Integrity testing of isolation means in an uninterruptible power supply

An uninterruptible power supply comprising:

• a supply input adapted to be connected to a main power supply;
• an output adapted to be connected to an electrical load;
• a rechargeable energy storage unit adapted to be charged from said supply input;
• a selective isolation means connected between said supply input and said rechargeable energy storage unit for isolating said rechargeable energy storage unit from said supply input during an emergency operation;
• a first means for establishing a reverse polarity across said isolation means for a test period during normal operation;
• and a second means for monitoring a voltage representative of an input voltage to said isolation means and outputting an error signal if the monitored voltage remains at or rises above a reference value during the test period;
• and
• a resistor connected in series between an input to said isolation means and an electrical ground, and wherein said first means includes a test switch connected between a main power supply and said isolation means.

An uninterruptible power supply comprising:

• a supply input adapted to be connected to a main power supply;
• an output adapted to be connected to an electrical load;
• a rechargeable energy storage unit adapted to be charged from Said supply input;
• a selective isolation means connected between said supply input and said rechargeable energy storage unit for isolating said rechargeable energy storage unit from said supply input during an emergency operation;
• a first means for establishing a reverse polarity across said isolation means for a test period during normal operation;
• and a second means for monitoring a voltage representative of an input voltage to said isolation means and outputting an error signal if the monitored voltage remains at or rises above a reference value during the test period;
• and a transformer having a primary winding connected between an output of said isolation means and an input of said rechargeable energy storage unit, and wherein said first means includes a secondary winding of said transformer, a resistor and a transistor connected in series between said input of said rechargeable energy storage unit and an electrical ground.

An uninterruptible power supply comprising:

• a supply input adapted to be connected to a main power supply;
• an output adapted to be connected to an electrical load;
• a rechargeable energy storage unit adapted to be charged from Said supply input;
• a selective isolation means connected between said supply input and said rechargeable energy storage unit for isolating said rechargeable energy storage unit from said supply input during an emergency operation;
• a first means for establishing a reverse polarity across said isolation means for a test period during normal operation;
• and a second means for monitoring a voltage representative of an input voltage to said isolation means and outputting an error signal if the monitored voltage remains at or rises above a reference value during the test period, wherein said second means includes a comparator connected to an input to the isolation means for comparing the input voltage to said isolation means with the reference value and a controller monitoring an output signal from said comparator.

An uninterruptible power supply comprising:

• a supply input adapted to be connected to a main power supply;
• an output adapted to be connected to an electrical load;
• a rechargeable energy storage unit adapted to be charged from Said supply input;
• a selective isolation means connected between said supply input and said rechargeable energy storage unit for isolating said rechargeable energy storage unit from said supply input during an emergency operation;
• a first means for establishing a reverse polarity across said isolation means for a test period during normal operation;
• and a second means for monitoring a voltage representative of an input voltage to said isolation means and outputting an error signal if the monitored voltage remains at or rises above a reference value during the test period, wherein said second means includes a first resistor network connected between an input to said isolation means and an electrical ground to generate a voltage proportional to the input voltage, a second resistor network connected between an output of said isolation means and the electrical ground to provide the reference value which is proportional to a voltage at an output of said isolation means, and a controller comparing the voltage proportional to the input voltage with the reference value.