Recognizing that air density and humidity affect dielectric breakdown, the standard provides procedures for correcting test voltages based on standard atmospheric conditions (temperature: 20°C, pressure: 101.3 kPa, absolute humidity: 11 g/m³).
| Term | Meaning | |------|---------| | | Maximum voltage the insulation is designed for, considering overvoltage category. | | Rated impulse withstand voltage (Uimp) | Peak voltage of a specified impulse waveform that insulation must withstand. | | Test voltage | The actual high voltage applied (AC, DC, impulse, or combined). | | Withstand test | Pass/fail test: apply specified voltage – no disruptive discharge allowed. | | Disruptive discharge | Flashover, puncture, or spark-over through or across insulation. | | Overvoltage category (IEC 60664-1) | Categories I–IV (e.g., Cat II for appliances, Cat IV for service entrance). Higher category → higher required Uimp. | iec 61180-1
: Because results can vary, the standard often requires a minimum of three impulses for each polarity (positive and negative) with at least one second between pulses. Recognizing that air density and humidity affect dielectric
❌ Applying AC rms voltage where impulse is required – different stress mechanisms. ❌ Ignoring waveform tolerance – a 1.5/40 μs impulse is not valid. ❌ Testing without a calibrated measuring system – results unrepeatable. ❌ Using wrong polarity – some insulation (e.g., polluted surfaces) is polarity-sensitive. ❌ Not correcting for altitude – above 2000 m, test voltage must be reduced (or air gaps increased). | | Test voltage | The actual high
: Typically performed at power frequencies ( ) to simulate standard operational conditions.