RU2226046C2 - Transformer-type electric water 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. Short-circuited single-turn secondary winding of nonmagnetic electricity conducting tubes functions as heating element. Novelty is that secondary winding is specifically designed so that short-circuited turn in each of its phases has active and passive sections. Active section is placed directly on phase leg of transformer core and passive section placed around same phase leg of transformer core is made in the from of two parallel conductors connected at their ends to active section. Short-circuited turns of phases are connected in series with respect to water flow and are shorted out by welds. Such design meets to advantage specific requirements to short- circuited secondary windings. EFFECT: enhanced safety and operating reliability. 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 B 6/10, publ. 07/22/86), which includes a three-phase magnetic circuit, a 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 to the lids of the tanks, a large number of welded joints are required here, which leads to the likelihood of a defect during assembly, therefore, reduces the reliability of the device.

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 non-magnetic electrically conductive non-magnetic pipes, consisting of three short-circuited turns, is used. The short-circuited coil consists of two parts laid directly on each rod of the phase of the transformer magnetic circuit. The first part is active. The second, passive part is made in the form of two parallel conductors with a counter current direction, connected at their ends to the active part. Electromotive force (EMF) in the passive part of the winding is not induced, since the parallel conductors of this part have opposite winding directions. The currents in the conductors of the passive part are directed in the opposite direction. Consequently, 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 three-phase single-turn short-circuited 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-circuit three-phase single-turn secondary winding 3 serves as the heating element. The short-circuited turn of each phase of the secondary winding 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 short-circuited coil of each phase of the secondary winding, consisting of the active part 4 and the passive part 5.

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 each core of the magnetic circuit over the primary winding, is made of 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 in the active part of the short-circuited loop of the short-circuited three-phase single-turn secondary winding of the EMF. 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 used to heat the water. The heat transfer rate depends on the speed of the water flowing through the pipe, as well as on the area of the heat transfer surface. To reduce unwanted heat flux from the outer surface of the tubes, this surface can be coated with a 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 primary and squirrel-cage secondary windings laid on its rods, characterized in that the coil of each phase of the short-circuited three-phase single-turn secondary winding is made in the form of curved non-magnetic non-magnetic pipes and contains the active part, laid on top of the primary winding on the magnetic core, of the phase rod as well as the passive part, covering the same core of the phase of the transformer magnetic circuit, and made in the form of two parallel of conductors with the opposite direction of winding, forming the opposite direction of the current in the conductors connected at their ends to the active part, and the turns of the individual phases are connected in series through water and are short-circuited.

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