Our new case study shows how resonances can be brought under control even in unstable island networks.

The ABM active broadband filter is THE tool for resonance damping and superharmonic compensation.

Safety lighting must function – even in the event of a power failure

Sports stadiums must have a safety power supply system that maintains the operation of safety-related equipment and facilities in the event of a power failure. This is especially important for lighting and floodlighting when they serve as security lighting. The emergency lights must function under all circumstances. Especially in an emergency, the fuses must not be allowed to blow. This case study illustrates the high voltage distortions that can be caused by modern ballasts when supplied by an emergency battery system. Currents increased by resonance lead to fuse failure. An active broadband filter eliminates the interference and ensures emergency lighting.


During the renovation of the electrical installation in a soccer stadium, the floodlighting and emergency lighting were also replaced. There are 2 safety lights installed on each of the floodlight poles, which are intended to light up in case of emergency in order to be able to provide sufficient luminosity for evacuation of the stadium. In the event of a power failure, a battery system with inverter ensures operation.
During operation, it was found that the circuit breakers of the safety luminaires tripped even though their rated current was not reached according to the data sheet. Thus, the functionality of the system in battery mode was not guaranteed. For a more detailed investigation of the problem, PQ ENGINEERING Nosswitz GmbH was commissioned.

Figure 1 Emergency power supply for safety lighting (rectifier and batteries)

The network analysis showed that the current consumption of the luminaires for normal operation and battery operation differed greatly. While in normal operation the actual load current is shown, in inverter operation a massive superposition of the resonance current is added. The supply voltage was so distorted that the inverter did not operate stably. As the power quality measurement showed, the resonance point shifts with the connection of each luminaire. As soon as eight luminaires are powered by the battery network, a significant harmonic current flows, which heats up the circuit breakers and thus promotes premature tripping.

Figure 2 Voltages of the three phases without filter

Figure 3 Currents of the three phases without filter


A voltage-controlled active broadband filter PQE ABM represents the ideal solution for subsequent problem solving. In contrast to a conventional active filter with current measurement, the PQE ABM is able to respond to and efficiently attenuate resonances that build up with a response time of less than 20 microseconds.

The resonance point is damped in battery mode and thus the high resonance current (= harmonic current) is also reduced via the circuit breakers.

Figure 4 Voltages of the three phases with PQE ABM switched on

Figure 5 Currents of the three phases with connected PQE ABM

In both mains and battery operation, the levels of harmonic voltages are significantly reduced, and resonance effects are damped. The conditions are in accordance with the standards. The supply voltage shows the ideal course again.


  • Stable supply voltage in all operating states

  • Fully automatic operation – the filter responds directly to the voltage distortions

  • Very low losses of the filter, thus no additional load on the emergency power supply

  • Easy integration into existing plants – Only the three phases need to be connected!

  • Low maintenance of the filter system

  • Compliance with DFB and DFL requirements

As a result of this measure, the emergency lights can now be operated stably, both in normal mode and in battery mode, and a contribution is made to increasing safety in the soccer stadium.

In the sense of the 4A concept of PQ ENGINEERING the problem was analyzed, the solution was designed and delivered and supported in the after sales service – everything from one source!

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