ever, spark gaps have a long deionization time and high ... use of a fast protective device based on triggered vac ... Based on a Triggered Vacuum Spark Gap.
ISSN 00204412, Instruments and Experimental Techniques, 2011, Vol. 54, No. 1, pp. 65–69. © Pleiades Publishing, Ltd., 2011. Original Russian Text © D.F. Alferov, D.V. Evsin, V.P. Ivanov, V.A. Sidorov, 2011, published in Pribory i Tekhnika Eksperimenta, 2011, No. 1, pp. 72–76.
ELECTRONICS AND RADIO ENGINEERING
A Device for Protection against Pulse Overvoltages Based on a Triggered Vacuum Spark Gap D. F. Alferov, D. V. Evsin, V. P. Ivanov, and V. A. Sidorov AllRussia Lenin Electrotechnical Institute, Krasnokazarmennaya ul. 12, Moscow, 111250 Russia Received July 2, 2010; in final form, August 26, 2010
Abstract—The scheme of an automatic protection device on the basis of a controlled vacuum spark gap with an operation time of 100 μs). This circumstance limits the service life of SGs and delays the time of switching an object to a source after the emergency regime is completed. A significant spread of breakdown voltages of SGs and comparatively high values of the residual voltage are a disadvantage of such devices. In recent years, along with protective spark gaps, overvoltage limiters (OVLs) without SGs have found ever widening applications. As an active element, new materials based on zinc oxide and having nonlinear current–voltage characteristics (CVCs) are used in them. Stabilitrons, stabistors, and limiting diodes, which are used to limit voltages in continuous and pulsed modes, have highly nonlinear CVCs. However, to limit overvoltages with large ampli tudes of an accompanying longduration current, one has to assemble a large number of individual elements connected in series and parallel, thus leading to an increase in the leakage current, a more complex design, large dimensions, and, consequently, a high cost of the OVLbased protective device. 65
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ALFEROV et al. U/Umin tr TVG
R
1.5 Upr 1.0
R1
Umin tr
0.5 Imin tr
1 Fig. 1. Schematic diagram of the protective device.
Currently, the production of TVGs of several types has been mastered, which were developed at the All Russia Electrotechnical Institute and designed for switching highpower capacitive energy storages in electrophysical plants and application in electricdis charge and magneticpulse technologies [2, 3]. A mul tiyear experiment of TVG operation has shown that they are capable of operating in wide ranges of pulse voltages (1–50 kV) and currents (0.1–300 kA). The voltage drop across an enabled TVG is 50–100 V, thus allowing a substantial decrease in the dissipated energy level in the TVG upon switching of high currents. A device based on a combination of a TVG and an OVL was proposed in [4]. The device contains a TVG connected in series to the damping resistor. The damping resistor consists of a nonlinear resistor (OVL) and a linear resistor connected in parallel. The TVG is switched on using a triggering unit, which, after apply ing a control pulse, feeds an igniting pulse with speci fied voltage and current parameters to the control electrode. Such a device can limit overvoltages with large amplitudes of a longduration accompanying current. The OVL protection level can be chosen equal to a value close to the nominal mains voltage. As a result, the energy dissipated in the OVL during the dis chargecurrent flow is significantly lower than in a cir cuit of its connection without a TVG. The parallel connection of the nonlinear and linear resistors also allows a decrease in the energy released in the nonlin ear resistor. However, the presence of the triggering unit in such a device limits the minimal time of its operation to a level of 10–15 μs. In addition, time is required for detecting the appearance of an overvolt age and forming a control pulse fed to the triggering unit. In this study, we propose a circuit of a device for automatic protection based on a TVG with an opera tion time 10 kV/μs of an acting volt age pulse may considerably exceed the statistical limi tation level.
U, V 1
30
When the circuit R1–R was disconnected from the TVG, we measured the voltage drop U R1 across the resistor R1 at its different values—7, 20, 40, and 76 Ω. Figure 5 shows the obtained dependence of U R1 on R1 and the voltage drop UR across the OVL as a function of R1. According to Fig. 5, the voltage drop across R1 for all R1 > 7 Ω is >5 kV, which is sufficient for breaking down the TVG triggering unit. The voltage drop across the OVL decreases, as R1 increases to Ulim ≈ 17 kV.
20 10 0 –10
2
0
5
10
15 t, μs
Fig. 6. Oscillograms of acting 1 and limited 2 voltage pulses.
3.1. Startup Characteristics of the Protective Device The limitation level of the protective device is determined by the OVL type and its frequency charac teristics. Figure 4 shows the timedependent change in the voltage across the OVL, to which a voltage pulse with an amplitude U0 = 30 kV and a voltage rise rate dU/dt ≈ 135 kV/μs is applied. The measurements were performed at R1 = 0 in the absence of a contact with the TVG control electrode. As is seen, a voltage surge limited at a level of 25 kV is observed at the pulse lead ing edge for 3.8 μs. Then, the voltage settles at a statis tical limitation level determined by the OVL type. Thus, the OVL limitation voltage Ulim (and, conse quently, the protectivedevice voltage) at steep leading U, kV
I, kA
4
400
Subsequently, the startup characteristics of the protective device were studied with the connected TVG control electrode at R1 = 20 Ω. Figure 6 shows typical oscillograms of the acting 1 and limited 2 volt age pulses. The switchingon time tsw = 180–210 ns of the pro tective device relative to the voltagepulse onset was determined by the breakdown moment of the TVG triggering unit. This unit was broken down when a voltage U R1 ≥ Uc.min = 5 kV was reached. After the breakdown of the triggering unit, an initiating dis charge was generated in the interelectrode gap of the TVG. The current Ic of this discharge with an ampli tude of ~1 kA was virtually independent of the resis tance R1. The current flow duration Δτ ≈ 0.5 μs of the initiating discharge was limited by the switchingon time (the time of filling the interelectrode gap with plasma of the initiating discharge) of the TVG, which shunted the OVL. U, kV
I, kA
20
20
U 3
300
15
2
200
10
1
100
5
0
0
0
15
I
U
10
I
0 0
0
200
400 600 t, μs
800
1000
5
Δt 4
8 t, ms
12
16
Fig. 7. Oscillograms of the current in and voltage across the protective device at a charging voltage U C = 2.8 kV and
Fig. 8. Oscillograms of the current in and voltage across the protective device at a charging voltage U C = 2.8 kV and
L0 ≈ 2 μH (first mode).
L0 = 178 μH (second mode).
0
0
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A DEVICE FOR PROTECTION AGAINST PULSE OVERVOLTAGES
3.2. Switching Characteristics of the Protective Device The switching characteristics of the protective device were measured in two modes, the highcurrent section of the test bench being enabled (Fig. 3): in the first mode, L0 ≈ 2 μH (inductance of the discharge cir cuit at the shortcircuited reactor); in the second mode, L0 = 178 μH. Figures 7 and 8 show oscillograms of the current I in and voltage U across the protective device at a charging voltage U C0 = 2.8 kV across the capacitance С0 for the first and second modes, respectively. It fol lows from the oscillograms that the protective device is capable of passing currents with an amplitude of ~300 kA and a duration of 1 ms and currents with amplitudes of tens of kiloamperes and durations Δt > 10 ms (at a current pulse halfheight). During switch ing of a short (long) current pulse, the voltage drop across the device was no higher than 300 V (60 V). 4. CONCLUSIONS The studies performed have experimentally con firmed the correctness of the engineering solutions
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and the serviceability of the TVGbased highspeed protective device against pulsed overvoltages. It is rea sonable to use such a device in networks with a long duration largeamplitude accompanying current. The limitation level of such a device is determined by the limitation voltage of the nonlinear resistor used. ACKNOWLEDGMENTS This study was supported by the Russian Founda tion for Basic Research, project no. 090800368a. REFERENCES 1. Chunikhin, A.A. and Zhavoronkov, M.A., Apparaty vysokogo napryazheniya (HighVoltage Devices), Mos cow: Energoatomizdat, 1985. 2. Alferov, D.F., Ivanov, V.P., and Sidorov, V.A., Elektro, 2002, no. 2, p. 31. 3. Alferov, D.F., Matveev, N.V., Sidorov, V.A., and Kha barov, D.A., Prib. Tekh. Eksp., 2004, no. 3, p. 94 [Instr. Eksp. Tech. (Engl. Transl.), 2004, no. 3, p. 360]. 4. Alferov, D.F., Belkin, G.S., Ivakin, V.N., et al., Elek trotekhnika, 2006, no. 9, p. 21.
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