Transcript basics_of_power_qual..

Understanding
Power Quality Monitoring
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Basics of Power Quality Monitoring
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Objectives
• What is Power Quality and how do we
determine Methods of test.
– Describe the nature of several different types of
power-related problems.
– Describe the methods for testing for the
different types of problems.
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What is Power Quality
Except for complete failure, most really don’t pay
close attention to the power we are supplied.
With the emergence of the “Electronics Age” there
has be a change in the requirement of our
electrical distribution systems.
Unlike traditional load, like lighting or motors,
Sensitive loads are more susceptible to power
disturbances.
Electronic equipment requires a much more stable
power source.
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Importance of Power Quality
• Consequences of poor Power Quality can result in:
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Lost productivity
Lost/corrupt data
Damaged equipment
Poor power efficiency
• U.S. companies waste an estimated $26 billion on
electrical power-related issues each year*
*Electrical Contractor Magazine, “Surveying
Power Quality Options” March 2000
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Power Quality
• There is no absolute definition of power quality, but many
define it as the degree to which both the utilization and the
performance of electric power affects the performance of an
electrical distribution system.
• Organizations such as the IEEE -Institute of Electrical and
Electronics Engineer and ANSI -American National
Standards Institute are setting Stringent requirements for
power Quality.
– IEEE 519-81 Recommended limits on Harmonics
– ANSI C84.1 Specification on normal voltage ratings and tolerances
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Power Quality
• Power and Power Factor
– Measure of how efficiently Power is used
• Disturbances
– Momentary disruptions to the Electrical system
• Harmonics
– Integers of the Fundamental Frequency which have an
effect on the electrical systems and loads
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Power Quality
Power And Power Factor
• Power is measured in KW or Kilowatts
• Kilowatt is defined as Volts x Amps x Cos Φ
– Φ is the phase angle difference between the Voltage and
current.
Most utilities have an
additional charge
if PF is less than .95
to .90
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Power Quality
Disturbances
• The NIST -National Institute of Standards and
Technology shows that disturbances can be
defined in two categories,
• Steady State or Intermittent.
– Steady state disturbances are Noise, Harmonics, long
term Over-voltage or Under-voltage conditions.
– Intermittent disturbances are Sages, Swells, Impulse,
Transients, and interruption,
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Power Quality
Power disturbances
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Voltage Sags and Swells
Under-voltage or Over-voltage
Transients spikes, impulses and surges
Outages
Harmonics
Noise
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Power Quality
• Voltage Sag
– Momentary decrease in line Voltage
– Caused by the start of heavy loads or
fault occurrence on source.
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Voltage Swells
–Momentary increase in line Voltage
–Occurs due to sudden load decrease or
de-energizing of heavy equipment.
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Power Quality
• Over-Voltage
– Abnormally high voltage
– Power voltage regulation
• Under-Voltage
– Abnormally low Voltage
– Result for clearing of a
fault or intentional utility
regulation.
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Power Quality
• Impulse (Transients):
– Short duration high
amplitude pulses are surges
that are superimposed on a
normal voltage waveform.
– Vary widely from twice the
normal voltage to several
thousand volts in time
from < microsecond to a
few hundreds of a second.
– Result for loads cycling on
and off in a building,
utility, or lighting
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Power Quality
• Outages
– Outage is a complete loss
of power lasting from a
few milliseconds to several
hours.
– Caused by power system
failure due to damage to
supply lines or equipment
failure
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Power Quality
• NOISE: is an unwanted
signal or distortion that is
superimposed on a
normal voltage waveform
– Normal Mode noise
– Common Mode noise
– RFI: Radio Frequency
interference
– EMI: Electromagnetic
interference
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Power Quality
Harmonics
• Harmonics are multiple of
the fundamental
frequency
• For us in the USA this is
60 Hz
– Harmonics in our electrical
systems are normally caused
by distortion of either our
Voltage or Current waveform
– Major cause of harmonics is
electronic loads that draw
there currents in short pulses.
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Power Quality
Harmonics
• Non-Linear loads
– Computers, printer,
copiers, electronics
lighting
– Adjustable speed drives
and other microprocessor
controlled equipment
– Effects on electrical
systems or odd harmonics
3rd, 5th, 7th etc.
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Harmonics
Harmonics
• Total Harmonic Distortion
– Expressed as %THD
– Percentage of distortion to the sine wave
– Should not exceed 5% of line voltage or 20% of current
• Harmonic FFT’s
– Breakdown of the THD to the individual harmonics
– Show the amount of harmonic as a percentage of the
fundamental.
Knowing each harmonic and its effect can help in determines
the impact on the system
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Power Quality- Standards
ITIC (CBEMA) Curve
• ITIC, Information
Technology Industry
Council is just one of
may professional or
governing agency that
have adopted
acceptable tolerance
for power delivered to
our sensitive
electronic equipment.
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Plan, Investigate & Test
• Where to start
– Plan your site survey
– Investigate suspected
areas
– Test or monitor
– Analyze results or date
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Plan
Make a block diagram of you facility.
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Investigate
• Investigate suspected
areas
• Try to establish time of
occurrence and duration
history
• Equipment usage cycles or
new equipment instillation
• Personnel
• Interview others- Find out
what they have observed
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Test
• Power and Power Factor, Inductive or Capacitive
reactance, or how efficient we use the power that is
delivered.
– A Power Analyzer is the tool of choose when the measurement of
Power usage are efficiency is desired.
• Disturbances, like Sage Swell and Impulse are
normally generated within a facility and affecting our
sensitive electronics equipment
– In the pass Power analyzers my have been used at a main or subpanel, but were not cost effective for branch circuit monitoring.
– Today, however we have a small inexpensive tools that can be
plug at the device or equipment that is being effected.
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Testing
• Most power quality failures may be tracked
down to one of three areas.
– Supply- Utilities and its distribution.
– Internal Distribution- Feeders and Branches,
Grounding, wiring and termination
– Internal Loads- load disturbances and
Harmonics
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Testing
Supply – Utilities Disturbance
• Supply Disturbances and
service area
– Utility faults,
• switching transients,
regulation
– Lighting,
• Transients, outages
– Accidents to Transmission
lines
• outages
– Failure of backup sources
• Outage, under of over
voltages
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Testing
Internal Disturbances
• Many studies have been conducted and found that
80% of power Quality problems are generated within
a facility
• Of this, 80% of those are related to inadequate wiring
or poor grounding.
• Power and Power reactance.
• Line to Neutral Voltage
– Sags& Swells, under-voltage & over-voltage,
Impulse, Distortion.
• Neutral to Ground Voltage
– High resistance grounds, Load imbalance, Harmonics
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Testing
• A Hospital is wanting to
add new diagnostic
equipment.
• Before the equipment is
added to the service they
need to determine if the
present system can handle
the additional load.
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Testing
• This is an example of data taking at a hospital in
North Carolina. Two observation can be made from
this data.
– First, is a drop in Voltage during Wednesday, not seen in any other
days data. Why?
– Second, is a load imbalance, where phase 2 and 3 are drawing
around 40 amps more that phase 1
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Testing
• When we look at the Power of each phase we can
also see that Phase 1 average is 4000 Watts less
that phase 2 and 3. Both phase 2 and 3 average
in the range of 7000 Watts.
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Testing
Branch Circuits
• Line to Neutral Voltage
– Transients, Sags& Swells,
Voltage drops, Flat toping
• Neutral to Ground
Voltage
– Tripling harmonics, High
ground impedance.
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Testing
Branch Circuits
• Voltage Distortion can be
caused by large harmonic
currents from Nonlinear loads
or Power sources with no
sinusoidal Voltage
Characteristic
• Linear loads have small
effects on voltage distortion.
• Non-Linear loads have a larger
effect on voltage distortion
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Excessive Current drawn as the Voltage waveform
reaches Peak can cause Voltage distortion. Referred
to as Flat Topping or Clipping.
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Testing
Branch Circuits
• Major loads affected
– Computers
– Copiers, Laser printers, and
other Large office loads
– HVAC Equipment
– Industrial equipment, Like
ASD’s (Adjustable
Speed Drives)
– Lighting
– UPS systems
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Testing
Key Points for comparison
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Only important evens are logged
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Events are sorted by Time (log)
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Events are sorted by Type (event)
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Waveform shape is measured for THD
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Testing
Events Log?
• Sag – low voltage for
brief periods (dips)
• Swell- high voltage for
brief periods (surges)
• Voltage Transientimpulses (spikes)
• THD for Total Harmonic
Distortion (noise)
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Testing
What cause the event
and When ?
• Amplitude of the event
• Number of Cycles
(duration)
• Time of event
• Date of event
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Test Equipment
• Test or Monitor , Basic
measurement tools
– Circuit Analyzer
– Multimeter or
ClampMeters
• (True RMS responded)
– Receptacle Event Recorder
– Power Quality Monitor.
– Infrared temperature
device
Always follow proper Safety precautions
Lock-out Tag-out, safety gear like glasses and gloves
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Test Equipment
• Most equipment, like circuit Analyzers,
meters and clamps are slow responding.
– They sample at speeds around 2 or 3 times a
second.
– OK for steady state problems
– To slow for intermittent disturbances.
– Intermittent disturbances require equipment
which samples at a number of samples per
cycle.
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Test Equipment
• 160 Series SureTest Circuit Analyzers
• 830 Voltage Performance Monitor
• 800 Series Power Analyzer
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SureTest
Circuit Analyzers
• Circuit Analysis
– Measures voltage drop
under full 15 Amp
load,
– Neutral to Ground
Voltage
– Ground Impedance
– Hot and Neutral
Conductor Impedance.
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830 Voltage Performance
Monitor
• 830 Voltage Performance Monitor is
great for evaluation clean Power on a
branch circuits.
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Sag
Swells
Impulses
%THD
• Depth and duration of each event is
log with time and date stamp
• The powerful box with the Power
Quality Engineer inside
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800 Series Power Analyzer
• Power measurements
– kW, Power Factor, kVA,
kVAR
• Harmonic measurements
– %THD, harmonic
factorization to 51st
harmonic
• Disturbances
– Capture level 2 transients
(0.5µs)
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