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Mitigating harmonic distortion with these critical steps

By Jonathan Duncan, VP Anglophone Africa, Secure Power Solutions at Schneider Electric

Datacentre operators and owners continue to enhance PUE (power usage effectiveness) with a number of technologies that allow for improved efficiency.  Cooling forms a critical part of improved PUE planning and integrating innovations such as electronically commutated (EC) fans and variable speed drives (VSD) are making important inroads in optimising operations.

However, an important factor to consider is that both EC fans and VSDs (in cooling system) can lead to harmonic distortion, thus negatively impacting electrical distribution equipment.

Harmonic distortion is caused by nonlinear devices such as ECs, VSDs and other power electronic devices like fluorescent lighting. These devices present nonlinear loads which then result in a current waveform that is not proportional to the applied voltage and causes reactive power within an electrical distribution system.

In the case of EC devices, its rectified/inverter package draws a distorted AC current waveform which effects a nonlinear load.  Similarly, VSDs use pulse width modulation (PWM) to control the speed of the motors and can result in the generation of a nonlinear loads and additional harmonic distortion in the electrical power network.

Without proper harmonic mitigation, nonlinear loads will distort the AC power distribution upstream and can cause significant issues within a facility such as:

  • Increased power losses.
  • Overheating of equipment.
  • Damage to power-sensitive devices like motors and transformers.
  • Power factor decrease with an increase in currents and voltage distortion.
  • Premature wear on filtering devices as employed within switch mode power supplies like IT equipment.

Monitor and control

To take advantage of the benefits that come with technologies such as VSDs and EC devices, organisations should measure and control harmonic distortion to ensure optimal performance and avoid possible long-term damage to equipment.

Fortunately, there are solutions available such as passive filters which are “tuned” for specific harmonic orders or Active Filters (AF) which are electronic devices that inject adaptative counter-harmonics to neutralise targeted harmonics, either stemming from one or several loads.

The use of a system extended PLC (SE PLC) can be very effective in coordinating the operation of VSDs in cooling systems. These SE PLCs are programmed to monitor and control the VSDs to provide more efficient performance of the cooling network. This allows for real-time adjustments to be made to the VSDs to optimise the performance of the cooling system.

Lastly, at Schneider Electric we recommend that organisations monitor their facility’s overall power quality to timely detect abnormal harmonic levels. This can be done locally through adapted power monitoring devices or globally on a large network through power management software and power reliability services.

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