Applicable to the off-line electrical measurement of partial discharges (PD) that occur in electrical insulation systems (EIS) when stressed by repetitive voltage impulses having a rise time of 50 us or less. Typical applications are EIS belonging to apparatus driven by power electronics, such as motors. Excluded are - methods based on optical or ultrasonic PD detection, - fields of application for PD measurements when stressed by non-repetitive impulse voltages.