**Harmonics in electrical systems:-**

Before discussing about consequences of Harmonics you must
know what are harmonics:-

Harmonics are electric current and voltages that causes
power quality problems. These are generated due to electronic equipment’s which
draws non linear loads with abrupt pulses. These pulses causes distorted current
and voltages causes of which will be discussed in this article.

Harmonics are classified according of level of harmonics
these are multiple of frequencies such as

2

^{nd}level, 3^{rd}level, 4^{th}level, and upto 11^{th}levels
Where 2

^{nd}level means Harmonics with frequency of 100 HZ
3

^{rd}level means Harmonics with frequency level of 150 HZ
And similar for other levels

Now 2

^{nd}level, 5^{th}level, 8^{th}level, and 11^{th}level will have –ve sequence of currents
3

^{rd}level, 6^{th}level and 9^{th}level will have zero sequence of currents
4

^{th}level, 7^{th}level, 10^{th}levels will have +ve sequence of currents
Harmonics are now integral part of electricity. Harmonics is
also known as pollution in electricity. Now days while power availability is
not a big concern so intention now shifts towards quality of electiricity.

There is an increase in harmonics levels in electricity
there are following few reasons for harmonics in electricity:-

1.
Increase in non-linear loads such as power
electronics equipment’s. Such as VFD, SMPS etc where power is chopped and used
as per requirements at low or other frequencies.

2.
There are various other devices which leads to
Harmonics in electrical systems such as :-

(a)
Arcing devices

(b)
Ferromagnetic devices

(c)
Appliances

(d)
Electronic switching power converters

There will be following effects due to harmonics in
electrical systems:-

(a)
Overheating of electrical equipment’s as more
eddy currents are produced due to these harmonic levels.

(b)
Due to overheating and other losses this will
leads to reduction in life of equipment

(c)
These harmonics will leads to premature failure
of equipment’s

(d)
Harmonics will leads to malfunctioning of equipment’s

(e)
Harmonics will leads to more losses in systems

(f)
Harmonics will leads to interference in
communication signals

(g)
Harmonics will leads to Nuisance tripping of
circuit breaker and blowing off the fuses.

(h)
Harmonics will leads to more vibrations in motor
and other equipment’s.

(i)
This will leads to flickering of computers.

There are so many effects of Harmonics on various equipments

When there are harmonics in systems than we can’t be able
to get 1 Power factor as there are so many reactive powers associated with
these harmonics which will not get compensated using capacitor banks. Even when
we try to compensate the same by installation of more and more capacitors then
we lose a hafety amount on installation of capacitors and also this will leads
to higher losses due to capacitor banks.

Earlier we known that Power factor=

__Voltage X Current X Power factor__
Voltage X Current

Now days due to these Harmonics there are Distortion
power factors which will be calculated as below:-

Where THDi Stands for Total harmonics distortion in
currents

And THDv Stands for Total Harmonics distortion in
voltage.

Now Total Power factor is given as = Power factor X
Distortion power factor

As Distortion power factor will never will be unity so
Total power factor of system will never will be unity.

*There are following effects of harmonics on Transformers and Motors:-*
1.
There will be more eddy current loses in
Transformers.

2.
Harmonics will leads to more losses due to skin
effect.

3.
Harmonics will leads to overheating of coils and
that will cause premature failure of Transformers

4.
Harmonics will leads to more Hysteresis and eddy
current losses in motors as Hysteresis losses are directly proportional to
frequency and eddy current losses are directly proportional to square of frequency.

5.
There will be more winding eddy current losses,
High frequency Rotor and stator losses, and tooth pulsations in motors due to
harmonics

6.
More harmonics will be leads to more I

^{2}R losses in both Transformers and motors
7.
There will be increased over temperature due to
these losses and leads to premature failure

*There are following effects of harmonics on Cables and Capacitors:-*
1. There
will be Higher Proximity effects and Skin effects in cables

2. There
will be additional losses in cables

3. These
will cause additional overheating of cables

4. This
will decrease insulation level of cables

5. Harmonics
will cause increased Resistance

6. Harmonics
will cause derating of cables

7. Harmonics
will leads to higher neutral currents in cables and leads to unbalanced loads
on cables.

8. Harmonics
will leads to resonance with 7

^{th}Harmonics in capacitor banks which will leads to lower capacitive reactance.
9. Harmonics
will leads to more electricity bill due to increased losses due to harmonics.

10. Harmonics will leads to more KVA demand as stated earlier due to increased losses.

For reducing harmonics visit link:-

http://electrialstandards.blogspot.com/2016/09/methods-for-reducing-harmonics-in-system.html

For reducing harmonics visit link:-

http://electrialstandards.blogspot.com/2016/09/methods-for-reducing-harmonics-in-system.html

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