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HARMONICS

Causes, Effects, Solutions

K - FACTOR TRANSFORMERSHARMONIC MITIGATING TRANSFORMERS

I-TRAP NEUTRAL CURRENT REDUCER

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HARMONICS: A sinusoidal waveform with a frequency that is an integral multiple of the fundamental frequency.

60hz Fundamental

120hz 2nd Harmonic

180hz 3rd Harmonic

240hz 4th Harmonic

etc...

Note: Each individual harmonic is sinusoidal.

What are Harmonics?

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Fundamental (60hz) & 5th Harmonic (300hz)

• Both the fundamental (60 HZ) and the fifth harmonic (300HZ) are purely sinusoidal.

• All harmonic frequencies are sinusoidal when viewed individually.

• They appear as complex or distorted waves when viewed simultaneously.

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Harmonic Frequencies

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Sum of Fundamental & 5th harmonic

• Typical wave form of fundamental and fifth harmonic together. Notice distorted or non-linear shape.

Harmonic Frequencies

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360

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• Harmonics primarily originate in electronic power converters.

• Harmonics originate any time current is being drawn in short rapid pulses rather than in a smooth continuous manner.

• These can be found in:

1. Switch Mode Power Supplies

2. Electronic Ballasts

3. Variable Frequency Drives

4. Oven and Furnace Controls

5. Rectifier Circuits

Where do Harmonics Originate?

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• Overheated Neutrals

• Overheated Transformers

• Malfunctioning of Equipment due to excessive voltage distortion

• Burned-out Motors

• Tripped Circuit Breakers

• Blown Fuses

Major side effect of harmonics is extra heating in all system components.

Problems Created by Harmonic Currents

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• Triplen harmonics include the 3rd harmonic and all the odd multiples of the 3rd.

• Example: 3rd, 9th, 15th, 21st, 27th, 33rd, etc

• Note: Triplen harmonics tend to add up in the three phase neutral conductor.

Triplen Harmonics

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• Triplen harmonics add up in the three phase neutral because they are in phase with each other.

• 60 HZ or fundamental currents tend to cancel in the three phase neutral because of the 120 degree phase shift between adjacent phases.

Typical 208Y/120 System

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Effects of Harmonics on Transformers

• Increased temperature rise

• Increased neutral current flow

• Increased core losses

• Increased sound level

• Decreased efficiency

• Stray losses in the conductors get multiplied by the K - factor of the load to increase winding rise.

• Triplen harmonic currents add up in the three phase neutral.

• Harmonic voltages tend to increase losses in the iron core.

Harmonic Effects

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• K - Factor is a mathematical formula for calculating the heating effects of harmonics.

• A measure of a transformer’s ability to withstand the heating effects of non-sinusoidal harmonic currents created by much of today’s electronic equipment.

• The stray losses of the transformer are multiplied by the K-Factor of the load resulting in increased heating of the unit.

• It is only logical that it is a UL term, since UL has control of the insulation systems used in most electrical products.

K - Factor

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AC / DC Losses

• DC losses = I^2 x R

– I^2 x R losses can be easily determined from current and resistance.

• AC losses = stray losses

– Transformer total losses can be measured by putting watt meters in the primary supply circuit. The I^2 x R losses can be subtracted from this total and the remainder would be the stray losses

• Total conductor losses = AC + DC losses

Note: Stray losses get multiplied by the K-factor of the load.

Transformer Conductor Losses

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• 75 kVA, 3-Phase, 480 - 208Y/120, 150° rise

Total conductor losses at K-1 (linear load) = 2860 + 135 = 2995

• If K=20 (non-linear load), new conductor losses are:

– 2860 + (20 x 135) = 5560 watts

Rise @ K-1 = 150°C

Rise @ K-20 = 244°C

• These transformers use a 220°C insulation system per the following:

– Ambient: 40°C

– Winding rise: 150°C

– Hot spot: 30°C

Example: Temperature Rise

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1. K - Rated Transformers (traditional)

2. Harmonic Mitigating Transformers (zig-zag)

3. I-Trap Neutral Current Reducer

Three Solutions to Harmonic Problems

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• K - Rated or Non-Linear transformers do not eliminate harmonics!

• They are only designed to tolerate the heating effects of harmonics created by much of today's electronic equipment.

• K-rated transformers are traditional Delta-Wye transformers

– They are designed with lower flux densities and no load losses as well as lower I²R losses resulting in a larger and heavier unit.

– They do not eliminate or cancel harmonics

K – Rated Transformers

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• Available in K-Factors of 4, 13, and 20

• Aluminum or Copper windings.

• Available temperature rises of 150, 115, or 80

• UL listed and CSA certified

K – Factor Features

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• As of January 1, 2007 K-Rated transformers must comply to the efficiency standards (TP1) of the National Energy Bill

• They are only required to comply with a connected load condition of K1 (no harmonics)

K – Factor and TP1

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Acme Mitigating Transformer

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How do they Work?• They consist of a Delta primary and a Zig-Zag secondary. The Zig-Zag

secondary causes a phase shift in the triplen harmonics which results in a canceling effect. This prevents the triplen harmonic losses from being coupled back into the primary and results in cooler operation and increased energy efficiency.

Harmonic Mitigating Transformers

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• The secondary winding on each magnetic leg of the core is wound in two separate sections. These sections are Then transposed between different legs of the core to Create the Zig-Zag secondary. Each 120 v output of the transformer consists of two sections from different magnetic legs resulting in a magnetic phase shift

( Zero degree angular displacement)

What is a Zig-Zag Winding?

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Acme Catalog Numbers

• CMT-53312-4S 30 KVA

• CMT-53313-4S 45 KVA

• CMT-53314-4S 75 KVA

• CMT-53315-4S 112.5 KVA

• CMT-53316-4S 150 KVA

• CMT-53317-4S 225 KVA

Optional “TVSS” available on 208Y/120 output

Harmonic Mitigating

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Benefits1. Unlike K-Rated transformers, Mitigating transformers actually treat the

triplen harmonics in the Zig-Zag secondary winding

2. Reduce supply voltage flat topping caused by non-linear loads

3. Improve overall power factor of supply system

4. Suitable for K-Factor loads

5. Improved energy efficiency (Meet TP1 at K-1 load)

Harmonic Mitigating

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Features• Copper foil conductor to minimize “skin effect” of harmonic currents

• Taps: 2 x 2.5% ANFC and BNFC

• 220 Degree C insulation system with 150 Degree C rise

• UL listed and CSA certified

• Zero degree angular displacement between Primary and Secondary windings

Mitigating Transformers

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Notes• Harmonic mitigating transformers don’t treat harmonics or neutral

current until they reach the transformer windings

• Transformer has 200% Neutral Bar

• Neutral conductor from transformer to Load Panel should be sized at 200%

Harmonic Mitigating

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1. Acme utilizes special winding techniques and “foil” conductors in both its K-Factor and Harmonic Mitigating transformers to minimize the heating effects of harmonic currents. (Skin effect)

2. The use of foil conductor increases the dielectric strength of the insulation because one layer is only one turn. Foil also eliminates the effects of axial forces which can result in failure of wire wound transformers.

Acme Advantages

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Skin Effect Illustrated

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60 Hz Higher Hz

Foil conductor is very thin and much wider Minimizes skin effect at higher Hz

No current flow in center of conductor - Skin effect

Thinner but wider conductor

Full current flow

Round or Rectangular Wire

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• Hospitals and Health Care Facilities

• Commercial & Educational Facilities

• Airport Facilities

• Telecom Facilities

• Broadcasting Facilities

• Internet Service Providers

• Data Centers

Applications

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Technical Description:

• Low impedance - Zero sequence Auto Zig-Zag transformer

I – Trap Neutral Current Reducer

Applications:

• It is used to reduce excessive current flow in the neutral of a 3 phase 208Y/120 volt system.

• It is available in ampere ratings of 100, 150, 300, and 450. It includes a front mounted amp meter for monitoring neutral current.

• Target areas: Data processing centers, Hospitals, Radio and TV stations, Large computer labs, etc. (Any area having numerous electronic 120v loads powered from a 208Y/120 system)

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How does it work?• Third harmonic currents are in-phase (additive) in the three phase neutral.

• The low impedance and auto Zig-Zag characteristics of the I-Trap target the third harmonic currents causing them to become “out of phase” in the three phase neutral, resulting in a canceling effect. Reductions of 50% to 90% are typical.

• In many applications, the Acme I-Trap provides an easier and more affordable solution than replacing existing Neutral conductors.

I – Trap Neutral Current Reducer

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Performance• Reduction in Phase Current:

Before After

Phase A 49.4 42.9

Phase B 39.2 40.1

Phase C 63.2 53.6

Average 50.6 45.5

• Max phase amps reduced from 63.2 to 53.6 (18%)

• Phase unbalance reduced: Before - 62% ; After – 34%

• I-Trap helps reduce unbalance in the phases, which helps reduce neutral current.

I – Trap Neutral Current Reducer

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Performance Data

I – Trap Neutral Current Reducer

Phase

A B C

Out In Out In Out In

RMS 49.4 42.9 39.2 40.1 63.2 53.6

1H 39.0 40.0 31.0 38.0 51.0 50.0

3H 27.0 1.0 21.0 3.0 34.0 10.0

5H 13.0 15.0 11.0 13.0 15.0 16.0

7H 4.0 4.0 4.0 5.0 3.0 4.0

9H 1.0 --- 1.0 1.0 1.0 1.2

11H 1.0 --- 1.0 --- 1.0 ---

Har. Dist. 78.2% 37.7% 77.6% 39.0% 73.2% 38.0%

K – Factor 5.5 4.4 5.8 4.3 4.8 3.8

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Reduction in Neutral Current

• Total neutral current of 84.8 is greater than highest phase current of 63.2.

• Notice that total neutral current has been reduced by almost 90% (84.8 to 8.1 amps).

I – Trap Neutral Current Reducer

I – Trap Out In

RMS 84.8 8.1

1H 17.0 1.0

3H 83.0 8.0

5H 3.0 ---

7H 2.0 ---

9H 1.0 ---

11H 1.0 ---