EP0702504A2 - Thermal tube and method for induction heating of impregnated electrical assemblies - Google Patents

Abstract

The inductive heating device has a primary circuit (1), acting as an energising circuit supplied with an AC signal and a secondary circuit (2) provided by a thermic compound sheet metal thermic pipe (3). This has an inner pipe of a ferromagnetic material and an outer pipe lying adjacent the primary circuit, made of a non-magnetic, electrically-conductive material. A variable airgap is provided between the primary circuit and the secondary circuit. Pref. the thermic pipe is formed by 2 or more circular segments, hinged together in pairs and partially overlapping one another, with flexible conductors for electrically connecting them together.

Description

Technical field

The invention relates to a device and the method for inductive heating, in particular for curing and drying impregnated windings of electrical machines with concentrated or distributed winding in electrical engineering.

State of the art

In electrical engineering in the manufacture of high-quality electrical machines, a major problem is the design and manufacture of the entire insulation system. The insulation system determines the resilience and the lifespan of the products. High mechanical, electrical and thermal properties of the insulation of the windings are required. This can only be achieved by combining different insulating materials and reactive resins, e.g. Epoxy resins or silicone resins. This insulation means that air pockets are excluded.

In order to fill all the free spaces between the laminated core and the winding material on the one hand and the winding material and slot fastening on the other and to generally soak the several layers of insulating tape, it is necessary to choose the viscosity of the reactive resins as low as possible.

In order to avoid the harmful air pockets, vacuum pressure impregnation processes are largely chosen today. In complex impregnation systems, the existing air is first largely evacuated in order to then introduce the impregnation resin into the free spaces between the grooves with overpressure. After the impregnation, the impregnated electrical machines are dried and hardened in special ovens. The necessary heat of reaction acts from the outside on the insulation in the grooves of the laminated core. This means that the hardening process that begins with the gelation begins in the outer zones and continues inside. In the case of the highly reactive and quickly gelling impregnating resins, this leads to considerable internal tensions and to gas and shrinking voids.

In addition, it takes a relatively long time for the heat to be introduced from the outside to such an extent that the gelling process begins.

The thin resin partially runs out again until the gelling process. Therefore, the viscosity cannot fall below certain limit values, which, however, makes it more difficult for the reactive resin to penetrate all free spaces.

To prevent leakage, additional catalysts are used as accelerators for the gelling process. The entire soaking and curing process is very time and energy consuming.

Due to the long drying time, the environmentally harmful solvents that are still present in the reaction resins evaporate and form undesired smallest gas voids inside the gelling reaction resin.

DE 33 23 154 discloses a method for impregnating and embedding electrical windings which partially avoids these disadvantages. The reaction resin and the windings are first dried and then impregnated or cast using a vacuum pressure process. Drying and degassing in ovens is supported by current heat in the electrical conductor of the winding. The temperatures that can be achieved are up to 140 ° C. This is followed by further curing in normal drying ovens at higher temperatures.

Critique of the state of the art

This process has the disadvantage that the heating period is still relatively long and further curing in normal drying ovens is required.

problem

The invention has for its object to provide a device and a method for inductive heating of impregnated or non-impregnated electrical assemblies of electrical machines, which allows a high heat input in a short period of time, improves the efficiency of heat generation and the heat sources in and immediately and concentrated at the optimal point and thus simplifies the heating of the component and enables both resin securing and complete curing.

Achievable advantages

With the invention of the thermal tube, the primary and secondary heat sources act directly on the component to be hardened.

The advantages result from the direct heat radiation at the right place and the optimal air flow for the convective heat input into the respective assembly and an optimal heat conduction within the assembly to be heated. This results in the advantages of making the temperatures more uniform, shortening the curing time and improving thermal efficiency.

With the so-called resin fuse, the first skin formation of the resin is achieved, thus optimizing resin binding after soaking. Furthermore, complete curing can be carried out with the thermal tube. This gives a further increase in quality.

Further embodiment of the invention

Advantageous embodiments of the invention are specified in claims 2 to 10. The developments according to claim 2 represent a special case in which the magnetic yoke is eliminated. The developments according to claim 3, 4, 7 and 8 serve to better adapt the thermal tube to the different diameters of the primary circles. The developments according to claims 5 and 6 serve for good electrical connection of the circular segments of the thermal tube. A further training in which the primary circle and Secondary circuit are interchanged, is described in claim 9. With the development of claim 10, the thermal effect of the device is enhanced. The method using the device according to the invention is described in claim 11.

Description of the exemplary embodiments and the method steps

An embodiment is shown in the drawing and will be described in more detail below.

• Fig. 1 die schematisierte Darstellung des Primärkreises und des Sekundärkreis als thermisches Rohr und
• Fig. 2 die schematisierte Darstellung des thermischen Rohres mit paarweisen Kreissegmenten innerhalb des Primärkreises.

Show it

• Fig. 1 shows the schematic representation of the primary circuit and the secondary circuit as a thermal tube and
• Fig. 2 shows the schematic representation of the thermal tube with paired circle segments within the primary circuit.

The device according to the invention is used for drying and curing components of electrical machines impregnated with impregnating varnish or resins, in particular primary circuits 1. A composite sheet metal tube 2, also referred to as a thermal tube 2, is used as the secondary circuit 2. The thermal tube 2 consists of an inner tube 3 with ferromagnetic properties, in the exemplary embodiment preferably from an approximately 3 mm thick iron tube. The outer tube 4 consists of a nonferromagnetic but electrically good conductive material, preferably a 1 mm thick copper tube in the exemplary embodiment. In the outer tube 4, which is closer to the primary circuit 1, heat is generated by the alternating field action of the primary circuit 1 via eddy currents which are associated therewith. For this purpose, an alternating voltage <0.4 U _{N is} applied to the primary circuit 1, which also generates heat in the winding of the primary circuit 1. The thermal tube 2 is the secondary heat source and the winding of the primary circuit 1 is the primary heat source. The AC voltage can have a frequency of 50 Hz, but other frequencies are also conceivable. In the exemplary embodiment, the voltage connection in three-phase stands is three-phase, but can also take place in a different phase, for example two-phase when the phase connections change over time. The AC voltage generates a rotating field in the stator winding or when connected <3-phase alternating field in the stator bore. The rotating or alternating field passes through the thermal tube 2 which is fixed in the stator bore. The iron portion of the inner tube 3 concentrates the magnetic yoke of the field while increasing the flux and also contributes, although to a lesser extent than the outer tube 4, via the action of eddy currents for heat generation. The thermal tube thus represents the main heat source for the process. The final temperature and the time constant of the temperature profile in the thermal tube 2 can be set both via the stator voltage (primary circuit voltage), its frequency and also via the air gap 5 between the thermal tube 2 and the primary circuit 1. Ensuring rapid and uniform heating of the assembly with immediate heating of the resin in the main insulation requires a stator current equal to or greater than the nominal current and rapid heating of the thermal tube 2 to the maximum permissible temperature. The uniform heating in the drying and curing process requires an air gap 5 of approximately 20 mm to 70 mm.

The adaptation of the thermal tube 2 to different process parameters and the universal use of this across several primary circuit sizes was achieved according to the invention in that the thermal tube 2 consists of at least two or more circle segments 6. The construction of the thermal tube 2 in the exemplary embodiment comprises four circular segments 6, two circular segments 6 each being connected in pairs via hinges 7. The length of the thermal tube 2 corresponds at least to the largest laminated core length of a primary circuit 1. The thermal tube 2 is locked to the primary circuit inner bore by means of an adapter using the contact pressure due to the thermal expansion of the thermal tube 2 or by means of a cross 9 with elongated holes, preferably over the centering edge of the primary circuit 1. The circle segments 6 of the thermal tube 2 are preferably connected by flexible electrical conductors 8 and can overlap. For better handling and adjustment of the The device can be arranged on the inside of the thermal tube 2 in the area of the hinges 7.

In order to increase the thermal effect, in the exemplary embodiment a fan is arranged in a thermally insulated envelope structure, which circulates the air through the primary circuit bore on both sides of the thermal tube 2 and over the primary circuit outside.

The combination of the heating of the primary circuit winding and the thermal tube 2 acts primarily on the winding-slot-tooth areas which are decisive for the dielectric strength, as a result of which the temperatures of the winding in the slot and winding head area and over the main insulation in the slot area become more uniform compared to conventional heating. This forms the basis for shortening the heating-up time and achieving the degree of curing of the main insulation faster, which technically leads to a shortening of the curing time.

The device of the embodiment includes a three-phase connection. The voltage is regulated in 20% steps via a control transformer. To minimize the transformer output, the inductively loaded and heated module is compensated on the secondary side of the transformer. The voltage setting of the transformer is regulated via the measured values of the process-determining temperatures on the assembly to be hardened.

The compensation system switches on at 20% of the heating voltage and compensates automatically at the beginning of the process. The respective set capacity is maintained during the drying and curing process.

With this device, the process can also be run with 20% to 40% of the heating voltage. The effect of the thermal tube 2 is brought back to the comparable end temperature by shortening the air gap 5 by shortening the thermal time constant and thus increased significantly.

The main heat source in this process is therefore the thermal tube 2. The heat source primary circuit winding acts due to the smaller current that comes in square, only subordinate.

In order to avoid larger circumferential forces on the thermal tube 2 with small air gaps 5, the three-phase winding can also be connected to voltage in two phases.

The complete exchange of the facility is feasible, i.e. the primary circuit 1 as the excitation circuit can be inside and the outside around the primary circuit 1 is the thermal tube 2. This variant is used for drying and curing the rotors of electrical machines. If the rotor is a short-circuit rotor, a high frequency must be used in the excitation circuit.

In a further variant, the thermal tube 2 can also consist only of a non-ferromagnetic but electrically highly conductive material. The normally inner tube 3 of the composite sheet is then omitted. This reduces the amount of heat that is required to heat the thermal tube 2.

In contrast to conventional methods, the entire curing process can be divided into three process steps. In the first process step, the resin is gelled in the winding area in the shortest possible time. A resin fuse thus occurs. Before curing, the resin layer should be quickly warmed up to the temperature at which the polymerisation of the resin begins (e.g. in epoxy-anhydride systems approx. 85 °) where the closed nature of the resin system is particularly important with regard to insulation C). This phase is completed in this resin system due to the lower mobility of the molecular groups at approx. 120 ° C. Then comes the second phase, heating up to the curing temperature with an equalization of all temperatures of the assemblies. The third phase corresponds to the conventional curing phase. Due to the rapid reaching of the curing temperature also in the winding area, the overall process is shortened.

A further shortening of the process can be achieved by additional air heating. However, this coupling with a conventional method would result in a deterioration in efficiency.

In special cases, the elimination of the first phase may also be desired. Nevertheless, the method enables a constant temperature rise over all areas of the component to be hardened with almost the same energy savings.

With this method, a substantial increase in the heat radiation can be achieved by reducing the air gap 5, which influences the surface resin layers on the main coil insulation, on the coil circuit and on the slot wedges in such a way that a kind of skin formation occurs.

The resin lock can still be carried out within the impregnation container after the impregnation process has been completed. In contrast to the iron parts, the insulating parts with their low thermal conductivity support this process, as a result of which the iron parts do not influence the draining of excess resin.

The frequency of the voltage should be matched to the respective resin.

With a 2-phase connection, the connections can be changed. The thermal conductivity of the thermal tube 2 ensures temperature compensation on this.

Claims (12)

Device for inductive heating of assemblies of electrical machines, consisting of a primary circuit and a secondary circuit,
characterized,
that the primary circuit (1) is fed as an excitation circuit by an AC or three-phase circuit and the secondary circuit (2) is locked to the primary circuit (1) and consists of a thermal composite sheet tube (2), the inner tube (3) of the composite sheet from one consists of ferromagnetic material and the outer tube (4), which is closer to the primary circuit (1), consists of a non-ferromagnetic but electrically conductive material and the air gap (5) between the primary circuit (1) and the secondary circuit (2) is variable. Device for inductive heating according to claim 1,
characterized,
that the thermal tube (2) consists only of a non-ferromagnetic but electrically highly conductive material in the form of a tube, a perforated tube or rings. Device for inductive heating according to claims 1 and 2,
characterized,
that the thermal tube (2) consists of at least two or more circular segments (6), which are preferably connected in pairs with hinges (7). Device for inductive heating according to claims 1 to 3,
characterized,
that the circular segments (6) of the thermal tube (2) partially overlap. Device for inductive heating according to claims 1 to 4,
characterized,
that the circular segments (6) of the thermal tube (2) are connected by flexible electrical conductors (8). Device for inductive heating according to claims 1 to 5,
characterized,
that the circular segments (6) of the thermal tube (2) are additionally provided on their outside in defined areas with an electrically highly conductive contact material. Device for inductive heating according to claims 1 to 6,
characterized,
that the circle segments (6) of the thermal tube (2) outside the primary circuit (1) are radially displaceable, are attached to a cross (9) attached to the primary circuit (1) with elongated holes or to a separate holding device. Device for inductive heating according to claims 1 to 7,
characterized,
that the circular segments (6) of the thermal tube (2) in the area of the hinges (7) on the inside have brakes (10). Device for inductive heating according to claims 1 to 8,
characterized,
that the thermal tube (2) in an independent inner tube (3) made of ferromagnetic material, which can also serve to hold the thermal tube (2) and is divided into an independent outer tube (4) made of non-ferromagnetic material, the air gap between these tubes can be variable. Device for inductive heating according to claims 1 to 9,
characterized,
that the primary circuit (1) as the excitation circuit is inside and outside around the primary circuit (1) is the thermal tube (2), the inner tube (3) and the outer tube (4) being exchanged, ie the tube with the ferromagnetic In this case, properties are on the outside. Device for inductive heating according to claims 1 to 9,
characterized,
that a fan for air circulation is arranged, which circulates the air so that the heat transfer from the thermal tube (2) is supported in the electrical assembly. Process for inductive heating, drying and hardening of impregnated or non-impregnated electrical assemblies while using the heat generated as a result of a current flow through this assembly,
characterized,
that the heating due to the flow of current through the electrical assembly and additionally through a thermal tube (2) as a result Radiation and convection takes place and in a first process step the so-called resin fuse is achieved by rapid heating, in a second process step the heating to the curing temperature and in a third process step the curing takes place, with the resin securing as skin formation but also as a comprehensive gelation of the resin can be carried out in the entire winding area.

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