VOLTAGE STABILIZER FOR ELECTRIFIED MINE TRANSPORT

V. N. MISHIN, V. P. LAYER, V. N. IVCHENKO, A. N. GOLOVACHEV

(Presented by the Scientific and Technical Seminar of the Scientific Research Institute of AEM)

In accordance with the requirements of the mining industry, contact and battery-operated mine direct-current electric locomotives must be equipped with stabilized power supplies for lighting and signaling devices. This requirement has been put forward because of significant changes in the voltage of the supply contact network or of the battery power source. According to operating data, the voltage variation of the contact-network power source is within the range \((0.7—1.3)\,U_{\text{nom}}\). In individual cases it may drop to \(0.5\,U_{\text{nom}}\).

On the one hand, this leads to premature burnout of incandescent lamps, and on the other—to a reduction in illumination of the rail tracks, which is inadmissible under safety regulations.

At the Scientific Research Institute of AEM, together with the Kharkov plant “Elektromashina,” a design has been developed for the SN-II pulsed thyristor voltage stabilizer, brief technical data for which are given in Table 1, and the schematic diagram in Fig. 1.

Table 1

The stabilizer circuit in Fig. 1 may be divided into the following functional units:

1. A thyristor switch \((D_7)\) with an artificial commutation unit \((C_4, D_{18}, L_1, L_3)\).

2. A control circuit implemented on triodes PT1÷PT3, representing a controlled blocking oscillator serving to form control pulses for the thyristor switch.

3. A smoothing filter—an \(LC\)-filter with a feedback diode \((L_2, C_6, D_{11})\).

4. Protection against overvoltages at the load \((D_{16}, D_{17})\).

The operation of the power circuit of the stabilizer is described in detail in the literature, for example in [1]. The control circuit consists of a blocking oscillator with a common emitter, comprising transistor PT3, transformer TR, and capacitor in the base circuit \(C_3\), the controlling transistor PT1, and the minimum-voltage blocking transistor PT2.

The controlling transistor PT1 performs the role of a comparison element, to whose input feedback voltages are applied:

1) by voltage at the converter output—the voltage divider \(R_{18}, R_{19}, R_{20}\), Zener diodes \(D_{12}, D_{13}\), and temperature-compensating diodes \(D_{14}, D_{15}\);

2) by current (current cutoff)—diode \(D_5\) and resistors \(R_7, R_{14}, R_{15}\);

3) monitoring of the charge of the commutating capacitor—Zener diode \(D_4\) and resistor \(R_6\).

The stabilizer can be started when the voltage of the supply network is above the setting of the minimum-voltage blocking unit, made on resistors \(R_1 \div R_4\), reference Zener diode \(D_2\), and transistor PT2, connected in a common-collector circuit, whose emitter–collector junction shunts the input of transistor PT3 of the blocking oscillator.

Fig. 2

The use of minimum-voltage blocking makes it possible to reduce the magnitude of the commutating capacitance.

Let us consider separately the influence of the feedbacks on the operation of the stabilizer.

Voltage feedback at the output of the stabilizer ensures that the voltage at the load is kept constant; this is achieved by shunting capacitor \(C_3\) by the controlling transistor PT1 when a positive mismatch signal is applied to its base, thereby delaying the application of control pulses to thyristor \(D_7\).

The use of feedback that monitors the charge of the commutating capacitor after commutation of the thyristor makes it possible, as a function of its signal, to inhibit the triggering of the control-pulse generator until the commutating capacitance is charged, and thus to eliminate failure of the subsequent commutation, i.e., overturning of the breaker.

Fig. 3

In connection with starting the stabilizer with “cold” filament-lamp strings when the filter capacitance \(C_6\) is uncharged, and also in order to limit short-circuit currents in the load circuit, a current cutoff is provided, which limits the current at the moment of circuit startup to

\[ I = 1.2 I_{\text{nom}}, \]

by reducing the pulse repetition frequency.

Stabilization of the voltage at the converter output under variations in the supply-network voltage and load current is also achieved by changing the repetition frequency of the pulses that switch on the thyristor, i.e., the method of frequency-pulse modulation is used.

The stabilizer provides protection against overvoltages in the load circuit, implemented with thyristor \(D_{17}\) and Zener diode \(D_{16}\), which shunts, through thyristor \(D_{17}\) and the inductance (low-resistance element) \(L_4\), the load circuit at voltages above \(1.5 U_{\text{nom}}\). This either causes the automatic circuit breaker AB to operate or switches the converter to current-cutoff operation with the load current limited to the value set by the current cutoff.

The results of testing the stabilizer are presented by the external characteristics in Fig. 2, the regulating characteristics in Fig. 3, and the change in efficiency in Fig. 4 at instability of the supply-network voltage \((0.7 \div 1.3)E_{\text{nom}}\) and load current \((0.1 \div 1)I_{\text{nom}}\).

Fig. 4

An experimental industrial prototype of the SN-II stabilizer, manufactured in accordance with [2] at the Kharkov “Elektromashina” plant, successfully passed industrial tests at the “40 Years of October” mine of the Kizelugol trust and was put into serial production by the plant. Reliability calculations showed the probability of failure-free operation of the stabilizer to be

\[ P(720\ \text{hours}) = 0.97. \]

Conclusions

1. Simplicity and high reliability make it possible to use the SN-II stabilizer as a power supply for DC devices operating in systems powered from networks with considerable voltage instability.

2. According to the results of the patent examination [3], the developed design can be exported to foreign countries.

LITERATURE

1. V. P. Laier, V. N. Mishin, Yu. P. Serdyukov. Analysis of the operation of a stabilized thyristor pulse converter with a linear commutating inductance. Proceedings of the VII Scientific and Technical Conference. Tomsk, 1971.

1. A. I. Zaitsev, V. N. Mishin, V. P. Laier et al. DC voltage converter-stabilizer. Positive decision of VNII GPE, No. 1494927/24—7 of June 7, 1971.

2. V. N. Mishin, V. P. Laier. Development of voltage stabilizers for mine electric locomotives. Technical report on topic No. 12/70—AEM, inf. No. 70058513, 1971.