HARMONIC POWER QUALITY ON NAVAL SHIP ELECTRIC SYSTEMS ( OVERVIEW OF STANDARDS – FIELD MEASUREMENTS ON HN "MEKO" CLASS )

I.K. HATZILAU(1), AR. MAGOULAS(2), S. PERROS(3), D. KAVOULAKOS(4), E. SAKIOTIS(4), E. CHRISTOFIS(4), F. MARTINOS(5), J. PROUSALIDIS(6)

(1) Prof. Dr. Ing., Chair of Electrical Engineering , Hellenic Naval Academy (HNA) Tel: +3010-4581332, Fax: +3010-4181768, e-mail: [email protected] (2) Dr., Lecturer, Chair Electrical Engineering, Hellenic Naval Academy (HNA) (3) Commander (HN), M.S.E.E. (4) Lieutenant Commander Hellenic Navy (HN), M.S.E.E. (5) Lieutenant Hellenic Navy (HN), MSc.M.E.S.E. (6) Dr., Lecturer, Naval and Marine Engineering Dept., National Technical University of Athens (NTUA) 9 Heroon Politechniou St, 15773 . Tel: +3010-7722869, Fax: +3010-7721117, e-mail: [email protected]

ABSTRACT: The main objective of this paper is a discussion on However, the main harmonic distortion is caused by the the power quality problems encountered on naval vessels with non-linear behavior of a number of electrical loads which, respect to the harmonic distortion limits imposed by relevant stan- even though driven by a purely sinusoidal voltage, they dards, namely IEEE-519 which refers to all electric systems and absorb a deformed current (magnetic current of transform- STANAG-1008 which is dedicated to warships. A brief discussion ers, induction motors, fluorescent lamps and mainly static is also made on the causes, consequences and remedies of har- monic distortion in the electrical plants, while measurements con- converters and power supplies of numerous electronic de- ducted onboard HN MEKO class frigates are presented. The vices). The flow of these non-sinusoidal currents through evaluation of the measurements indicates that it can not be easily the electric network creates voltage harmonic distortion in argued if the STANAG-1008 as well as IEEE-519 current restric- various points as a result of the distorted voltage drops on tions are violated or not, while the voltage distortion remains the internal impedance of all elements of the electric net- within the imposed limits. work. Furthermore, the main consequences of the high harmonic content in voltage and current are : Keywords: Naval vessel, power quality, harmonic distortion, STANAG 1008, IEEE-519. • increase of iron-losses in electric machinery resulting in efficiency decrease and overheating, I. INTRODUCTION • hums and vibrations in electric machinery, • malfunctions of electric devices, During the last years there has been a deterioration to the • over-voltage and over-current due to resonance result- problem of the harmonic distortion, observed in voltage ing in insulation fatigue and breakdowns, and current, in the electrical plants of modern warships. • EMI/EMC problems to neighboring communication This anomaly is caused by the increasing use of non- linear systems. electrical loads and the fact that many of the loads are sen- sitive to a voltage supply with a high harmonic content. The electric system of a ship can be regarded as a non- The problem is expected to become more severe in the fu- interconnected one, comprising a reduced number of gen- ture constructions due to the extensive use of devices with erators and an increased number of non-linear loads of low power electronics and the perspective of implementing or high voltage, e.g. 440V or 6.6 kV. Therefore, it can be electric propulsion utilizing electric converters feeding argued that the standards issued for ordinary electric sys- innovative A.C. motors. tems can be applied to ships, too. On the other hand, spe- cific standards have been released covering the electric In brief, the problem is stated as follows [1-2]: The genera- installations on shipboard taking into account their particu- tion of harmonic distortion has two causes. Synchronous larities, [3]. Similarly, referring to power quality problems, generators produce - due to structural asymmetries - power standards like IEEE-519 [1] can be applied to ships, al- with voltage harmonic distortion 1% approximately. though standards dedicated to ships have been issued, while particularly for warships the STANAG 1008 [4] is used.

In this paper, a discussion is made concerning the restric- tions on voltage and current harmonic distortion implied by STANAG 1008. This discussion is supported by field measurements on HN MEKO class frigates, while some problems emerged from the application of the standards, are highlighted. Finally it is argued that IEEE-519 can resolve most of these difficulties. II. POWER QUALITY STANDARDS AND MEAS- separate engine-rooms. The generators feed two main UREMENTS switchboards supplying thirteen Load Centers (LCi, i = 1,...,13). These LC distribute power (440/220/115V, 60Hz, A. STANAG-1008/ Edition 8 3-phase/1-phase and 24V DC) to all separate loads, see ref. [9],[10]. The specifications of the electrical power plants in NATO The instruments ‘DRANETZ 658 Power Quality Analyzer’ naval vessels are laid down in STANAG-1008 [4]. Ac- and ‘ELCONTROL VIP SYSTEM3' Energy analyzer’, cording to Editions 7 and 8 which hold for about fifteen which can analyze current and voltage measurements up to years, the Total voltage Harmonic Distortion (THD) of a the 50th and 25th harmonic respectively (for 50 and 60 Hz 60Hz and 400Hz network must not exceed 5%, while no systems), have been used. harmonic should exceed 3% of the fundamental. Measurements have been taken at load inputs (440V To achieve the above, STANAG 1008 provides design 115V), transformer (440/115V) primary and secondary constraints for current harmonics produced by each sepa- coils, 60/400Hz converter inputs (440V), LC inputs, and rate load presented in Table I. The constraints refer to the generator outputs, while generators were operating in nor- %portion of the ”rated full load (nominal) fundamental mal power levels. Representative results are shown in Fig. current”, I1fL, of each load. 2. The spectrum of the current harmonics in these meas- urements, and the respective limits according to STANAG- Table I. Current harmonic constraints by STANAG 1008 / 1008/Edition 8 are shown in Fig. 3. In Fig. 3(A) single Edition 8 consumers' current appears, while in Fig. 3(B) grouped consumers' current is presented (e.g. Load Centers, etc.) Harmonic order n Acceptable level of harmonic and finally in Fig. 3(C) the corresponding voltage har- value in % of the ”rated full monic spectrum is shown. load (nominal) fundamental From the measurements performed, it is evident that: current”, I1fL Loads < (1kVA/60Hz or 0.2kVA/400Hz and a) The highest harmonics of current are of the order 3, 5, 2A/115V/400Hz) and 7 with their values being fairly large.

n >1 100/n % b) The current harmonics measured appear to be of consid- Loads > (1kVA/60Hz or 0.2kVA/400Hz and erable portion of the corresponding (“actual load”) funda- 2A/115V/400Hz) mental. These figures appear to exceed by far the con- 2 ≤ n < 33 3 % straints of STANAG 1008/ Edition 8. Similar sets of meas- urements in ships of several NATO Navies have lead to the n ≥ 34 100/n % impression that these constraints are too strict. However, in The validity of this constraint has been more and more un- the authors opinion no safe conclusion according to Edition der reconsideration for the last years. The NATO 8 stipulation, can be drawn based only on “actual load” AC/141(NG/6)SG/4 Group which is the custodian of spectra as few electric loads operate near to their “rated STANAG 1008, considers the limitation of this STANAG power”. Typical examples of this category are power trans- with skepticism, since theoretical estimations and meas- formers and power electronic converters, with their THD urements in the electrical plants of naval ships indicate that being a function of their demand in electric power. For STANAG 1008 current constraints appear too strict on the instance, measurements at 60/400 Hz frequency converter harmonic distortion allowed. Moreover, the reference term of MEKO performed in the usually operating power range (“actual load”) indicate excessive current harmonic ”rated full load fundamental current”, I1fL has occasion- ally lead to misinterpretations as well as difficulties to vali- distortion, as shown in Fig. 4. However, STANAG con- date the STANAG constraints on shipboard, [5], [6], [7], straints are not necessarily violated, as, according to the [8]. Thus, the equipment rated power is often overesti- trend of the measurement points presented in Fig. 4, - mated so that its “actual load” is lower - and much lower in which trend is also confirmed by the calculations according some cases - than the “rated full load”. It is worth noting, to IEEE-519 - the more operating power increases towards that, in general, the harmonic spectrum in “actual load” its rated value (“rated power”), the more harmonic distor- could be considerably different from that in “rated full tion levels decrease, reaching eventually the permissible load”. This remark holds and is further supported by the limits. Therefore in many cases, it is difficult to assess the field measurements presented in the following. distortion of currents of a stand-alone equipment, as de- fined by STANAG, without resorting to manufacturers’ test results or laboratory experiments performed in rated B. FIELD MEASUREMENTS AND RESULTS load conditions, which in current practice are rarely avail- able. During a project investigating electric power quality in c) Nevertheless, no matter what the relevant values of the Hellenic Navy ships, several measurements on voltage and measured current harmonics are, the measured voltage dis- current harmonics have been conducted onboard HN tortion - referring to either the THD or the individual har- MEKO frigates, [9]. monics - is well beyond the imposed marginal values of STANAG. The electric plant (Fig. 1) in these ships is served by four generators (775KVA, 450V/60Hz, 3-phase), laid in two SC G1 G2 G3 G4 SC T.L

LC1 LC3 . . . LC7 LC8 . . . LC11 LC13 LC7 LC2 LC12

440V 115V 440V 115V 400Hz 400Hz 60Hz 2pT 2sT 60Hz

2.1 2.2 .... 2.i T2.1 . . . 24VDC C2.1 . . C2.i CT2.1 . . .

Fig. 1. Schematic Presentation of the Electrical Plant of F/G MEKO.

Volt Amps % FND Phase s 60 350 750 V I 150 300 500 100 50 250 250 50 40 200 0 0 30 150 -250 -50 20 -500 -100 100 10 -750 -150 50 0:34.735 0:34.740 0:34.745 0:34.750 0 0 sec Thd H05H10 H15 H20 H25 H30 H35 H40 A.1 Volt Amp % FND A.2 Phase 750 15 125 400 500 V I 350 10 100 300 250 5 75 250 0 0 200 50 150 -250 -5 100 -10 25 -500 50 -15 -750 0 0 0:36.810 0:36.815 0:36.820 0:36.825 sec Thd H05 H10 H15 H20 H25 H30 H35 H40 H45

B.1 B.2

Fig. 2. Voltage (V) and current (I) waveshape as well as Current magnitude and phase harmonic spectrum of a 100 kW rated power load on the 440 V/60 Hz system, in two different operating conditions (A and B).

Fig. 3. (A) Current harmonic spectra for independent loads (power ⊇1 kVA). (B) Current harmonic spectra for groups of loads (e.g. LC inputs etc.) (power ⊇1 kVA). (C) Respective voltage harmonic spectra.

Fig. 4. Current THD and 5th HD of the 60/400 Hz converter as a function of operating power

C. STANAG-1008/ Edition 9 basis”. This definition is much more readily applicable to any electric installation including the shipboard ones. As mentioned above, STANAG-1008 / Edition 8 is to be Moreover, at an initial approximation, the average maxi- replaced by Edition 9, being currently under ratification. mum load can be estimated by the service load simultane- In this edition, the voltage distortion constraints still hold, ous factors fs, which are extensively used at the electric whereas the current constraints have been completely re- balance of the ship power plant and are often readily avail- moved and substituted by (see also Table II): able for a great variety of ship types. Factors fs are defined as the ratio of the actual energy required on a daily basis “If the sum of the power of all loads which distort the cur- over the energy corresponding to the rated power for the rent waveform connected to the supply system, Σ Pdist is same daily interval, therefore: less than 1% of the short circuit power of the generation (average maximum load) = fs * (rated load) capacity, Ssc, with the largest single distorting load less Furthermore, the ship electric networks drop into the cate- than 0.5%, normally no measures are necessary to reduce gory between 120 V and 69 kV (section 10.2), while the current harmonics. This limit can be further extended to short circuit current over maximum load current ratio is 2% of Ssc, if this load is due to the sum of only small dis- normally less than 20 (ship grounding systems are de- torting equipment, each less than 0.1% of Ssc. If any of signed so that short circuit currents are just few times these limits is reached or exceeded by the distorting load, greater than the maximum load currents [12]). analyses to whether STANAG-1008 requirements are still met with respect to voltage harmonics and an early co- Consequently : identically to STANAG 1008, the voltage ordination between the system design authority and the distortion is limited to 5% while no harmonic should ex- equipment manufacturer should be undertaken”. ceed 3%. Concerning current distortion, this is limited as explained in the Table III. Table II. Current harmonic constraints by STANAG 1008 / Edition 9 Table III. Current harmonic constraints by IEEE-519

Condition Action required Harmonic Acceptable level of harmonic value P = 1%.S with No action order n in % of the maximum load current ∑ dist,k sc (fundamental), I at PCC k 1fL, n< 11 <4% Max (P ) = 0.5%.S k dist,k sc 11<=n<17 <2% No action 17<=n<23 <1.5% ∑ Pdist,k = 2%.S sc with k 23<=n<35 <0.6% Max (P ) = 0.1%.S 35<=n <0.3% k dist,k sc Otherwise Analysis However, it has to be stressed that even in the IEEE-519 Pdist,k: power of devices distorting current waveforms case, there have been discussions on the interpretation of Ssc: short circuit power level of the supply system the definitions of PCC, short circuit current and maximum load current values considered, as they may result in erro- Therefore, it is stressed that after this amendment, no tan- neous conclusions [11]. gible limitation on current (or any other quantity) distortion for each stand-alone power consumer is actually set in an effort to restrict the voltage distortion within the specified III. DISCUSSION limits. On the contrary, voltage distortion has to be inves- tigated by performing a plethora of costly power quality Taking into account the aforementioned points, it is under- analyses (simulations of operation of the entire electric lined that all standards require that the voltage total har- system and/or field measurements on it), where all alterna- monic distortion is less than 5%, a constraint proven to tive solutions from various manufacturers and at several hold almost by any measurements onboard. However, operating points must be taken into account whenever a there seems to be no clear way of estimating this voltage piece of equipment is to be installed or replaced. distortion e.g. by investigating the current distortion caused by each separate load. More specifically:

D. IEEE-519 a) STANAG 1008/Edition 8, makes the effort to set con- straints on current harmonics so that voltage distortion is According to IEEE-519 [1,11], the acceptable levels of kept within acceptable limits. However, these current dis- current and voltage distortion are defined at the Point of tortion constraints are, on the one hand, difficult to inter- Common Coupling (PCC), i.e. that busbar defined as the pret and finally measure, whereas on the other hand, it can border between the power generation and power consump- be argued they are often exceeded without, though, leading tion sections. The limit values depend on the voltage level to excessive values of voltage distortion. of the electric system studied and the ratio of short circuit current over maximum load current, the latter being the b) STANAG 1008/Edition 9, which is planned to succeed “average of maximum loads achieved on a 12-monthly Edition 8, does not offer an actual solution to the problem, by clarifying or even resetting the current harmonic distor- [9] Hatzilau, I.K., "Verification of Electric Power Quality on Shipboard ", tion constraints. On the contrary, Edition 9 simply states Research Project Progress Report, Hellenic Naval Academy (HNA), July 1999 (In Greek) that several analyses must be performed at the ship design [10] "MEKO 200 General Purpose Frigate (HN) "HYDRA" Class" - stage or at any revamp to reassure that voltage distortion "System Manual, Electrical System and Automation" , Doc. No. 0720-13- does not exceed the limit of 5%, without setting any guid- 00 File 01 ing constraints for each separate manufactured equipment. [11] McGranahan, M., “Overview of the Guide for Applying Harmonic Limits on Power Systems-IEEE 519A’’, Proceedings of 8th International Conference of Harmonics and Quality Power, Athens (Greece), 16-18 c) Finally, IEEE-519, which could be applied to shipboard October 1998, pp. 462-469. installations, appears more readily applicable referring [12] Bal, R.,Stephens, G.W., “Neutral Earthing of Marine Electrical more clearly to certain operating conditions and measure- Power Systems”, Trans I Mar E (TM), Vol. 95, Paper No 32, 1982. ments. Therefore, it is believed, that IEEE-519 constraints on current could be applied onboard despite the difficulty VI. BIOGRAPHIES to assess the average of maximum loads on a 12-monthly basis, as, even at the design stage, the service load simulta- Prof. Dr. Ing. I.K. HATZILAU (Electrical & Mechanical Engineer from neous factors fs can be used. NTUA/1965, Dr. Ing. from University of Stuttgart/1969). After few years in the industry, he joined the Academic Staff of HNA where he has been

for 25 years. He is also representative of HN in NATO AC/141(NG/6)SG/4 dealing with electric systems in warships. IV. CONCLUSIONS Dr A. MAGOULAS, (Electrical Engineer from NTUA/1985, PhD from In this paper a discussion is made on the power quality NTUA/2000). He has been Lecturer at the HNA since 1990 and is inter- harmonics on shipboard electric systems. The discussion is ested in Electromagnetic Scattering problems and also in Electrical Power systems. supported by field measurements on HN MEKO class frig- ates. Comparing the measurement results with the direc- Cdr. S. PERROS, (Engineer Officer from the HNA/1984, M.Sc in Elec- tives of STANAG 1008 / Edition 8, in many cases it is trical Engineering from Naval Postgraduate School in Monterey Califor- rather difficult to identify whether the suggested current nia, USA/ 1992). After many years of service in HN warships (including Frigate MEKO HN type), he is assigned now in HN General Staff. He is harmonic limits are violated or not, as they refer to often also an associate of the El. Engineering Chair of the HNA and is interested unattainable operating points. On the other hand, the volt- in the naval ships electric systems and the electrical power quality prob- age harmonic distortion in operating plants, which is the lems. ultimate objective, is measured to be well below the limits Lt. Cdr. D. KAVOULAKOS, (Deck Officer from the HNA/1988, M.Sc set by either STANAG-1008 or IEEE-519 (voltage THD in Electrical Engineering from Naval Postgraduate School in Monterey less than 5%, each voltage harmonic very less than 3% ). California, USA/ 1996). After many years of service in HN warships (in- cluding Frigate MEKO HN type), he is assigned now in HN General Staff. STANAG 1008 / Edition 9, which will replace Edition 8, He is interested in Communication Systems and also in Electric Power Quality problems on ship electric systems. practically sets no limits on current harmonics of each separate or group of loads. On the contrary, IEEE-519 sets Lt. Cdr. E. SAKIOTIS, (Engineer Officer from the HNA/1987, M.Sc in current distortion limits for the installed equipment and Electrical Engineering from Naval Postgraduate School in Monterey Cali- seems to be more readily applicable, as it refers to actual fornia, USA/ 1996). He has served in many HN warships (including Frig- ate MEKO HN type) and is now serving in Souda Naval Base as head of operating points. Energy Division and Electrical & Electronic Workshops Manager. He was also an associate of the El. Engineering Chair of the HNA.

V. REFERENCES Lt. Cdr. E. CHRISTOFIS (Deck Officer from the HNA/1988, M.Sc in Electrical Engineering from Naval Postgraduate School in Monterey Cali- fornia, USA/ 1996). After many years of service in HN warships (includ- [1] IEEE Std 519-1992 : "IEEE Recommended Practice and Require- ing Frigate MEKO HN type), he is assigned now in HN General Staff. He ments for Harmonics Control in Electrical Power Systems", IEEE, is interested in Communication Systems and also in Electric Power Quality NewYork, 12 April 1993. problems on ship electric systems. [2] Vokas, G. ,Gazithellis, D. , Katsikaris, C., Peponis, G., "Electric

Power Quality ", Technical Chamber of Greece, Athens, May 1993 (In Lt. F. MARTINOS (Engineer Officer from the HNA/1991, M.Sc in Mili- Greek). tary Electronic Systems Engineering from Royal Military College of Sci- [3] IEEE Standard 45-1993, "Recommended Practice for Electrical Instal- ence of Cranfield University ,UK/1997). At present he is positioned as a lations on Shipboard", IEEE Press, New York, 1993 Director of the Electronics Department (Electronics Officer) in H.S. [4] STANAG 1008 : "Characteristics of Shipboard Electrical Power SPETSAI (Frigate MEKO HN type) and he is an associate of the El. Engi- Systems in Warships of the North Atlantic Treaty Navies", NATO , Edi- neering Chair of the HNA and he is interested in the naval ships electrical tion 8, 21 Febr. 1994./ Edition 9 under ratification. systems and the Electric Power Quality problems. [5] NATO AC/141(SG/6)SG/4 FRANCE paper 93/08 (44)-8 Sept. 93, : "Harmonic pollution on Ship electric side circuit - Limitation of harmonic o Dr. J. PROUSALIDIS (Electrical Engineer from NTUA/1991, PhD from currents injected into side circuit" , DGA Note technique N 353/93 NTUA/1997). Currently, he is Lecturer at the Naval Architecture and SY/SEP, Paris 8 Sept. 1993. Marine Engineering Department of National Technical University of Ath- [6] NATO AC/141(SG/6)SG/4 paper (02)96/10-03.04.96 : ens, dealing with electric energy systems and electric propulsion schemes "STANAG 1008, Harmonic Distortion, Compilation of Replies to Ques- on shipboard focusing on electric power quality problems and analysis of tionnaire" transients. [7] NATO AC/141(SG/6)SG/4 GERMANY paper (07)97/24-12.12.97 : "Harmonic Distotion". [8] NATO AC/141(SG/6)SG/4 GREECE paper (03)00/28-03.04.00 : "Interpretation of Current Distortion Limits of STANAG 1008 Ed. 8”