First, under the action of DC voltage, the positive negative corona poles gather space charge near the tip electrode. In the negative corona, when the electron collision ionization, the electrons are driven away from the tip of the electrode space, and the formation of negative ions, near the surface of the electrode gathered odd positive ions, the electric field continues to strengthen, the positive ions are sucked into the electrode, at this time a pulse current, negative ions spread to the gap space. The next ionization and charged particle motions are then repeated. So that there is a lot of pulse form of Corona current. If the voltage continues to rise, corona current pulse frequency increases, negative increase, converted to glow discharge, voltage rise, a negative streamer discharge, because its shape is called plume discharge or brush-like discharge. When the negative streamer discharge can continue to develop to the opposite electrode, it will lead to spark discharge, the whole gap breakdown. Positive Corona near the tip of the electrode also distributes positive ions, but is constantly being pushed to the clearance space, and electrons are sucked into the electrodes, the same form of repetitive pulse current corona.

When the voltage continues to rise, a streamer discharge occurs, which can lead to gap breakdown. Corona discharge is characterized by a "hissing" sound, sometimes a faint glow, when the conductor on the surface of a small tip exists, will be corona discharge. Corona discharges may point to other objects or may not point to a particular direction. Corona discharge, near the tip of the electric field intensity is very strong, near the tip of the gas is ionized, the charge can leave the conductor, and far away from the edge of the sharp decline in field strength, ionization is not complete, so can only establish a small current. Corona discharges are characterized by a "hissing" sound, sometimes with a faint glow. Corona discharge can be continuous discharge or continuous pulse discharge, the energy density of corona discharge is much less than the energy density of spark discharge. 　　In some cases, if the potential of the tip conductor is elevated, the corona will develop into a spark to another object. Finished product test withstand pressure test, the conductor must be inserted into the copper joint, tighten the fixing screws, so that it firmly fixed in the cable head, with cotton cloth to take anhydrous alcohol will be insulated exposed parts carefully wiped, if the conductor and high-pressure site contact is not good also lead to cutting-edge corona discharge. In three insulation core to do high pressure test, the insulating medium must be separated, to prevent corona discharge, in strict accordance with the operating procedures, in the stripping of the cable end to the exploitation of the half conductive shielding layer, stripping insulation and conductor shielding, exploitation length 8.7/15kv and the following is greater than 15cm,12/20kv~20/ 35KV is greater than 20cm, peel thickness requirements to just peel off insulation half conductive shielding layer is appropriate, pay attention to the last knife action, the root should be round, no sharp angle, after the insulation part of the stripping is not allowed to have a deep knife or black half conductive shielding debris.

The use of large terminals stripping insulation and conductor shielding should be exposed to 5cm conductor, small terminals only need to peel outside shielding, the surface is not allowed to have any cutting-edge. Corona, for high-voltage electrical equipment, will gradually destroy the equipment insulation performance, corona discharge space charge under certain conditions and improve the gap breakdown strength. In the pressure test, we should strengthen preventive measures to prevent corona discharge and improve the efficiency of finished product inspection.