Measuring power quality and finding a bugbear in the network which is messing with the power are considered a highly paid job. Every electrical network and its problems with harmonics, transients, or disturbances are unique and need careful planning, setting the stage, measuring, and finally understanding where the problem is. That’s what power-quality engineers do.
This technical article is not about the basics of power quality, but the power quality instruments, how to read data, and what to measure. Measurement of power quality requires the use of proper instrumentation to suit the application. The user of the instrument must be well trained in the use and care of the instrumentation.
Power quality work has its rewards. One that every power quality engineer cherishes the most is the satisfaction of knowing that he has left clients happier than when he first met them. That’s what they do, every time.
Harmonic analyzers or harmonic meters are relatively simple instruments for measuring and recording harmonic distortion data. Typically, harmonic analyzers contain a meter with a waveform display screen, voltage leads, and current probes.
Some of the analyzers are handheld devices and others are intended for tabletop use. Some instruments provide a snapshot of the waveform and harmonic distortion pertaining to the instant during which the measurement is made. Other instruments are capable of recording snapshots as well as a continuous record of harmonic distortion over time.
According to Sankaran’s experience (the author of the book “Power Quality”), measurements to the are sufficient to indicate the makeup of the waveform. Harmonic analyzers from various manufacturers tend to have different, upper-harmonic-frequency measurement capability.
Harmonic distortion levels diminish substantially with the . In order to accurately determine the frequency content, the sampling frequency of the measuring instrument must be greater than twice the frequency of the highest harmonic of interest. This rule is called the .
According to Nyquist criteria, to accurately determine the frequency content of a 60-Hz fundamental frequency waveform up to the 25th harmonic number, the harmonic measuring instrument must have a minimum sampling rate of 3000 (25 × 60 × 2) samples per second
Of course, higher sampling rates more accurately reflect the actual waveform. Measurement of voltage harmonic data requires leads that can be attached to the points at which the distortion measurements are needed. Typical voltage leads are 120 to 180 cm long. At these lengths, are not a concern, as the highest frequency of interest is in the range of 1500 to 3000 Hz (25th to 50th harmonic); therefore, no significant attenuation or distortion should be introduced by the leads in voltage distortion data
Iron-core current probes are susceptible to an increased error at high frequencies and saturation at currents higher than the rated values. Prior to installing current probes for harmonic distortion tests, it is necessary to ensure that the probe is suitable for use at high frequencies without a significant loss in accuracy.
Manufacturers provide data as to the usable frequency range for the current probes. The probe is useful between the frequencies of for a maximum current rating of .
– Handheld harmonic analyzer showing voltage leads and current probe for voltage and current harmonic measurements
It should be understood that, even though the probe might be rated for use at the higher frequencies, there is an accompanying loss of accuracy in the data. The aim is to keep the loss of accuracy as low as possible. At higher frequencies, currents and distortions normally looked at are considerably lower than at the lower frequencies, and some loss of accuracy at higher frequencies might not be all that important.
Typically, a , if the waveform contains significant levels of higher-order harmonics.
Figure 2 shows the use of a handheld harmonic measuring instrument. This particular instrument is a single-phase measurement device capable of being used in circuits of up to 600 VAC.
. Along with harmonic distortion, the relative phase angle between the harmonics and the fundamental voltage is also given. The phase angle information is useful in assessing the direction of the harmonic flow and the location of the source of the harmonics.
. Along with harmonic distortion, the relative phase angle between the harmonics and the fundamental voltage is also given. The phase angle information is useful in assessing the direction of the harmonic flow and the location of the source of the harmonics.
A point worth noting is that the harmonics are shown as a percent of the total RMS value. IEEE convention presents the harmonics as a percent of the fundamental component. Using the IEEE convention would result in higher harmonic percent values. It does not really matter what convention is used as long as the same convention is maintained throughout the discussion.
Figure 3 shows a for measuring harmonic distortion snapshots and harmonic distortion history data for a specified duration.
Figure 4 provides the current waveform and a record of the current history at the panel over 5 days. The harmonic distortion snapshots along with the history graph are very useful in determining the nature of the harmonics and their occurrence pattern.
– Current waveform and current history graph at a lighting panel supplying fluorescent lighting
Transient-disturbance analyzers are advanced data acquisition devices . As one might expect, the sampling rates for these instruments are high.
It is not untypical for transient-disturbance recorders to have sampling rates in the range of 2 to 4 million samples per second. Higher sampling rates provide greater accuracy in describing transient events in terms of their amplitude and frequency content. Both these attributes are essential for performing transient analysis.
The amplitude of the waveform provides . The frequency content informs us as to how the events may couple to other circuits and how they might be mitigated.
Figure 6 shows a transient that reached a peak amplitude of with frequency content of approximately . Once such information is determined, equipment susceptibility should be determined. For instance, a 200-V peak impulse applied to a might not have any effect on motor life; however, the same impulse applied to a process controller could produce immediate failure.
Equipment that contains power supplies or capacitor filter circuits is especially susceptible to fast rise-time transients with high-frequency content.
Measuring power quality and finding a bugbear in the network which is messing with the power are considered a highly paid job. Every electrical network and its problems with harmonics, transients, or disturbances are unique and need careful planning, setting the stage, measuring, and finally understanding where the problem is. That’s what power-quality engineers do.
This technical article is not about the basics of power quality, but the power quality instruments, how to read data, and what to measure. Measurement of power quality requires the use of proper instrumentation to suit the application. The user of the instrument must be well trained in the use and care of the instrumentation.
Power quality work has its rewards. One that every power quality engineer cherishes the most is the satisfaction of knowing that he has left clients happier than when he first met them. That’s what they do, every time.
Harmonic analyzers or harmonic meters are relatively simple instruments for measuring and recording harmonic distortion data. Typically, harmonic analyzers contain a meter with a waveform display screen, voltage leads, and current probes.
Some of the analyzers are handheld devices and others are intended for tabletop use. Some instruments provide a snapshot of the waveform and harmonic distortion pertaining to the instant during which the measurement is made. Other instruments are capable of recording snapshots as well as a continuous record of harmonic distortion over time.
According to Sankaran’s experience (the author of the book “Power Quality”), measurements to the are sufficient to indicate the makeup of the waveform. Harmonic analyzers from various manufacturers tend to have different, upper-harmonic-frequency measurement capability.
Harmonic distortion levels diminish substantially with the . In order to accurately determine the frequency content, the sampling frequency of the measuring instrument must be greater than twice the frequency of the highest harmonic of interest. This rule is called the .
According to Nyquist criteria, to accurately determine the frequency content of a 60-Hz fundamental frequency waveform up to the 25th harmonic number, the harmonic measuring instrument must have a minimum sampling rate of 3000 (25 × 60 × 2) samples per second
Of course, higher sampling rates more accurately reflect the actual waveform. Measurement of voltage harmonic data requires leads that can be attached to the points at which the distortion measurements are needed. Typical voltage leads are 120 to 180 cm long. At these lengths, are not a concern, as the highest frequency of interest is in the range of 1500 to 3000 Hz (25th to 50th harmonic); therefore, no significant attenuation or distortion should be introduced by the leads in voltage distortion data
Iron-core current probes are susceptible to an increased error at high frequencies and saturation at currents higher than the rated values. Prior to installing current probes for harmonic distortion tests, it is necessary to ensure that the probe is suitable for use at high frequencies without a significant loss in accuracy.
Manufacturers provide data as to the usable frequency range for the current probes. The probe is useful between the frequencies of for a maximum current rating of .
– Handheld harmonic analyzer showing voltage leads and current probe for voltage and current harmonic measurements
It should be understood that, even though the probe might be rated for use at the higher frequencies, there is an accompanying loss of accuracy in the data. The aim is to keep the loss of accuracy as low as possible. At higher frequencies, currents and distortions normally looked at are considerably lower than at the lower frequencies, and some loss of accuracy at higher frequencies might not be all that important.
Typically, a , if the waveform contains significant levels of higher-order harmonics.
Figure 2 shows the use of a handheld harmonic measuring instrument. This particular instrument is a single-phase measurement device capable of being used in circuits of up to 600 VAC.
. Along with harmonic distortion, the relative phase angle between the harmonics and the fundamental voltage is also given. The phase angle information is useful in assessing the direction of the harmonic flow and the location of the source of the harmonics.
. Along with harmonic distortion, the relative phase angle between the harmonics and the fundamental voltage is also given. The phase angle information is useful in assessing the direction of the harmonic flow and the location of the source of the harmonics.
A point worth noting is that the harmonics are shown as a percent of the total RMS value. IEEE convention presents the harmonics as a percent of the fundamental component. Using the IEEE convention would result in higher harmonic percent values. It does not really matter what convention is used as long as the same convention is maintained throughout the discussion.
Figure 3 shows a for measuring harmonic distortion snapshots and harmonic distortion history data for a specified duration.
Figure 4 provides the current waveform and a record of the current history at the panel over 5 days. The harmonic distortion snapshots along with the history graph are very useful in determining the nature of the harmonics and their occurrence pattern.
– Current waveform and current history graph at a lighting panel supplying fluorescent lighting
Transient-disturbance analyzers are advanced data acquisition devices . As one might expect, the sampling rates for these instruments are high.
It is not untypical for transient-disturbance recorders to have sampling rates in the range of 2 to 4 million samples per second. Higher sampling rates provide greater accuracy in describing transient events in terms of their amplitude and frequency content. Both these attributes are essential for performing transient analysis.
The amplitude of the waveform provides . The frequency content informs us as to how the events may couple to other circuits and how they might be mitigated.
Figure 6 shows a transient that reached a peak amplitude of with frequency content of approximately . Once such information is determined, equipment susceptibility should be determined. For instance, a 200-V peak impulse applied to a might not have any effect on motor life; however, the same impulse applied to a process controller could produce immediate failure.
Equipment that contains power supplies or capacitor filter circuits is especially susceptible to fast rise-time transients with high-frequency content.
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