ABSTRACT

Uninterruptible Power Supply or commonly known as UPS, thought to be designed for emergency power supply, is a very common device in India. However, along with emergency power supply, it is also now used to correct other power quality problems. An UPS can be used to solve power quality issues such as over voltage, under voltage, constant frequency, noise and voltage dips. For power supply to critical equipments, UPS is also used as an isolated mode of power supply where common mode noise needs to be filtered out and protect the equipment from neutral related faults or issues in the main supply network.

But like a coin, there are two sides to everything. UPS is a solution to lot of power quality problems; it also generates harmonics, which has its own negative impact on the system. In loads like IT industries, data centers typically all loads except HVAC is fed through UPS, or in industries where major loads are fed through UPS, harmonics generated through the UPS could be a major issue. These current harmonics can cause reliability and safety issues apart from causing energy loss and derating of equipments such as transformers, motors, cables etc.

There are cases where many such installations are opting for harmonic filters to mitigate harmonics generated from UPS. However, if care is taken during the purchase of UPS, then additional investment, infrastructure and maintenance budget would not have been required for harmonic filter.

This case study presents a comparison of two UPS on test bench. The test was carried out to demonstrate low harmonics UPS.

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