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Five problems you will never uncover with a digital multimeter

Five vital measurements

Even with a True RMS digital multimeter (DMM), you might miss five vital measurements that could be causing problems in your electrical distribution system:

  1. Harmonic current is current flow in the system at a whole number multiple frequency of the fundamental frequency. The third harmonic current is current that flows at 180 Hz (the third harmonic of 60 Hz). While harmonic currents not only distort the fundamental 60 Hz sine waves, excessive harmonics can cause severe overheating and reduce motor efficiency. Once identified, filters can be installed to limit harmonic effects.
  2. Total harmonic distortion (THD) is a measure of how much harmonic content there is in a waveform and should not exceed 5 % of voltage for reliable operation. If maximum acceptable THD is exceeded, locate and isolate the source of the harmonics, adding filters if needed.
  3. Sags and swells are a brief decrease (sag) or a brief increase (swell) in the nominal rms line voltage. Any such fluctuations in voltage can cause problems— from improper operation of electronic equipment to inadvertent relay operation.
  4. Transients are extremely short variations in voltages, often due to lightning strikes and load switching, and can cause equipment to shut down.
  5. Power factor represents the volt-amp loss in a system due to reactance. While poor power factor can mean utility penalty charges, the charges can often be corrected with the installation of power factor correction systems.

While the DMM is a valuable and indispensable tool for the electrical professional, it does have limitations. Be prepared to use a power quality analyzer to uncover those hidden potential problems.

Which power quality analyzer?

The importance of investing in the right set of tools to monitor power quality issues, and prevent them in the future, can’t be emphasized enough. Fluke offers an extensive range of excellent power meters and other power quality tools for troubleshooting, preventive maintenance, and long-term recording and analysis in industrial applications and utilities.

Fluke’s range of power meters includes both single-phase and three-phase power quality analyzers for predictive maintenance, quality of service compliance testing and load studies. The three classifications are:

  • Power quality troubleshooters. Dedicated power and power quality clamp meters for frontline troubleshooting. Single-phase and three-phase power quality analyzers for predictive maintenance, quality of service compliance testing and load studies.
  • Power quality loggers. Power loggers for characterizing power quality, conducting load studies and capturing hard-to-find voltage events over a userdefined period of time.
  • Power quality recorders. Advanced power quality recorders for capturing comprehensive details of power disturbances, trend analysis and Class-A “quality of service” compliance testing over a userdefined period of time.