How to Prevent Corona Discharge During Cable Testing

In the partial discharge will be accompanied by a corona discharge, in order to prevent corona discharge, we must first know how the corona discharge is formed.

Under DC voltage, positive and negative corona poles gather space charges near the tip electrode. In the negative corona, when the electrons collide and ionize, the electrons are driven away from the space of the tip electrode and form negative ions. When the electric field is strengthened, the positive ions are attracted into the electrode. When a pulse current, negative ions are diffused to the interstitial space. After that, the process of ionizing and charged particles was started again. This cycle, so that there are many pulses in the form of corona current. If the voltage continues to rise, the pulse frequency of corona current increases, the negative value increases, the conversion into a glow discharge, the voltage then increased, the negative flow injection, because of its shape, also known as feather discharge or brush discharge . When the negative injection current can continue to develop to the opposite electrode, it will lead to spark discharge, so that the entire gap breakdown. The positive corona distributes positive ions in the vicinity of the tip electrode, but is constantly repulsed into the interstitial space, while the electrons are drawn into the electrode, again forming a repetitive pulsed current corona. As voltage continues to rise, a streamer discharge occurs and can result in a gap breakdown.

Corona discharges are characterized by a "hissing" sound, sometimes faint glow, and corona discharge when a small tip is present on the surface of the conductor. Corona discharges may or may not point to other objects in a particular direction. Corona discharge, near the tip of the electric field intensity is strong, near the tip of the gas ionization, the charge can leave the conductor; and far away from the tip of the field abruptly weakened, incomplete ionization, which can only establish a small current. Corona discharge characteristics are accompanied by "hissing" sound, sometimes faint glow. Corona discharge can be continuous discharge, it can be continuous pulse discharge, corona discharge energy density is much smaller than the spark discharge energy density. In some cases, if the potential of the tip conductor is raised, the corona can develop into a spark that leads to another object. Finished product withstand voltage test, the conductor must be inserted into the copper connector, tighten the set screw to make it firmly fixed to the cable head, with cotton cloth 醮 take anhydrous alcohol to carefully clean the exposed part of insulation, if the conductor and high pressure parts Poor contact also results in cutting-edge corona discharge. In the three insulated core to do high-voltage test, the insulating medium must be separated to prevent corona discharge each other, in the stripping head in strict accordance with the operating procedures, with a plane from the cable end of the exploitation of semi-conductive shield inward, stripping and insulation Conductor shielding, the length of the exploitation of 8.7 / 15KV and below greater than 15cm, 12 / 20KV ~ 20 / 35KV is greater than 20cm, peel thickness just stripped insulation semi-conductive shielding layer is appropriate, pay attention to the final retraction action, the root should be round, Not allowed to have sharp corners, after stripping the insulation part does not allow a deep knife marks or black semi-conductive shielding debris. Use large terminal strip insulation and conductor shielding should be exposed conductor 5cm is appropriate, the small terminal only stripped of the outer shield, the surface is not allowed to have any cutting edge.

Occurrence of corona, for high-voltage electrical equipment, equipment will gradually undermine the insulation properties of space charge of corona discharge under certain conditions, but also improve the breakdown strength of the role. In doing pressure test, to strengthen preventive measures to prevent the occurrence of corona discharge, improve product inspection efficiency.