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VI. Power Quality Measurement Tools
Ammeters
Voltmeters
multimeters
oscilloscopes
flicker meters
electrostatic voltmeters
infrared detectors
radio-frequency interference
electromagnetic interference meters
harmonic and spectrum analyzers
power quality monitors
Measurement tools
various types of wiring and grounding testers
measure, display and store electrical parameters (voltage, current, frequency & impedance of
an electrical distribution system) for the purpose of helping solve PQ problems
choose right tool to match a particular PQ problem - difficult problem itself three-step
process:
1. Knowledge of the various types of PQ problems , voltage swells, voltage sags, various
types of interruptions, overvoltage, under voltage, harmonics, and transients
2. types of instruments to measure those disturbances
three primary types of instruments are multi-meters, oscilloscopes & analyzers especially
designed to measure and record PQ disturbances
3. how to match the instrument to PQ problem
Matching Measurement Tools to Type of Disturbance
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Kilowatt-Hour Meter called a revenue meter
displays and records amount of electrical energy the electrical company charges its customers
measures the amount of electrical energy in kilowatt-hours
called analog meter because it uses the current and voltage to directly move the meter dials
Ferraris kilowatt-hour meter
Other types of standard non digital (analog) electrical meters include:
ammeters -n measure the current flowing in a wire in amperes
Voltmeters - measure the voltage between two points in volts
Ohmmeters- measure the resistance in a wire in ohms
Often voltmeters combine with ohmmeters to form volt-ohmmeters or VOMs
Non-digital volt-ohmmeter (VOM)
Multimeters
Clamp-on current probes
often referred to as DMMs, or digital multimeters
more accurate and reliable than analog meters
use analog-to-digital converter to convert the electrical quantity being measured into digital
measure the total area under the alternating current waveform? NO
measure the peak value of the alternating current? Depend
Users need to measure current that is proportional to its heating effect
designed multimeters to measure effective, or root-mean-square, amperes
effective ampere?
is the alternating current (ac) equivalent to the direct current (dc) value of the sine wave
Voltage probe
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perform this measurement in two steps
1.determine the rms amperes
2. calculate the peak value by simply multiplying the average value by 1.414, or sq.root of 2
Average-responding versus true rms multimeters
true rms multimeters measure the “true” rms of a distorted sine wave
True rms digital multimeters
True rms versus average-responding DMM readings
Average-responding rms inaccuracies
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Crest factor and bandwidth
Bandwidth or frequency response of the true rms
wrong crest factor can cause inaccurate measurements of current and voltage
Manufacturers design multimeters to measure voltage and current within a certain frequency
range or bandwidth
ratio of a waveform’s peak or crest to its rms voltage or current
measures the maximum sine wave current or voltage applied to a particular piece of equipment
Frequencies outside the capability of the multimeter will result in incorrect measurements
front panel should read “truerms.”
crest factor for a sinusoidal wave always equals 1.414
specifications should provide the crest factor and bandwidth capability of the meter
crest factor for a nonsinusodial wave will differ from one wave to another
crest factor of a multimeter can limit the true rms measurement
For ex, harmonics typically have peaking signals with values higher than those of 50-Hz sine
Crest factors for true rms multimeters can vary from a low of 2 to a high of 7
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