What is Uninterruptible Power Supply (UPS) Input Current Harmonic?
UPS systems distort input current and voltage, leading to voltage waveform notches. To mitigate this distortion, a generator should be oversized by a ratio of 2:1 relative to the UPS capacity (e.g., a 100kVA UPS requires a 200kVA generator). Laser printers and lighting circuits should not be connected to UPS systems due to increased harmonic distortion. True ON-Line UPS are better as they provide cleaner power. Only loads requiring clean power should connect to a UPS to avoid distortion and bypass issues.
Most UPS systems inherently distort the input current and voltage powering them as they electronically endeavour to harmonise the wave patterns.
A cause to oversizing generators backing up UPS Systems. This non-linear current causes the notches seen in the voltage wave shape form. This distortion is overcome by either a 6 or 12 pulse rectifier within the UPS. Generators and non-UPS connected loads see this distorted voltage as their power source. Since most loads desire a clean voltage source, the UPS-caused voltage notches create a potential problem.
Sizing the generator on the basis of 2:1 with the UPS will overcome this problem. For example, a 100kVA UPS will require a 200kVA Diesel Generator as both standby and prime power source. The clean waveform is apparent as well as nearly unity power i.e. 1:1.
Additionally, it is NEVER wise to put laser printers or lighting circuits onto any UPS. These will cause greater harmonic distortion. Harmonic distortion is less of an issue when using True ON-Line UPS. Producing their own power from AC to DC and then back to AC. Only items requiring CLEAN power should be connected to the UPS. This avoids distortion issues in the future as well as preventing the UPS from going into bypass. Protecting itself against wild or extreme wave form patterns.
