JPH0727830B2 - Heat treatment method for transformer core - Google Patents

Description

The present invention relates to a heat treatment method for a transformer core.

Improving its efficiency is a primary requirement for transformers,
For this purpose, it is necessary to reduce each loss such as iron loss and copper loss.

On the other hand, a laminate of electromagnetic steel sheets is used as the iron core of the transformer, that is, the transformer core, and it is well known that the transformer core greatly affects the iron loss.

The present invention relates to a heat treatment method for a transformer core capable of reducing the iron loss and reducing the quality variation.

<Conventional Technology and Its Problems> Conventionally, in order to eliminate internal strain and the like of the transformer core and reduce its iron loss, the manufactured transformer core is first heated to 300 to 400 ° C. in an oxidizing atmosphere, Then, a method of annealing in a reducing atmosphere is performed. The transformer core is manufactured, for example, by punching a thin plate of an electromagnetic steel sheet having an insulating coating applied on both sides, and then laminating the thin plate. The heating in the oxidizing atmosphere is performed in the process of manufacturing the transformer core. It is carried out to decompose and remove the oil that has been used and left attached, mainly punching oil used during punching. However, according to such a conventional method, the carbon decomposed and produced from the oil remains between the laminated thin plates, and the carbon causes partial energization between the thin plates, resulting in eddy loss which is one of the iron loss. There is a problem that the current is lost. Also,
Even if the annealing itself is performed in a reducing atmosphere, since the thin plates are laminated in the air during the manufacturing process of the transformer core, the transformer core is annealed with air being introduced between the thin plates. As a result, there is a problem that the insulating coating applied on both sides of the thin plate is oxidized and deteriorated to cause partial insulation failure, which also becomes an eddy current loss which is one of iron loss. Then, there is a problem that the carbon that is decomposed and produced from the oil as described above and the air that is brought in eventually cause a large variation in quality.

The conventional method has the above-mentioned essential problems. Therefore, in order to reduce iron loss alone, it is unavoidable to apply physical shock to the transformer core after heat treatment to partially insulate the thin plates. The reality is that defects are eliminated. However, this is not an essential solution to the problem, and it goes without saying that there is an extra step for newly applying a physical impact after the heat treatment, which is troublesome.

<Problems to be Solved by the Invention and Means for Solving the Problems> The present invention essentially solves the above-mentioned conventional problems, and does not require any physical impact on the heat-treated transformer core. The present invention provides a heat treatment method for a transformer core, which can reduce the iron loss value and the quality variation.

The present invention, however, preheats the transformer core at a high temperature within a range in which the oil remaining in the process of making the transformer core does not seize during the heat treatment for eliminating the internal strain of the transformer core, The present invention relates to a heat treatment method for a transformer core, which comprises performing vacuum purging in this preheating state, restoring the pressure in a reducing atmosphere, and further annealing in a reducing atmosphere.

In the present invention, first, the manufactured transformer core is preheated at a temperature at which the oil used in the manufacturing process of the transformer core and remaining adhered does not seize. This type of oil is mainly punch oil used when punching a thin electromagnetic steel plate that constitutes a transformer core, but there are various types of oil. Therefore, although the temperature of the preheating can be appropriately changed depending on the type of oil, it is usually a high temperature in a range where oil does not seize.

The preheated transformer core is then vacuum purged. The vacuum purge targets the transformer core in a preheated state.However, in the vacuum purge, the preheat and the vacuum purge may be simultaneously performed by the same device, or the vacuum purge device may be connected immediately after the preheat device. Therefore, preheating and vacuum purging may be performed separately. In either case, it is usually sufficient to perform a vacuum purge at about several mmHg, and the vacuum purge evaporates the oil remaining on the transformer core, and at the same time, the mutual thin plates as described above that compose the transformer core. Remove the air that was brought in between.

Then, after vacuum purging as described above, the pressure is restored in a reducing atmosphere. It is convenient to use a reducing gas in the subsequent annealing for the recompression.

Finally, the transformer core preheated as described above, vacuum-purged, and decompressed in a reducing atmosphere is annealed. For the annealing itself performed in the reducing atmosphere, conventional conditions using an annealing furnace may be applied.

According to the present invention, prior to annealing, the oil remaining on the transformer core and the air introduced between the thin plates constituting the transformer core have been removed in advance, so that the above-mentioned problems occur. Since it does not occur originally, and the dew point of the atmosphere during annealing can be made higher than before, it is possible to promote decarburization of the thin plate and improve product quality. To further improve product quality, use residual heat during annealing during annealing, or heat after annealing and heat treat the transformer core separately in an oxidizing atmosphere (so-called bluing). It is good to prevent the generation of rust.

Hereinafter, in order to further clarify the configuration and effects of the present invention,
Examples will be given.

<Example> Using the heat treatment apparatus shown in FIG. 1, the transformer core was heat-treated under the conditions described below. The illustrated heat treatment apparatus comprises a preheating chamber 1, a vacuum purge chamber 2, and an annealing furnace 3 which are partitioned by an openable / closable door, which are connected in this order. The annealing furnace 3 includes a heating chamber 3a and a slow cooling chamber 3b. The rear chamber 4 is connected to the slow cooling chamber 3b.

Heat treatment conditions: Preheating chamber temperature: 100 ° C, vacuum purge chamber pressure: 1 mmHg, reducing gas used for recompressing vacuum purge chamber; same as reducing gas during annealing, annealing furnace temperature; 750 ° C, inside annealing furnace Atmosphere gas; C
A reducing gas with 8% O and a dew point of 20 ° C.

Separately, as a comparative example by the conventional method, the same transformer core was heated to 350 ° C. in an oxidizing atmosphere and then annealed in the same manner without vacuum purging (however, the dew point of the atmospheric gas was 15 ° C.).

The iron loss of each example is 50 Hz, a relative value at 1.5 terraces, 1.05 after annealing in the case of the comparative example, 1.0 after subjecting it to a physical impact by spontaneously dropping it from a height of 500 mm, The value according to the example was 0.9. Further, the standard deviation of the iron loss was 0.5 according to the example when the value obtained by adding the physical impact of the comparative example to 50 heat-treated transformer cores was 1.0.

<Advantages of the Invention> As described above, the present invention essentially solves the above-mentioned problems that cause iron loss and quality variation of the transformer core, and provides a transformer core after heat treatment. There is an effect that iron loss of the transformer core can be sufficiently reduced and physical quality variation can be reduced at the same time without any physical impact.

[Brief description of drawings]

FIG. 1 is a general view illustrating a heat treatment apparatus that can be used for implementing the present invention. 1 ... Preheating chamber, 2 ... Vacuum purge chamber 3 ... Annealing furnace, 4 ... Rear chamber

Claims (2)

[Claims] 1. A heat treatment for eliminating internal strain or the like of a transformer core, the transformer core is preheated at a temperature at which the oil remaining in the process of making the transformer core does not seize, and in this preheated state A heat treatment method for a transformer core, which comprises performing vacuum purging, restoring pressure in a reducing atmosphere, and further annealing in a reducing atmosphere. 2. The method according to claim 1, wherein preheating or heat treatment is separately performed in an oxidizing atmosphere during or after annealing during annealing.
A heat treatment method for a transformer core according to the item.