Role of UPS in minimising Total Harmonic Distortion

Last Updated on: 11-01-2023

Today, almost every aspect of human life is driven by technology, electrical and electronic systems play a vital role in that mix. Right from server farms that power our social media interactions to advanced robotics in hypercritical manufacturing applications and the mammoth data that gets processed every second in acres of data centers, the role of electronics cannot be understated.

Electricity is the key to powering electronic components, and with increasing complexity and load differentials, the need for stable and continuous power is vital.

Power Quality and Harmonic Distortion

The primary representation of critical power quality is harmonic distortion. When a load is connected to a power source, it draws current to function. This load can be linear (e.g., a motor or capacitor) or a non-linear load (e.g., a variable frequency drive, printers). It is notable that before the 1960s, non-linear loads were completely absent.

Today, the situations are mostly reversed, and we have a plethora of non-linear loads in operation in industrial, commercial and residential applications. Linear loads draw a sinusoidal current, and thus there is no distortion. However, non-linear loads can pull current that is non-sinusoidal, thereby causing distortion.

Harmonics have frequencies that are integer multiples of the waveform’s fundamental frequency. So harmonic distortion represents the deviation between the ideal sinusoidal waveform the network voltage or the load current should have and what is present.

In India’s context of electrical supply, it means that given a waveform with a fundamental frequency of 50 Hz, the 2nd, 3rd, and 4th harmonic components will be at 100Hz, 150Hz and 200Hz, respectively.

Total harmonic distortion (THD) comes in THDI for current and THDV for voltage. THD is the summation of all harmonic components of the voltage or current waveform compared against the fundamental component of the voltage or current wave.

The formula for THDI is given below.

Total Harmonic Distortion

The same formula is applicable for THDV also, with the values of current being substituted with the value of voltage.
The higher the THD percentage, the greater the distortion of the waveform. The ideal sine wave has no harmonic components, as it does not have any disturbance to distort the perfect wave.

Effects of Total Harmonic Distortion

THD could lead to:

  1. Efficiency loss in electrical systems
  2. Overheating leads to the shortening of life in motors and electrical systems
  3. Degradation of insulation materials
  4. Malfunctioning of motors and generators
  5. Unexpected resonance, interference and ‘‘singing.’’
  6. Tripping of MCBs and blown fuses
  7. Damage to power systems
  8. Fire risk

To understand the above effects better by considering the example of a motor.
High harmonic content lowers the power factor, and this causes a double whammy of high power bills and reduced efficiency in motor operation. Added to these, higher eddy currents are being formed, and hysteresis losses to count.

This is because it is harder to magnetise iron and copper—unwanted heat generation degrades the motor core.
The heat also degrades the grease used in bearing lubrication. Any thermal power protection system can also trip, thereby adding to the danger of sudden and unexpected stoppages.
Uncontrolled harmonics can also cause bearing currents to circulate, which causes arching and may cause the bearing to seize while increasing the friction loss.

In a really bad case, negative harmonics of higher frequency can cause the motor to stall and break due to pulsations. The shaft can also break due to the high torsion forces created or vibrating when in operation.

Role of a UPS System in Mitigating THD

When the mains are connected to a critical load via a UPS battery, the UPS system has a two-pronged function:

  1. It ensures that there is an uninterrupted power supply to the load
  2. It ensures that battery power is supplied when the load is high.

Thus, a well-designed UPS system with its combination of filters, rectifiers ensures seamless connectivity, excellent power conditioning and continuity, thereby minimising the detrimental effect of a THD. In applications where distortion in power or interruption can lead to single or multiple power failures, a UPS system acts as the vanguard to ensure safety and system reliability.


With the increase in non-linear loads across organisations and manufacturing units, electrical power must be stable and well-conditioned. While passive filter devices may seem an easy solution, a well-designed UPS system offers the best reliability. Where there are no absolute standards for minimising THD or catering to the same, guidelines from leading institutions like IEEE and the BSI can design systems and achieve reliability. Numeric has rich experience in this niche and has offered solutions for mission-critical applications. For more details, contact us

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