P. 9
The philosophy of limiting harmonics according to STUDY IN CESC SYSTEM
IEEE 519 at the PCC between the customer and the
utility is to: To study the presence and amount of harmonics in
CESC LT distribution system, a series of power quality
➣ Limit the harmonic injection from individual measurements were conducted in conjunction with
customers so that they will not cause Testing Department.
unacceptable voltage distortion levels for
normal system characteristics FLUKE 435 series II Power Quality and Energy
Analyzer was used for this purpose which can measure
➣ Limit the overall harmonic distortion of the up to 21st harmonic.
system voltage supplied by the utility
A number of DTRs were chosen based upon certain
DETRIMENTAL EFFECTS DUE criterion (e.g. power factor, KVAR loading, load profile,
TO HARMONICS etc.) and instantaneous THD values were measured at the
feeder cables in feeder Pillar Boxes of those DTRs.
➤ Overheating of equipment: The distortion caused
by harmonics increases the voltage and current, An attempt has been made to identify the nature of load
which results in the power system overheating in that contributes to highTHD values in the current waveform.
presence of Harmonics, leading to decreased kVA
capacity. Some major findings in our study are provided below:

➤ Over voltages: Higher value of harmonic current ➤ Case Study I: In Moulali Yuba Kendra O/T, the total
flowing through the system impedances may cause voltage THD values are within limit (less than 5%) but
severe problem of over voltages in the network. individual phase voltage 3rd harmonic content are
well outside the prescribed limit (greater than 3%).
➤ Increased system losses: Presence of harmonics Moreover the 5th Harmonic content in current for R
causes increased Joule loss in the network, and B phases and neutral are high and the current
increased Hysteresis and Eddy current loss in system THD values in all 3 phases and neutral are quite high.
➤ Case Study II: In Rashbehari Avenue (S) O/T, the 3rd
➤ CB failures due to Overloading of neutral: Power Harmonic in current of R and Y phase are quite high
system protection relays very often operate on the and in case of neutral current, the current THD value
basis of the neutral current which when rises to is very high of which the 3rd Harmonic content is
abnormal values due to zero-sequence harmonics, severely large.
may lead to erroneous tripping of protective gear.
➤ Case Study III: In Broad ST (E) O/T No. 2, all the THD
➤ Low true power factor: Power factor reduces in values are within the prescribed limit but in case of a
presence of harmonics which may be described by service to Repose Nursing Home from the aforesaid
the following equations: DTR, the 5th and 7th harmonics in current are outside
the limit in several phases.

Table 3:

Voltage THD Value % Carrent THD Value %

DTR Load Load at time of 3rd 3rd 5th 7th
Details Nature Phase inspection (A) THD harmonics THD Harmonics harmonics harmonics

Moulali Commercial R 70 3.3 8.8 29.1 8.8 7.3 3.5
Yuba (o ce Y 70 2.4
Kendra space) B 75 3.4 4.6 27.9 4.6 3.9 4.6
O/T N 7.9 1.6
3.1 9.3 22.9 9.3 7.7

72.4 75.7 7.4

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