Power Quality Measurement Devices & Monitoring

1. Power Quality Measurement Devices
Prepared by :
Shivam
Course : POWR QUALITY & MANAGEMENT

2. Content :
• PQ Measurement Introduction
• Need for PQ Measurement
• Common Objectives Of Power Quality Monitoring
• Power Quality Measurement Devices
• Harmonic Analyzers
• Transient-disturbance Analyzers
• Oscilloscopes
• Data Loggers And Chart Recorders.
• Important factors considered when choosing the instrument
• Test Locations
• Instrument Setup

3. PQ Measurement Introduction
• Power quality Measurement is the process of gathering, analyzing,
and interpreting raw measurement data into useful information.
• The process of gathering data is usually carried out by continuous
measurement of voltage and current over an extended period.
• The process of analysis and interpretation has been traditionally
performed manually, but recent advances in signal processing and
artificial intelligence fields have made it possible to design and
implement intelligent systems to automatically analyze and interpret
raw data into useful information with minimum human intervention.

4. Need for PQ Measurement
• Power quality monitoring programs are often driven by the demand
for improving the system wide power quality performance. Many
industrial and commercial customers have equipment that is sensitive
to power disturbances, and, therefore, it is more important to
understand the quality of power being provided.
• All data deemed to be relevant should be prioritized and analyzed to
obtain a solution to the problem. It should be stressed once again
that some power quality problems require not a single solution but a
combination of solutions to obtain the desired end results.

5. Common Objectives Of Power Quality
Monitoring
• Monitoring to characterize system performance need to understand
its system performance and then match that system performance
with the needs of customers
• Monitoring to characterize specific problems - performing short-
term monitoring at specific customer sites or at difficult loads.
• Monitoring as part of an enhanced power quality service-A provider
and customer can together achieve this goal by modifying the power
system or by installing equipment within the customer’s premises
• Monitoring as part of predictive or just-in-time maintenance -
Equipment maintenance can be quickly ordered to avoid catastrophic
failure.

6. Power Quality Measurement Devices
• Harmonic Analyzers
• Transient-disturbance Analyzers
• Oscilloscopes
• Data Loggers And Chart Recorders.

7. Harmonic Analyzers
• 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.
• There are basically three categories of instruments to consider for
harmonic analysis :
• Simple meters
• General-purpose spectrum analyzers
• Special-purpose power system harmonic analyzers

8. Simple meters
• It may sometimes be necessary to make a quick check of harmonic levels at
a problem location. A simple, portable meter for this purpose is ideal.
• There are now several hand-held instruments of this type on the market.
Each instrument has advantages and disadvantages in its operation and
design.
• These devices generally use microprocessor-based circuitry to perform the
necessary calculations to determine individual harmonics up to the 50th
harmonic, as well as the rms, the THD, and the telephone influence factor
(TIF). Some of these devices can calculate harmonic powers (magnitudes
and angles) and can upload stored waveforms and calculated data to a
personal computer.

9. General-purpose spectrum analyzers
• Instruments in this category are designed to perform spectrum
analysis on waveforms for a wide variety of applications. They are
general signal analysis instruments.
• The advantage of these instruments is that they have very powerful
capabilities for a reasonable price since they are designed for a
broader market than just power system applications.
• The disadvantage is that they are not designed specifically for
sampling power frequency waveforms and, therefore, must be used
carefully to assure accurate harmonic analysis. There are a wide
variety of instruments in this category

10. Special-purpose power system harmonic
analyzers
• Besides the general-purpose spectrum analyzers just described, there
are also a number of instruments and devices that have been
designed specifically for power system harmonic analysis.
• These are based on the FFT with sampling rates specifically designed
for determining harmonic components in power signals. They can
generally be left in the field and include communications capability
for remote monitoring

11. Transient-disturbance Analyzers
• Transient-disturbance analyzers are advanced data acquisition devices
for capturing, storing, and presenting short-duration, subcycle power
system disturbances. 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.

12. • The frequency content informs us as to how the events may couple to
other circuits and how they might be mitigated
• When measuring fast rise time or higher frequency transients, the
length of th wires used to connect the instrumentation to the test points
becomes very important

13. Combination disturbance and harmonic
analyzers
• The most recent instruments combine harmonic sampling and energy
monitoring functions with complete disturbance monitoring functions as
well. The output is graphically based, and the data are remotely gathered
over phone lines into a central database.
• Statistical analysis can then be performed on the data. The data are also
available for input and manipulation into other programs such as
spreadsheets and other graphical output processors
• One example of such an instrument is shown in Figure This instrument is
designed for both utility and end-user applications, being mounted in a
suitable enclosure for installation outdoors on utility poles. It monitors
three-phase voltages and currents (plus neutrals) simultaneously, which is
very important for diagnosing power quality problems.

14. A power quality monitoring instrument capable of monitoring
disturbances, harmonics, and other steady-state phenomena on
both utility systems and end-user systems.

15. Oscilloscopes
• Oscilloscopes are useful for measuring repetitive high-frequency waveforms
or waveforms containing superimposed high-frequency noise on power and
control circuits. Oscilloscopes have sampling rates far higher than transient-
disturbance analyzers. Oscilloscopes with sampling rates of several hundred
million samples per second are common.
• Such data are not within the capabilities of
harmonic analyzers and transient-
disturbance recorders. Digital storage
oscilloscopes have the ability to capture and
store waveform data for later use.
• Using multiple-channel, digital storage
oscilloscopes, more than one electrical
parameter may be viewed and stored.

16. • Selection of voltage probes is essential for proper use of oscilloscopes. Voltage
probes for oscilloscopes are broadly classified :
• passive probe
• active probes
• Passive probes use passive
components (resistance and
capacitance) to provide the necessary
filtering and scale factors necessary.
Passive probes are typically for use in
circuits up to 300 VAC. Higher voltage
passive probes can be used in circuits
of up to 1000 VAC.
Three-phase harmonic and disturbance analyzer for measuring
voltage and current harmonics, voltage and current history over a
period of time, voltage transients, and power, power factor, and
demand.

17. Current waveform and current history graph at a
lighting panel supplying fluorescent lighting.

18. Data Loggers And Chart Recorders
• Data loggers and chart recorders are sometimes used to record voltage, current,
demand, and temperature data in electrical power systems.
• Data loggers and chart recorders are slow-response devices that are useful for
measuring steady-state data over a long period of time. These devices record one
sample of the event at predetermined duration, such as 1 sec, 2 sec, 5 sec, etc
• The advantage of data loggers is that they are relatively inexpensive compared to
power quality recording instrumentation. They are also easier to set up and
easier to use. The data from the device may be presented in a text format or in a
graphical format.
• They are designed to operate using the low level output of suitable voltage,
current, or temperature transducers; however, care should be exercised in the
installation and routing of the wires from the transducers to ensure that the
output of the transducers is not compromised due to stray noise pickup

19. Current data from a data logger for one month of tests.

20. Examples :

21. Instantaneous Sag Event :

22. Instantaneous Sag Event :

23. Harmonic & Interharmonic Spectrum

24. Important factors considered when choosing
the instrument
1. Number of channels (voltage and/or
current)
2. Temperature specifications of the
instrument
3. Ruggedness of the instrument
4. Input voltage range (e.g., 0 to 600 V)
5. Power requirements
6. Ability to measure three-phase
voltages
7. Input isolation (isolation between
input channels and from each input to
ground)
8. Ability to measure currents.
9. Housing of the instrument
(portable, rack-mount, etc.)
10. Ease of use (user interface,
graphics capability, etc.)
11. Documentation.
12. Communication capability
(modem, network interface)
13. Analysis software

25. Benefits of Continuous PQ Monitoring
• Power Quality monitoring provides a continuous
“Health Check” of a facility’s power system …
• for example:
• Harmonic interaction between loads and power
conditioning equipment spotted
• High Inrush currents from equipment startup detected o
Transients from load switching are seen
• It provides data to see, diagnose and avert looming
problems – “like squeaky brakes on a car”
• Trends can be detected
• JIT equipment maintenance programs can be established

26. Power Quality Measurements
• The first step in solving power quality problems is to determine the
test location or locations. Even the best available power quality
instrumentation is only as good as the personnel using it.
• Setting up instrumentation at a location that is not optimum with
respect to the affected equipment can yield misleading or insufficient
information. Electrical transients are especially prone to errors
depending on the type of the instrument used and its location.

27. Test Locations
• If at all possible, power quality tests should be conducted at multiple
locations simultaneously. The data obtained by such means are useful
in determining the nature of the power quality problem and its
possible source as quickly as possible.
• If simultaneous monitoring is not feasible due to cost or other factors,
each location may be individually monitored, taking care to ensure
similar operating environments for testing at each location to allow
direct comparison of information. The number of test locations would
depend on the nature of the problem and the nature of the affected
equipment.

28. • If power quality problems are observed at location C and not at B, it is not necessary
to monitor A. On the other hand, if problems are noticed at C and B, then location A
should be tested as well as location D, if necessary. The experience of the power
quality engineer becomes important when trying to resolve the different scenarios.

29. Instrument Setup
• Setting up instruments to collect power quality data is probably the most
critical aspect of testing and also one that most often can decide the end
results. Setting up is a time when utmost care must be exercised.
• The first step is making sure to observe certain safety rules. In the majority
of cases, power to electrical equipment cannot be turned off to allow for
instrument setup. The facility users want as few interruptions as possible,
preferably none.
• Personal protective equipment (PPE) is an important component of power
quality testing.
• Minimum PPE should contain electrical gloves, safety glasses, and fire-
retardant clothing. While removing panel covers and setting up instrument
probes it is important to have someone else present in the room.

30. Proper personal protective equipment (PPE), which is essential to performing power quality instrument setup and testing.
The photograph shows the use of fire-retardant clothing, safety hat, and shoes. Safety glasses must be worn while
connecting instrument probes to the test point. The test location shown here is properly barricaded to prevent unauthorized
persons from entering the area.

31. Conclusion
• 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.
• The engineer should be knowledgeable in the field of power quality.
Most importantly, the engineer should be safety conscious. All these
factors are equally important in solving power quality problems.
• Power quality work has its rewards