57th Science Conference of Ruse University, Bulgaria, 2018 [625790]

57th Science Conference of Ruse University, Bulgaria, 2018
Copyrights© 2018 ISSN 1311 -3321 (print), ISSN 2535 -1028 (CD -ROM), ISSN 2603 -4123 (on -line) XXX -X.XXX -X-XXX -XX
CHARACTERIZATION OF THE TOTAL HARMONIC D ISTORTION
FACTOR IN MARINE POWER SYST EMS

Prof. Vasile DOBREF , PhD
Department of Naval Electrical and Electronics Engineering ,
Naval Academy “Mircea cel Bătrân” Constanța, Romania
E-mail: [anonimizat]

Assoc. Prof. Florentiu DELIU , PhD
Department of Naval Electrical and Electronics Engineering ,
Naval Academy “Mircea cel Bătrân” Constanța, Romania
E-mail: [anonimizat]

Lecturer Petric ă POPOV , PhD
Department of Naval Electrical and Electronics Engineering ,
Naval Academy “Mircea cel Bătrân” Constanța, Romania
E-mail: [anonimizat]

Abstract: With the increase in the number and types of electric propulsion in both civilian and military naval
vessels, the problem of the electric power quality on -board is a challenge . In this respect, a large number of static
power converters, DC power co nverters, inverters, etc. are present in the power generation systems, whose powers
reach the order of tens of MW.
The high number of these devices that work at high powers , inevitably leads to the appearance , in the power
distribution system , of harmonics with very high weights .
This paper presents a study of the THD index from the perspective of the quality of electricity and several relevant
measurements made onboard of naval vessel under the conditions of using the ship's finite power plant.
Keywords: Total Harmonic Distortion , static power converters, current and voltage harmonics

I. INTRODUCTION
Total Harmonic Distortion (THD). The massive introduction of power electronics into
electrical installations has made the study of harmonics taken seriously in all sectors of economic
activity, especially since the most harmonic generating equipment is often of major importance
for the economic activities.
The most frequently used ha rmonic and interharmonic indices are [1 ]:
• Harmonic Distortion (HD);
• Total Harmonic Distortion (THD)
• Total Interharmonic Distortion (THID);
• Total Demand Distortion (TDD);
• Distortion Band Factor (DBF).
THD – (Total Harmonic Distortion) characterized the type and weight of harmonics in a
circuit and it is specific for both voltage and current harmonics:
𝑇𝐻𝐷 (𝐼)=√∑ 𝐼𝑛2 ∞
𝑛=2
𝐼1 ×100% (1)
𝑇𝐻𝐷 (𝑈)=√∑ 𝑈𝑛2 ∞
𝑛=2
𝑈1 ×100% (2)
Generally, THD ignores the phase angle information, and only considers a small range of
frequency components, usually, fundamental and its integer multiples (not higher than 51th

57th Science Conference of Ruse University, Bulgaria, 2018
Copyrights© 2018 ISSN 1311 -3321 (print), ISSN 2535 -1028 (CD -ROM), ISSN 2603 -4123 (on -line) harm onic). In order to consider the impact of other frequency components or phase angles, new
alternative indices have been defined: Crest Factor, K-factor, Telephone inference factor (TIF),
and extended THD [2].
Total harmonic distortion is calculated in a ra nge of 50 -th harmonics. In this range, the
total harmonic voltage distortion should be equal or less than 5% as measured at any point of
common coupling (PCC) with any individual harmonic voltage distortion not exceeding 3% of the
fundamental .[3]
On a dedi cated system, higher level of harmonic distortion may be permissible as long as
the equipment can operate safely at the higher limits.
Lately, there was an increase in the number and variety of electric propulsion ships being
built around the world. This change has occurred , thanks to the development of electronic power
contro l technology, which is used for the electric propulsion system. The se units regulate the
velocity of the propeller by modifying the supply voltage frequency, and this was made possible
by developing high -power switching devices.
Regarding at harmonic standards for electric shipboard power systems, these have been
adopted dir ectly from the power utility standards. The characteristics of shipboard power systems
regarding harmonic distortion have been defined by both commercial and military standards : IEEE
Standard 519 [3], IEEE Standard 45 [4 ], and MIL -STD -1399 Section 300 [5].
Some studies indicate very little problems with harmonics on shipboard (only 10% of
those surveyed indicated potential problems, others reported that values over 10% VTHD might
create communication problems [6] [7 ].
Harmonic currents are generated by non linear loads. These include:
I. Single -phase loads, for example:
 Swiched mode power supplies (SMPS) used on TVs, computers, other office
equipment (copiers, fax machines) and so on. The advantage for the equipment manufacturer is
that the dimensions, cost and weight are significantly reduced and the energy unit can be made
practically for any form factor required. The disadvantage – in addition to the other types – is that
the power source absorbs a current in the form of pulses of current containing a larg e quantity of
three or more harmonics.
 Electronic ballasts for fluorescent lamps – have become popular in recent years due
to the need for increased efficiency. Generally, they are only slightly more efficient than the best
magnetic ballasts, and in fact, the highest gain results in the fluorescent lamp, the level of
illumination can be maintained for a longer lifetime by controlling the currents in the lamp. The
main inconvenience is that it generates harmonics in the power supply.
• Uninterruptible power supplies (UPS) with similar operation to switching power
sources.

Fig. 1 Ideal harmonic spectrum for 6,12,18 pulse convertor and welding installations .
II. Three -phase loads, for example:
– Variable speed drives for asynchronous or DC motors;
– Large Unint erruptible Power Supplies (UPS);

57th Science Conference of Ruse University, Bulgaria, 2018
Copyrights© 2018 ISSN 1311 -3321 (print), ISSN 2535 -1028 (CD -ROM), ISSN 2603 -4123 (on -line) – Industrial equipment (welding machines) ;
– Devices requiring electromagnetic saturation (transformers) .

Fig. 2 Voltage waveform for: 6,12,18 pulse convertor .

It can be noticed that with the increase of the number of pulses in a converter there is an
improvement of the shape of the voltage or current waveform s. This will occur in the decrease of
the THD value due to the small weights of the constituent harmonics of the signal
For a 50 Hz fundamental harmonic frequency, the expression of voltage for 6, 12 or 18 pulse
converters will look like this:
𝑢6(𝑡)=10sin(314𝑥)+(10
5)∙sin(5∙314𝑥)+(10
7)∙sin(7∙314𝑥)+
+(10
11)∙𝑠𝑖𝑛(11∙314 𝑥)+(10
13)∙𝑠𝑖𝑛(13∙314𝑥)+(10
17)∙𝑠𝑖𝑛(17∙314 𝑥)+
+(10
19)∙𝑠𝑖𝑛(19∙314 𝑥)+(10
23)∙𝑠𝑖𝑛(23∙314𝑥)+(10
25)∙𝑠𝑖𝑛(25∙314 𝑥)+
+(10
29)∙𝑠𝑖𝑛(29∙314 𝑥)+(10
31)∙𝑠𝑖𝑛(31∙314𝑥)+(10
35)∙𝑠𝑖𝑛(35∙314 𝑥)+
+(10/37)∙𝑠𝑖𝑛(37∙314 𝑥)
𝑢12(𝑡)=10𝑠𝑖𝑛(314 𝑥)+(10
11)∙𝑠𝑖𝑛(11∙314𝑥)+(10
13)∙𝑠𝑖𝑛(13∙314 𝑥)+
+(10
23)∙𝑠𝑖𝑛(23∙314 𝑥)+(10
25)∙𝑠𝑖𝑛(25∙314𝑥)+(10
35)∙𝑠𝑖𝑛(35∙314 𝑥)+
+(10
37)∙𝑠𝑖𝑛(37∙314 𝑥)
𝑢18(𝑡)=10𝑠𝑖𝑛(314 𝑥)+(10
17)∙𝑠𝑖𝑛(17∙314𝑥)+(10
19)∙𝑠𝑖𝑛(19∙314 𝑥)+
+(10
35)∙𝑠𝑖𝑛(35∙314 𝑥)+(10
37)∙𝑠𝑖𝑛(37∙314𝑥)

The presence of harmonics in naval distribution networks degrades the quality of
electricity. This phenomenon can have many negative effects, the most common being: overloads
in distribution networks caused by increa sing the efective current value; premature aging of
capacitors used to compensate the reactive energy; disturba nces in communications networks;
damage of conductor insulation due to the appearance of the skin effect (for harmonics exceeding
350 Hz) .
The presence over a certain limit of the harmonics in the power supply networks has major
negative economic effects, producing: premature aging of the equip ment (which requires
premature replacement if it has not been oversized since the beginning, oversize also costly)
estimated from about 5% for transformers, 18% for three -phase motors, up t o 32.5% for single –

57th Science Conference of Ruse University, Bulgaria, 2018
Copyrights© 2018 ISSN 1311 -3321 (print), ISSN 2535 -1028 (CD -ROM), ISSN 2603 -4123 (on -line) phase motors; overload distribution network that required higher generated power due to increased
losses ; distortion of the current waveform that may cause unexpected triggering of the protection
relays, resulting in losses by stopping machinery, equipment or production processes.
Another important issu e in terms of the quality of electricity is represented by the presence
of interharmonics and other associated components . Harmonics are sinewaves voltages or currents
whose frequency is a multiple of the fundamental frequency of the source. A rigorous ana lysis of
voltage and current should take into a ccount the following components:
 harmonic s – f = nf 1, where n is an integer greater than zero;
 DC component – f = nf 1 for n= 0;
 interharmonics – f ≠ nf 1 , where n is an integer greater than zero;
 subharmonic s – f > 0 Hz, and f< f 1.
Where: f1- fundamental harmonic of the voltage or current.
Regarding voltage or current interharmonics , these have a sinusoidal variation with a
frequency that is not an entire m ultiple of the source frequency, a lthough they have always been
present in power systems. T he interest in interharmonics has increased with the increase in their
amplitude due to the widespread of power electronics in electrical installations.
Generally, two basic mechanisms that generate interharmonics are considered:
The first is the generation of components in the lateral bands of the fundamental frequency
as a result o f amplitude and phase variation due to the disturbances caused by electrical loads in
long or short -term transient modes or. These disturbances are largely random, depending on the
electrical load variation, during different technological processes.
The second mechanism is the asynchronous switching (not synchronized with the supply
voltage frequency) of the semiconductor e lements in the static converters. A typical example is
offered by pulse width modulation (PWM) converters.
As a results , interharmonics can be generated at any voltage level and can be transferred to
a different voltage level, for example, interharmonics generated in high -voltage and medium
voltage networks (MT) can be injected into low v oltage networks and vice versa.

EXPOSITION
The frequency measuring devices provide correct information when the measured signal
consists only of harmonics. These instrume nts use a phase sync circuit to synchronize the
measurement with the fundamental frequency component and to sample the signal for one or more
periods in order to apply the analysis using FFT (Fast Fourier Transformation). Due to phase
synchronization, samp les acquired over a period can give a fair representation of the curve
spectrum only if it does not contain interharmonics. If non -harmonic frequencies are present in
relation to the measurement period and the sample curve is not periodic, difficulties may arise
during this time to interpret the results.
To carry out our study aboard a ship , the measurements have been achieved for two distinct
power supply cases, namely: from an infinite power source (connection to shore electricity
network) and from a finite power source (the onboard generators).

a. finite power source (the onboard generators)

57th Science Conference of Ruse University, Bulgaria, 2018
Copyrights© 2018 ISSN 1311 -3321 (print), ISSN 2535 -1028 (CD -ROM), ISSN 2603 -4123 (on -line)
b. infinite power source (connection to shore electricity network)
Fig. 3 Welding machine case

The power source on board was a Diesel Generator with the following characteristics:
 Three phase voltage – U = 400V/230V;
 Frequency –f=50Hz;
 Apparent power S=15KVA;
 Maximum single phase I=23A
The experimental determinations were performed for different operating regimes and will
primarily aim to highlight the waveform distortions of the voltages and currents.

Fig. 4 . Type of connection 3P3W2M

Measuring instrumen ts used for data acquisition were : AMPROBE PQ55A power
analyzer and RIGOL DS -1052E digital oscilloscope. In this instance, they were able to perform a
FFT (Fast Fourier Transformation) analysis, up to the 31st harmonic.
Measurements were made for two case s: 6-pulse converter and welding machine powered
from a 400V three -phase network in a triangle connection. Measurement was made for an Aron
connection – Measurement type 3P3W2M of connection mode.
For the case of infinite power source (connection to shore electricity network), in both
situations, the weight of current and voltage harmonics was insignificant. Along with switching to
the the onboard generator the weight of harmonics has increased.
The weights in the signals for current and voltage harmonics, up to the harmonics no. 31,
were obtained with FFT analyzes The harmonics weights allowed the automatic calculation of
THD, and its values were:
• For 6 -pulse converter:
– finite power source (the onboard generators):THD I = 9.92% and THD U = 4.5 4%;
– infinite power source (connection to shore electricity network): THD I = 2,19% and THD U
= 1,73%;

57th Science Conference of Ruse University, Bulgaria, 2018
Copyrights© 2018 ISSN 1311 -3321 (print), ISSN 2535 -1028 (CD -ROM), ISSN 2603 -4123 (on -line) • For welding machine case:
-finite power source (the onboard generators):THD I = 10.37% and THD U = 7.61%;
– infinite power source (connection to shore el ectricity network): THD I = 3,14% and THD U
= 2,12%;
From the obtained values we could see a higher THD for the current harmonics in both
situations.

CONCLUSION
The two analyzed cases highlighted the importance of monitoring the power system in
terms of THD values . By determining the weight of each constituent harmonic of the signal it can
be determined the most important contributors to the distortion of the useful signals, thus limiting
their influence on the electric power system by installing filters with punctual action.
Under these circumstances many of equipment manufacturers (especially three -phase
converters) take some measures to reduce the amplitude of harmonic currents, some of them
declaring that their equipment is in compliance with G5/4-1 normative , although it is applica ble
to a complete installation not for each constituent equipment.
Under these conditions, by limiting the harmoni cs, there is the certainty that the power
system will work properly, keeping the harmonic levels within the limits set by the regulation.

REFERENCES
[1] Mindykowski J., Tarasiuk T., “Measurement of supply voltage properties in ships’
electrical power systems”, Metrology and Measureme nt Systems. Polish Scientific Publishers
PWN, vol. IX, No. 1/2002 Warsaw 2002, pp. 19 -30
[2] M. Steurer, P. Ribeiro, Y. Liu Re-Evaluating Electric Power System Harmonic
Distortion Limits for Shipboard Systems, Center for Advanced Power Systems (CAPS) -Florida
State University, June 25, 2004
[3] IEEE Std 519 -1992, IEEE Recommended Practices and Requirements for harmonic
control in Electrical Power Systems
[4] IEEE STD 45™ -2002 – Revision of IEEE Std 45 -1998, “IEEE Recommended Practice
for Electrical Installa tions on Shipboard.”
[5] MIL -STD -1399 (NAVY), Section 300A, 13 October 1987, “Interface Standard for
Shipboard Systems, Electric Power, Alternating Current.”
[6] I. Jonasson, L. Soder, “Power Quality on Ships. A Questionnaire Evaluation
Concerning Island Power System,” International Conference on Harmonics and Quality of Power,
October 2000, Vol. 2, pp. 639 -644.
[7] P. M. Nicolae, “Modeling the Influence of External Residual Harmonic over the Three –
Phase Short -Circuit Transient Electromagnetic Processes in a Cylindrical Rotor Synchronous
Generators,” Electric Machines and Drives, 1999. International Conference IEMD '99, 9 -12 May
1999, Pages: 311 – 313.

ABOUT THE AUTHORS
Professor PhD eng, Vasile DOBREF, Naval Academy “Mircea cel Bătrân”, Department of
Naval Electrical and Electronics Engineering, Constanța, Romania, e -mail:
vasile.dobref@anmb.ro
Associated Professor PhD eng Florentiu DELIU , Naval Academy “Mircea cel Bătrân”,
Department of Naval Electrical and Electronics Engineering, Constanța, Romania, e -mail:
florentiu.deliu@anmb.ro
Lecturer PhD Petrică POPOV, Naval Academy “Mircea cel Bătrân”, Department of Naval
Electrical and Electronics Engineering, Constanța, Romania, e -mail: petrica.popov@anmb.ro