Modern Power Quality Challenges - EnerNex Power Quality Challenges ... Electricity Metering...

© 2011 EnerNex. All Rights Reserved. www.enernex.com

Modern Power Quality Challenges

Aaron F. Snyder, Ph.D.Vadim Zheglov


Outline

Power and Metering Fundamentals

Power Quality and Harmonics

Curiosities


Power Fundamentals

What we learn in school (power triangle)

Im

Re

S jQ

P

P = Real Power, Watts

Q = Reactive Power, VARs

S = Apparent Power, VA

S = P + jQ


Power Fundamentals Instantaneous power: p(t) = v(t)i(t) Active power: P = VIcosΘ

– sinusoids

Reactive power: Q = VIsinΘ– sinusoids

Apparent power: U = VI Phasor power: S = P + jQ

– S = U for sinusoids

Distortion power: D = sqrt(U2 – S2) Fictitious power: F = jQ + kD Nonreactive power: N = iP + kD Vector power: U = iP + jQ + kD Power factor: = P/U = cosΘ

Phasor Power Fictitious Power

Nonreactive Power Vector PowerSource: IEEE Tutorial, p.32

D

D

D

D

P P

P P

Q Q

QQ

U

N

F

S


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.


Electricity Metering Technology

Most common residentialNot a Blondel meterValid due to “balance”

Source: Handbook for Electricity Metering, 10th Ed., Edison Electric Institute, 2002.


Electricity Metering Technology




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. VARh3. Vh: based on Vrms measurement4. Ah: based on Irms measurement5. V2h6. A2h



Apparent Power– Phasor/Vectorial– Arithmetic– IEEE 1459

Four‐quadrant metering

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.



Outline



Curiosities


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.


Quantifying HarmonicsTHD and RMS

True PF vs. Displacement PF

Total Demand Distortion

Im

Re

S jQ

P

1 2

∑ 2

2

1∙ 100%

2

11 ∙ 1 2

∑ 2

2


What Causes Harmonics?The distortion comes from nonlinear devices, principally loads:– Compact Fluorescent Lamps– Power electronic Devices– Magnetic Core Saturation– Rotating Machines– Arc Furnaces


Effects of HarmonicsUndesired Operation of Breakers and FusesTransformer OverheatingFailed Capacitor BanksOverloaded Neutral ConductorsCommunication System InterferenceRelay MalfunctionEffects in Rotating MachinesElevated Neutral to Earth VoltagesMetering


Mitigating HarmonicsPassive FiltersActive FiltersPower ConvertersTransformersCapacitor BanksRotating Machines


Examples – Phase Currents


Examples – Neutral Currents


Outline



Curiosities


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.


BC Hydro Case Study

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

Data Analysis - 2*150hp ASD, I5th=40%



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.



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


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


THANK YOU!

Aaron Snyder [email protected] Zheglov [email protected]

Modern Power Quality Challenges - EnerNex Power Quality Challenges ... Electricity Metering...

Documents

Transcript of Modern Power Quality Challenges - EnerNex Power Quality Challenges ... Electricity Metering...