Hazards And Characteristics Of Corona Discharge Of High-voltage Motors

Hazards and characteristics of corona discharge of high-voltage motors

In the production process of high-voltage motors, if the insulation structure itself is defective, or there are problems with coil wrapping, shaping or end fixing during the manufacturing process, such problems are easy to occur.

The electric field on the surface of the insulated coil at the end of the stator winding of the high-voltage motor and the notch part in the radial ventilation channel is high and unevenly distributed, and when the local field strength reaches the critical field strength, the gas is locally ionized or electrons collide and is released, forming a continuous chain reaction of "electron collapse" discharge. At this time, blue fluorescence appears on the surface of the ionized insulating coil, that is, the phenomenon of electricity. Corona produces thermal effects and oxides of ozone and nitrogen that damage insulation.

When the surface layer of the stator thermosetting insulation coil and the groove wall are in poor contact or unstable and channeling, due to the oscillation of electromagnetic force, the contact point is separated immediately, causing the electric spark discharge in the tank, so that the local temperature rises, reaching hundreds to thousands of degrees Celsius, the insulation surface is subject to serious galvanic corrosion, causing pockmarks and spots up to 1 mm and above in a very short time, and the electrocorrosive part changes with vibration and contact conditions rather than regular changes, resulting in insulation breakdown.

Compared to other insulating materials, air is more prone to corona discharge. Therefore, the high-voltage motor coil wrapping, end tightening and immersion process are the key to control.

What are the characteristics of corona discharge?

During the test and operation of the high-voltage motor, there is sometimes a "hissing" sound, which is what we call the corona discharge sound.

Corona discharge is characterized by a "hissing" sound, sometimes a faint glow: a charge discharge occurs when a tip with a small radius of curvature is present on the conductor. The corona discharge may or may not be directed in a particular direction.

When the electricity is discharged, the field strength near the tip is strong, the gas near the tip is ionized, and the charge can leave the conductor; The field strength away from the tip is sharply weakened, and the ionization is incomplete, so only a small current can be established.

Corona discharge can be either continuous or discontinuous pulse discharge. The energy density of corona discharge is much smaller than that of spark discharge. In some cases, if the potential of the tip conductor is raised, the corona develops into a spark leading to another object.

The degree of unevenness of the electric field required to form corona has a lot to do with the type of gas. In a negative gas, corona discharge occurs when the electrode is a plane of the ball and the gap between the electrodes is a sphere radius. Conversely, if the gas is non-electronegative, corona discharge is not generated.

The polarity of corona discharge is determined by the polarity of an electrode with a small radius of curvature. If an electrode with a small radius of curvature has a positive potential, a positive corona discharge occurs, and vice versa. In addition, corona discharge can also be divided into DC corona, AC corona, and high-frequency corona according to the type of voltage supplied. According to the number of corona electrodes present, it is divided into unipolar corona, bipolar corona and multipole corona.