RU2226045C2 - Transformer-type electric heater - Google Patents

Abstract

FIELD: fast water heating appliances. SUBSTANCE: device has three-phase laminated electric steel core whose legs carry aluminum-wire primary winding. Three- phase single-turn short-circuited secondary winding made of nonmagnetic electricity conducting tubes is used as heating element. Novelty is that secondary winding of proposed device is specifically designed so that its short- circuited turn in each phase has active and passive sections. Active section is wound directly on core phase leg. Passive section is wound on all three legs of transformer core; it is made in the form of two parallel conductors whose ends are connected to active section. Short-circuited turns of phases are series-connected with respect to water flow and are shorted out by welds. EFFECT: enhanced safety and operating reliability of device. 1 cl, 2 dwg

Description

The invention relates to electric heating devices and is intended for use in everyday life, in small industrial and agricultural facilities for the preparation of fixed temperature hot water in a quick manner.

The closest in technical essence to the claimed invention is an induction electric heater (application US, No. 4602140, MKI N 05 V 6/10, publ. 07/22/86.), Which includes a three-phase magnetic circuit, the primary winding, designed for a voltage of a certain fixed frequency . The magnetic circuit has three rods on which the primary winding is located. The secondary winding includes many direct non-magnetic electrically conductive pipes located between and outside the cores of the magnetic circuit, connected at the ends with the lids of the tanks, which serve to close the fluid circuit and phase currents. All pipes are parallel to each other between two tanks. The tanks have removable covers for inspecting the inner surface of the pipes.

The disadvantages of this device include the complex technology of connecting the ends of the pipes with the lids of the tanks; it requires a large number of welded joints, which leads to the likelihood of a defect during assembly.

The invention consists in the following. The invention is aimed at improving the operational properties of an electric heater.

In the process of solving the problem, a technical result is achieved, which consists in increasing the safety and reliability of the electric heater.

This is achieved by using a three-phase magnetic circuit in an electric water heater with a primary winding laid on its rods, calculated by a technique similar to the calculation of standard power transformers. As a heating element, a short-circuited three-phase single-turn secondary winding in the form of curved electrically conductive non-magnetic pipes, consisting of three short-circuited turns, is used. The short-circuited coil consists of two parts, the first, active part is laid directly on the phase core of the transformer magnetic circuit, the electromotive force (EMF) of the phase is induced in it. The second, passive part covers all three rods of the magnetic circuit and is made in the form of two parallel conductors with a counter current direction, connected at their ends to the active part. EMF in the passive part is not induced, since the resulting magnetic flux from the three phases of the transformer is zero. The currents in the parallel conductors of the passive part of the winding are directed in the opposite direction, therefore, the resulting magnetic scattering flux created by the currents of the passive part is very small. The secondary inductance due to this flow is also small. Since both parts of the coil are connected in series, the same current flows through them, causing heat losses that are evenly distributed over the surface of the coil. The turns of a short-circuited three-phase single-turn secondary winding are connected in series through water, i.e. Heated water sequentially washes all three turns of the winding. The material and size ratios of the secondary winding are determined by the required temperature level of the heated water.

In the proposed electric heater, the secondary winding design has the following features. It has one short-circuited coil in each phase, which is necessary to ensure the required safety during operation of the electric heater, the electromotive force of the phase of the three-phase single-turn secondary winding should not exceed 2-4 V. In addition, the use of one short-circuited coil allows for a minimum dissipation inductance, therefore, the maximum possible value of the power factor of the device, which leads to an improvement in its energy performance. On the other hand, the short-circuited coil has a sufficiently large contact surface with the heated medium, which provides the required specific surface power, and therefore, eliminates the formation of scale on the inner surface of the tube. This design provides the maximum possible active resistance of the secondary winding, which is necessary to achieve a given power at minimum current.

The invention is illustrated in figures 1 and 2. Figure 1 shows the assembled active part of the electric heater. The primary winding 2 is located on the rods of the three-phase magnetic circuit 1. The short-circuited three-phase single-turn secondary winding 3 serves as the fuel element. The short-circuited turn of each phase of the secondary winding (Fig. 2) consists of the active part 4 and the passive part 5. The turns of the secondary winding are short-circuited by welded joints 6. Figure 2 shows the short-circuited turns of each phase of the secondary winding.

A primary winding made of aluminum wire is laid on the rods of a three-phase charged magnetic core made of electrical steel. A short-circuited three-phase single-turn secondary winding, laid on the terminals of the magnetic circuit over the primary winding, is bent from a non-magnetic electrically conductive tube. The short-circuited coil of the secondary winding consists of active and passive parts. To create a short-circuited coil in each phase of the winding of the tube are welded in three places indicated in figure 1. The size ratios and material of the secondary winding are selected as a result of electromagnetic calculation, which is based on the value of the required temperature of the heated water.

The device operates as follows. The primary winding located on the magnetic circuit is connected to a three-phase AC network. A current begins to flow through the winding, creating an alternating magnetic field in the three-phase magnetic circuit. This magnetic field induces an electromotive force (EMF) in the active part of the short-circuited loop of the short-circuited three-phase single-turn secondary winding. Under the influence of this EMF, an electric current flows both in the active and in the passive part of the coil. The heat losses caused by this current are spent on heating the water flowing through the pipe. The heat transfer rate depends on the speed of the water flow, as well as on the area of the heat transfer surface. To reduce heat transfer to the environment from the outer surface of the tubes, this surface can be coated with heat-insulating material.

Thus, in this invention the required level of safety and reliability of the device is achieved, the proposed invention is similar to the prototype in terms of water heating efficiency, but in contrast to it, the above requirements for the constructions of secondary short-circuited windings are best satisfied here.

Claims (1)

An electric heater containing a three-phase magnetic circuit with a primary winding laid on its rods, characterized in that the coil of each phase of a short-circuited three-phase single-turn secondary winding in the form of curved electrically conductive non-magnetic pipes contains an active part, laid on top of the primary winding on the phase terminal of the transformer magnetic core, as well as a passive part, covering all three rods of the transformer magnetic circuit and made in the form of two parallel conductors with a counter current direction, connected at their ends with the active part, the turns of the individual phases are connected in series through water and are short-circuited.

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