For smaller capacities, the windings are created using enamelled copper or aluminium wire, adopting the vertical concentric coiling technique. With this technique, the coils present a degree of thermal dissipation which is approximately 12% higher than in traditional layer-type insulation windings; a decrease of about 8-12% in the volume of the winding is also obtained, depending on the situation. Windings which we produce using this technique were experimentally subjected to repeated impulse testing with successful results. The tests occurred up to a level of 170 KV and the windings were subsequently supercharged with an induced voltage of up to 200 Hz, up to 3 times the rated voltage.
STRIP WINDINGS AB 1000 winding machine
For higher capacities the winding is produced with aluminium or copper strips, using automated, horizontal-winding equipment.
Form of the winding
The windings we create are normally cylindrical in shape, with the taps points located on the "terminal-mould" side. For smaller capacities and for low-voltage transformers rectangular-shaped coils can also be supplied.
We have performed partial-discharge measurements on several of our coils in accordance with the IEC 726 standards, detecting values constantly below the level of 10 pico-coulomb (pC). We guarantee this level of partial discharge for the user, provided the assembly of the transformers respects the necessary dimensional and procedural parameters, and in particular the distance between HV and LV coils and distances to ground.
We have submitted numerous transformers assembled with our coils to impulse tests in accordance with the IEC 76.1.5 standards and a positive outcome has been obtained. Also for this type of test the observations concerning partial discharge tests remain valid and, that is, that the transformers must be assembled in accordance with the dimensional parameters.
Thermal-shock test according to IEC 726
The test consists in lowering the temperature of the coil to -25° C over a period of 8 hours, and maintaining this temperature for a further 12 hours. It must then be powered with a current at twice the rated value, rising to an excess-temperature of 110° C without causing cracks.
The windings are supplied with an identification tag and each coil has its own serial number. The following tests are normally carried out:
Upon request, the following test is performed:
PLASTICK BLOCKS AND SILICON RUBBER
On request, we can provide clients with pressure pads, which are used to maintain low-voltage windings centred and levelled with respect to the cast-resin coils. The pressure pads are produced with a highly resistant plastic material. As is known, the rubber plugs are used to compensate for slight differences in the sizes of HV and LV coils and, above all, to offset the dimensional variations of the coils caused by working temperatures.
TEMPERATURE DETECTION AND CONTROL UNITS
On request, we also provide electronic control units for the detection of the temperatures of the three LV windings and of the core. Besides monitoring the temperature of the 4 sensors, these units provide the relay contacts for an alarm signal usable for the release of the transformer.
The client's logo can be set in the resin at a depth of 2-3 mm in the terminal-strip section at the front of the coil. The location of the logo will be agreed with the client.
Prices are determined in budgetary proposals on the basis of the client's specifications.
The coils are guaranteed for 24 months from the date of delivery. The guarantee will be signed in a specific contract established by both parties.