Which Features do you need?

Power Quality Monitors Start Page Uses of Power Quality Monitors Which Features do you need?

In general, the more features your instrument has, the more you will pay for the instrument. Following are a few questions you should ask before calling the instrument salesperson:

• Do you need to monitor current as well as voltage? Voltage probes and recorders are less costly than current devices. If you suspect your facility is being impacted by harmonics from inside or outside, you may want to spend the extra to monitor currents.
• Do you need three-phase monitoring and recording?  If you are mainly working on single phase circuits, the additional wires and probes just get in the way. However, if you are hoping to catch a voltage sag on any phase, a three phase monitor will be needed.
• Will neutral currents be of interest?  This requires a meter with four current probes. Neutral currents are needed when analyzing triplen harmonics, 3rd, 6th, 9th etc. that normally show up in the neutral. Computer power supplies generate the triplen harmonics.
• What will you do with all the data?  Monitor memory can fill up rapidly depending on the sample rate selected.  You can store on a computer or portable memory device, or just not save past data.  Different manufactures have different approaches to analysis, storage and retrieval. You want the best for your situation. 
• What frequency of response is needed?  If your equipment is relatively insensitive to transients and higher harmonics, a lower frequency monitor is sufficient and will be less costly.  Examples include electric heating processes, aluminum reduction cells, and refrigeration systems.
• Will lightning be a likely problem?  If so, your monitor should be able to record the transient.
• Might switching transients interrupt operations? Variable speed drives and motor contactors are often susceptible. Computers can also drop out. Your monitor should be good for 25th harmonic or higher.  Monitors with 50th harmonic capability have better resolution, but tend to cost more.
• Would you like to see the actual waveform of the event?  Waveform capture is a common feature.
• Will some level of harmonic distortion cause transformer and other equipment overload, or miss-operation?  You need a reliable measure of total harmonic distortion.
• Do you wish to link the monitor to a central data collection system? Monitor manufactures offer telephone modem and network connections and software to facilitate data collection and display.  Displays usually include:
  • list of PQ disruptions with magnitude and time
  • data tables
  • history of parameters versus time
  • density of probability, with cumulated values
  • statistics of events versus standard curve (e.g. CBEMA/ITI Curve)
• Do you need to quantify rapid changes in voltage for light flicker? Monitor should include an IEC 1000-4-15 calculation.
• Does the unit have enough storage to record necessary data until you can download the data? Will you access daily, once a week, or twice per month?
• If you will be sharing data with others, does the unit meet the IEEE 519 and 1159 or IEC 1000-4-7 standards?
• Other considerations include ease of use, ease of setup, environment monitor will be installed in, support, and warranty.