Applications Guide, April 2001
Published by Fluke Corporation
This chapter provides applications of problems and phenomena that are likely to occur in a lighting system.
Figure 3. Distribution System: Lighting Loads
Measuring Current Harmonics
Check whether the lighting system causes excessive harmonics. These may influence the system.
- Look at the harmonics spectrum and read the THD value. If the current THD is less than 20%, the harmonic distortion is probably acceptable.
Consider replacing lights with a better quality (which produces less harmonics) or install a harmonic filter to avoid the injection of harmonics into the system.
Measuring Power on Single Phase Loads
Inductive loads, such as fluorescent lamps, cause a phase shift between the voltage and the current. This influences the real power consumption.
- Look at the W reading. It shows the real power consumption of the lights.
- Look at DPF (cos ϕ) reading. Low DPF means that corrective measures have to be taken such as installing capacitors to correct the phase shift between the voltage and the current.
Note: If PF and DPF differ greatly, this indicates the presence of harmonics. Check for harmonics first, before installing capacitors.
Measuring Surge Current
Check for a high inrush currents that may cause voltage sags in a ‘weak’ lighting system. A system is considered ‘weak’ when it has a high impedance.
- Read the peak current. It indicates the maximum current during the moment the lights were turned on.
Tip: Perform a sags and swells measurement (see chapter 2: “Monitoring rapid Voltage Fluctuations”) while turning on the lights to examine whether voltage sags will occur in other parts of the distribution system.