harmonics presentation by baldev raj narang ceo clariant power system ltd

Apr 18, 2023 1It's All About Saving Your Money !!!

HARMONICS Presentation by Baldev Raj Narang CEO Clariant Power System Ltd

The Basics of Harmonic Resonance

kVAr

kVASccN res

)(

Vn

Harmoniccurrent

source (In)

Magnified In

kWLoading

SystemImpedance

PFCCapacitors

Variation of system impedance with harmonic(400 kVAr capacitor connected to 1000 kVA transformer)

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)Effects of Harmonic Resonance

Linear load = 0 kW

Linear load = 300 kW

Power System Impedance

• At low frequencies Power System Impedance is determined by the impedance of the Transformer and the Transmission lines. At Higher frequencies it is determined by the impedance of the Power Factor correction Capacitors.

• There is an intermediate range of frequencies where the Capacitive and Inductive effects combine together to give a very high impedance. A small Harmonic Current within this Frequency range can give a very high and undesirable Harmonic Voltage.

• This is the condition which is called Resonance

HARMONIC RESONANCE

• Harmonic resonance is generally caused by parallel resonance between the Power Factor Correction capacitors connected to a load and the transformer supplying that load. When a number of harmonic current sources are injecting currents into the supply and the frequency of one of the harmonics coincides with the resonant frequency of the supply transformer and Power Factor Correction capacitor combination, the system resonates and a large circulating harmonic current is excited between these components. The result of this is that a large current at this harmonic flows in the supply transformer, thus resulting in a large harmonic voltage distortion being imposed upon the load voltage.

HARMONIC RESONANCE CONTD---

• THE FORMULA TO DETERMINE THE ORDER OF HARMONIC THAT MAY CAUSE RESONANCE IS

• Hr = • SUPPOSE 20 MVAR CAPACITOR IS CONNECTED

ACROSS A SYSTEM OF 1000MVA SOURCE THERE WILL BE CONDITION OF RESONSNCE AT 7TH HARMONIC

• THE POSSIBILITY OF RESONANCE SHOULD BE EXPLORED AND ELIMINATED DURING ANY MODIFICATION OR ADDITION OF LOAD IN THE POWER SYSTEM


Resonance Frequency

• Resonance occurs at a frequency where system inductive impedance equals capacitive impedance

• 2πftL =

• ft =

• In a typical system the order of Harmonic (Hr) where resonance occurs can be calculated as

• Hr =

• For 1000 MVA source and 20 MVA capacitors

• Hr = = = 7.07

Power System Impedance

• Harmonic Order Nr where Resonance can occur is given by ‘Square Root’ of • Short Circuit MVA of Source divided by MVAR of connected Capacitors. • • Nr = • For 100 MVA Short Circuit Level and 800 KVAR Connected Capacitors Nr = • This is close to 11th Harmonic which may be present due to certain loads and will cause Resonance at this undesirable point. • If the Connected Capacitors are reduced to 500 KVAR then Nr increase to 14.1 and the risk of resonance at undesirable frequency close to some prevalent Harmonics is eliminated.

HARMONIC RESONANCE CONTD

• SINGLE LARGEST CAUSE OF SEVERE HARMONIC DISTORTION IS RESONANCE

• A NORMAL HARMONIC MAY BE AMPLIFIED 10 TO 25 TIMES IF RESONANCE OCCRSC AT OR CLOSE TO CRITICAL FREQUENCIES

• IT OCCURS MAINLY DUE TO INDISCRIMINATE USE OF PF CAPACITORS OR BECAUSE OF INCORRECT APPLICATION OF FILTERS

LOAD ALLOCATION ON A TRANSFORMER

• If a Transformer is loaded with mainly non linear load the supply is highly corrupted as there is no Damping of Harmonics Amplification due to absence of linear load.

• Allocating combination of linear and non linear loads on a Transformer is advisable as it dampens the Harmonic Amplification and minimizes Filtration needs

OVERCOMING RESONANCE

• SERIES COMBINATION OF REACTOR AND CAPACITOR TO CONTROL SYSTEM IMPEDENCE TO AVOID RESONANCE CONDITION WHICH CAN AMPLIFY HARMONIC CURRENT.

• THE COMBINATION SHOULD BE INDUCTIVE AT CRITICAL FREQUENCY BUT CAPACITIVE AT FUNDAMENTAL FREQUENCY FOR THIS TUNING FREQUENCY SHOULD BE BELOW LOWEST ORDER HARMONIC 5TH (250 HZ)

OVERCOMING RESONANCE CONTD---

• HARMONIC RESONANCE WAS NOT A CONCERN EARLIER WHEN NON LINEAR LOADS WERE NOT SIGNIFICANT

Harmonic Generation by Nonlinear Loads

• UPS• DC DRIVES• VFD• THYRISTOR CONTROLLED HEATING• INDUCTION FURNACES• ELECTRONIC CHOKES FOR FUORESCENT LAMPS• BATTERY CHARGER• WELDING CONTROLS AND RECTIFIERS• SMPS SUPPLIES

ADVERSE EFFECTS OF HARMONICS

• INCREASED HEATING DUE TO IRON AND COPPER LOSSES AT HARMONIC FREQUENCIES

• CHANGE IN PERFORMANCE CHARACTERISTICS OF ELECTRICAL AND ELECTRONIC EQUIPMENTS

• OVERLODING OF NEUTRAL • CAPACITOR FAILURES• SPURIOUS TRIPPINGS• ERATIC OPERATION OF CONTROLS

ADVERSE EFFECTS OF HARMONICS

• INTERFERENCE WITH COMMUNICATIONS• MEASUREMENT ERRORS IN METERING

DEVICES

RELEVANCE OF HARMONICS TODAY

• HIGH NON LINEAR LOADS • VISIBILITY OF PROBLEM BECAUSE THE

MEASURES TO TACKLE HARMONICS ARE NOT IN PLACE

• INCEASED USE OF CAPACITORS FOR PF IMPROVEMENT LEADING TO AMPLIFICATION OF HARMONICS

Series Resonance

At tuning frequency ft

XL = XC

• 2πftL =

• ft =


• Capacitive Reactance decreases with frequency and inductive reactance increases with frequency

• The total reactance of the combination takes minimum value at resonance frequency

• The total reactance of the combination takes minimum value

at resonance frequency

• For 7% resonance frequency = 189Hz


Series resonance• Tuning frequency for 7% detuned reactor in LC series

circuit• Detuning ratio p = 0.07• Fundamental frequency = fn• Tuning frequency = ft• L = Inductance• C = Capacitance

• 2πfnL = x 0.07

• fn2 = x 0.07

Series Resonance –Tuning Frequency

• ft2 =

•

HARMONIC FILTERS

• DETUNED FILTERS• TUNED FILTERS• ACTIVE FILTERS

DETUNED FILTERS

• DETUNED FILTER IS A SERIES LC CIRCUIT TUNED TO AVOID RESONANCE CONDITION. IT OFFERS LOW IMPEDENCE PATH TO SELECTED HARMONIC FREQUENCIES DETERMINED BY THE TUNING FREQUECY. IT PROVIDES CAPACITIVE KVAR TO THE SYSTEM AND A NOMINAL REDUCTION OF HARMONICS

DETUND FILTERS CONTD---• VOLTAGE RISE ACROSS CAPACITOR Vrise % = ( )2 x 100

Fn is Network Frequency Ft is Tuning Frequency of LC combination• 5.67% DETUNED FILTER– 210 HZ TUNING

FREQUENCY• 7% DETUNED FILTER – 189 HZ TUNING FREQUENCY• 14% DETUNED FILTER – 134 HZ TUNING

FREQUENCY

Typical Solutions Applied to Resonant Power Systems – Detuning Reactors

• This solution involves connecting a reactor in series with the Power Factor Correction capacitor such that the tuning frequency of the L-C combination is 189Hz (50 Hz system). This tuning frequency is chosen in order to ensure that this capacitor branch appears inductive for all of the major harmonics on the system, thus eliminating the possibility of a resonance occurring. Any resonance involving the 3rd harmonic is ignored as Power Factor Correction capacitors are generally connected in a Delta configuration, this preventing any 3rd harmonic (zero sequence) current flow. The tuning frequency is chosen to be far enough below the 5th harmonic to avoid the Power Factor Correction capacitor filtering the 5th harmonic current but not so low that an excessive voltage rise is produced across the capacitor at the fundamental frequency.

Typical Solutions Applied to Resonant Power Systems – Partial Filtration

• This solution involves connecting a reactor in series with the Power Factor Correction capacitor such that the tuning frequency is approximately 210Hz (50 Hz system). This configuration is series resonant quite close to the 5th harmonic (250Hz) and as such affords a degree of harmonic filtration. Using this configuration will remove typically 50% of the 5th harmonic current and 30% of the 7th harmonic current. This configuration would be used where the existing harmonics are higher than the ideal level but not so high that a full filtration system is required.

Typical Solutions Applied to Resonant Power Systems – Full Filtration

• This configuration involves a number of capacitor arms being tuned very close to particular harmonic frequencies with the express purpose of removing these harmonics. In the example shown the 5th and 7th harmonics are being targeted.

• TUNING FREQUENCIES ARE 240 HZ AND 334HZ

TUNED FILTERS

• TUNED FILTER IS AN LC CIRCUIT THAT IS TUNED TO PROVIDE BOTH A HARMONIC CURRENT REDUCTION WHILE AVOIDING A RESONANCE CONDITION. IT IS TUNED CLOSE TO THE FREQUENCY OF A SPECIFIC HARMONIC CURRENT WITH THE GOAL OF PROVIDING A LOW IMPEDANCE PATH TO THAT HARMONIC CURRENT THUS REDUCING THE AMOUNT OF THAT HARMONIC CURRENT FROM BEING INJECTED INTO THE DISTRIBUTION NETWORK

Comparison of Harmonic Resonance Solutions

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Zs Plain Capacitor

Zs Detuned Capacitor

Zs Partial Filter

Zs Full Filtration

Comparison of Harmonic Resonance Solutions

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Vn

(%)

Vn Plain Capacitors

Vn Detuned Capacitors

Vn Partial Filtration

Vn Full Filtration

SYSTEM HARMONIC IMPEDANCE

• This graph shows how the system harmonic impedance varies with 400 KVAr connected in the various configurations detailed in the previous slides. Clearly, the plain capacitor solution results in the highest peak harmonic impedance at the 7th harmonic. The full filtration has two peaks at the 4th and 6th harmonics. However, these harmonics do not naturally occur and the impedance at the significant harmonics (5th and 7th) is very low. The other systems provide a moderately low impedance throughout the harmonic range but most importantly, avoid any resonant peaks.

COMPARISON OF HARMONIC RESONANCE SOLUTIONS

• This slide shows the harmonic voltage distortion resulting from the implementation of the four capacitor configurations mentioned earlier. The voltage distortion resulting from the connection of plain capacitor banks is not acceptable whereas that resulting from all the other solutions is.

Objectives of Harmonic Mitigation

• To have normal operation of all electrical equipments and to get their normal expected life

• To obtain operational efficiency and energy efficiency

• To maintain power quality• To meet the harmonic current and voltage

distortion limits prescribed by international standards or by utility supply companies.

Why to use Segmented Film MPP Capacitors

• Inherently safe and Environment friendly construction• Can safely clear an internal fault or a voltage transient without

isolating the capacitor• Can isolate the capacitor safely at the end of service life or in extreme

loading conditions • Fine manufacturing tolerances• Absence of any trapped moisture and impurities • Better suitability for handling high frequency harmonics due to their

low ESR values• High power density leading to compact low space construction • Excellent quality uniform metal layer end connection with metal spray• Lower CO2 emission requirements

Capacitors with High Current Carrying Capacities

• The IEC standards require capacitors to be capable of continuously handling 130% of rated current but in harmonic environment this value can be exceeded and values higher than 200% can only be considered safe. This is now becoming possible with the advent of segmented MPP type low ESR capacitors which have excellent over current handling capabilities. ESR value assumes higher significance in view of high frequency harmonics being handled by capacitors. ESR value had a limited significance when fundamental frequency current was the only consideration.

Problems with APP Capacitors

• Absence of inherent safety features• High dissipation factor• High manufacturing tolerances• Poor quality of bimetallic end connections• Abnormally high operating temperatures• Loose winding with trapped moisture and impurities• Low power density leading to higher space

requirements• Higher CO2 emission requirements

Inherent Capacitor Safeties

• The absence of any inbuilt safety mechanism to clear internal faults leads to continued operation under abnormal conditions of over temperature, over pressure and degradation of oil, thus leading ultimately to complete failure under unsafe conditions. The undesirable mode of failure under heavy loads, or at the end of service life has made APP capacitors unusable worldwide for LT applications. The ongoing research for development of HT capacitors with a superior and safer technology may soon phase out APP capacitors for HT applications too

Ventilation and Cooling Requirements

• Capacitor panels need adequate ventilation and cooling. Present day practice where reactors and thyristor switching are increasingly becoming part of capacitor panels, the cooling needs assume greater significance. Compartmentalized construction is unsuitable and needs to be discontinued. Similarly these reactive power systems should not be clubbed with MCC and PCC panels as the design, performance and operating requirements are more complex and need specialized attention.

Where to apply Harmonic Mitigation Scheme

• The technical benefits of applying harmonic solutions are available upwards of the point

• of application. Most solutions today are applied by users close to the point of utility company’s supply to meet mainly statutory requirements. The harmonic solutions need to be shifted downwards closer to the harmonic generating loads in order to pass on the benefits to both the utility company and the user.

Reactors • Reactors should have Class F or Class H insulation level, less than

10 watts per Kvar power loss, continuous current handling capacity of 150% of rated value or higher, Linearity of 175%. In a changed scenario the utility companies are moving towards imposing significant penal charges for not maintaining harmonic levels below specified values. At times the specified maximum limits are more stringent than those recommended as per IEEE519. This calls for following an elaborate and accurate designing process for reactor selection. A hitherto common practice of using a 7% reactor which was mainly meant to provide some protection to capacitors may have to be done away with in favor of reactors which can provide filtration to achieve desired harmonic levels. Reactors also dampen effect of transients during capacitor switching.

Step configuration

• Step configuration involving sizing of individual steps and number of total steps needs to be carefully selected to avoid resonance occurrence at switching of any step. It may be necessary to skip a particular step to achieve this purpose. Most designers will have specific software developed for the purpose. Indiscriminate selection of step sizes and number of steps may lead to some undesirable combination resulting in resonance occurrence and resultant pitfalls thereof. Here the clients and consultants who often inadvertently suggest particular step combinations need to be warned of the possible dangers. It is best to leave this exercise to the designers after giving them the broad guidelines about the least count of power factor correction over the normal operating range.


IEEE 519 1992

Total Harmonic Distortion (Current)

• Where I1 is fundamental component

Total Demand Distortion (Current)

• Where IL is the maximum demand load current of the facility within 15 or 30 minutes demand window.


Detuning Frequencies

• For series LC Detuned Filters the tuning frequency (Ft) is set below the lowest Harmonic with remarkable amplitude which is normally the fifth Harmonic

Where f = fundamental frequency P = Detuning Ratio in percentage

• For 7% Detuning Ratio


• For 5.67% Detuning Ratio

• For 14 % Detuning Ratio


Power Factor Correction

Case 1• KVA Capacity of source required is 100 KVA, Active power is

80 KW and Reactive Power is 60 KVAR• Reactive power is supplied by the source


Power factor correction in the presence of Harmonic Generating Loads

• Capacitors provide low impedance path to harmonics• If the resonance caused by addition of capacitors occurs near

any of the generated harmonics then the harmonics get amplified

• Capacitors get stressed due to flow of harmonics through them


Reactive Power Requirement

• Initial power factor Cos ᴓ1 • Desired power factor Cosᴓ2• Initial reactive Power Q1 =

Ptanᴓ1 • Final reactive Power Q2 = P

tanᴓ2• Required reactive Power

= ᴓ1 - ᴓ2

= P tanᴓ1 - P tanᴓ2

= P (tanᴓ1 - tanᴓ2)

= P (Multiplying factor)


Voltage across Capacitor in a series LC Filter

Vc = Voltage across capacitor

Vn = System voltage

P = Detuning Ratio in percentage

For 7% detuning ratio

• Plus 10 % Tolerance = 520 V• Next available standard voltage is 525 V

• For 5.67% Detuning Ratio

Next available standard voltage is 525 V


Capacitor inrush current Isolated bank

• Isolated bank •

• Ipk = inrush current

• Ft = inrush transient frequency• Io = Steady State current value• Fo = power frequency

• Ipk is 5 to 15 times the normal capacitor current

Apr 18, 2023 50

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Discharging of capacitors

• IEC 60831-1 Clause 22 • Each capacitor unit/bank is provided with a means for

discharging each unit in 3 min. to 75 volts or less

• From an initial peak voltage of times rated voltage Un

• In a single phase unit


• R = Discharge Resistance in Ω

• t = Discharge time from Un to Ur in seconds

• Un = Rated voltage in volts

• Ur = Residual voltage in volts

• K = Coefficient depending on connection module of resistor to capacitor (k=1 for R in parallel with C )

• C = Capacitance in Farads• Indian standards

Discharge time = 1 min

Residual voltage = 50 V

•


6-pulse diode rectifier

• The most common rectifier circuit in 3-phase AC drives is a 6-pulse diode bridge. It consists of six uncontrollable rectifiers or diodes and an inductor, which together with a DC-capacitor forms a low-pass filter for smoothing the DC-current. The inductor can be on the DC- or AC-side or it can be left totally out. The 6-pulse rectifier is simple and cheap but it generates a high amount of low order harmonics 5th especially with small smoothing inductance.

• If the major part of the load consists of converters with a 6-pulse rectifier, the supply transformer needs to be oversized and meeting the requirements in standards may be difficult. Often some harmonics filtering is needed.

12-pulse diode rectifier

• The 12-pulse rectifier is formed by connecting two 6-pulse rectifiers in parallel to feed a common DC-bus. The input to the rectifiers is provided with one three-winding transformer. The transformer secondaries are in 30° phase shift. The benefit with this arrangement is that in the supply side some of the harmonics are in opposite phase and thus eliminated. The major drawbacks are special transformers and a higher cost than with the 6-pulse rectifier

18 pulse and 24-pulse diode rectifier

• 18 pulse converter uses three sets of 6 pulse bridge rectifiers that are supplied from three different power sources each of which are phase shifted by 20 electrical degrees. This results in cancellation of the 5th, 7th, 11th and 13th harmonics

• 24-pulse rectifier has two 12-pulse rectifiers in parallel with two three- winding transformers having 15° phase shift. The benefit is that practically all low frequency harmonics are eliminated but the drawback is the high cost.

FORMULAE

• KVAR = 2 π f CV² (Capacitive KVAR 1 Ph)• KVAR = √3 2 π f C V² (Capacitive KVAR 3 Ph)• KVAR = V²∕ 2 π f L (Inductive KVAR 1 Ph)• KVAR = √3 V²∕ 2 π f L (Inductive KVAR 3 Ph)

FAULT LEVEL CALCULATIONS

Transformer Fault MVA = Transformer MVA Capacity/ Per Unit ImpedanceFor 10 MVA Transformer having 9 % Impedance

Fault MVA = 10/.09 = 111MVA

Conclusion

• There is increasing presence of non linear loads leading to harmonic generation and their further amplification due to resonance conditions induced by capacitors. To safeguard their installation utility companies are rightly coming out with penal tariff structures. Correctly designed effective harmonic solutions designed by using ETAP or equivalent software which can provide greater filtration volumes are imperative. Precautions need to be taken while allocating loads on transformers, ensuring avoidance of resonance while adding capacitors steps and selecting only reliable and technologically superior components. A casual approach in selecting capacitor steps and reactor detuning factor may lead to resonance and associated problems.

Apr 18, 2023 59sis

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harmonics presentation by baldev raj narang ceo clariant power system ltd

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