RU2402829C1 - Smoothing reactor for motor smooth-starter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: smoothing reactor for motor smooth starter contains a double-core magnetic system fabricated of thin-sheet cold-rolled anisotropic electrical steel, insulation cylinders, power windings, fixture elements represented by plates of a non-magnetic material installed at the butt-ends of the cores designed to be integral. The distance between the cores and their height are defined by the required reactor inductivity. The power winding wire cross section is selected subject to tolerable wire heating on starting the motor. The power winding wire is fabricated of a material with a high thermal capacity, at least - aluminium. On one of the insulation cylinders there are two power windings arranged.

EFFECT: considerable reduction of labour intensity, production prime cost and basic materials consumption.

4 cl, 3 dwg

Description

The invention relates to the field of electrical engineering, in particular to transformer building, and can be used in the DC link of soft starters for electric motors.

Known smoothing reactor (Nomenclature catalog for 2000 OJSC Holding Company "Electrozavod", Moscow) type RCC-2000/10, containing a copper winding, placed on a core made in the form of a rod of electrical steel. Between the network winding and the core are installed wedges made of insulating material, rigidly fixing the winding on the rod in cross section. At the ends of the core, supports are installed with pressing elements that rigidly fix the winding in the longitudinal direction. The specified reactor is widely used in soft starters of powerful synchronous electric motors with a voltage of 6-10 kV, for example, the UBPVD-S series. The reactor has a large air gap and slightly reduces inductance at currents 1.5-2 times higher than the nominal value, which is good for UBPVD-S devices.

The disadvantages of this reactor are the high consumption of wire of the network windings, electrical steel, insulation and other materials that cause the high cost of the reactor.

These shortcomings are due to the following circumstances:

As you know, the inductance of the reactor is directly proportional to the cross section of the core, also the square of the number of turns of the network winding and inversely proportional to the size of the air non-magnetic gap in the core. And since there is only one rod, the air gap is large. This leads to the need to significantly increase the cross-section of the rod or the number of turns of the network winding. As a result, the length of the wire spent on the network winding increases significantly. The consumption of insulating materials in the network winding also increases significantly, including the organization of air cooling channels in the network winding.

The network winding of the reactor is designed for long-term operation of the reactor and when operating in short-term mode (up to 20-60 seconds), it heats slightly. This leads to a very inefficient use of copper network winding.

Known smoothing reactor series SROS-160/6 (Nomenclature catalog for 2000, OJSC Holding Company "Electrozavod", Moscow), containing a magnetic system made of 2 rods and 2 yards made of cold rolled anisotropic sheet electrical steel. The rods are made with a dispersed non-magnetic gap in the form of insulating spacers between the inserts of the rods of the magnetic system. Two identical coils made of copper wire are installed on the rods. Coils are connected to the network connection buses in series or in parallel. This reactor has a small non-magnetic gap, which allows you to get the necessary inductance at a significantly lower consumption of electrical steel and wire network windings.

The inductance of the reactor in series connection of network windings is determined by the formula:

where µ is the magnetic permeability of the steel rods;

µ ₀ - magnetic permeability of air (non-magnetic gap);

w is the number of turns of the network windings;

Q is the cross section of the rod;

l is the length of the air (non-magnetic) gap in the rods.

The disadvantages of the reactor include:

- high consumption of wire network windings and electrical steel. The high consumption of electrical steel is due to the presence of two yarns, the weight of which is about 60% of the weight of all steel. The high copper consumption for the wire of the network windings is due to the fact that the cross section of the wire of the network windings is selected from the conditions of continuous operation of the reactor. During the operation of the reactor as part of the starting devices, the wire of the network winding of the reactor does not have time to heat up significantly, which indicates the redundancy of its cross section;

- the complexity of the manufacturing and assembly of the magnetic circuit, due to the fact that the rods consist of a large number of ferromagnetic inserts and non-magnetic gaps;

- increased noise due to electromagnetic forces acting on the insert;

- saturation of the magnetic system of the reactor in starting conditions with a current above the nominal.

The closest analogue in technical essence to the claimed reactor adopted for the prototype is a smoothing reactor (Patent RU No. 50042 U1 with priority from 2005.07.19). The reactor contains a two-core magnetic system made of cold-rolled anisotropic electrical steel sheet, fixation elements in the form of a jerk with ties, insulating cylinders, network windings. The rods are made with a dispersed non-magnetic gap, and the couplers and pressing beams with a yoke are made of non-magnetic materials.

Due to the fact that the couplers and beams of the reactor are made of non-magnetic material (stainless steel), their heating and noise characteristics of the reactor are significantly reduced.

The disadvantages of the prototype are:

- the complexity of the technology for the manufacture and assembly of rods with a distributed non-magnetic gap, due to the alternate gluing of the plates of the inserts of the rods in the special tool and the polymerization of glue in the furnace at high temperature, the need to manufacture two yarns and their exact joining and crimping with the rods;

- high consumption of electrical steel, due to the use in the design of the reactor two jerk;

- increased consumption of wire network windings due to its large cross-section;

- saturation of the magnetic system and a decrease in the inductance of the reactor during its operation in the soft starter of the electric motor with currents up to 1.5 times higher than the nominal value.

In this mode (on a sharply falling section of the dependence of the reactor inductance on current) due to current ripples, significant fluctuations in the dynamic inductance of the reactor occur, leading to a decrease in the stability of the soft starter and to a decrease in the reliability of starting powerful mechanisms.

The technical result of the claimed invention is a significant reduction in the complexity of manufacturing and consumption of basic materials, namely: electrical steel, wires of network windings, insulation materials, as well as a decrease in the fluctuations of the dynamic inductance of the reactor by reducing the saturation of the magnetic system at starting currents up to 1.5 times higher than the nominal values.

The technical result is achieved in that in a smoothing reactor for a soft starter of an electric motor containing a two-rod magnetic system made of cold-rolled anisotropic electrical steel sheet, fixing elements with ties, insulating cylinders, network windings, and the rods of the magnetic system are made integral, and the distance between them and the height are set by the required reactor inductance, the fixing elements are made in the form of plates of non-magnetic material and installed at at least along the ends of the rods of the magnetic system, forming a single reactor design. The cross section of the wire of the network windings is selected from the condition of its allowable heating during the start of the electric motor. The wire of the network winding is made of a material with a high heat capacity, at least of aluminum. On one of the insulating cylinders are two network windings.

The essence of the proposed technical solution lies in the fact that, in comparison with the prototype, high technical and economic indicators are achieved by simplifying the design of the reactor, reducing material consumption, as well as manufacturing costs.

Since the nonmagnetic gap is outside the rods and the diameter of the windings is significantly reduced due to a decrease in the wire cross section, it became possible to install the rods close to each other and obtain the required inductance with a significant simplification of the reactor design.

The claimed technical solution is illustrated by drawings, in which Fig. 1 shows a front view of the proposed smoothing reactor, Fig. 2 is a side view and a section A-A, in Fig. 3 is a diagram of a connection of a reactor to a motor soft starter.

The following notation is accepted:

rods - 1;

network windings - 2;

insulating cylinders - 3;

plates - 4;

screeds - 5;

spacer profiles - 6;

smoothing reactor - 7;

controlled rectifier - 8;

inverter - 9;

motor windings - 10;

the switch is 11.

The reactor contains a two-rod magnetic system, the rods 1 are integral, on which network windings 2 are installed, wound on insulating cylinders 3, plates 4 (fixing elements with couplers) made of non-magnetic material (for example, fiberglass) installed on the ends of the rods 1 of the magnetic system . The rods 1 with plates 4 are fixed on two longitudinal sides with steel ties 5, forming a single reactor design. Insulating cylinders 3 protrude from the windings 2 to the required distance, ensuring their electrical isolation from the steel rods 1.

The insulating cylinders 3 are centered on the inner diameter relative to the longitudinal axes of the rods 1 using insulating spacer profiles 6.

Two network windings 2 can be located on one of the insulating cylinders 3.

The proposed reactor design simplifies the manufacturing technology of the reactor rods, reduces the consumption of materials and the cost of the reactor as a whole.

Given the short run time of the reactor in start-up mode, power losses and heating in the screeds 5 are negligible.

The smoothing reactor 7 is connected to the direct current circuit between the controlled rectifier 8 and the inverter 9, the outputs of which are connected to the windings of the electric motor 10. During the start-up, the rectifier 8 smoothly increases the voltage at its outputs, the reactor 7 smooths out the current ripples, the value of which is equal to 1.5 of the nominal value , the inverter 9 smoothly increases the frequency and magnitude of the voltage on the electric motor 10, accelerating it to the rated speed. Then, the switch 11 is turned on and connects the electric motor 10 directly to the mains. The soft starter turns off.

The soft start time of the electric motor usually does not exceed 20 seconds. According to the technical conditions for soft starters and established practice, it is possible to start three electric motors from one device with 5-minute pauses between starts. The wire of the reactor winding must withstand not only heating with an inrush current for 60 seconds with pauses of 5 minutes, but also with additional heating with a short-circuit current in the soft starter during the operation of the protection installed at the input of the device. Typically, the response time of the protection does not exceed 0.5 seconds, and the magnitude of the emergency current is 5-10 times higher than the nominal value. The specific value of the emergency current from this range is determined mainly by the residual inductance of the reactor, which is determined in turn by both the number of turns of the windings and the size of the windings and the distance between them.

Thus, the minimum cross-section of the wire of the network winding depends on a number of factors: from heating the wire during start-up and cooling during pauses, from heating the wire with the emergency current of the device, from changing the specific resistance of the wire due to its heating.

In addition, the cross section of the wire must have the necessary mechanical strength under the action of dynamic forces on it both inside the network winding and between the windings. This circumstance is especially important for reactors with a reduced wire cross-section (it should be noted that in reactors operating in continuous operation, the wire cross-section is several times higher than in our case, therefore, checking the wire for dynamic stability of the network winding under emergency currents is of an auxiliary character) .

Thus, the choice of the optimal cross-section of the wire, taking into account the above circumstances, is a complex and multi-criteria problem, which was solved using simulation of thermal, electromagnetic and electrodynamic processes using the Elcut 5.5 program.

The selection of the optimal reactor parameters to obtain the required inductance is also a difficult task, since the reactor inductance depends not only on the number of turns in the windings and the cross section of the rods, as in the above reactors, but also on the height of the rods and the distance between them. The distance between the rods and their height depend, in turn, on the method of winding the windings - the number of turns in the layer and the number of layers.

Thus, the selection of the optimal reactor parameters in order to obtain the required inductance is performed simultaneously with the selection of the optimal wire cross section using the Elcut 5.5 program.

In comparison with the prototype, the exclusion of two jerks from the reactor design and the dispersed non-magnetic gap made it possible to significantly reduce the complexity of manufacturing and the consumption of electrical steel. Optimization of the cross section of the wire of the winding in accordance with the parameters of the start-up mode of the electric motor allowed to significantly reduce the consumption of wire.

The choice of wire material with high heat capacity (with high heat storage properties) can further reduce the wire cross section.

By reducing the cross-section of the wire, it was possible to reduce the diameter of the network windings and the distance between the rods, and due to the optimal choice of turns of the windings and installing the rods at the required distance, we obtained the required inductance at 1.5 times the starting currents of the electric motor.

Two prototypes of the reactor were made, which confirmed the possibility of reducing the consumption of materials: electrical steel by 2–3 times, wires and insulating materials by 2–5 times, and labor intensity by 2–3 times in comparison with the specified prototype and analogues.

The developed reactor can be used in continuous operation while reducing the current by 3-4 times.

The inventive reactor has been successfully tested and its serial production is planned in the near future.

Claims (4)

1. A smoothing reactor for a soft starter of an electric motor, comprising a 2-rod magnetic system made of cold-rolled anisotropic electrical steel sheet, fixing elements with ties, insulating cylinders, network windings, characterized in that the rods of the magnetic system are made integral, and the distance between them and the height are set by the required reactor inductance, the fixing elements are made in the form of plates of non-magnetic material and installed at least at the ends of the rods netic system, forming a single reactor structure. 2. The smoothing reactor according to claim 1, characterized in that the cross-section of the wire of the network windings is selected from the condition of its allowable heating during the start-up of the electric motor. 3. The smoothing reactor according to claim 1, characterized in that the wire of the network winding is made of a material with high heat capacity, at least aluminum. 4. The smoothing reactor according to claim 1, characterized in that on one of the insulating cylinders there are two network windings.

Images