RU2633393C1 - Device to control and protectthree-phase load with possibility of non-contact control of phase skew - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: according to the invention, the device for controlling and protecting the three-phase load with the possibility of non-contact control of the phase skew comprises: an artificial neutral, a relay which contacts break the circuit for disconnecting load from network, a grounding, an additional inductance coil, a measuring device containing ferroprobe which contains an excitation winding, a measuring winding and a compensation winding, a rectangular pulse generator, a connecting capacitor, a registration unit with a measuring instrument and a compensator. The measuring device is made with possibility for checking the phase skew value based on constant magnetic field value of the additional inductance coil, and the relay and the additional inductance coil are connected in parallel to each other to the rectified voltage between the artificial neutral and the grounding.

EFFECT: expanded functionality by providing device operation with both four-wire and three-wire three-phase network, increased reliability of the device due to provision of non-contact check of the phase skew value, which makes it possible to keep track of skew value change in real time.

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Description

FIELD OF THE INVENTION

The invention relates to the field of electrical engineering and can be used to control and protect a three-phase load with the possibility of contactless control of phase imbalance of a three-phase supply network.

State of the art

A device is known for protecting three-phase consumers from asymmetric operating modes (RU 2269191). This network device is designed for a four-wire three-phase network and assumes the presence of a zero working wire, which is a drawback. In addition, the device does not allow to control the amount of phase imbalance.

A device for controlling a three-phase load with protection against phase imbalance and alarm (RU 2285320). The device also assumes the presence of a neutral wire and, therefore, has the same drawback. The device provides control of each phase individually with the help of two-color LED indicators signaling the absence or presence of a skew of a specific phase. The disadvantage of this device is that the alarm is two-level, which allows you to record only the presence of bias, but not its value.

Similar capabilities and the same disadvantages have a device for controlling a three-phase load with protection from phase imbalance and an alarm (RU 2291539).

For the prototype of the invention adopted the device described in the literature [Bastanov V.G. 300 practical tips. M .: Moscow Worker, 352 p. (S. 17-19)] or on the Internet at the email address: http://cxema.in/radio-shema120.html. The present invention is based on the scheme of the prototype device, the refinement of which expands the functionality and allows you to eliminate the disadvantages characteristic of the prototype. These disadvantages are as follows.

Firstly, for the prototype device to work, a neutral wire is needed, which may not exist if a three-wire three-phase network is used to power a load. And, secondly, there is no control of the phase imbalance.

Disclosure of invention

The objective of the invention is to eliminate the above disadvantages.

The technical result of the invention is to expand the functionality by ensuring the operation of the device with both a four-wire and a three-wire three-phase network, as well as increasing the reliability of the device by providing non-contact control of the phase imbalance, which in real time allows you to monitor the change in the magnitude of the bias.

To achieve the above technical result, a three-phase load control and protection device with non-contact control of phase imbalance is proposed, including a flux gate containing an excitation winding, a measuring winding and a compensation winding, a rectangular pulse generator, a connecting capacitor, a recording unit with a measuring device and a compensator, while it contains grounding and an additional inductor connected to the rectified voltage between the artificial neutral Strongly and ground and adapted to determine the magnitude of the skew in the phases of the three-phase network controlled by the magnitude of the magnetic field strength of its own.

The technical result is achieved as follows.

1. By creating additional grounding, allowing the device to work without a neutral wire.

2. By introducing into the device a special inductor connected to the rectified voltage between the artificial neutral and ground. In the presence of phase imbalance in a three-phase network (four-wire or three-wire), a constant magnetic field arises in the coil, the magnitude of which is proportional to the magnitude of the phase imbalance. The tension can be controlled contactlessly using a measuring device built on the basis of a flux-gate transducer. And, therefore, it is possible to control the amount of phase imbalance.

Brief Description of the Drawings

In FIG. 1 is a diagram of a three-phase load control and protection device.

In FIG. 2 shows a measuring device for monitoring the magnitude of the phase imbalance.

In FIG. 3 shows a diagram of a rectangular pulse generator.

SUMMARY OF THE INVENTION

The device operates on the principle of creating artificial neutral using three capacitors C1, C2, C3 (see Fig. 1). As a result of an overload of one of the phases and, moreover, its breakage, a voltage arises between the artificial neutral and the ground. Moreover, unlike the prototype, it is proposed to use additional grounding, which ensures the operation of the device also in a three-wire three-phase network. The resulting voltage is rectified using a diode bridge (VD1-VD4). The rectified voltage is applied to the parallel relays K1, coil L1 and capacitance C4. When one of the phases breaks, relay K1 is activated, which breaks the power supply circuit of the coil of the KM magnetic starter with its contacts, and the load, for example, motor M, is disconnected from the network. It is also envisaged to disconnect the coil of the magnetic starter using the thermal relay KK. The capacitance of the capacitor C4 is selected in such a way as to exclude the relay in the starting mode.

The main distinguishing feature of the circuit, in addition to additional grounding, is the presence of an inductor L1, which creates a constant magnetic field, the intensity of which is proportional to the value of the rectified voltage between the artificial neutral and ground. This tension, which characterizes phase imbalance, can be measured non-contact by a device based on a flux-gate transducer.

The use of fluxgates for measuring a constant magnetic field is described in detail in the literature: Afanasyev Yu.V. Fluxgate devices. L .: Energoatomizdat. 1986. 188 p., Milovzorov V.P. Electromagnetic automation devices. A textbook for students of the specialty "Automation and Telemechanics" of universities. M .: Higher. School, 1974. 416 p. These devices have proven themselves in various automation and control circuits. The devices are compact, simple and low power consumption.

The use of magnetic field strength meters allows you to remotely, without interference with electrical circuits, to control in real time the amount of phase imbalance of a three-phase network. The scale of the measuring device is graduated in danger levels of phase imbalance for three-phase consumers. Thus, at high levels of danger, the load can also be disconnected by the operator by pressing the Stop button in the power circuit of the coil of the magnetic starter.

The device uses a DC relay of type RP21 (with an operating voltage of 24 V) and a winding resistance of 200 Ohms. Capacitors C1-C3 paper with a capacity of 4-10 microfarads for a voltage of at least twice the phase voltage. Inductor L1 contains 4500 turns of wire PEV-2, diameter 0.2 mm. Coil resistance 330 ohms. The core of the coil is open.

The measuring device diagram (see Fig. 2), built on the basis of a flux-gate transducer, contains the following components:

- a flux gate with three windings - an excitation winding L1, consisting of two counter-wound identical halves L1 'and L1' ', a measuring winding L2 and a compensation winding L3;

- a rectangular pulse generator, made, for example, on elements NOT, with the ability to control the frequency within 2-200 kHz (Fig. 3);

- a connecting capacitor C1, transmitting a signal from the output of the generator to the excitation coil of the flux gate, which eliminates the constant component of the signal from the generator and, as a result, reduces the power consumed by the generator;

- a registration unit, connected to the output of the measuring winding, with any measuring device - a voltmeter or ammeter - and with the corresponding switching circuit. The readings of the measuring device correspond to the phase imbalance;

- a compensator to set the recording instrument to zero using a variable resistor R2 in the absence of a measured magnetic field strength, which eliminates the influence of extraneous magnetic field sources on the measurement results.

The square wave generator is shown in FIG. 3 and contains four elements NOT (chip K561 LN2), powered by a 9 volt source. At this voltage, the K561 series microcircuits operate stably at frequencies above 2 kHz. The generator itself is the first three elements NOT. The fourth element is NOT (DD1.4) useful for eliminating the influence of the excitation winding of the flux gate on the operation of the generator. Resistor R1 and capacitance C1 are frequency-setting elements. Resistor R1 provides frequency control of the generator. The frequency is selected to obtain the greatest sensitivity of the flux gate. The generator circuit is simple, characterized by low power consumption and allows for a compact and economical implementation of the entire measuring device as a whole.

A measuring device with a flux gate is installed in the immediate vicinity of the winding L1 of the three-phase load control and protection device. The location of the measuring device is determined by the sensitivity of the flux gate and the convenience of its placement. The selected installation location should be kept constant during the monitoring process.

Thus, the proposed control device and protect the three-phase load has the ability to contactless and continuous control of the level of danger of phase imbalance. Preliminary tests of the device showed reliable protection of induction motors from phase imbalance, as well as the convenience and necessity of real-time contactless monitoring of a three-phase network in order to analyze its malfunction. Such an analysis is useful for understanding the reasons for the protection to operate.

Claims (1)

A control and protection device for a three-phase load with the possibility of contactless control of phase imbalance, comprising an artificial neutral and a relay, the contacts of which break the circuit to disconnect the load from the network, characterized in that it contains grounding, an additional inductor, a measuring device containing a flux gate, which contains an excitation winding , a measuring winding and a compensation winding, a square-wave generator, a coupling capacitor, a recording unit with a measuring device and a compensator, while the measuring device is configured to control the phase imbalance based on the magnitude of the constant magnetic field of the additional inductor, and the relay and the additional inductor are connected in parallel to each other to the rectified voltage between the artificial neutral and ground.

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