The main factors affecting the breakdown voltage of solid dielectrics and the equipment used:
1 Voltage action time
The longer the voltage is in action, the lower the breakdown voltage. When the voltage acts long enough to cause thermal breakdown or electrical agingBreakdown voltageSteep decline. Therefore, when choosing insulating materials, insulation structures, working field strengths, etc., it is necessary to pay attention to long-term electrical strength.
2 Temperature
When the ambient temperature is high to a certain level, the electrical breakdown turns into thermal breakdownBreakdown voltageUB has dropped dramatically. And the higher the ambient temperature, the hotterBreakdown voltageThe lower.
3 Uniformity of the electric field
In a uniform field, UB increases linearly with increasing dielectric thickness;In an inhomogeneous field, the greater the dielectric thickness, the less homogeneous the electric field is, and the UB no longer rises in a straight line. When the dielectric thickness increases to the point where heat dissipation is difficult and thermal breakdown occurs, it makes no sense to continue increasing the dielectric thickness.
4 Types of voltages
ShockBreakdown voltageHigher than the peak breakdown voltage of the power frequency. Low loss under DC, DCBreakdown voltagealso than the peak of the power frequencyBreakdown voltageHigh. Partial discharge at high frequencies is severe, and the heating is also severeBreakdown voltageMinimum.
5 Cumulative Effects
Since the damage of solid insulation is irreversible, if a certain degree of insulation damage occurs each time when the same amplitude voltage is applied multiple times, the damage to the insulation can gradually accumulate and eventually break down at this voltage. When the voltage is low, there is no cumulative effect.
6 Partial discharge
Partial discharge is a great threat to the long-term electrical strength of the insulating material. Taking oil-paper insulation as an example, once partial discharge occurs, it will have electrical, thermal, chemical and other corrosive effects on oil-impregnated paper, which is very harmful. In order to improve the partial discharge resistance and improve the electrical strength of the oil-paper insulation under long-term voltage, it is possible to improve the air absorption performance of the impregnating agent and increase the dielectric constant of the impregnating agent. Partial discharge is not allowed to occur under the action of long-term working voltage, otherwise the expansion of the electrical equipment shell (such as the capacitor iron shell) and premature damage will occur under the action of long-term partial discharge.
7 Polar effects
The breakdown of solid dielectrics has a pronounced polar effect, similar to that of gases, which is usually positiveBreakdown voltageBreakdown voltage below negative polarity.
8 Edge Effects
Different structures are used for dielectricsBreakdown voltageDuring the test, due to the different electrode edge structures of different structures, the breakdown voltage will be different.
9 Damp
Whether it is damp or not has an extremely important impact on the breakdown of solid dielectrics, and for materials that are not easy to absorb moisture, such as PTFE, after moistureBreakdown voltageDrop by about half;For materials that are easy to absorb moisture, such as paper, fiber, etc., after being wetBreakdown voltageThere may be only a few hundredths left.
10 Mechanical load
Mechanical stress may cause the insulation material to crack and loosen, makingBreakdown voltageDecline.
Aerospace vertical and horizontal ZJC-50KV voltage breakdown tester: