Expertise for professional power factor correction

Expertise for professional power factor correction

Cause determination for faulty power factor correction systems and problem resolution

The failure of power factor correction systems can have a considerable negative impact on economic processes and high financial consequences. The use of correction systems should help to provide relief to cables. However, instability in the grid can cause overloading, which in turn gives rise to production standstills and increased power costs as a result of a failure to achieve the cos-phi power factor in accordance with the TABs. Qiagen N.V. approached Janitza electronics GmbH for advice on combatting the problem of faulty power correction systems.

Qiagen N.V., headquartered in Hilden, is renowned for the development and production of sample-preparation and testing technologies for molecular diagnostics, the pharmaceutical industry, academic research and applied testing (source: Wikipedia).

The problem is not only one which affects the network.

Qiagen‘s laboratories use dozens of non-linear loads, which means that the network is subject to not only a high level of dissymmetry, but also high harmonic loads and load fluctuations.

High harmonic loads increase the power consumption of capacitors, resulting in increased generation of heat, especially in filter circuit reactors. These temperature increases lead to permanent capacitor damage and therefore a reduced life expectancy. If the mechanical resistance of the dielectric is impaired, the breakaway device may cease to function, giving rise to considerable safety deficiencies.

In contactor-controlled systems, the controller is forced to wait until the capacitors have discharged before switching them on again. This gives the systems a certain sluggishness.

The discharge time of capacitors is typically around 40 seconds, although more often they are set to one minute. If a contactor were to switch every minute, the number of switching operations would be 525,600 per year, although conventional capacitor contactors are designed for a maximum of just 100,000 switching operations over their service life. This would see the permitted number of operations being reached after just three months. This tells us that contactors are highly unsuitable for switching capacitors with rapidly changing load conditions.

On two power factor correction systems operated by a competitor company, this problem led to a significant increase in the need for repairs during the systems‘ six year service life (faulty contactors and capacitors), as well as malfunctions and, ultimately, system burnout.

Image 1: An evaluation as per the standard considers the number of limit violations as a percentage of the total number of all values of a measurand
Image 1: An evaluation as per the standard considers the number of limit violations as a percentage of the total number of all values of a measurand
Image 2: Overview of measurement data set
Image 2: Overview of measurement data set

Procedures and solution processes

As soon as Janitza electronics had been called in, it set to work performing a week-long power quality measurement, and the problems outlined above were soon apparent. The new systems were subsequently designed to incorporate the following features:

Owing to rapid load fluctuations, the systems were designed to be partially controlled by thyristor controllers, instead of (sluggish) contactors. This hybrid switching approach helped to prevent excessive switching of contactors and capacitors.

In addition, the systems were given a reinforced design, incorporating higher-voltage capacitors (525 V) as well as filter circuit reactors with a larger copper cross-section, so as to prevent overloading due to harmonics, and the resulting excess temperatures.

As a purely precautionary measure, more powerful filter fans were also installed.

Conclusion

The service life of a capacitor is largely determined by the switching frequency, rather than the duty cycle. Voltage peaks experienced when switching lead to partial discharging in the dielectric and to more rapid ageing of the capacitor. Capacitor contactors can also suffer from excessive switching frequencies.

The use of hybrid power factor correction has helped to prevent the premature ageing of contactors and capacitors, as the rapid switching operations handled by thyristors take place at the zero crossing, preventing the occurrence of peaks. Only the slowly changing base load is compensated by the more sluggish contactors.

The Prophi 6R6T power factor controller from Janitza is currently the world‘s only power factor controller to provide the ideal conditions for this. It also allows dynamic compensation at roughly the same price as conventional power factor correction systems.

Image 3: System design
Image 3: System design
Image 4: The Prophi power factor controller has optimum control performance
Image 4: The Prophi power factor controller has optimum control performance

Author

Qiagen N.V.
www.qiagen.com/en

Company profiles

Janitza® electronics GmbH

Janitza electronics GmbH is a German company and has been active for 50 years in the manufacturing of systems for efficient power application, energy measurement and cost savings. As a globally renowned manufacturer of network monitoring and energy management systems, digital integrated measurement devices, power factor controllers and compensation systems, the company stands for the highest quality standards and innovations. Products are manufactured according to leading-edge expertise with state-of-the-art production technology. At Janitza, quality management is an ongoing managerial task (e.g. ISO 9001). Comprehensive know-how, competent consultancy and concept generation, right through to the commissioning of tailored solutions, ensure fulfilment of customer wishes and requirements.

Qiagen N.V.

The company as it is today was established on 29 November 1984 by a team of scientists from Heinrich Heine University Düsseldorf. Qiagen‘s first activities included the development of new methods for the purification of nucleic acids as carriers of genetic information. To work with the different molecules of a cell, such as nucleic acids (DNA and RNA) and proteins, they must first be separated from other cellular components and cleaned. The discovery shortened the two to three-day preparation time for plasmids, the small circular DNA molecules of a bacteria cell, to just two hours.

Further milestones in the evolution of the company include its flotation on the American technology-focused stock exchange NASDAQ in 1996, the first German company to do so, and the foundation of the holding company QIAGEN N.V. in the Dutch city of Venlo. The following year saw the company listed on the Frankfurt stock exchange TecDAX (source: Wikipedia).

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