Making Watt-Hour Measurements with Fluke Power Quality Analyzers

May 9, 2021 | Power quality

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The need to manage power is never more critical than when power prices skyrocket and power quality becomes suspect. Electrical technicians today are more aware of power consumption and are on the watch for consumption that's higher than anticipated. Once that occurs, technicians must become detectives and try to trace the power consumption back to its source.

Fluke single and three phase power quality analyzers are excellent tools for conducting the portable energy audits necessary to track down energy draining devices.

This application note details the procedures for using Fluke power quality analyzers for average watt measurements and converting those to watt-hours.

Average Wattage to Watt-Hours Conversion

Fluke power quality analyzers can provide a reading of average wattage over time, a value that can be easily used to determine watt-hours. To convert average watts to watt-hours, simply multiply the average watts reading by the amount of time over which the average was measured.

For example, the following calculations are for continuous loads (for cycling loads, see load cycle considerations):

  • A one-watt averaged load measured for one hour is equal to one watt-hour; a 1000-watt averaged load measured for one hour is equal to one kilowatt-hour.
  • A 60-watt averaged load measured for two hours is equal to 120 watt-hours.
  • A 60-watt averaged load measured for 15 minutes (one-quarter hour) is equal to 15 watt-hours.

This technique for measuring real power consumption (kWh) can also be applied to apparent power (kVA) and reactive power (kVAR). Simply set the power quality analyzer to calculate the running average kVA or kVAR, then multiply by the recording time to get kVAh or kVARh used by the load.

Load cycle considerations

When making average watt measurements, be sure to take into consideration the load cycles you're working with.

Long cycle loads: If the load creating the watt draw has a long on/off cycle, like a refrigerator, be sure to measure long enough to include several on/off cycles to get a good representation of the average watts. If possible, try to stop the measurement at an even number of on/off cycles to reduce measurement errors.

Short cycle loads: If loads can cycle on and off or make large changes faster than one per minute, use an advanced three phase analyzer to ensure the wattage valves are captured.

Making average watt measurements with the Fluke 430 Series

On the three phase 430 power quality analyzers, the energy function automatically measures and calculates Watts/VA/VARs. Simply connect the clamps and leads and select energy from the menu.

Using the Fluke 43B for average watt measurements

  1. Connect the 43B.
  2. Connect the voltage leads and current clamp before starting the record mode.
  3. Select the power mode and make sure the wattage readings are correct.
  4. Press the record button and select watts for reading #1. Reading #2 is not required, so you may select any of the other items - VA (volt amperes) would be a good choice for reading #2 unless you have some other need.
  5. Selecting record time:
    • If you do not know how long you are going to be making the watt average measurements, then use endless which has a 16-day maximum. Be sure to keep an accurate record of how long the measurement was made; longer is better to keep timing errors to a minimum.
    • If you know how long you want to measure, then select one of the preset times (four minutes to eight days). Use that time value to calculate the watt-hours unless you stop 43B record mode before it stops itself. In that case, record the measurement time at which you stopped the recording.
  6. Start the recording.
  7. Press the hold button to stop recording unless you are going to let it automatically stop on one of its preset values.
  8. Before turning off the 43B or disconnecting the voltage leads and the current clamp, write down the average watt values or save the screen information in one of the save memories.
  9. Convert watts to watt-hours as described on page 1.

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