Modern Power Quality Challenges
Aaron F. Snyder, Ph.D.
Vadim Zheglov
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Outline
Power and Metering Fundamentals
Power Quality and Harmonics
Curiosities
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Power Fundamentals
What we learn in school (power triangle)
P = Real Power, Watts
Im
Q = Reactive Power, VARs
S = Apparent Power, VA
S = P + jQ
S

P
© 2011 EnerNex. All Rights Reserved. www.enernex.com
jQ
Re
Power Fundamentals
F
 Instantaneous power:
 Active power:
–





Q = VIsinΘ
D
Q
sinusoids
 Apparent power:
 Phasor power:
–
D
sinusoids
 Reactive power:
–
p(t) = v(t)i(t)
P = VIcosΘ
U = VI
S = P + jQ
P
Fictitious Power
U
= sqrt(U2
S2)
D
–
F = jQ + kD
N = iP + kD
U = iP + jQ + kD
= P/U = cosΘ
Source: IEEE Tutorial, p.32
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Q
P
Phasor Power
S = U for sinusoids
Distortion power:
Fictitious power:
Nonreactive power:
Vector power:
Power factor:
S
N
D
D
Q
P
Nonreactive Power
Q
P
Vector Power
Metering Fundamentals
Blondel’s Theorem (in words):
– If energy is supplied to any system of conductors through N wires, the total power in the system is given by the algebraic sum of the readings of N wattmeters, so arranged that each of the N wires contains one current coil, the corresponding voltage coil being connected between that wire and some common point.
– If this common point is on one of the N wires, the measurement may be made by the use of N‐1 wattmeters.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Electricity Metering Technology
Most common residential
Not a Blondel meter
Valid due to “balance”
Source: Handbook for Electricity Metering, 10th Ed., Edison Electric Institute, 2002.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Electricity Metering Technology
Source: Handbook for Electricity Metering, 10th Ed., Edison Electric Institute, 2002.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Metering Fundamentals
 P = Vrms*Irms*cosΘ to ultimately get watt‐hours
1. VAh: by measuring Vrms and Irms then integrating VA=Vrms*Irms as done for real power by comparing it to a VAh threshold 2. VARh
3. Vh: based on Vrms measurement
4. Ah: based on Irms measurement
5. V2h
6. A2h
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Metering Fundamentals
Apparent Power
Four‐quadrant metering
– Phasor/Vectorial
– Arithmetic
– IEEE 1459
Under all voltage and load conditions, the
arithmetic sum will always be equal to or
greater than the vector sum and will more
accurately meter the true volt-ampere load.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Source: Handbook for Electricity
Metering, 10th Ed., Edison Electric
Institute, 2002.
Outline
Power and Metering Fundamentals
Power Quality and Harmonics
Curiosities
© 2011 EnerNex. All Rights Reserved. www.enernex.com
What are Harmonics?
Harmonics are sinusoidal voltages and currents with frequencies that are integer multiples of the fundamental frequency (60 Hz in U.S.).
The value of the multiplier corresponds to the harmonic order.
Frequencies other than the fundamental are generally undesirable in a power system.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Quantifying Harmonics
THD and RMS
∑
Im
2
2
∙ 100%
1
2
1
2
∙ 1
1
True PF vs. Displacement PF
2
1
Total Demand Distortion
∑
© 2011 EnerNex. All Rights Reserved. www.enernex.com
2
2
S
jQ

P
Re
What Causes Harmonics?
The distortion comes from nonlinear devices, principally loads:
– Compact Fluorescent Lamps
– Power electronic Devices
– Magnetic Core Saturation
– Rotating Machines
– Arc Furnaces
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Effects of Harmonics
Undesired Operation of Breakers and Fuses
Transformer Overheating
Failed Capacitor Banks
Overloaded Neutral Conductors
Communication System Interference
Relay Malfunction
Effects in Rotating Machines
Elevated Neutral to Earth Voltages
Metering
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Mitigating Harmonics
Passive Filters
Active Filters
Power Converters
Transformers
Capacitor Banks
Rotating Machines
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Examples – Phase Currents
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Examples – Neutral Currents
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Outline
Power and Metering Fundamentals
Power Quality and Harmonics
Curiosities
© 2011 EnerNex. All Rights Reserved. www.enernex.com
BC Hydro Case Study
BC Hydro performed a meter exchange at a water pumping station with 2 ASDs (Ithd=26%)
The new meter showed an 8% PF decrease!
Subsequent trial with other electronic meters gave 0.96, 0.96, 0.95 vs. this meter’s 0.88 PF Why the difference? Which is correct?
Source: Brent Hughes, BC Hydro (retired). Used with permission.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
BC Hydro Case Study
Data Analysis - 2*150hp ASD, I5th=40%
P
Q
S
PF
Fundamental
118.57 20.09 121.37 97.7%
Traditional
118.41 19.97 121.19 97.7%
Trad./Fund. 99.87%
99.40% 99.85% 100.0%
IEEE 1459
118.41 55.86 131.11 90.3%
1459/Fund.
99.87% 278.0% 108.0% 92.4%
Grossly exaggerated
Source: Brent Hughes, BC Hydro (retired). Used with permission.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
BC Hydro Case Study Conclusions
When harmonics are present, a customer’s bill will depend on the utility’s choice of meter. Quantities affected are kVA, kVAh, kVAR, kVARh, p.f.
IEEE 1459 methods cannot distinguish between harmonic sources and sinks‐both penalized.
PF and harmonics have different system impacts. Different billing rates req’d. IEEE Std. 1459 lumps it all together.
Harmonics penalty charges may not be justified by utilities or authorized by Utility Commissions.
Source: Brent Hughes, BC Hydro (retired). Used with permission.
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Curiosities from testing standpoint
Radian Research Investigation mid 2000’s
– Eight VAR definitions
– Five VA definitions
– Four meters tested
• When method matches: 0.03‐0.09% error
• When method mismatches: 19.1‐26.2% error
ANSI C12.24 TR
– Definitions for Calculations of VA, VAh, VAR, and VARh for Poly‐Phase Electricity Meters
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Summary
The power system is well managed and controlled using varying degrees of measurement granularity
There is no single, agreed‐upon measurement of VA, hence no agreed‐upon determination of power factor
Simple blind adoption of advanced measurement techniques may have deleterious effects on business processes and utility customers
The industry is keenly aware of the issues from the M&V standpoint and working to build understanding and methodologies
© 2011 EnerNex. All Rights Reserved. www.enernex.com
Aaron Snyder
Vadim Zheglov
aaron@enernex.com
vzheglov@enernex.com
THANK YOU!
© 2011 EnerNex. All Rights Reserved. www.enernex.com