It is about Harmonics which is responsible for premature failure of Distribution Transformers feeding Non-linear loads in Office complexes & large commercial complexes.

1. K K Murty 1
JAI JAGANNATH

2. 14NWET–2023,AT SILICON INSTITUTE OF
TECHNOLOGY, BHUBANESWAR
0N THE 16TH & 17TH DECEMBER 2023
By K. K. Murty, BE( Hons) FIE, CE(Ind) M CIGRE.
Retd.Chief Engineer (Testing & Commun.)
M. P. Power Transmission Co. Ltd.
Jabalpur

3. HERTZ: Replaces the earlier term
"CYCLE PER SECOND."
 Hz – This is the Acronym of the word Hertz, named after
Heinrich Rudolf Hertz (1857–1894),a German physicist
 He discovered this phenomenon equivalent to one Cycle/
Sec.
 *1 Hz=1 cycle/sec.
* Pl see next slide
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4. 1 HZ =1 CYCLE/SEC &
NO. OF CYCLES(FREQUENCY) IN THE POWER SYSTEM
 Power frequency;50Hz
 The sinusoidal curve for 1 Hz
is shown along side
 1x50 Hz ie such 50 such curves
shall be held in 1 sec.
 Time taken for 1cycle
=20ms(1000ms/50) ;where
1sec=1000ms
 Harmonic wave nos.;
 Fundamental harmonic
wave=50 Hz
 2nd harmonic wave=100Hz
 3rd harmonic wave =150 Hz
 5th harmonic wave=250 Hz.
ie no of harmonic wave
=no.x50Hz
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5. HARMONICS IN POWER SUPPLY- CONCEPT THEREOF.
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6. MODERN TECHNOLOGY ATTRIBUTES TO “HARMONICS”
 Growth in Technology :By leaps & bounds in the field of Communication,
IT, Computer Science, Artificial Intelligence and In the Power Sector (
Metering, SCADA & automation) too .
 Modern Office gadgets:Use of modern Electronic gadgets/machines
enable in saving in money, man-power & time, in smooth functioning of
the Offices & Commercial stalls/units.
 Non-linear Loads:- Predominantly electronic gadgets are non-linear
loads. Switched mode Power supplies (SMPS), Variable speed motors
and drives, UPSs(Un-interrupted Power Supplies), PCs(Personal
Computers), Laser printers, Photocopiers, FAX machines, Florescent
Light Ballasts, Battery chargers, etc.
 Irony :- Contrary to maintaining Power Quality, modern electronic gadgets
in-turn pollute the power supply by producing “HARMONICS”.
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7. CATEGORIES OF VOLTAGES/VOLTAGE WAVES DEPRIVE
QUALITY P0WER
TO THE CONSUMERS.
 Interruption.
 Sag’
 Swell.
 Long duration variations.
 Transients.
 Harmonic Distortion.
 Voltage fluctuations
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Note: Till recently , In India we were following IEEE 1159, however BIS has
released a Standard for Distribution System Supply Voltage Quality as

8.  Procurement of DTRs irrespective of their location of installation by
DISCOMS & Distribution Utilities confirms to IS: 1180 Part-I (up to &
including 33kV, 2500 kVA)
 Allowed Harmonic distortion for the DTRs :Linear loads with a tolerance
to withstand Total harmonic distortion in voltage due to harmonic
currents is: distortion of 5%(Bureau of Energy Efficiency Std.) which is
also stipulated in the IEEE Std 519-2014 .
 Reporting failures of DTRs : Pre-mature failure of Distribution
Transformers installed for feeding load of Office complexes and
Commercial complexes are generally reported as Over loading &/ or
short-circuit in the LV side network/loads.
 THE ROOT-CAUSE OF PRE-MATURE FAILURE OF DTRS IN OFFICE
& COMMERCIAL COMPLEXES IS “HARMONIC CURRENTS” CAUSED
DUE TO NON-LINEAR LOADS.
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ALLOWED HARMONIC LIMITS IN DISTRIBUTION
TRANSFRMERS

9. “SUPPLY VOLTAGE QUALITY VIDE IS: 17036- 2018-MANDATORY ON THE
PART OF DISCOMS TO ABIDE BY THIS IS & MAINTAIN;
 Frequency ;
a) Supply frequency limits of the source connected to synchronized system
+ 4% / − 6%.
a) Supply frequency limits of the source without having connection to
Synchronized system ±15% of 50Hz.
 Voltage Magnitude : In the band of Un ± 10 %.
 Waveform: Low voltage harmonic distortion Limits.
[Note: * Includes Hospitals and Airports.
# Exclusively dedicated to converter loads.]
 Supply Voltage Unbalance : 95%
V2
V1
≤ 2%,
 where V1= rms value of positive phase sequence component (fundamental).
V2= rms value of negative Phase sequence component (fundamental).
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Parameter *Special application General system #Dedicated system
THD 3.5% 5% 10%

10. WHAT CAUSES
HARMONICS?
 Harmonics are generated by electronic equipment with non-linear
loads drawing in current in the form of abrupt pulses .These short
pulses cause distorted current waveform which in-turn cause
Harmonic current to flow into the power system.
 Harmonics producing loads on Transformers & Power Systems:
Non-Linear loads
 Predominantly electronic gadgets are non-linear loads.
Switched mode Power supplies (SMPS), Variable speed motors
and drives, UPSs(Un-interrupted Power Supplies),
PCs(Personal Computers), Laser printers, Photocopiers, FAX
machines, Florescent Light Ballasts, Battery chargers, etc
 Single phase non-linear loads are prevalent in the modern offices
and commercial complexes responsible for developing Harmonics.
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11. GRAPHICAL REPRESENTATION OF LINEAR LOADS AND NON-
LINEAR LOADS –GENERATION OF HARMONICS
 Harmonics are generated by electronic equipment with non-linear loads
drawing in current in the form of abrupt pulses.
 These short pulses cause distorted current waveform which in-turn
cause Harmonic current to flow into the power system.
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12. VOLTAGE & CURRENT PROFILES OF
LINEAR & NON-LINEAR LOADS;
LINEAR LOAD NON-LINEAR LOAD
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13. SAMPLE HARMONIC PROFILE OF A CONSUMER LOAD;
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14. FORMULAE FOR THD (TOTAL HARMONIC DISTORTIONS) AND
TDD (TOTAL DEMAND DISTORTION);
 i)Current Distortion;
 Where n=harmonic no, In= Amplitude of Current at nth Harmonic, I1=
Amplitude of fundamental Current.
 ii)Voltage Distortion;
 Where n=harmonic no, In= Amplitude of voltage at nth Harmonic, U1=
Amplitude of fundamental voltage.
 iii)Total Demand Distortion;
 Where I max Demand
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15. PH. SEQ. ROTATION OF ODD HARMONIC CURRENT
COMPONENTS AND EFFECT THEREOF;
 Distorted waveform in Power Systems contains only odd
harmonic components,
 Odd Harmonic phase sequence rotations are shown here-
under;
 Harmonics of the order h = 1, 7, 13,… are purely
positive sequence.
 Harmonics of the order h = 5, 11, 17,… are purely
negative sequence.
 Triple N Harmonics (h = 9, 15, …) are purely zero
sequence. Thus, are co-phasal.
[Note; All odd harmonics which are divisible by 3 are
categorised as triple N harmonics]
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16. DERIVATION OF SEQUENCE ROTATION OF
ODD HARMONIC CURRENTS
Harmonics A B C Phase rotation
Fundamental 0O 120O 240O (+)Ve
3rd 0O 3x120O (0O) 3x240O (0O) Zero
5th 0O 5x120O (240O) 5x240O (120O) (-)Ve
7th 0O 7X120 O (120O) 7x240O (240O) (+)Ve`
9th 0O 9x120O (0O) 9x240O (0O) Zero
11th 0O 11x120 O (240O) 11x240 O (120O) (-)Ve
13th 0O 13x120 O (120O) 13x240 O (240O) (+)Ve
15th 0O 15x120 O (0O) 15x240 O (0O) Zero
17th 0O 17x120 O (240O) 17x240 O (120O) (-)Ve
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17. PHASOR REPRESENTATION OF ODD- HARMONIC CURRENTS;
 It may be born in mind that;
 the Positive sequence odd
harmonics currents rotate in
the ABC rotation.
 the negative sequence odd
harmonics currents rotate in
the ACB rotation.
 thus they cancel each other.
 3rd harmonic & Triple N harmonic
currents being Zero sequence in
nature , thus they are co-phasal
and shall pass through the
neutral.
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18. CURRENT DISTORTION LIMITS FOR VOLTAGE
(120 V TO 69 KV); AS SPECIFIED IN IEEE 519-2014;
Maximum Harmonic current distortion % of IL
Individual Harmonic order(Odd Harmonics)
ISC/IL 3≤h<11 11≤h<17 17 ≤h<23 23≤h<35 35 ≤h<50 % TDD
< 20 4.0 2.0 1.5 0.6 0.3 5.0
20< 50 7.0 3.5 2.5 1.0 0.5 8.0
50<100 10.0 4.5 4.0 1.5 0.7 12.0
100< 1000 12.0 5.5 5.0 2.0 1.0 15.0
> 1000 15.0 7.0 6.0 2.5 1.4 20.0
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Isc = maximum short-circuit current at PCC(Point of Common
Coupling).
IL = maximum demand load current (fundamental frequency
component) at the PCC under normal load operating conditions.
%TDD= %(Total Demand Distortion).
Concept of PCC on next slide.

19. PCC (POINT OF COMMON COUPLING).
 PCC for HT consumer  PCC for LT consumer
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20. DETRIMENTAL EFFECTS OF HARMONICS (GENERALIZED):
 Flaring of Fire in multi-storied residential complexes.
 High voltages and circulating currents caused by harmonic
resonance.
 Equipment malfunctions due to excessive voltage distortion.
 Increased internal energy losses in connected equipment,
causing component failure.
 Shortening of Life-expectancy of Power equipment.
 False tripping of branch circuit breakers.
 Metering errors.
 Fires in wiring and distribution systems.
 System power factor, resulting in penalties on monthly utility
bills.
 Overheating of electrical distribution equipment, cables and
Distribution.
 Increase in neutral current.
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21. DETRIMENTAL EFFECTS OF HARMONICS ON THE 3 PH
DISTRIBUTION TRANSFORMERS;
 Increase in iron-losses; Due to hysteresis loss & eddy
current loss components, as;
 hysteresis loss ∝ f
 eddy current loss ∝ 𝐟𝟐
 Increase of copper-losses and stray flux losses;
 Increase in Copper-loss is due to increased square of the
harmonic current.
 Skin-effect associated high-frequency harmonics.
 Presence of Harmonic circulating currents in the Delta
windings.
 circulation of 3rd harmonic and triple N harmonic
currents in the delta winding heat the winding .
 resulting into reduction in the life expectancy.
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22. GRAPHICAL REPRESENTATION OF ADDITION OF 3RD &
TRIPLE N HARMONIC CURRENTS TO NEUTRAL CURRENT.
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23. HAZARDS DUE TO HARMONIC CURRENTS.
 Excessive heating of the
DTRs give rise to;
 Deterioration of insulation.
 life expectancy reduces by
half with every 6 deg.C.rise
in temperature between 80
deg.C to 140 deg.C.
 Threat of fire hazards;
 cannot be ruled out.
 in the office complexes,
residential complexes
 Commercial complexes
like shopping malls etc.
 Fire in Residential
complex depicted on
along side.
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24. REMEDIAL MEASURES: THEREOF;
 1) Levying of Penalty- if any consumer exceeds the limit beyond
as that mentioned in the Table 1 against stipulation in IEEE Std.519
(2014) at the PCC,
 2)Monitoring of WTI of DTRs; restrict load to 70% to avert pre-
mature failures of the transformers procured confirming to IS: 1180
(part 1),
 Note:
 a) Distribution Transformers confirming to IS: 1180 (part-1) are
capable of feeding linear loads only.
 b) De-rating of 70% of the DTRs is required to be done if utilized
for feeding Harmonic loads as stipulated in ANSI/IEEE 57-
110:2008.
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25. CONTD,
 3)Use of Harmonic Filters.
 4)*Use of K-rated transformers,
 which are developed to carry triple N harmonics currents
developed due to the use of on-linear loads.
 they do not remove harmonics from the power supply but
are made robust enough with increased neutral conductor
size.
 *Note: Salient points regarding K-rated transformers is
narrated in slide no24&25 and algorithm for calculation of K -
factor is narrated in Slide No. 26.
 5) Use of Natural or Synthetic Ester fluids ;They have flash point
.300 deg.C.
 a) the existing DTRs in the Office and Commercial
complexes may be retro-filled with Natural or Synthetic Ester
fluids .
 b)neutral return cable capable of carrying double the Phase
current. K K Murty
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26. WHAT ARE K-TYPE TRANSFORMERS
 *K-Type transformers’: UL(Underwriters Laboratories-A
Global scientific Laboratory which issues Standards for
equipment for equipment safety) has established K-
factor ratings in the Std. UL1561: As K-1,4,9,13,20,30,40
& 50.,
 Salient features; Described in slide no.25 & 26.
 The actual K-rating transformer describes the ratio of
non-linear load to linear load it can handle.
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27. SALIENT FEATURES OF K-TYPE Transformers?
Salient Design features;
i. Design of neutral conductor to withstand 200% of Ph
current.
ii. Smaller parallel windings on the secondary side of the
transformers to compensate for skin effect associated with
high frequency harmonics.
iii. Transposed delta winding conductors.
iv. Electrostatic shielding between primary and secondary
winding.
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28. CONTD;
 K-1 Transformer is capable of feeding 100% linear load only.
 K-4 Transformer shall handle100% linear+50% non-linear load.
 K-13 Transformer shall handle100% linear+100% non-linear load.
 K-20 Transformer shall handle100% linear+125% non-linear load.
 K-30 Transformer shall handle100% linear+150% non-linear load.
 Algorithm for calculation of K-factor
 𝑲 = 𝒉=𝟏
𝒉𝒎𝒂𝒙
(𝒇𝟐𝒉.𝒉𝟐)
𝟏
𝒉𝒎𝒂𝒙(𝒇𝟐𝒉)
 Where fh is the frequency in Hz of harmonic h. 28

29. CONCLUSION AND RECOMMENDATIONS
 Strict monitoring by Distribution Utilities for limiting
TDD(Total Demand Distortion) of each consumer as
defined in the IEEE 519.
 For averting failure of conventional DTRs installed for
feeding office complexes and commercial complexes,
loading up to 70% is recommended as per IEEE C 57 -110-
2008.
 For meeting load demand, higher capacity Distribution
Transformers are to be installed..
 Example: If the demand is 200KVA then adequacy of
capacity would be;
 200/0.70=285.71KVA,
 the nearest rating available is 300 MVA therefore
instead of 200KVA ,a 300KVA Distribution Transformer
is recommended to be installed.
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30. Cont;
 For procurement of such higher capacity Distribution
transformers, enhanced financial burden has to be borne by
DISCOMS & Distribution Utilities .
 DISCOMS and Distribution Utilities in India must procure K-
13 rating transformers for the office complexes and
commercial complexes, wherein the neutral is equal to
Triple n harmonic current.
 The neutral current in such transformers was calculated
as 173% of the phase current.
 Therefore in this Distribution Transformer the neutral
conducer size is provided such that it can carry 200% of
the Phase current.
 In the present day scenario, the existing DTRs in the Office
and Commercial complexes may be reprofiled with Natural
Ester fluids which have flash point >350deg.C as against 140
deg.C of conventional mineral oil, with neutral return cable
capable of carrying double the Phase current.
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31. Gratitude & Acknowledgements;
 I extend my sincere thanks to the 14 NWET-2023
Organizing committee for giving me this opportunity to
present my paper in this prestigious platform of SIT at
Bhubaneswar.
 I extend my sincere thanks to the august gathering of
distinguish guests, expert professionals and SIT faculties,
students & researchers for patiently listening to my
deliberation.
 I dedicate this paper to my beloved wife Late Mrs.K.Vijaya
Murty, who had been always a source of inspiration and
encouragement to me.
 Er.K.K.Murty.BE( Hons),FIE ,CE(Ind),M-CIGRE
 Mob:+91 9425154250
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