Method and apparatus for testing electrical insulation

Claim 1

IN AN APPARATUS FOR CONDUCTING LOW FREQUENCY VOLTAGE TESTS OF ELECTRICAL INSULATION, THE COMBINATION OF MEANS ADAPTED TO SUPPLY ALTERNATING VOLTAGE OF A PREDETERMINED MAGNITUDE AND FREQUENCY, MEANS FOR VARYING THE MAGNITUDE OF THE VOLTAGE WAVE SUPPLIED, THE VOLTAGE WAVE DEFINING AN ENVELOPE WAVE HAVING A FREQUENCY SUBSTANTIALLY LESS THAN THE SUPPLY FREQUENCY, MEANS FOR INCREASING THE MAGNITUDE OF THE ENVELOPE VOLTAGE, MEANS FOR IMPRESSING A PORTION OF THE ENVELOPE VOLTAGE WAVE HAVING A FIRST POLARITY ACROSS THE INSULATION, MEANS FOR IMPRESSING A PORTION OF THE ENVELOPE WAVE HAVING AN OPPOSITE POLARITY ACROSS THE INSULATION, MEANS FOR SWITCHING THE SUPPLY VOLTAGE FROM THE MEANS FOR IMPRESSING VOLTAGE HAVING THE FIRST POLARITY TO THE MEANS FOR IMPRESSING THE VOLTAGE HAVING THE OPPOSITE POLARITY WHEN THE ENVELOPE WAVE SUBSTANTIALLY REACHES A ZERO VALUE, MEANS FOR SWITCHING THE SUPPLY VOLTAGE FROM THE MEANS FOR IMPRESSING VOLTAGE HAVING THE OPPOSITE POLARITY TO THE MEANS FOR IMPRESSING THE VOLTAGE HAVING THE FIRST POLARITY WHEN THE ENVELOPE WAVE SUBSTANTIALLY REACHES A ZERO VALUE, AND MEANS FOR REMOVING THE CHARGE FROM THE INSULATION WHEN THE ENVELOPE VOLTAGE WAVE SUBSTANTIALLY REACHES MAXIMUM VALUES.