In particular, this invention refers to an improved method of insulating turns of coils of synchronous machines having salient poles, and to the resulting product.

The stator of synchronous machines of the prior art is formed by a plurality of metal plates, being usually provided with three-phase windings, which receive the electric current, in the case of a motor, or in which the electric charge is developed, in the case of a generator.

The rotor of a synchronous machine has hubs at which respective poles are fixed. Each of these poles has a coil which, in the case of large-size machines, has a single layer of windings and is manufactured from the solder of copper bars having an adequate length, or still from the fold of copper strips, which form turns where the magnetic field of the machine is developed. These turns are fed with a direct current, generating a continuous magnetic field which turns in synchrony with the rotor.

The rotation of the synchronous machine depends on the frequency of the net- work and the number of poles of the field, as expressed in the following equality: n = 60 x f/p, wherein "f' is the frequency (in Hz), "p" is the number of pairs of poles, and "n" is the rotation (in rpm).

Although the electric insulation of the turns of these pole coils typically includes not only a main insulation, but also an additional insulation, the maintenance of the insula- tion between the turns made in accordance with the prior art is problematic.

Thus, the respective synchronous machines have to be turned off for repairs, or at least some of their pole coins have to be disconnected, for the purpose of eliminating short-circuits between the turns and with the ground.

Such short-circuits occur principally because of unwanted contacts caused by moisture or dirt, or else due to the fact that the main or additional insulation has peeled or is insufficiently glued.

According to the techniques known today, attempts are made to overcome these drawbacks by making the main or additional insulation of the turns with layers of "Nomext paper, either overlapped or glued to each other. The pole coil thus formed is then painted with insulating varnish.

However, the insulating properties of said varnish are not sufficient to avoid the problems mentioned above. In addition, these steps can only be effected manually, which makes the automation of the method impossible.

In view of the above considerations, the main objective of this invention is to provide a method for applying insulation to turns of poles of synchronous machines, which is made in a continuous way and so that the final insulation will not be sensitive to moisture or dirt.

A further objective of the invention is to provide a method for applying insulation to turns of poles which can be automated.

According to the invention, these objectives are achieved by a method for ap- plying insulation to turns of a pole coil of synchronous machines, characterized by including a step of applying an insulating powdered varnish onto the turns.

This invention further relates to a pole coil characterized in that it comprises turns coated with an originally powdered insulation.

The present invention will be better understood from the following description given by way of example, with reference to figure 1, which is a cross-sectional view of a pole of a synchronous machine.

As known from the prior art, a pole coil 2 of a large-size machine is manufac- tured from the solder of copper bars having an adequate length, or else from the fold of copper strips.

Specifically according to the method of this invention, the individual turns 3 of the coils 2 are then spaced away from each other by an appropriate device (not shown).

According to a preferred embodiment, the turns 3 rest, on the outer side, against a sepa- rating comb made of an insulating material.

Four coil combs are used, positioned at the longitudinal ends, opening the verti- cal or horizontal turns. The turns 3 are maintained at a distance preferably of 3 centimeters from each other by this separating comb.

Prior to the use, the separating comb is advantageously coated with a demold- ing material (for example, silicone oil), thus favoring the cleaning and disassembling proc- ess, and enabling it to be reused.

Then the coil 2 and separating comb assembly is suspended with a hoist inside an electrostatic painting cabin (not shown), thus enabling the application of the powdered varnish throughout the surface of the turns 3, except for the contact points of the separating comb.

In this way, the turns 3 are coated with a powdered varnish having electric and thermal characteristics that are described below, the varnish being then hardened by raising the temperature, either by introducing the coil 2 into an oven (not shown), or by passing an electric current through the turns 3, thus generating heat by the Joule effect.

Then said separating comb is spaced away from the coil 2, being coated with varnish and maybe glue at the points where the former contacted the turns 3.

Finally, the coil 2 is ready to be fit onto the pole 1 of the synchronous machine.

As far as the powdered varnish is concerned, according to the invention, on the turns 3 one should use a product which resists temperatures of up to 1550 C and which has an insulating capacity of 25 kV1mm, so that a thin layer of varnish will be sufficient for a po- tential difference of 250V between the turns. Of course, by applying a thicker layer of pow- dered varnish, this type of insulation can withstand potential differences at the turns ranging from 1,500V to 5,000V, thus enabling it to be used as a main insulation between the wind- ings and the pole body itself which is grounded.

One should bear in mind that the above description of the method and the prod- uct resulting therefrom is merely explanatory, the scope of the invention being defined ex- clusively by the accompanying claims.