Understanding Power Quality
Dean Sempio
July 2020
Outline
I.
Power Quality (PQ) Definition
II. Distribution Utility Parameters & Limits
III. Types of PQ Problems
IV. Solution to PQ Problems
Power Quality Before 2001
• Daily 2 hour blackouts during the summer
is common
• Low voltage especially in provincial areas
(florescent lights need to be switched on as early
as possible)
Power Quality (PQ) Purpose
PDC 2017
Power Quality (PQ) Definition
The quality of the voltage, including its
frequency and the resulting current, that are
measured in the Distribution System during
normal conditions
PDC 2017 Chapter 3.2.1.1
Power Quality (PQ) Definition
PQ is also about
electromagnetic compatibility
• Equipment operates within its environment
without causing disturbance either to itself or
other equipment, or back to utility source
• End-use equipment (load) rating matches
supply voltage rating and variations
• Mismatch can be avoided right from the
design stage
Power Quality (PQ) Definition
PQ is also about
electromagnetic compatibility
• Utility service standards must be considered
before purchase of end-use equipment for
compatibility of ratings
• A mismatch is costly in terms of bridging
incompatibility
Parameters and Limits
Customers must take note of the following PDC limits when designing
systems and equipment for their facilities.
Parameter
Limit/s
Frequency Variations
Frequency shall be 60 Hz, with allowable
variation of 59.7 to 60.3 Hz
Service Voltages
Secondary Nominal Voltages
230 Volts, 400 Volts, 460 Volts
Primary Nominal Voltages
13.2 kV, 13.8 kV, 34.5 kV, 69 kV, 115 kV
Voltage THD
Within 5%
Voltage Unbalance
Within 2.5%
Flicker Severity
1.0 for Short Term
0.8 for Long Term
PDC 2017 Chapter 3
Parameters and Limits
Guaranteed Service Level
Parameters and Limits
Parameters and Limits
Effect of Utility Variations on Equipment Ratings
Nominal Service
-10% (90% of +10% (110% of
Voltage
nominal
nominal)
230
207
253
460
414
506
Equipment Rating:
200
220
440
480
% of service
% of service
variation lower variation upper
limit
limit
103.5%
126.5%
94.1%
115.0%
94.1%
115.0%
86.3%
105.4%
Parameters and Limits
Better?
PQ Problem Illustrated
A
Normal
Failure
B
C
PQ Problem Illustrated
A
Failure
Fault
Failure
B
C
Electric Grid
Fault/s anywhere in the network may result to power disturbances
of varying magnitude and duration depending on the type and
proximity of fault.
Types of PQ Problems
Voltage Unbalance
Maximum deviation from the average of the three-phase
voltages divided by the average of the three-phase
voltages, usually expressed in percent
t
(Maximum deviation from Average) X 100%
Voltage unbalance =
Average voltage
Types of PQ Problems
Voltage Unbalance
Maximum deviation from the average of the three-phase
voltages divided by the average of the three-phase
voltages, usually expressed in percent
t
•Unbalanced distribution of single phase loads
•Unstable system neutral
•One-phase out power supply
Types of PQ Problems
NEMA MG 1-14
Types of PQ Problems
Total Harmonic Distortion (THD)
THD is the measure of the effective value of the harmonic
components of a distorted waveform, that is, the potential heating
value of the harmonics relative to the fundamental
Green Building Code 2015
PDC 2017
Voltage Harmonic Distortion
•If it isn’t broke, don’t fix it
•Choose equipment with “built-in” harmonic
mitigating solutions (either with reactor or harmonic
filter)
•Choose equipment with “real sine wave” output
Types of PQ Problems
Voltage Sag
A decrease in RMS voltage between 10% to 90% of the
nominal value for duration from half cycle to 1 minute
1 minute
or less
• Starting of electric motors
• Switching “on” of large loads
• Fault on either distribution, transmission or generation systems
Electric Grid
Fault
Electric Grid
Fault/s anywhere in the network may result to power disturbances of
varying magnitude and duration depending on the type and proximity of
fault.
Types of PQ Problems
Voltage Sag
•
•
•
•
Nominal Voltage: 460V
Magnitude: 88.41%
Duration: 4 cycles
Cause: Fault on the
adjacent feeder
Susceptibility Curve
Information Technology
Industry Council (ITIC) curve
was developed to
accurately reflect the
performance of computertype equipment.
It is generally applicable to
other equipment containing
solid-state devices.
Susceptibility Curve
Semiconductor Processing Equipment Voltage Sag
Immunity Semi F47 curve was developed for Semicon
companies to provide sag-resistant tools
Solutions to PQ Problems
AVR vs UPS
Can handle
"fluctuations"
(between plus 10% to
minus 10% of
nominal voltage)
Can handle
"fluctuations" and
power interruptions
< 2 AC Cycles
On line
Cannot handle
voltage sags
Can handle voltage
sags and power
interruptions
Solutions to PQ Problems
Universal Power Supply
(UPS)
• Provides improved voltage sag tolerance.
Solutions to PQ Problems
Sag Correctors
• Small to large applications
Solutions to PQ Problems
MERALCO
• Equipped with On-load Tap Changer (OLTC)
• Use of insulated conductors
• Separation of customer types
Power Quality (PQ) Definition
…the concept of powering and grounding
electronic equipment in a manner that is
suitable to the operation of that equipment and
compatible with the premise wiring system and
other connected equipment
IIEE Std 1159-2009
Reasons for Grounding
Personnel Safety
From Meralco Handbook on Grounding and Bonding of Low Voltage Services, 2009
Grounding
Proper Grounding Practices
From Meralco Handbook on Grounding and Bonding of Low Voltage Services, 2009
Reasons for Grounding
Operation of Overcurrent Protective Device
From Meralco Handbook on Grounding and Bonding of Low Voltage Services, 2009
ANSI J STD 607
Commercial Building
Grounding and
Bonding
Requirements for
Telecommunications
Reasons for Grounding
Electric Low Frequency ELF
ELF is extremely low frequency (ELF) electromagnetic
field
Fundamental frequency is between 3 Hz to 3 kHz
ELF electric and magnetic fields emanates comes
from power lines, electrical equipment and
appliances
Electric Low Frequency ELF
Electric Low Frequency ELF
Electric Low Frequency ELF
Solutions to PQ Problems
Problem Evaluation
• Problem Category Identification
• Power Measurements & Data Collection
• Solution Range Identification
• Solution Evaluation
• Optimum Solution
Solution to PQ Problems
Solution Evaluation
LEAST COST APPROACH
Equipment
Specification
Control
Protection
1
Controls
Motors
Over-all
Protection
Inside Plant
Utility
Solution
2
3
Other Loads
INCREASING COST
4
Even without buying PQ conditioning equipment we may
already be paying for it from costs associated with current
problems that our equipment are dealing with.
Thank You!