RU2195732C2 - Augmented electromagnetic operating mechanism of switching device - Google Patents

Abstract

FIELD: electrical engineering; augmented operating mechanisms for switching devices. SUBSTANCE: augmented operating mechanism designed for switching devices incorporating vacuum arc-control chambers where high contact pressure is required has electromagnet coil, controlled electronic switch, timer with operating- mechanism end-position and/or time setting, periodic square pulse generator, two-position switch, and electromagnet coil shunting diode. EFFECT: reduced power requirement. 2 cl, 2 dwg

Description

 The invention relates to electrical engineering, in particular to forced electromagnetic drives, including switches or contactors with a large starting current and holding them in the on position with a small holding current. Forced drives have significantly smaller dimensions and weights than non-forced drives with the same static traction characteristics. The use of such drives for switching devices with vacuum interrupter chambers is especially effective because of the required large efforts to compress their contacts.

 The present invention allows the timer to open a controlled electronic key, for example, a transistor, through the on-off switch, thereby supplying voltage to the electromagnet coil, for the time the drive is turned on, set either by the timer setting or by the drive end element, after which the on-off mechanical or electronic switch connects the control electrode the specified key to the generator of rectangular pulses, thereby connecting the coil of the electromagnet periodically to the source Tanya, wherein the minimum frequency and duty cycle determined by the time constant of the electromagnet and current confinement.

 The device contains an electromagnet coil, a controlled electronic key, for example, in the form of a transistor, a timer with a setting for the end position of the drive and / or time, a rectangular pulse generator with pulse-width modulation, a two-position switch - electronic and / or mechanical - with kinematic connection with the drive shunting coil diode. Achievable technical result is to reduce the energy consumed by the drive from the power source, proportional to the fill factor of the control signals.

 A known method of controlling an electromagnetic drive (B.E. Kots. Forced DC electromagnets. M .: Energia, 1973, p. 9, Fig. 2, scheme 3), by which when a constant voltage is applied to a solenoid coil and the additional resistance is switched on, through a timer in the form of an RC circuit in the base circuit, a controlled electronic key in the form of a bipolar transistor, shunting this resistance. In this case, the entire voltage is applied to the coil for the time the drive is turned on, determined by the time constant of this RC circuit. After charging the capacitor and closing the transistor, the supply voltage is divided between the active resistance of the coil and the additional resistance, and the main part of the voltage is applied to the additional resistance, since the drive holding current, which is determined by the sum of the indicated resistances, is much less than the starting current, which is explained by the minimum gap in the magnetic circuit of the electromagnet in the on position.

 In addition to the indicated main drawback - unproductive consumption of electricity, the analogue has the disadvantage that the control signal will not be rectangular due to the exponential decrease in the base current after turning on the drive, therefore, it is necessary to use a more powerful transistor.

 The third drawback is the lack of an end element along the drive, which removes the trigger control signal. Hence the need for a large margin of the time interval due to the instability of the mechanical operation of the drive and, therefore, excessive power consumption when turned on.

 The drive shuts off when the supply voltage is removed.

 The closest in technical essence to the proposed are the control sequence of the device of the electromagnetic drive of the switching apparatus (RF patent 2074430, H 01 F 7/08, H 01 H 47/32, 1997). Here, as in the analogue, when the drive is turned on, The signal in the control electrode circuit of the transistor is the base circuit. The signal is taken when the end closing contact is triggered or according to the RC time setting when opening the threshold-key element, for example, a dynistor, shunting the base circuit of the transistor. The indicated elements can be considered as a timer. When the transistor is turned off, the inductive energy accumulated in the coil is absorbed by the active resistance of the coil through a diode shunting it. This circuit has advantages over its analogue - it gives a rectangular control pulse and reduces power consumption when it is turned on due to the shorter time for supplying a control signal removed by the end contact. When used in the circuit, instead of a non-linear, conventional resistor, designed for the holding current, it is similar to the previously considered circuit in terms of the control sequence.

 The proposed solution allows to eliminate the main disadvantage of the analogue and prototype - unproductive power consumption of the power source in the long-term on state of the switching device. To do this, in the method of controlling a forced electromagnetic drive, based on the supply of a control signal to a controlled electronic key, during the drive turn-on time, after removing this signal, a periodic pulse control signal with the repetition period and for the entire state of the switching device is turned on minimum duty cycle, determined by the time constant of the electromagnet and the holding current.

 In a device containing a serially connected controlled electronic key in the form of, for example, a transistor and an electromagnet coil with a diode shunting it, connected to a constant voltage source, to the positive pole of which a timer is connected, a two-position switch is added, the first input of which is connected to the timer output, the second the input is connected to a generator of periodic rectangular pulses connected to the specified voltage source, and the output of the switch is connected to the control he electrode of said key.

The essence of the proposed method is illustrated by timing diagrams in FIG. 1, where:
on figa presents a diagram of the control pulse of the timer;
on figb is a diagram of the control pulses of the generator;
in FIG. 1c is a diagram of currents in a drive coil.

 FIG. 1a and 1b correspond to the times of application of the supply voltage to the coil.

In FIG. 1 is indicated by:
U _p - applied to the coil voltage;
i is the current in the coil;
i _m is the steady-state current in the coil, limited by its active resistance;
i _y is a constant holding current;
Δi - current fluctuations in the coil in a long drive holding mode;
T is the period of succession;
t _and - the duration of the control pulses of the generator;
t _o is the beginning, t ₁ is the end of the control pulse of the timer;
t _oya - the moment of stop of the armature of the electromagnet.

Figure 2 presents the device in which the proposed method can be implemented, where it is indicated:
1 - coil of an electromagnet in the form of an active-inductive load;
2 - controlled electronic key in the form of, for example, a transistor;
3 - timer;
4 - a generator of rectangular pulses;
5 - diode;
6 - mechanical or electronic switch;
7, 8 - switch inputs;
9 - switch output;
10 - timer start contact.

 In the device, the coil 1 is connected in series with the collector of the transistor 2. The free output of the coil is connected to the positive pole of the power source, and the emitter of the transistor to the negative pole. Diode 5 shunts the coil. The output of the timer 3, powered by the same source, is connected to the first input 7 of the switch 6, the second input 8 of which is connected to the output of the square-wave generator 4 connected to the same power source; output 9 of the switch is connected to the base - the control electrode of the transistor. At the input, the timer has a contact 10.

 The device operates as follows. In the initial state, when the drive is disconnected, pin 10 is open and the voltage to the base of transistor 2 is not supplied, although switch 6 is closed to timer 3. The transistor is closed, and all the supply voltage is applied to it.

When a command is issued to turn on the drive — by closing contact 10 — the timer starts supplying voltage to the base of the transistor, which opens and is in saturation mode during the entire operation of the timer. In this case, almost the entire supply voltage is applied to the coil 1 (minus a small voltage drop across the transistor). This time corresponds to time t _o in the time diagrams of figure 1. Inrush current begins to flow through the coil (Fig. 1c), the armature of the electromagnet starts moving - the drive starts to turn on. At time t _{oy, the} armature of the electromagnet stops. Before this, switch 6 starts to switch. If it is mechanical, then the time of its switching can take several milliseconds and cause the current in the coil to rise to the moment t ₁ , which corresponds to disconnecting the transistor base from the timer. After this, the current in the coil begins to decrease with a large time constant, since the inductance of the switched on electromagnet is maximum and can range from fractions to units of Henry. The decay time of the current to the holding current can be tens of milliseconds. After switching the switch to the generator of 4 periodic rectangular pulses, the latter begin to supply power to the base of the transistor, opening it for a time t _and , making up a small fraction of the time period T of the pulses. These pulses correspond to the frequency of application of the supply voltage to the coil. Therefore, a periodic component will be superimposed on the decaying current, the value of which is much less than the amplitude of the inrush current. After some time, the process of changing the current in the coil becomes steady periodic. The current fluctuations Δi are determined by the frequency of the signals of the pulse generator and the time constant of the electromagnet: with increasing frequency and time constant, the current fluctuations decrease; the increase in frequency is limited by the losses during the switching of the transistor and in the magnetic circuit, and the increase in the time constant is associated with an increase in the consumption of active materials of the electromagnet, its dimensions and turn-on time.

The minimum value of the current in the coil should be higher than the constant holding current (dashed line in figv). In forced electromagnets, the holding current is one to two orders of magnitude less than the steady-state current i _m determined by the active resistance of the coil. This is due to the fact that the included electromagnet develops the greatest force with a minimum air gap in the magnetic circuit compared to the disconnected position with the maximum gap with a fixed magnetizing force. The current can increase to a maximum value if, instead of a mechanical switch, an electronic switch is used that switches from the time setting of the timer, which is selected with a margin to the temporary instability of the drive. On figa this corresponds to an increase in the interval t ₁ -t _oy .

The diagrams show that the average current in the holding mode is proportional to the average voltage on the coil (dotted line in figa), which is proportional to the duty cycle of the pulses Q = t _and / T. On figa the dot-and-dot line shows the voltage applied to the coil and the ballast resistance according to the schemes of the analogue and prototype. In this case, the dotted line corresponds to a constant voltage across the coil. It follows that the energy spent unproductively on heating the ballast in the drive holding mode is proportional to the difference between the supply voltage (dash-dot line) and the hold (dashed line). That is, the saving of energy consumed in the drive holding mode according to the proposed method and device compared with the analogue and prototype is inversely proportional to the fill factor of the control pulses.

In the analogue and prototype, the choice of ballast resistance should be made taking into account fluctuations in the supply voltage, which according to standards can drop to 0.6U _p . Accordingly, the set holding current and energy loss increase. In the present invention, it is sufficient to carry out a pulse-width-wave-pulse generator with pulse-width modulation, which, in the holding mode, maintains the average voltage on the coil unchanged regardless of the supply voltage of the drive. With a decrease in the supply voltage, the duty cycle of the pulses increases and Δi slightly increases. But the current fluctuations in the coil make up a few percent of the holding current with the right choice of the frequency of the generator pulses, taking into account the time constant of the drive electromagnet. Consequently, the increase in energy consumption will be negligible. It follows that when using pulse-width modulation of the generated control signals, maximum savings are obtained in the energy consumed by the drive in a long holding mode.

 As a timer, a prototype circuit can be used. In the simplest case, a timer can be a serial circuit of a make contact and a current-limiting resistor in the base circuit of the transistor using a mechanical limit switch kinematically connected to an electromagnetic drive.

 Instead of a bipolar transistor, a field effect can be used. Then the gate will correspond to the base, and the drain and the source will correspond to the collector and emitter.

 Thus, it is clear from the description that, from a technical point of view, the fundamental difference between the present invention and the analogue and prototype in the hold mode is the use of reactive - inductive current limitation instead of resistive, causing irreversible energy loss.

An example is a vacuum contactor for a rated current of 1500 A and a rated voltage of 10 kV with the parameters of an electromagnet:
U _p = 110 V; R _coils = 16 ohms; i _y = 0.1 A.

When using the prototype, taking into account the fluctuation of the supply voltage and the impact on the drive of external mechanical factors, the holding current was chosen 0.34 A, the ballast resistance r _b = 310 Ohm, the energy released for the ballast resistance of about 36 W, on the coil less than 2 W.

Using the invention:
T = 1.11 • 10 ^-3 ; Q = 0.02; the minimum average voltage on the coil in the holding mode is U _k = 2.24 V, with a margin taken U _k = 4 V, i _y = 0.25 A, the power allocated to the coil is about 1 W. When U _{p min} = 0,6U _{p nom} ; t _and = 37 • 10 ^-6 s.

 For high-speed circuit breakers, the energy savings of the drive will be several times greater.

Claims (2)

 1. A forced electromagnetic drive of the switching apparatus, comprising a serially connected controlled electronic key and an electromagnet coil with a diode shunting it, other terminals of which are connected to different poles of a constant voltage source, a timer connected to the positive pole of the specified voltage source, characterized in that it is additionally introduced two-position switch, the first input of which is connected to the output of the timer, the second input is connected to the output of the generator rectangular rectangular pulses connected to the specified voltage source, and the output of the switch is connected to the control electrode of the specified key.  2. The device according to claim 1, characterized in that the generator of periodic rectangular pulses is made with pulse-width modulation.

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