Excitation transformer is a device which provides three-phase AC excitation power for synchronous generator excitation system.

In addition to the characteristics of ordinary dry transformer with high insulation strength, small partial discharge, strong short-circuit resistance, outstanding flame retardant performance, low operating loss, low noise, maintenance-free, convenient installation and debugging, epoxy cast dry excitation transformer also has the following characteristics:

1. Iron core

The iron core is the magnetic circuit and skeleton of the transformer, which is composed of silicon steel sheet and clamping device. The core material is made of high-quality cold-rolled grain oriented silicon steel sheet, 45° full oblique joint structure, and the surface is sealed with special resin; The saturation magnetic flux density of cold-rolled grain-oriented silicon steel sheet is about 2.1T, and the output voltage rises when the generator is strongly excited. In order to avoid core saturation, the suitable working magnetic density must be selected. Under this working magnetic density, the no-load loss of the transformer is usually very small, and the noise is also very low, which is a low noise and energy-saving product.

2. Winding

The winding is the most important component of a dry-type transformer, mainly composed of wires and insulation structures (resin). The structure of the winding determines the rated capacity, rated voltage, and operating conditions; High voltage windings are generally Y-junction wires, which can withstand low voltage and high current. Therefore, larger wire cross-sections, good mechanical strength, and strong resistance to sudden short circuits can be selected; The low-voltage winding is connected to the D line, which is short circuited to odd harmonics, and the phase potential waveform is close to a sine wave; This type of wiring group reduces the impact of harmonic currents on the transformer core and winding, and improves the working efficiency of the transformer.

3. Isolation

The load of the excitation transformer is a thyristor rectifier, which makes the winding current non sinusoidal. In order to reduce the overvoltage on the low voltage side and suppress the interference of high-order harmonics, a Faraday shielding layer is installed between the high and low voltage windings, which is reliably grounded together with the iron core.