Parsing the shock high voltage flashover test method for you
the following analytical shock high voltage flashover test method for you, in the point of failure when resistance is not very high, if use direct method, due to the dc leakage current is larger, the voltage dropped to almost all the internal resistance of high pressure test equipment, the voltage on the cable is very small, not form flashover failure point. Need to use the shock high voltage flashover test method, referred to as 'flash method. Most impact flash method is also suitable for testing flashover fault, open circuit and low resistance, short circuit fault. Of course, due to the direct method of waveform is relatively simple, easy to obtain more accurate results, should try to use direct flash test.
( 1) Connection
impact flash method of wiring, it with the method of connection are basically the same, the difference is in the energy storage capacitance C and G series of people a spherical clearance between cable. First of all, by adjusting the pressure regulating booster for capacitance C charge, when the capacitance C voltage is high enough, the spherical gap breakdown, G cable capacitance C to discharge, a process that is equivalent to the dc power supply voltage of the internal resistance is close to zero suddenly added to the cable.
( 2) Fault click wear or not judgment
is one of the key impact flash method is to determine whether a fault point breakdown discharge. Some inexperienced testers tend to think, as long as the ball discharge gap, the breakdown point of failure. Obviously this idea is not correct. Ball gap breakdown is related to the gap distance and the applied voltage amplitude. The greater the distance, the higher the breakdown voltage required clearance, through ball clearance to the higher the voltage on the cable. And the breakdown of cable fault point is dependent on whether the fault point voltage exceeds the critical breakdown voltage, if the clearance is small, the impact of the cable on high pressure is less than wear fault click voltage, obviously, will not appear breakdown phenomenon.
in addition to according to the recorded waveform judgment, but also through the following phenomenon to determine whether the fault point breakdown.
1) cable fault points breakdown, not generally ball gap discharge voice hoarse, not crisp, weak and spark; And fault click wear, the ball discharge gap is ringing loud, spark is bigger.
(2) the cable fault point breakdown, not an ammeter swing is small; And when fault click wear, ammeter pointer swing range is larger.
( 3) Directly breakdown of pulse current waveform
in the high voltage equipment through ball gap to the high voltage signal amplitude on the cable is greater than the critical breakdown voltage, the point of failure voltage wave through the point of failure after a certain time, fault point ionization and breakdown discharge, this situation is called high voltage pulse breakdown directly.
the pulse current waveform of the first pulse is ball gap capacitance caused by cable discharge breakdown, the second pulse by fault point from the point of discharge current pulse and in the result of measurement point reflected pulse amplitude is twice that of discharge current pulse is 2 e/Zo Considering transmission losses, the actual value is smaller) 。 After pulse is popular electric wave bounces back and forth between the fault point and measurement point, negative pulse waveform on the second and third time lag between the negative pulse delta t = 2 r, corresponding to the current pulse in a back and forth between the fault point and measurement point, the time needed for the available to calculate the distance between the fault point and measurement point.
( 4) Breakdown of cable fault point
both direct flash method and flash method and only make the fault point discharge and is fully discharge, get the right pulse current waveform, can correctly measure the fault distance. Form here to discuss the cable fault point of breakdown, and measures of how to make the cable fault point fully discharge.
click cable fault in the form of wear. Cable fault click wear basically can be divided into two forms, electric breakdown and thermal breakdown. Electric breakdown when the voltage is high, the field strength is enough big, medium, small amounts of free electrons will exist in the collision occurs under the electric field is free, free electron collision neutral molecules, make its motivation of free and generate new electrons and positive ions, these electrons and positive ions for electric energy and other neutral molecules collide with each other, after the development the process, make the medium electron flow 'avalanche' intensified, dielectric breakdown, caused by the formation of conductive channel, the point of failure is powerful electron flow moment short circuit. Used in cable fault test, dc high voltage or high voltage impact make cable fault click wear, effect time is very short, belongs to the electric breakdown.
thermal breakdown is cable insulation medium under the action of electric field, due to the heat generated by the dielectric loss insulating medium temperature. If the calorific value is greater than the surrounding medium emit heat, the temperature rising. With temperature rising, the dielectric happened burnt, cracking or partial melting, and then lead to breakdown. Time is long, the thermal breakdown voltage generally occur in the process of cable operation. Cable fault test, fault point in dc arc or impact under the action of high pressure, appear breakdown phenomenon, every breakdown, will lead to further into the insulating medium damage, plasma channel is widening. In general, will make the point of failure resistance is reduced, the critical breakdown voltage drop. And in some special cases, such as fault point be affected with damp be affected with damp is more serious, due to the heat generated by the arc fault point discharge fault point moisture evaporation, drying effect, it will appear high insulation resistance phenomenon.
that's analytical shock high voltage flashover test method for you all, hope to inspire you and help.