SU1582271A1 - Device for protection of electric installation with inductance from turn-to-turn short circuits - Google Patents

Abstract

The invention relates to the protection of induction heating systems operating at industrial frequency currents and intended for the heat treatment of reinforced concrete and concrete products, as well as drying installations. The aim of the invention is to increase the selectivity in accordance with the process conditions. The goal is achieved in that the device contains chains 1 for selecting current signals at each phase with inverting amplifiers 6 and chains 7 for selecting voltage signals, an organ of comparison 9 for phase current and voltage signals, consisting of adders 10, controlled current sources 11 and the threshold element 12. The controlled current source 11 carries an amplified signal to the threshold element 12 and serves to set the trigger level of the threshold element 12 consisting of three emitter repeater, specified for this heating installation. Installed on each phase, and the logical element 2I-NOT. If there is a short circuit between the turns of the induction heating system, then the phase shift between the current and voltage signals will change. This change will entail a change in the duty cycle of rectangular pulses at the outputs of the adders 10. Then the voltage levels at the inputs of the emitter followers will be below the threshold, and the input of the logic element will be low, corresponding to the logical "0", and at its output - logical "1". Therefore, the signal corresponding to the logical "1", will go to the executive body 18 on the transistor switch 19. 2 Cp f-ly, 3, il.

Description

The invention relates to protection | Electrical installations with inductance operating at industrial currents, frequency, against interturn short circuits in | windings, are intended to prevent damage to expensive building structures and inductors (electromagnetic installations for the heat treatment of concrete products) and can be used in electrical installations -, magnetic installations, intended for the drying of building products, wood, etc., as well as for the protection of reactors.

The purpose of the invention is to increase the selectivity of protection of an induction heating plant in accordance with the requirements of the technological process.

FIG. 1 shows a functional diagram of the device; in fig. 2 is an electrical circuit of a controlled current source and threshold organ; in fig. 3 timing diagrams illustrating the operation of the device in normal mode and short-circuit mode.

The proposed device for protection of an induction heating unit against inter-turn short-circuits contains chains of current signals (i) 1 on each phase, included in the circuits of ammeters 2 of inductor 3. Current is fed to ammeters from current transformers k. Inductor 3 is connected to an ABC line circuit. The current selection circuit 1 includes shapers of rectangular pulses 5 made of two diodes connected in parallel (not shown). Inverting amplifier 6 serves to amplify the current signal to match the voltage signal and invert it by 180, which prepares the signal for processing in the adder with a small error. The voltage selection circuit (s) 7 is directly connected to the linear wires ABC and also contains the simplest square formers of the pulse 8. The phase comparison of the current and voltage signals 9 consists of adders 10, controlled current sources 11 and a threshold element 12. The outputs of the square pulse formers 8 and the inverting amplifiers 6 are connected to the inputs of the adders 10, which are part of the current phase and voltage comparison unit 9, in which the logical signals of the current and phase phases are combined. Yield direct voltage adders 10 are connected to inputs of controlled current source 11, which with a threshold body 12 also within the body composition for comparing current signals and voltage phase 9.

The controlled current source 11 (Figo 2) provides an amplified signal to the threshold organ 12. To set the threshold element level specified for a given induction heating device, a variable resistor 13 is used to amplify and correct the signal — the emitter follower on the base of transistor 1, and to maintain a constant signal level — a capacitor 15.

The threshold element 12 (Fig. 2) consists of three emitter repeaters on transistors 16 mounted on each phase and one logical element 2I-NOT 17. Executive body 18 contains a transistor switch 19 whose input is connected to the output of the logic element 17 of the threshold element 12. The transistor switch 19 controls the relay 20 through the amplifier 20. Conclusions

the power supply of the controlled power sources is connected to the corresponding terminals 22 and 23 of the power source.

The device works as follows.

The device is prepared for operation in relation to this induction heating installation. For this, the variable resistor 13 sets the required threshold for operation. In normal operation of the induction heating installation (Fig. 3), the current and voltage are sinusoidal, and the angle between current and voltage is equal to nominal. The signals characterizing the phase of the current and voltage pass through the pulse shaper 5, where pulses form that are close in shape to rectangular. The current phase signals pass through inverting amplifiers 6, which invert the signal by 18 (J °). The resulting sequences of square pulses, corresponding to the current and voltage phase signals, are fed to the current adders 10 of the current phase and voltage signals 9, where there is a logical addition of the signals characterizing the phases of the current and voltage, after which the signals from each phase are fed to the controlled current sources 11. With the help of capacitors 15, constant levels are maintained at the inputs of the emitte transistors 16 Since in a normal mode of operation of an induction heating installation, the duty cycle of a sequence of rectangular pulses at the outputs of the adders 10, depending on the phase shift of the current and voltage, is equal to the nominal, the voltage level at the inputs of the emitter followers 16 is higher than the threshold, and at the input of the logic element 17 there is a high level corresponding to logical 1, and at the output of it is logical O, therefore the signal to the executive body 18 is not received and it does not work.

If there is a short circuit between the turns of the induction heating unit, then the phase shift between the current and voltage signals is measured

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no with . This change entails a change in the duty cycle of rectangular pulses at the outputs of the adders 10. Then the voltage levels at the inputs of the emitter followers 16 are below the threshold, and at the output of the logic element 17 a low level corresponding to the logic O, and

the output is logic 1. Therefore, the signal corresponding to logic 1 is fed to the actuator 18 by the transistor switch 19, then through the amplifier 20 to the relay 21 and turns off the installation.

The technical and economic advantages of the proposed device in comparison with the known ones consist in a large selective protection ability, which responds only to a short circuit of coils and does not react to various load changes that may occur both during the technological process and in case of its violation and negligence. . This protects the heating installation from fires and, therefore, eliminates the cost of refurbishment work.

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Claims (3)

1. Device for protection of an electrical installation with inductance against inter-turn short-circuits, containing current sensors for installation in corresponding phases of an electrical installation, formers of rectangular current pulses, formers of rectangular voltage pulses, threshold organ, actuator, characterized in that In order to increase the selectivity in accordance with the conditions of the technological process, inverting amplifiers were additionally introduced by the number of current sensors, the inputs of the mentioned amplifiers were the corresponding rectangular current pulse drivers are connected to the outputs of the respective current sensors, and the outputs of these amplifiers are connected to the first inputs of the newly introduced adders by the number of current sensors, the second inputs of these adders are connected to the terminals for connecting the supply mains through the corresponding rectangular voltage pulse drivers , the outputs of the adders through the newly I entered corresponding controlled current sources are connected to the corresponding inputs of the threshold organ, Exit which is connected to the input of the executive authority. 2. The device according to claim 1, wherein each controlled current source is made of a transistor, the emitter of which through a resistor is connected to the positive terminal of the power source, the collector is connected to a variable resistor, the free output of which is connected to the minus terminal The power supply terminal, the connection point of the resistor and the positive terminal of the power source is connected to the "first capacitor lead, the second terminal of which is connected to the collector of the transistor and is the output of a controlled current source, the input of which is the base of the transistor. 3. The device according to claim 1, characterized in that the threshold organ is made up of transistors according to the number of controlled current sources, the bases of which are the corresponding inputs of the threshold organ, the emitters are interconnected and connected to the input of logic element 2I-NOT, output which is the output of the threshold organ, and the collectors of all transistors are connected to the negative terminal of the power supply. to the executive body 12 Thebes. 2 I illl ii i l; in1 AND Th Inber. mop and , 2I-NOT and Time element ABOUT .W  L1 thresholds ..OOMRI Fig.Z t