www.p3-inc.com 2014

Power Factor

& Harmonics

Andy Angrick

2014

www.p3-inc.com

www.p3-inc.com 2014

• Harmonic problems are becoming

more apparent because more

equipment that produce

harmonics are being applied

to power systems

Harmonic Distortion

Grounding

Surge Transient

Voltage Variations

Harmonics

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Electrical Loads of the Past

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Electrical Loads Today

Computers Fluorescent Lights

and Ballast's

Variable Frequency

Drives

All equipment that uses

an AC to DC power supply

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Which came first?…..

• In this case…the Egg! – Current distortion causes Voltage distortion

– Voltage distortion is created by pulling distorted current through an impedance

– Amount of voltage distortion depends on:

• System impedance

• Amount of distorted current pulled through the impedance

• If either increases, VTHD will increase

Voltage Distortion Current Distortion

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Filter

480 V

Xs

M

XT

+ -

M

Blocking

Filter

G

UPS

w/Filter

Welder

Low Distortion Electronic Ballast

Oversized

Generator

K-Rated

Active

Filt

er

12

Pulse M

Harmonic Solutions

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100%, 60 Hz

2%, 780 Hz

20%, 180 Hz

12%, 300 Hz

4%, 420 Hz

2%, 660 Hz

%100...

%1

2

4

2

3

2

2

I

IIITHD I

Total Harmonic Distortion (THD) –

(voltage or current) represents a ratio of the

root-mean-square of the harmonic content

to the fundamental quantity, expressed as a

percent of the fundamental.

Harmonics

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H = NP+/-1

i.e. 6 Pulse Drive - 5, 7, 11, 13, 17, 19,…

Source Typical Harmonics*

6 Pulse Drive/Rectifier 5, 7, 11, 13, 17, 19…

12 Pulse Drive /Rectifier 11, 13, 23, 25…

18 Pulse Drive 17, 19, 35, 37…

Switch-Mode Power Supply 3, 5, 7, 9, 11, 13…

Fluorescent Lights 3, 5, 7, 9, 11, 13…

Arcing Devices 2, 3, 4, 5, 7...

Transformer Energization 2, 3, 4

* Generally, magnitude decreases as harmonic order increases

Expected Harmonics

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“Harmonics are not a problem

unless they are a problem!”

Remember

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Harmonic Sources - Transformer

Inrush

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Harmonic Sources – Arc Furnace

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Harmonic Sources - Switch Mode

Power Supplies

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Harmonic Sources - Switch Mode

Power Supplies – Neutral of Panel

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1 Nph

Harmonic Sources - VFD’s

• The input side (AC) of all AC or DC drives are usually very similar.

For most drives today, the input is a 6-pulse rectifier circuit.

• The harmonic current produced is related to the drive pulse number

by the formula:

– where h = the harmonic number

– N = an integer multiplier beginning with 1

– p = the pulse number.

• Theoretically, for a 6-pulse drive, the harmonic current produced

would include

– 5th, 7th, 11th, 13th, 17th, 19th, 23rd, 25th, etc.

– Called the drive characteristic harmonics, and for the most part, their

magnitudes decrease as their harmonic number increases

– No even harmonics would be generated.

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• For a 12-pulse drive, the characteristic harmonic currents

produced would include

– 11th, 13th, 23rd, 25th, 35th, 37th, etc. No even harmonics would

be generated.

– Realistically, power electronic manufacturing tolerances, firing

circuit timing variations, and component degradation or failure

cause drives to produce harmonic currents in addition to the

characteristic harmonics.

– 12-pulse drives will produce some small magnitudes of 5th, 7th,

17th, 19th, etc. harmonics. These are called noncharacteristic

harmonics of the 12-pulse drive. Small magnitudes of the 2nd,

3rd, and 4th harmonics are also generated, usually 1 to 4

percent.

Harmonic Sources - VFD’s

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Harmonic Sources - VFD’s

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From

IEEE519A Draft

Active Filters

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Effect of Drive Line Reactors

(IEEE519A)

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Fundamental = 100%

Harm

onic

= 1

00%

Fundamental = 100%

Harm

onic

= 2

0%

Total Current

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Harmonic Sequence Harmonic Sequence

1 + 10 +

2 - 11 -

3 0 12 0

4 + 13 +

5 - 14 -

6 0 15 0

7 + 16 +

8 - 17 -

9 0 18 0

Motor Heating & Vibrations

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60 Hz Rotation

5th Harmonic

Rotation

“Negative Sequence Current”

– Tries to Rotate Motor in

Opposite Direction

– Causes Motor and Heating

and Vibrations

Motor Heating & Vibrations

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If a capacitor exists on

the power system

AND

Harmonic producing

loads are in use

You MUST check for

harmonic resonance

(series and parallel)

Harmonic Resonance

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• Capacitors not only supply reactive power to the loads

in an electrical distribution system they also change the

resonance frequency of the system.

• Capacitors are also a “sink” for harmonic currents

present in a system (series resonance).

• When the resonance frequency of a system with PF

correction capacitors is close to the frequency of a

harmonic current generating load parallel resonance

can occur.

Harmonic Resonance

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• AC circuits characteristically have inductive and capacitive components and have the

means to transfer energy between these components.

• Harmonic resonance occurs when the inductive reactance of a circuit is equal to the

capacitive reactance. Resonance can be either series or parallel.

• Recall that inductive reactance increases as the power system frequency increases and

the capacitive reactance decreases as the power system frequency increases by the

following equations:

and

where XL = inductive reactance in ohms

XC = capacitive reactance in ohms

f = power system frequency in Hz

L = component inductance in henries

C = component capacitance in farads.

• At 60 Hz, the capacitive components have a much higher impedance than the inductive

components.

LjLfjX L 2

Cj

CfjXC

1)(

2

1

Harmonic Resonance

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Harmonic Problems-Capacitors

Example:

Xc = 1 / 2fc

A capacitor bank has reactance, measured in Ohms.

Lets say we have a Power Correction capacitor that has a

reactance of 12 ohms at 60HZ.

Then,

12 ohms = 1 / 2 x 3.14 x 60Hz x .00022F

If this capacitor is in a 480 Volt circuit 40 Amps will flow

in the capacitor (480Volts / 12 ohms = 40 Amps).

If we have 3rd (180 Hz) harmonics present.

Then,

Reactance = 1 / 2 x 3.14 x 180Hz x .00022F

Reactance = 4 ohms

We will now see 120 Amps flow in the capacitor.

(480 Volts / 4 ohms = 120 Amps)

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MSB

480Y277

3000A

600A Branch

feeding a

600A Busway

Motor Motor Motor

160Amps

of

other

Equipment

480V

50 Hp

65 Amps

each

Power Correction Capacitors

- 480V, 12 Cap, 40 Amps each

Harmonic Problems-Capacitors

Linear Load Example:

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MSB

480Y/277

3000A

600A Branch

feeding a

600A Busway

Motor Motor Motor

160Amps

3rd

Harmonic

(180Hz)

Generating

Equipment

480V

50 Hp

65 Amps

each

Power Correction Capacitors - 480V, 12 Cap, 40 Amps each

120Amps each

4 ohms

with 180Hz

Harmonic Problems-Capacitors

Non-Linear Load Example:

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Parallel Resonance

Harmonic

Current

Source X

C

X

L

CL

CLEQUIVALENT

XjjX

XjjXX

)(

)(

Equivalent Parallel Resonant Circuit

• The parallel combination of impedance is:

• Since XL and XC have opposite signs, the denominator can equal

zero if XL = XC. In reality, the only limiting factor is the difference in

resistance between the capacitor and reactor.

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This graph shows a typical frequency scan for a power system with unfiltered capacitance. This

is a “borderline” case for which a detuned filter would typically be recommended. The scan

shows parallel resonance at the 7.9th harmonic order. The scan magnitude at the peak is

approximately 615 ohms. The scan magnitude at the 7th harmonic is about 19 ohms (which is

not particularly high). However, the parallel resonant point of an unfiltered capacitor is very

sensitive to both the upstream source impedance and capacitance on other substations. A

source impedance change (such as being switched to a different transformer) could easily

cause the parallel resonant point to shift to the 7th harmonic or lower.

Parallel Resonance

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This graph shows an updated frequency scan for the same power system with the addition of a

series tuning reactor immediately upstream of the capacitors. Note the series resonant point at the

4.2nd harmonic. The addition of the series resonant point “anchor” has forced the parallel resonant

point down to the 3.7th harmonic. Also note that the magnitude at the parallel resonant point has

been reduced to approximately 110 ohms. The chances of exciting this parallel resonant point

would be very low, for a typical industrial power system. If the electrical system has specialty loads

that generate large amounts of low-order harmonics, such as EAFs (Electric Arc Furnaces), custom

filter design and analysis would typically be necessary. The new parallel resonant point will exhibit

some shift for source impedance changes, but these shifts will generally be minimal. Typically, we

want the parallel resonant point to land at approximately the 3.5th harmonic with all steps of the PFC

filter online.

Parallel Resonance

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The series combination of impedance is:

Since XL and XC have opposite signs, the summation can

equal zero if XL = XC. In reality, the only limiting factor is the

difference in resistance between the capacitor and reactor.

Equivalent Series Resonant Circuit

Harmonic Current Source X

C

X

L

CLEQUIVALENT XjjXX )(

Frequency Scan

0.1

1

10

100

1000

60 180 300 420 540 660 780 900 1020 1140 1260 1380 1500

Frequency in Hz

Imp

ed

an

ce in

Oh

ms

Series Resonance

Frequency Scan for Series

Resonant Circuit

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Utility

Utility Bus

1000 kVA

480 V Bus

Capacitor Fdr

CAPACITORLOAD

If other loads on the

system are “Non-Linear”,

consider installing a

harmonic filter in lieu of an

“unfiltered” capacitor to

avoid RESONANCE

Harmonic Modeling - Example

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Parallel Resonant Frequencies for Various Capacitor Sizes

0

50

100

150

200

250

300

350

400

450

500

0

100

200

300

400

500

600

0 5 10 15 20 25

Harmonic Order

Ca

pa

cit

or

Siz

eHarmonic Modeling - Example

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Harmonic Distortion Standards

IEEE 519-1992 Maximum Harmonic Current Distortion

ISC / IL TDD

1-20 5%

20-50 8%

50-100 12%

100-1000 15%

1000+ 20%

ISC=Maximum short circuit current

IL= Maximum demand load

TDD= Total Demand Distortion

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IEEE 519-1992 -Current

Typical Office Building

1200A 208Y/120 service

30K AIC

The Maximum IEEE Harmonic

distortion is:

30,000 AIC / 960 = 31

31 on the IEEE chart is 8%

Example:

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IEEE 519-1992 -Current

IEEE 519-1992 Maximum Harmonic Voltage Distortion

Voltage TVD

69kV and below 5%

TVD=Total Voltage Distortion

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Troubleshooting Methods

IEEE1159

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Future of IEEE 519 (2006)

• More concise document

• PCC clarified

• New voltage range

– 1.0 kV and below

• 8% THDV

• 5% individual voltage harmonics

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Utility Source

2.3% THD

Generator

Source

5.7% THD

Harmonics & Generators

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Transformers & Harmonic Currents

• Many people incorrectly assume that ALL harmonics are

trapped by delta-wye transformers. The fact is:

– only the balanced third harmonics (and multiples of the third)

circulate in the delta winding and are therefore trapped.

– other harmonic currents (5th and 7th, for example) and the

unbalanced multiples of the third harmonics can pass through the

transformer

– harmonic currents are inductively coupled along with the 60 Hz

current by the ratio of the primary turns to the secondary turns.

• Higher order harmonics (> 25th) may or may not be

inductively coupled through the transformer.

• Sometimes, higher frequency harmonics are capacitively

coupled from secondary to primary (not by the turns ratio).

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Power Factor & Harmonics

END