assessing the impact of harmonics on distribution

Hardik M. SakariyaGujarat Power Research and Development Cell

GUVNL, IIT-Gandhinagar, Gujarat

Assessing the Impact of Harmonics On DistributionTransformer Having Solar Rooftop PV Installations

30th August,2019

National Conference on Maladies in Distribution Sector & its Remedies

Gujarat Power Research and Development Cell, GUVNL, IIT-Gandhinagar

Sources of Harmonics

2

Semiconductor market in India is growing

rapidly, Harmonics in Power distribution

network is increasing rapidly.

Source:https://solarrooftop.gov.in/notification/Notification-24012017.pdf

Sources of Harmonics :-

VFDs in industrial applications

Compressor load with Inverter like AC,

Fridge, etc.

SPV systems

Industries like IT Parks


Effect of Harmonics on transformer losses

3

Transformer is basic component of power system and designed to work on linear

load.

Harmonics produced by nonlinear load and PV Inverters

• Increases Losses

• Increases Heating

• Increases ageing of insulation

• Reduces Transformer capacity

• Results in premature failure of transformer.

Transformer losses are generally classified into No load losses and Load losses.

Transformer losses that are affected by the harmonic current loadings are the

I2R loss, winding eddy current loss and the stray losses

Gujarat Power Research and Development Cell, GUVNL, IIT-Gandhinagar 4

Due to harmonics components, RMS value of the load current is increased.

Accordingly, the I2R loss will also be increase.

So, If the Total Harmonic Distortion(THDi) will increase by 40%

Than, the RMS value of Current will increase by 8 %

That means the I2R loss will increase by 16 %

Effect of Harmonics on transformer losses

Gujarat Power Research and Development Cell, GUVNL, IIT-Gandhinagar 5

Winding Eddy Current Losses are in square proportional to the

• Frequency component (f2)

• Load current component (I2rms)

Effect of Harmonics on Winding Eddy Current Loss of Transformer

As per IEEE C57110.2018, Eddy current loss can express as follows in the Equation


To determine the capability of a transformer to cater to the nonlinear load, the increase

in winding eddy current losses due to harmonics has to be considered.

FHL is a proportionality factor applied to the winding eddy losses, which represents

the effective rms heating as a result of the harmonic load current.

Where,

PEC-O = Winding eddy-current loss at Power frequency

PEC = Winding eddy current losses due to the harmonics

Effect of Harmonics on Winding Eddy Current Loss of Transformer


Other stray loss in the core, clamps, and structural parts will also increase at a rate

proportional to the square of the load current and the harmonic frequency to

the 0.8 exponential power.

Effect of Harmonics on Other Stray Loss of Transformer

Where,

POSL = Other Stray loss

POSL-R = Other Stray losses under rated conditions

Ih = RMS current at harmonic h

IR = RMS fundamental current under rated frequency

FHL-STR is a harmonic loss factor for other stray losses.


The consumer statics connected on this distribution transformer and Transformer

Parameters are as below

Sr. No.

Parameters Values

1 DT Rating (KVA) - Connected 200 KVA

2 Total Nos of Residential Consumers 40 No.s

3 Total Contracted demand 283 kW

4 Installed solar rooftop capacity 33 kW

5 Transformer Ratio 11/0.433 kV

6 No Load Loss (Watt) 106.7 Watt

7 LV Side DC resistance at ambient temp. (Ohm) 0.035425 Ω

8 Total Load loss (Watt) at 75 °C 2013.68 Watt

9 Total I2R loss (Watt) at 75 °C 1920.99 Watt

Case Study of 200 KVA Distribution Transformer


Graphical Representation of Cumulative Average of Current Harmonics


To evaluate the effects of Harmonics on DT having Solar PV

penetration, power quality analyzer with real-time data

acquisition and monitoring facility was installed and data

acquisition interval was kept 5 min. for the period of 56 days.

The average values of electric parameters and harmonics

are as tabulated below

Measured Data

Average Harmonics Data Calculation Table

Case Study of 200 KVA Distribution Transformer


Type of LossRated

Loss (W)

Multiplier for

Per unit

Loading (PLL)

calculation

Load Loss

assuming

100% Loading

(W)

Harmonics

Multiplier

Corrected Loss

at rated Load

A B C = A*B D E=C*D

No Load 106.70 106.70 106.7

I2R 1920.99 1.085 2084.27 2084.27

Winding Eddy 55.61 1.085 60.34 2.306 139.15

Other Stray 37.08 1.085 40.23 1.144 46.02

Total Losses 2120.38 2291.54 2376.14

Increase in Loss (W) 255.76

Increase in Loss (%) 12.06%

For Rated Load (100% Load) PLL(pu) = (1.0416)2 * (1.0)2

= (1.085) * 1 = 1.085

Where, PLL(pu) is the per-unit load loss

Harmonics Loss Calculation table on 100% DT Loading


Type of LossRated

Loss (W)

Multiplier for

Per unit

Loading (PLL)

calculation

Load Loss at

22.09%

Loading (W)

Harmonics

Multiplier

Corrected Loss

at 22.09 %

Loading

A B C = A*B D E=C*D

No Load 106.70 106.70 106.7

I2R 1920.99 0.0529 101.62 101.62

Winding Eddy 55.61 0.0529 2.94 2.306 6.78

Other Stray 37.08 0.0529 1.96 1.144 2.24

Total Losses 2120.38 213.22 217.35

Increase in Loss (W) 4.12

Increase in Loss (%) 1.93%

For 22.09% loading PLL(pu) = (1.0416)2 * (0.2209)2

= (1.085) * (0.04879) = 0.0529

Where, PLL(pu) is the per-unit load loss

Harmonics Loss Calculation table on 22.09%(Actual) DT Loading


During Peak Solar Hours,

1. Fundamental value of

current reduced at

Transformer level. This

magnifies Current THD value.

2. Solar inverter harmonics

added into the network.

As current THD increases

the transformer load

losses also get increases

as shown in figure

Graphical Representation of Cumulative Increase in transformer losses due to harmonics

In THDi, Ih/I1,

I1 reduces due

to SPV

Generation

therefore THDi

increases

Increase in

Losses due to

harmonics

during solar

peak hours


During solar PV

generation Period,

factor of Harmonics

load factor for Eddy

current, Other stray

Loss and Ohmic loss

Increases as Current

Harmonics value

Increases.

Graphical Representation of Cumulative Increase in various harmonic loss factors


Increase in Harmonics will not only cause losses

but also reduce the actual transformer KVA

loading capacity (i.e. De-rate the transformer).

Because of derating the transformer is able to

cater lower load demand rather than actual one.

This ultimately affect the insulation of the

transformer and cause premature failure of

transformer.

Transformers that are required to supply power to

nonlinear loads must be derated based on the

percentages of harmonic components in the load

current and the rated winding eddy current loss.

The maximum permissible per-unit

nonsinusoidal load current with the

given harmonic composition,

expressed by following Equation

For Example if values of

Imax (pu)= 0.89 then, he transformer

capability is approximately 89% of its

sinusoidal load current capability

Effect of HarmonicsOn Derating of Transformers


However, this issue is particularly cause problem when

the transformer is heavily loaded during solar hours

and solar generation is quite low, which is rarely the

case

Effect of HarmonicsOn Derating of Transformers

Reduction in

KVA loading

during solar

hours

Increase in

Derating % due

to penetration of

SPV plants

% derating is in

line with the SPV

generation

Another case study of 100 KVA DT, where no SPV

installations and huge inverter and SMPS loads

where loading is crossing the derating limit.

DT loading is

crossing the

Derating limit –

Overloaded on

low loading


For Linear Load

For Non Linear

Load

Source: schneider Ele. By Dr John Cheng, CEng, CEM, CEA, CMVP

3-D Power factor with cumulative effect of Displacement and Distortion power factor


Effect of PV Penetration onReactive Power and True Power factor

Reactive Power

Drawl from Grid

remain almost

Constant

True PF

Deteriorates

significantly

during peak solar

hours

Active/Apparent

Power Reduces

due to SPV

Generation


High Current

unbalance due

to penetration of

SPV generation

results in current

unbalance and

excessive

neutral current.


Conclusion• With the increasing consumption of non-linear device, the cancer of harmonics has

already reached Stage-3 and is rapidly but silently deteriorating the power

system.

• The Harmonics is just one parameters, flicker, voltage fluctuations, Current

Unbalances, etc. power quality related issues will also increase.

• In absence of any strict penalty/regulatory provision, the same is going to create a

huge fuss to the DISCOMs and ultimately the consumers in nearby future.

• The recent transitions by ministry to the smart meters needs to re-calculated with the

Smart meter with power quality parameters measurement otherwise after 10 years

the utility will again be in the race to replace a smart meter with smart meter with

power quality functions. This will create a huge financial burden to the utility.


Thank You

Th!nk New

21

Hardik M. Sakariya/ Sachin P. Rathod

R&D Engineer

Gujarat Power Research & Development Cell,

GUVNL, IIT-Gandhinagar

[email protected],

sprathod.guvnlrnd@gmailcom

mailto:[email protected]

mailto:sprathod.guvnlrnd@gmailcom

assessing the impact of harmonics on distribution

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