Harmonic distortion in pharmaceutical industry power systems

Text: Amit R. Ingle – Elomatic India

The Indian pharmaceutical industry currently tops the list of the country’s science-based industries and is set to grow at a compound annual growth rate of 20% over the coming years. One of the challenges faced by the growing sector is ensuring the required power quality to sustain high-speed production. Harmonic distortion, which generally results from nonlinear loads in the power system, poses one of the greatest threats to power quality in the sector. For power utility boards, the goal is to meet the pharmaceutical industry’s power demand, while ensuring low losses and improved electrical loading patterns. 

Pharmaceuticals production is increasingly relying on the use of microprocessors and/or electronics-based automated machinery. The use of such equipment increases nonlinear loads in the system and induces a lagging power factor. A nonlinear load with a low power factor draws more current from the source and increases energy losses. 

Such losses and the high current drawn adversely affect the life-expectancy of electrical switch gears, equipment and cables. This also results in significant losses in the electrical energy being supplied by the state. Power utility boards, as such, are quick to issue heavy penalties on end-users in an attempt to curb such energy wasting.  

Capacitator banks can recover lagging power factor  

In order to minimise such losses and the adverse effects on the electronic systems of the plant, it is critical to recover the lagging power factor. Many companies have opted to install a capacitor bank at source level to achieve this. The disadvantage, however, is that it results in an increase in the total harmonics level in the system, which in turn, may create problems in switch gears and cause the electrical failure of a unit or the entire plant. 

The power utility board supplies the ideal sinusoidal voltage waveform (a wave with a smooth repetitive oscillation) at every consumer point. However, the end-user (or the plant utility equipment in this case) may not be able to maintain these ideal conditions. This results in a distorted voltage and current waveform, which is known as harmonic distortion (see the info box for more on harmonic distortion). The main concern of the power utility board is to maintain a sinusoidal voltage waveform at user-points to minimise energy losses. 

Harmonics can be generated in the plant, or it may enter a plant from the power utility board (at the main supply level). The generation of harmonics can cause a wide range of problems, including power losses, malfunctioning of equipment and reduced life-expectancy of switch gears etc. Ultimately, the impact is on the power-factor. If the power utility board needs to correct the power factor, it may sanction users for this intervention. 

Reducing harmonic current with filters 

As capacitor banks do not solve harmonic distortion problems, other innovative solutions such as filters are required. The following paragraphs outline the different kinds of filters available on the market. 

Passive harmonic filters are installed at the individual load level. The filter size is calculated based on the connected load and the reactive power requirements. Harmonic frequencies can be adjusted as per the composed LC circuit within the device. 

A clear advantage of passive harmonic filters is that they reduce the total harmonic distortion at the voltage level THD (U). At full load conditions they improve the power factor and minimise harmonic currents. These filters are, however, expensive and require advanced design skills to implement on connected and running loads. If the system overloads, the current and voltage characteristics may change and exhibit a non-linear load pattern. The range of losses for passive harmonic filters is between 0.5–1.5%.

Active harmonic filters can be connected in series as well as in parallel to the AC networks to reduce harmonic current at non-linear loads and for voltage alteration in grids. The standard voltage distortion range is 5–9%. This range is recommended in some areas, but adherence is, however, not mandatory.

Industrial areas and power utility boards follow the standard guidelines of IEEE 519. This enables them to provide a disturbance-free and pure sinusoidal waveform at the end point. 

Harmonic filters offer the following advantages:

• Increase the productivity and efficiency of equipment
• Reduce energy losses in the system
• Resolve power quality issues
• Energy savings of 10–20% can be achieved
• Reduce total energy cost of the facility
• Increase the life-expectancy of switch gears, cables and other electrical equipment
• Reduce the overall system maintenance cost
• Power factor can be maintained at above 0.95
• Breakeven period for the investment is short

Hybrid filters can be connected either in series or in parallel to the electrical loads and are, in essence, a combination of active and passive filters. The passive filter provides the basic filtering in the system and the active filter mitigates the other harmonics present in the system.

High pass filters are used to minimise the 5th and 7th harmonics levels produced in the system. According to EN-61000-3-4 and IEEE-519 the following factors, among others, should be considered when incorporating high pass filters in designs:

• It reduces losses at the lower and higher harmonic levels. As high pass filters are very expensive, the level of losses needs to be sufficiently high to generate a proper ROI.
• The filter capacity should be designed and calculated as per the requirement, otherwise it may be affected by fast flickering and transient spikes during the process. 
• Sometimes harmonics are generated in the system due to sudden momentary spikes. In such cases the harmonics need to be mitigated immediately. As such, the response time is also crucial.
• Inter-harmonics is a major issue in a facility’s electrical systems. Hence, load synchronisation needs to be conducted properly. If inter-harmonics occurs in a system at source, the type of active filter needs to be reviewed and changed.
• The active harmonics filter rating selection is determined based on the nominal load at the end point.
• The common range of active filters is 380V to 415V and up to 480V. A higher voltage range is also available between 600 and 690V without a step-up transformer.

Conclusion

Capacitor banks can be used at the consumer level to maintain a power factor close to unity and the supplied sinusoidal waveform. A thorough understanding and monitoring of power quality is required in order to minimise losses and save energy.

Active harmonics filters are required for some industrial applications, such as variable frequency drives (VFD), heaters, furnaces, wind and solar plants, CFL lighting, UPS systems and welding. All these applications generate harmonics in the power network. An active filter is a guaranteed solution to mitigate harmonics present in the system, meet all the requirements, and save energy. 

References

IEEE Standard 519-2014, https://standards.ieee.org/findstds/ standard/519-2014.html

“Electric Utility Power System”. A text book by John Smith & McGraw-Hill.