is to be improved. In order to meet the development requirements of modern circuit breakers and to better simulate the network, testing capabilities have to be expanded. According to the existing equipment and testing conditions of main domestic test house, a new testing circuit for synthetic making test of high voltage circuit breakers is proposed. During synthetic making test a high speed launching device is necessary, which connect the switchgear under test to current source immediately after pre-strike during closing operation[2,3].

High-voltage circuit breakers are the main control and protective devices in electrical transmission network. They must switch and clear the circuit reliably. The testing of high voltage circuit breakers is done in the high-power laboratory, where the test conditions prescribed by IEC, ANSI and national standards[4,5]. With the development of power system, to test these equipments, direct testing, using power system or short-circuit generator, is no longer feasible and economical. This means that synthetic tests become virtually important, which now no longer considered as an alternative to direct tests but as equivalent to them.

Synthetic making test circuit scheme introduced in [6] is shown in Fig.1, Fig1(a) and Fig1(b) illustrate the applied voltage using a parallel and series arrangement of current and voltage sources respectively.

The schematic diagram of synthetic making test adopted in this research is presented in Fig.2, one circuit supplying the full rated voltage to initiate pre-strike and

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another circuit to supply the short circuit current (at reduced voltage) succeeding the pre-strike. In Fig. 2 uc and uv is the current and voltage source respectively. QFt is the switching device under test. SW the fast making device, which is makes up of TVS and FVCB, according to the making current and applied voltage in test the basic optic-controlled module can be arranged in parallel and series to form the fast making device.

QFtGc Gv

Lc

CgRr

Cr

Rv Lv

Lo Co

X

Y

X

Y

SW

Fig. 1(a) Parallel type arrangement of current and voltage sources

QFt

Gc Gv

Lc

CgRr

Cr

Rv Lv

Lo Co

Y Y

SW

X X

Fig. 1(b) Series type arrangement of current and voltage sources

Fig. 1. Experiment circuit setup schemes of synthetic making test for high-voltage circuit breakers

Switching on short-circuit current leads to pre-arcing in the switching device. Pre-arcing affects the capability of switchgear to close and latch. When the switchgear closing, the gap between electrodes will break down and current will be initiated when the dielectric withstand of the gap less than the applied voltage. During synthetic making test a high speed making device is necessary to connect the switching device under test immediately after pre-strike during closing operation under applied voltage. The making device must be designed such that it can withstand the static and transient voltage and can conduct short-circuit current without excessive erosion. Moreover it ought to be hair-triggered and control accurately.

C0

R0

T1

QFt

QFa

DSPController

PhaseDetection

Lc LvSW

Rogowski Coil

i i'1

2 3

uc

T2

uv

Rv Gap

C

Y

X

Y

X

Fig. 2. Schematic diagram of synthetic making test

The constitute of current source introduce switch (A new type fast making device), two basic

optic-controlled module connected in series is shown in Fig.3. Once pre-strike occurs in QFt, the closing command of TVS and FVCB is sent simultaneously. TVS connects QFt to current source rapidly and accurately. FVCB turns on subsequently to protect and reduce the wear of TVS[7,8].

TVSTVS

FVCB FVCB Fig. 3 The constitute of current source introduce switch (A new type

fast making device)

III. THE TRIGGERING CHARACTERISTIC RESEARCH

OF TVS

Triggered vacuum switches (TVS), is also named triggered vacuum gap (TVG), have found fast growing applications in the field of power system and pulse power. A closing switch is the necessary controlling device of power supply of an ElectroMagnetic Launcher (EML) system and synthetic making test of high-voltage circuit breakers for short-circuit current introduce, which should have the ability to quick connect the circuit and precisely control the moment of connection. It also should isolate the high power storage, then close the circuit at a set time[9-12].

In our research, a series experiments have been carried out on the sample TVS with DC and AC load between the main electrodes. The triggering and delay characteristics of TVS were emphatically expounded in AC case. An elaborated circuit for controlling the TVS is proposed herein. The triggering energy of the controller can be adjusted conveniently. By means of changing the triggering energy, the experimental results show that the delay and jitter times decrease with increasing triggering energy. The delay and jitter times decreases magnificently with the increasing voltage in the main gap. By increasing the main-gap voltage, the triggered probability increases. With the same DC and AC amplitude, the DC case has better performance in triggering and delay characteristics than AC one. With enough triggering energy, it is possible to fire the TVS in AC load condition.

A. Sample Triggered Vacuum Switch

The typical structure and practical photo of TVS as shown in Fig.4.The electrode material is copper–chromium alloy (50%wt). The trigger pin is made out of molybdenum and with coat of hydride titanium. Under normal conditions TVS is at OFF state, which implies an insulating gap between the main electrodes. When TVS is triggered, a high voltage pulse is applied to a trigger pin that is attached to one of the main electrodes. This pulse causes dielectric breakdown between the main electrodes, and subsequently forms

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arc plasma there. The arc plasma propagates quickly from one main electrode to another main electrode as a result of the so-called vacuum diffusion in the applied electric field and finally establishes arc plasma between the two main electrodes. At this stage the TVS is regarded to be at its ON state. For an alternating current, the arc will extinguish at a current zero and a TVS can thus turn off automatically[1].

Fig. 4. The structure and photo of Triggered Vacuum Switch

B. Triggering Test of TVS under AC condition

The triggering circuit for TVS used in this research is provided in Fig.5. The upper part of Fig.5 is the typical trigger circuit set used in other research[3].According the function of the electrical arrangement, the upper part trigger circuit can be mark off two section. One section is called high power pulse generating circuit, which include the components as follow, current limiting resistance R01, charge diode D01, energy storage capacitance C01, SCR and high power pulse transformer T. The other section of the upper part is called low voltage and current sustaining circuit, which include the following components, current sustaining Dc1, Rc1 and Cc1 constitutes the low voltage and current sustaining branch. The function of Rx1 and Dx1 is to charge Cc1.

R01 D01

C01

SCR

D02

Rc1

Cc1

Rx1Dx1

Dc1

D11

Rc2

Cc2

Rx2Dx2

Dc2

R11

C

GAP TVS

AC220V

T01

AC220V

AC220V

T11

AC220V

T

Fig. 5. The triggering circuit setup of Triggered Vacuum Switch

The working process of upper part in Fig.5 is discussed as follow. When the trigger command of TVS is sent, the SCR will action and induce capacitance C01 to discharge. So an induced high power pulse will ignite the trigger gap of the TVS. If the trigger pulse strong enough, the low voltage and current sustaining circuit will work. The Cc1 discharges through its conducting channel and a high-current pulse will be generated.

From above illumination, we know the upper

circuit of Fig.5 can trigger TVS independently. In order to decrease the trigger time delay and its scatter and improve the triggering characteristic of TVS further, a steepened high-voltage trigger pulse generating circuit is introduced as the lower part of Fig.5. The working principle of this segment is similar with the upper one, which add a spark gap GAP. When the spark gap GAP fired, the charged high power capacitor C could discharge directly and rapidly breakdown between the main electrodes of TVS will be resulted. In this way, a high reliability of trigger will be achieved.

The controller of the test system adopt TMS320F2812 as the CPU, which fulfill tasks such as phase detect of applied voltage, signal analysis, triggering command control etc. Synchronous switch technology is imported to control the triggering phase. In fig.6 the waveform of typical phase detection and triggering control is provided, in which the triggering point of TVS is at the positive crest of applied AC voltage. Where CH1 stands for the triggering command from DSP 2812, and CH2 denotes the AC voltage load between the main electrodes of TVS. The controller detects the phase of the voltage across the main electrodes in real-time. When the zero of the reference voltage was detected, after a set time delay the DSP send the triggering command and control TVS act at expectant phase.

Fig. 6. Waveform of positive crest trigger of applied AC voltage

C. Typical Triggering Pulse for TVS

The typical pulse waveform generated by the upper and lower part of Fig.5 are given in Fig.7. The oscillogram shown in Fig.7(a) is the no-load triggering pulse generated by the upper and lower part of triggering circuit respectively of Fig.5. When applied these pulses between the cathode and triggered pin of TVS, the measured waveform are provided in Fig.7(b) for the upper and lower part.

Fig. 7(a)

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Fig. 7(b) Fig. 7. Waveform of triggering pulse

D. Triggering Result at applied AC voltage crest

Fig.8 present the test result of TVS triggered at the crest of applied voltage. In the left waveform of fig.7, the peak value of applied AC voltage is 5kV, and in the right waveform of fig.8 the peak value of applied AC voltage is 8kV. As we can see from Fig.8, the triggering characteristics of TVS are affected in a certain extent by the voltage between the main electrodes under AC load. The triggered extent is much larger in the right waveform than in left one.

Fig. 8. Triggering extent compare between 5kV and 8kV for peak value of applied AC voltage

IV. CONCLUSION

The launching device of current source, which based on triggered vacuum switch (TVS) andfast vacuum circuit breaker (FVCB) to form the basic unit, and synthetic making test circuit at full rated voltage are introduced in our research.Delay characteristics of TVS’s were experimentally verified in the cathode mode(firing on the cathode) of operation. A refined triggering and control system for TVS has proposed herein. The triggered power of the controller can be adjusted conveniently by changing the capacity of power storage capacitor and the charge voltage on it. With the increasing of the triggering energy, the delay and jitter times of TVS drastically decreased.

ACKNOWLEDGMENT

This work was supported by the National Natural Science Foundation of China under Grant 51067002, and by the scientific research projects of Guangxi Education Department of China under Grants

201010LX105, 201106LX157 and 201106LX218,and by 2011 Guangxi billion dollar industry of major scientific and technological projects under Grants 11107014-9, and supported by Program for Excellent Talents in Guangxi Higher Education Institutions.

REFERENCES

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[2] Fan Xing-ming; Zhang Xin; Zou Ji-yan. Experimental investigations on the triggering characteristic of triggered vacuum switch under DC and AC load[]. 23rd International Symposium on Discharges and Electrical Insulation in Vacuum,2008, Page(s): 215 – 218.

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E-mail of the author(s): fanxm_627@163.com Fan xing-ming was born in Inner-Mongolia province, China, on 31 July 1978. He received the B.S degree (2001) from Inner-Mongolia University. He received the M.S. (2003) and Ph.D. degree (2007) from Dalian University of Technology. He is presently an associate professor in Guilin University of Electronic Technology. He currently engaged in intelligent apparatus, electrical measurement and high-voltage technology. Zhang xin was born in Inner-Mongolia province, China, in 1976. She received the B.S degree from Inner-Mongolia Normal University. She is presently an instructor in Guilin University of Electronic Technology.