Harmonics Presentation

7/28/2019 Harmonics Presentation

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BYJyothimon AbrahamStudent of MSc in Power SystemsUniversity of Bath

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Introduction

Load Profile of building power system Commercial Bank load profile Single line diagram of Bank Harmonic Pollution Conditions for Resonance Industry standards for Harmonics-IEEE519 Harmonic current spectra of Building loads THD of system Filter Design Harmonic mitigation with filters Harmonic Resonance Harmonic Power flow Optimization of Filters Summary

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A linear electrical load is one, which draws a purely sinusoidal current whenconnected to a sinusoidal voltage source, e.g. resistors, capacitors, andinductors. Many of the traditional devices connected to the power distribution system,such as transformers, electric motors and resistive heaters, have linearcharacteristics. A non-linear electrical load is one, which draws a non-sinusoidal currentwhen connected to a sinusoidal voltage source, e.g. diode bridge, thyristorbridge, etc. Many power electronic devices, such as variable speed drives, rectifiers andUPSs, have nonlinear characteristics and result in non-sinusoidal currentwaveforms or distorted waveform. By Fourier series analysis, we can show that a Periodic Distored wave formcontains Harmonics, ie, Multiples of Fundamental Frequency waveform

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Electronic Equipments occupy most part of Load inBuilding now a days. It includes1)For Lighting Dimming Ballasts2)Computers, Printers, Fax Machine3)VFD operated Equipments like Chillers, Pumps

4)UPS, Servers

A Commercial Bank Installation ofG+24 Floors atMiddle East is studied and Its Load Profile consists ofTotal Load 5200KW Load supplied through 4

numbers of 1500KVA Transformers. 77% Loads are NonLinear Loads and only 23% are Linear Loads.

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Sl.No Category KW

1 Chiller 1500

2 MCC 800

3 UPS 630

4 Dimmer 495

5Computer, Printer, Fax

Machine630

6 Linear Loads 1145

TOTAL 5200

5

29%

15%

12%

10%

12%

22%

LOAD PROFILE OF BUILDING1 Chiller 2 MCC 3 UPS

4 Dimmer 5 Computer 6 Linear


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U

MCC- 4 DIMMER-4CMPUTERS-4 L4

UPS-3 DIMMER-3L3

CHILLER-4C2

C3

C4

U1

L1

L2

MCC- 3

MCC- 2 COM PUTE R-2

F0F1 F2

F3

C0

COMPUTER-1

B0

0.415 kV

B1

0.415 kV

B2

0.415 kVB3

0.415 kV

CHILLER-2

Bus

11.00 kV

HILLER-1MCC-1

DIMMER-2

DIMMER-1

6

11kv BUS

415V BUS-1

415V BUS-2

415V BUS-3

415V BUS-4


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1. Current DistortionCurrent distortion is characterized by THDi index. It is defined as

2. Voltage DistortionVoltage distortion is characterized by THDv index. It is defined as

i denotes i-th harmonic

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1. Lower System Power Factor Harmonics do not contribute to Average Power or Reactive Powerdirectly It does increase RMS current and hence they decrease power factor ascan be seen from following equation:

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2. Flowing Effects Each of Characteristic harmonics can be defined as positive,

negative or zero sequence as per their direction of flow Positive sequence -7,13,19

Negative Sequence - 5,11,17

Zero Sequence-Triplen Harmonics

Reverse flowing harmonics cause heating effect in Motors

Triplen Harmonic cause current in neutral.

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Two types of Resonances occur:

1.Parallel Resonance Parallel resonance occur when the system inductive reactance and

capacitive reactance are equal at same frequency

If combination of capacitor banks and system inductance resultsin a parallel resonance near one of the characteristic harmonicsgenerated by the Nonlinear Load, that harmonic current will excitethe Tank Circuit

It causes an amplified current to oscillate between energy storagein the inductance and energy storage in the capacitance

This high oscillating current cause Voltage distortion and

Telephone Interference. In Impedance Scan this appear as PEAKS.

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2.Series Resonance Series resonance presents a low impedance path to

harmonic

currents and tend to trap any harmonic current to whichit is tuned

Series resonance can result in High voltage distortionlevels between the inductance and capacitors in series

circuit In Impedance scan, this appears as VALLEYS.

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Harmonic source stiffness is important in defining the extent ofwaveform distortion Weak systems(Low Isc) are associated with a large source

impedance and stiff systems are associated with a small impedanceTherefore, weaker systems will produce larger voltage drops fromharmonic currents than stiff systems.

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CHILLER-->12.5%

Harmonic Order 3 5 7 9 11 13 15 17 19

% Harmonic 0 9.3 4.9 0 5.2 4 0 1.4 1.2

MCC-->7.5%

Harmonic Order 3 5 7 9 11 13 15 17 19

% Harmonic 0 5.6 2.9 0 3.1 2.4 0 0.9 0.7

UPS-->5%

Harmonic Order 3 5 7 9 11 13 15 17 19

% Harmonic 0 4.4 1.7 0 1.3 0.8 0 0.6 0.6

DIMMER-->7.5%

Harmonic Order 3 5 7 9 11 13 15 17 19

% Harmonic 5.6 3.4 2.6 0.8 1.7 1.3 0 0.9 0.6

COMPUTERS-->2.5%

Harmonic Order 3 5 7 9 11 13 15 17 19

% Harmonic 2.1 0.6 0.5 0.2 0.5 0.7 0 0.4 0.4

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U

B4

U0

S0

THD

(

A)

19.17%

THD ( A) = 2.20%

B3

B0

C3

L3

tx-3 hp

F0

THD

(

A)

60.

04%

THD

(

A)

60.

02%

tx-3 5th

MCC-3 UPS-3 THD ( A) = 5.20%

THD ( A) = 18.28%

DIMMER-3

THDv(%) THDi(%)

TX-1 7.58 5.85

TX-2 9.08 21.45

TX-3 18.28 60.02

TX-4 5.2 7.15

TOTAL AT UTILITY BUS 2.2 19.17

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Two types of Passive Filters are mainly used. They are:(i) Single Tuned(ii)Damped Filters

Single tuned will eliminate only particular harmonic frequency towhich it is tuned, while damped filter acts as filter for corner

frequency and frequencies above it.

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Steps involved in Design are:

1.Capacitor to improve power factor is replaced by equivalent FilterCapacitance(Qc)

2.Evaluate Capacitive reactance at fundamental frequency Xc =

KV2/Qc

3.Calculate reactor size trapping at h harmonic XL =Xc/h2

4.Calculate R for specified Quality Factor(q) R =XLq

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U

B4

U0

S0

THD

(

B)

2.

63%

THD

(

B)

2.

10%

THD ( A) = 0.70%

B0

B3

L3DIMMER-3

tx-3 3rd-1tx-3rd 5th-1

F0

THD

(

A)

2.31

%

THD

(

A)

2.31%

tx-3rdhp-1

MCC-3 UPS-3

THD ( A) = 2.09%

THD ( A) = 2.54%

THDv(%) THDi(%)

TX-1 2.23 1.52

TX-2 3.02 3.17

TX-3 2.09 2.31

TX-4 2.54 2.68

TOTAL AT UTILITY BUS 0.7 2.63

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As shown from Figures, Resonance is reduced after Filter Usage. As shown from Previous slidesharmonics also reduced to acceptable limits as per IEEE-518.

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For Conventional power flow, (2n-1) Equations arerequired for n-bus power system solution For Harmonic power flow, (2n-1)+(2nq) equations are

required where q is number of harmonic frequencies ofinterest

In a 2-bus system we assume a 3rd harmonic load is at

Bus-2.So 2(n-1)+2nq=2(2-1)+2*2*1=6 Equations to solvefor V2(1), V2

(3) ,V1(3),2

(1), 2(3), 1

(3),ie,6 unknowns So in addition to Power Flow Equation, we have to use KCL

Equations for Harmonics & Fundamental frequency.

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Process of optimization of a Nonlinear system ofEquations can be done through a Concept calledLagrange Multipliers.

General Body of System of Equation are:

objective function which is the costfunction of filter to minimize cost

penalty function

Constraint due to limitation of Harmonic load flow

and THD.

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In Buildings, Nonlinear Loads occupy significantportion of Total Load which produces Harmonics.

Harmonics cause Voltage and Current Distortionwhich cause Equipment malfunction.

Harmonic spectra of building loads need to becollected and to be analysed in the Modellingsoftware.

Harmonic mitigation measures like Installation of

Filters to be done if distortion levels exceedslimits set by IEEE519 standard.

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THANK YOU!!!

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Harmonics Presentation