An uninterruptible power supply (UPS) system provides power to a critical load when the input power source, typically the mains power fails. The true online UPS provides continuous protection from input power interruptions or surges by means of storage batteries and associated electronic circuitry

HOW DO UPS SYSTEMS WORK? The power conversion process isolates the critical load from the normal mains borne disturbances and similarly isolates the mains from load induced reflected harmonics affecting other loads connected to the input mains feeder. The rectifier converts AC power into

DC for charging a storage battery such as maintenance free lead acid, vented lead acid or Nickel Cadium, it also provides the necessary DC for the continously rated capacity of the inverter. IGBT semiconductor devices are used in our Pulse Width Modulation (PWM) inverters and the control logic creates the precise sinusoidal output waveform with a very low harmonic content. The uninterruptible power sources are

intended for use in the oil, gas, petrochemical and process engineering, power stations, aerospace, airports and defence type applications, where

14 FEBRUARY 2021 | IRISH MANUFACTURING absolutely reliable power is demanded.

MODES OF OPERATION: NORMAL The rectifier converts normal input AC power into DC for the inverter and for charging the battery. The inverter is synchronised with the mains providing it is within the tolerances permitted by the logic, the inverter delivers its closely regulated frequency and voltage through the static switch to the load. Where the reference frequency and

voltage are outside the permitted limits, the inverter will ‘uncouple’ from the mains and will ‘free run’ using its internal oscillator to assure the high stability power for the load.

LOSS OF INPUT POWER In the event of input power failure, the inverter will operate from the battery until the low DC threshold is reached or the input power to the rectifier is restored. When the input AC power to the

rectifier is reinstated, the rectifier resumes the provision of DC for the inverter and it will simultaneously recharge the battery, feed the inverter and the connected critical load. The critical load connected to the

inverter will not be disturbed during the loss and restoration of the input AC power feeding the rectifier.

BYPASS OPERATION The inverter is provided with a sensing circuit which can detect transient overload conditions, sustained overloads and short circuits. The sensing circuit initiates ‘current limit’ which causes the static switch of the inverter to transfer the critical load to the static bypass switch in the emergency alternate line without interruption to the load. The bypass logic will automatically

initate a retransfer of the load from the bypass alternate line, synchronised, without a break back to the inverter once the inverter and reference power source are within the predetermined limits. Our UPS Systems deliver high stability

power with low audible noise. They respond instantaneously to non linear loads and transient load changes in high ambient temperatures in arduous, harsh environmental conditions.

Power Systems International T: +44 (0)1494 871 544


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