RU44008U1 - DEVICE FOR PROTECTING ELECTRICAL EQUIPMENT AGAINST VOLTAGE - Google Patents

Abstract

The utility model relates to electrical engineering, and in particular to devices designed to protect electrical equipment, in particular isolation of high-voltage motors, transformers and cable lines from switching overvoltages, as well as from overvoltages arising in the mode of an arc single-phase earth fault (OZZ) in networks 6- 10 kV industrial enterprises. The objective of the utility model is to increase the efficiency and reliability of the device, reducing its size. The objective of the utility model is solved in that the device for protecting electrical equipment against overvoltage includes three sealed units enclosed in a sealed enclosure, in each of which a resistor and a capacitor are rigidly fixed in series, separated by a dielectric, sealed partition, the clamps of each RC chain are brought out with using two bushing of different levels of insulators.

Description

The utility model relates to electrical engineering, and in particular to devices designed to protect electrical equipment, in particular isolation of high-voltage motors, transformers and cable lines from switching overvoltages, as well as from overvoltages arising in the mode of an arc single-phase earth fault (OZZ) in networks 6- 10 kV industrial enterprises.

A known device is a limiter of internal overvoltages, designed to protect three-phase electric networks with isolated neutral from internal overvoltages (RU 20850002 C1, 1997.07.20). The device is made in the form of two independent stars, each of which contains two groups of zinc oxide resistors. The first group of resistors is connected by one output to the phase of the network, and the other forms the common point of the star, to which the resistor of the second group is connected, the second terminal connected to the ground. Three consecutive diodes are included in each of the independent stars.

The disadvantages of this device include the fact that when the device is operating in a single-phase earth fault due to neutral displacement and burning of an alternating arc, nonlinear resistors experience significant thermal overloads on the intact phases of a three-phase network, which leads to the destruction of resistors.

Closest to the claimed device is a device for protecting high-voltage electrical equipment from overvoltages (A.V. Shmakov, D.M. Rakhimov. Overvoltage protection for high-voltage equipment switched by vacuum circuit breakers. J. Electric, 2003, No. 4), which is an overvoltage limiting cabinet , which is based on a three-phase resistive-capacitive surge suppressor circuit. This device, selected for the prototype, consists of 3 single-phase RC chains, consisting of series-connected

a capacitor and a resistor, with parallel connection to each of the chains of a nonlinear surge suppressor and insulators.

The disadvantages of the known device are, firstly, the use of hinged resistors in it, which are subjected to mechanical vibrations when using the device in moving installations, for example, mining machines, which can cause a reduction in the air gap between live parts and lead to electrical breakdown of the air gap, and secondly , due to the large dimensions due to the presence in the device of nonlinear surge arresters and mounted resistors, it is impossible to place it in a close proximity to the protected object - an electric motor, transformer, in addition, grounding the neutral point in this surge suppressor leads to an increase in the capacitive current of a single-phase earth fault, which requires reconfiguration of the protection against a single-phase earth fault or additional compensation of the capacitive current, in addition to single-phase earth fault nonlinear surge arresters can undergo thermal destruction if the duration of the earth fault exceeds 2-3 minutes. Although the known device allows you to limit the amplitude of the overvoltage, effective suppression (smoothing) of overvoltages does not occur.

The objective of the utility model is to increase the efficiency and reliability of the device, reducing its size.

The technical result achieved by this utility model is expressed in smoothing the high-frequency components of the current, limiting the slew rate of the voltage pulse at the time of switching or in the single-phase earth fault mode by increasing the capacitance between the windings of the electric motor or transformer and eliminating the re-ignition of the arc between the switch contacts.

The objective of the utility model is solved in that in a device for protecting electrical equipment from overvoltages, which includes three single-phase RC circuits enclosed in a housing, each of which consists of a series-connected capacitor and resistor and insulators, the device case is sealed with three sealed units in it , in each of which a resistor and a capacitor are rigidly fixed, separated

a dielectric, sealed partition, the clamps of the RC chain are brought out with the help of two bushing of different levels of insulators.

RC chains can be assembled in a “star” pattern with an isolated neutral point.

RC chains can be assembled in a “triangle” pattern.

RC chains can be assembled in a “star” or “triangle” pattern using a bus.

The tire can be made of aluminum.

The tire may be made of copper.

The presence in the device of rigidly fixed resistors and capacitors eliminates their mechanical vibrations during operation.

The use of two different-level insulators and the absence of nonlinear surge arresters in the device allows minimizing the dimensions of the device and using it in the immediate vicinity of the protected object.

The enclosure of the device in a sealed enclosure, and each RC-chain, consisting of a series-connected capacitor and resistor, in separate sealed units increases the intrinsic safety of the device. Allows you to use the device in conditions with high humidity and dust, as well as in environments with a high probability of ignition (pulverized coal compartments of thermal power plants, coal opencasts, oil drilling rigs).

The separation of the resistor and capacitor by a dielectric sealed partition does not allow a sharp change in the temperature regime of the capacitor.

The use of two insulators in each RC-circuit allows you to collect RC-chains according to the "star" scheme with an isolated neutral point or according to the "triangle" scheme, allows you to use the same device in networks with different voltage levels. The use of the "triangle" circuit allows to increase the efficiency of protection against switching overvoltages by 12-15%.

The isolated neutral point of the claimed device makes it possible to not affect the magnitude and nature of the current of a single-phase earth fault, does not require readjustment of protection against a single-phase earth fault or additional compensation of capacitive current.

The utility model is illustrated by drawings, where figure 1 schematically shows a General view of the device according to the "star"; figure 2 is a plan view of the "star"; figure 3 is a side view of the sealed unit with insulators; figure 4 - electrical diagram of the device.

A device for protecting electrical equipment against overvoltage consists of three single-phase RC circuits 1, which, in turn, consist of a series-connected high-voltage capacitor "C" 2, a resistor "R" 3, assembled according to the "Star" or "Triangle" scheme using a bus 4. The capacitor "C" 2 and the resistor "R" 3, each of the three RC circuits 1 are placed in a sealed unit 5, the clamps of the RC chain 1 are brought out using two through-level insulators 6 and 7. The whole device is enclosed in a sealed enclosure 8.

A device for protecting electrical equipment from overvoltage is as follows.

The device is installed in close proximity to the motor or transformer and connected to the terminals of the motor or transformer using a cable jumper. The housing 8 of the device provides for floor or wall mount. If the distance between the motor and the circuit breaker box does not exceed 50 m, the device can be installed in the circuit breaker box.

In the operating mode, when the voltage in the phases of the network is equal to the nominal or slightly exceeds its operation, the device reduces to the fact that a small active-capacitive current flows through the RC circuits, which partially compensates the inductive component of the load current and, thereby, reduces power losses in cable or overhead lines.

When the load is disconnected, the effect of “current cutoff” is observed, the magnetic energy stored in the windings of the electric motor or transformer will be converted into electric field energy. The energy exchange is accompanied by high-frequency oscillations, the frequency of which can reach 120 kHz, and an increase in voltage at the terminals of the electric motor or transformer, i.e. to the appearance of overvoltages and cause a breakdown in the insulation of the windings of the electric motor, transformer or cable cut.

To limit the rate of increase in voltage by smoothing the high-frequency components of the current, to limit the amplitude of the overvoltage, it is necessary to increase the capacitance between the windings of the electric motor or transformer, which follows from the expressions:

where U is the magnitude of the overvoltage io is the current slice L is the inductance of the motor winding or transformer;

C is the capacitance between the windings of an electric motor or transformer.

where - is the voltage rise rate. More capacity between dt

windings of an electric motor or transformer, the slower the voltage at the terminals of the electric motor or transformer will increase.

The inventive device allows to increase the capacitance between the windings of an electric motor or transformer due to the implementation of the "star" circuit with an isolated neutral point or the "triangle" circuit. In the device selected for the prototype, there is an increase in capacitance between the motor windings and the ground, in this case the amplitude of the overvoltage is limited, but the speed of the voltage rise is not limited.

Thus, the claimed device with small dimensions, ensuring its mobility and ease of use, can effectively reduce switching overvoltages and overvoltages in the mode of an arc single-phase earth fault. The level of limitation of switching and arc overvoltages is 1.5 Cz and, thus, the negative impact of high voltage on the insulation of motors or transformers is minimized. The device improves the phase characteristic of a 6-10 kV network in the single-phase ground fault mode, facilitates the process of disconnecting short circuits by smoothing high-frequency components and partially compensates the inductive component of the load current, which reduces power losses in cable or overhead lines.

Claims (6)

1. A device for protecting electrical equipment from overvoltage, including three single-phase RC circuits enclosed in a housing, each of which consists of a capacitor and a resistor connected in series, and insulators, characterized in that the housing of the device is sealed with three sealed units placed in it, each of which a resistor and a capacitor are rigidly fixed, separated by a dielectric, hermetic partition, the clips of the RC circuit are brought out using two loop-through insulators of different levels. 2. A device for protecting electrical equipment from voltages according to claim 1, characterized in that the RC circuits are assembled according to the “star” scheme with an isolated neutral point. 3. The device for protecting electrical equipment from overvoltages according to claim 1, characterized in that the RC circuits are assembled according to the "triangle" scheme. 4. A device for protecting electrical equipment from overvoltage according to claim 2 or 3, characterized in that the RC circuits are assembled in a “star” or “triangle” pattern using a bus. 5. A device for protecting electrical equipment from overvoltage according to claim 4, characterized in that the tire is made of aluminum. 6. A device for protecting electrical equipment from overvoltage according to claim 4, characterized in that the busbar is made of copper.