Improved Industrial Modeling and Harmonic Mitigation of a Grid Connected Steel Plant in Libya

Currently, we are living in a new transition process towards the fourth phase of industrialization, well known as the purported Industry 4.0. This development backbone supposes a sustainable manufacturing. Were optimal functionalities of a factory components especially energy rationalization and enhanced power quality are nonetheless a privilege but an obligation to introduce efficiently artificial intelligence AI, smart metering SM and automated decision making ADM. In the same axis of mitigating power quality issues, this paper is introduced first to draw innovatively a virtual reality (VR) complex grid connected steel power plant and then to depict harmonic sources in order to moderate them which are caused essentially by nonlinear installed loads manifesting power system quality issues and exhibiting periodic signal distortion. Accordingly, it was essential to assay the diverse origins of harmonic problems and to present the most accommodate and economic solution techniques. Related voltage and current harmonic flows at 30 kV levels, of the General Electricity Company of Libya GECOL located in Tripoli city, are examined. Afterward, inquire jointly their harmful effects on plant components. In order to attenuate distortion, a harmonic analysis has been investigated. Then appropriate filters design have been sized, designed, simulated and appended to the panel. Simulation results are presented and validated using ETAP industrial software under real measurement arena. Keywords—Industry 4.0; distribution systems; THD; harmonic load flow; passive filters


I. INTRODUCTION
Over the last few years in developing countries many linkage reinforcement attempts between researchers, industry stakeholders and the socioeconomic world aiming to promote the fourth [1][2][3][4] industrial revolution.Engineering researchers have been focusing on power system studies especially after the massive introduction of new renewable energies sources [5 -7] affecting the overall radial electrical system compartments.Power quality issues are generally caused by non-linear loads; corrective operations are not automatically gained with the same action due to devices nature [8][9] and response differences.One of the key ascertainment to gain towards migrating into 4th industrial revolution and enhancing power quality is mitigating harmonic disturbances which come largely from equipment with non-linear current and voltage characteristic causing severe damages on voltage supply network.As real manufacturing domain suffering from harmonic disturbances we quote induction melting furnaces [10] which use electric current to dissolve metal.Where exceeded Harmonic Distortion THD and its moving average TDD compared to the 519_1992 IEEE Standard can cause overloading of power factor correction, over voltage and extra currents, increased error in energy meters, malfunctions of protective gears, relays, circuit breakers, tripping of machines at smaller loads and inductive interference [11][12] with neighboring electrical grid.
A. Industry 4.0 Manufacturing industry is ongoing a deep permeating process, where physical and virtual worlds will be fused through Virtual-physical systems.This process is fuelled by high technology enablers like; Smart metering and monitoring Mobile Devices , Internet of Things IOT, Internet of Every Things IOE, Cloud computing, Big Data, 3 D printing … aiming to achieve the Smart Factory Paradigm.In the same context: Authors in [13] Provides a review of electrical energy metering state-of-the-art in, with a meticulous focus on energy metering in complex manufacturing establishments.They highlighted quantification and visibility in energy consumption.Where habitually, operation of complex manufacturing facilities planning decisions have been based only on conventional metrics without considering energy consumption rationalization and taking into account its energy standards which ought to be one of the keys of manufacturing strategies as well demonstrating the importance of power quality statistics instance; such as voltage sags and harmonic distortion.
Further in [14], authors offered an overview of different opportunities for sustainable manufacturing in Industry 4.0 in addition to a use case for the upgrading of manufacturing equipment as a specific opportunity for sustainable manufacturing.
In [15], authors underlined the fact that several manufacturing systems are not ready to manage big data due to the lack of smart analytics tools.Management of big data as well as the readiness level of smart predictive informatics tools has been drawn to achieve transparency and productivity.

B. Power System Analysis
The global growing of nonlinear loads applications, coming mostly from the wide use of power electronic devices, have resulted power quality issues more than ever seen before.Here appears the power System study and analyses as compulsory parts of any power system engineering for quantification query, in this same axis: [16] is an assessment of harmonic disturbances seen in a real smart grid.Then, solution to www.ijacsa.thesai.orgmaintain the operation of the distribution photovoltaic system plant and electrical cars within imposed standards PQ limits.
Authors in [17] focused on benefits of the detailed analyses by using ETAP software, which performs several numerical calculations of a huge integrated power system.

C. THD
Harmonic analysis, modelling and mitigation new techniques [18] Drawn a lot of ink hereunder we noted some of annexed works.
In [19], authors gave a summary on new design energy conversion system and methods such as Particle Swarm optimization, Genetic Algorithm, and Differential Evolution advantages and limitations.
For the case of [20], a classification of most commonly used methods of power system harmonics estimation reviewed based upon analysis tools and applications type.Diverse harmonics estimation techniques are gathered besides standards, papers and books.
Whereas in [21], the authors investigated harmonic effects on radial distribution grid losses and transmission lines capacities.The presented harmonic assessments have a real harmonic measurement and computer-based system modeling background in local distribution substations with ETAP.
As a consequence, many industrial software tools and new virtual reality approaches modeling and simulation have been performed to assay the grid.Computer based software are leading the revolution in recent advances in electrical and industrial engineering.In our case a mutinous harmonic load flow analyses is performed through ETAP industrial software based on practical measurement and overall on-line monitoring to distinguish the immediate effects of furnaces load on the Point of common coupling PCC.The one line diagram drawing is used to scrutinize the overall power system state from top grid source until the load which is the steel plant.All power components like transformers, CT's, PT's, Furnaces, motors, cables etc.… are exactly modelled thanks to ETAP real ratings library.This paper represents a novel approach to analyze and monitor the industrial grid connected power system by just using real time software, ETAP.Then, Harmonic analyses of current and voltage waveforms when sinusoidal voltage is applied to a non-linear load like furnaces are made finally the auto-sizing filter feature is presented to mitigate distortion and bring it within standards.Section 2 is the global single line diagram of the system under study; this diagram is implemented based on practical data in ETAP for simulation purpose in Section 3. Section 4 contains analyses which include monitoring of this large power system and harmonic load Flow.Section 5 deals with adopted harmonic solution method.Section 6 is the Conclusion of this research work.

II. USE DESCRIPTION OF THE FACTORY SUBSTATION
First of all we propose to introduce the factory substation modeling in Fig. 1 which is fed from 30kV / 11kV, 20 MVA transformers inside the factory substation, which, in turn, feeds the Al-Taba substation 30 KV through two overhead transmission lines 30KV.

III. LOAD FLOW ANALYSIS
Load flow analysis [22] examines the continuous operation of the power system to determine the main operating parameters, especially voltage levels on buses and load levels on power grid elements.It is necessary to study the load flow at the factory maximum loading to ensure that the voltage changes in all buses is conform to the required limits.All transformers, cables and buses are satisfying nominal equipment functionality specifications.
The worst scenario to connect the factory to the Al-Taba substation (30KV) GECOL's Tripoli at the maximum load operation of the factory without taking into account the development of required improvements (power factor correction equipment, use of tap change for in-plant transformers) to determine the full factory operation to find out extent impact and changes on the network (voltage levels, power factor) ensuring the required limits described in [23].

A. First Work Sequence
The first condition set-up is done by assuming that all factory loads (furnaces, motors, auxiliary loads) are not connected to be sure about highest reachable voltage at all connected buses via Al-Taba substation at 30KV.First notable condition, as shown in Table 1, buses may suffer from high voltage exceeding 5%.
We conclude from Table 1 that the voltage changes are within operational limits ± 5%.

B. Second Work Sequence
The second assumed condition is that all furnaces, motors and auxiliary loads are feed by setting both factory transformers 30 / 11KV on normal tap change as drawn in Table 2.
We conclude from Table 2 that the voltage doesn't change at maximum factory loading, even with setting up both factory transformers 30 / 11KV on the normal tap change voltages still are within ± 5% limits in all buses.

IV. HARMONIC ORIGINS ASSESSMENT
Mainly harmonic origins in industrial steel systems are classified into three origin types; single and three phase loads, harmonics generated by transformers [24] and harmonics created by induction furnaces [25].A special interest will be done in this section to fetch and inhibit these issues and eliminate their causes.
First of all, we propose the modeling of induction furnaces conversion chain which are coupled in our case using 11 / 1kv transformer as drawn in Fig. 2: Fig. 2. ETAP Modeling of the Induction Furnace.www.ijacsa.thesai.orgCurrent and voltage harmonic distortions are measured throughout the factory and the electrical network buses then compared with standards.The point of common coupling (PCC) bus is located at 30KV level between the factory and the grid; Captured figures below describe the voltage waveform and spectrum at every bus and gave a clear idea of harmonic sources.Indeed, we prove objectively that the main source of grid distortion is induction furnaces loads, due to generated harmonics through transformers current, which in turn impact grid elements.Table 5 declares the current distortion levels at overall factory, network buses and compared them to acceptable standard values.
We notice that some buses are out of ITHD allowable ranges.Table 6 summarizes the odd harmonic currents (5, 7, 11, and 13) at steel plant PCC.

V. ADOPTED HARMONIC MITIGATION METHOD
Harmonic filters [26] are used to reduce the distortion in voltage and current waveforms by controlling the flow of harmonic currents to reach acceptable standard levels of distortion in voltage and current waveforms.
There are several types of used harmonic filters to reduce THD and compensate the reactive power.Among these filters passive filters, active filters, 12 pulse rectifiers, 18 pulse rectifiers …and active front end (AFE) drives which are cited in order form complexity, efficiency and performance point of view.In fact, sophisticated mitigation techniques are not widely used in industry like passive filters due to their effectively high cost and complex control techniques.Our strategy was to achieve best results with www.ijacsa.thesai.orgminimum of cost and implementation complexity depending of the industrial customer budget and fair obtained results.

A. Passive Filter Design using ETAP
ETAP provides an auto-sizeable modeling feature of filters as shown in Fig. 13 hereunder:

B. The Parameters Calculation of the Single Tuned Filter
Table 7 illustrates (R, L, and C) parameters for selected used filters frequencies at 5th, 7th and 11th harmonic orders.

C. Results with Filters
Load flow calculations were performed after harmonic filters introduction to improve voltage levels, rectify power factor and omit undesirable harmonics.Moreover, there are two assumed simulation sequences: The first sequence is all factory loads (furnaces, motors, auxiliary loads) are disconnected except operational filters at Al-Taba substation 30KV.Results are shown in Table 8.
In the second sequence we reconnect all furnaces, motors and auxiliary loads with filters by setting the two transformers 30 / 11KV of the factory on normal tap change.Furthermore setting the 11/1 KV level 4 transformers on the 5% tap change, 11/6 KV transformer on 2.5% tap change and the 11/0.4KVtransformer on 3.75 % tap change.
The load flow results show a clear improvement in voltage levels at all buses as shown in Table 9.Table 11 shows the current distortion levels compared with standard values after connecting passive filters at PCC.The current distortion levels at all buses are acceptable and within standard limits.Table 12 shows the content of current odd harmonics (5, 7, 11, and 13) at PCC steel plant bus 30KV Comparing before and after states we notice that voltage magnitudes are between 95% and 105% at all buses.THDi and THDv values are acceptable compared with the standard limits after filters introduction.As well as, our criterion; which was from the beginning to achieve the most suitable results with lowest implementation cost and fastest implementation technology, respecting the industrial customer requirements.

VI. CONCLUSION
The harmonic distortions in steel factories are manifesting a big power quality mile stone concern inevitable to eradicate in order to meet the 4.0 industry requirements from power quality enhancement point of view.In the present paper a rigorous THD analyses has been underlined.Furthermore, THDV at PCC initially was measured 8.48% and the total harmonic current distortion THDI at same bus was 19.81%.A passive filter was proposed to improve harmonic distortion caused by factory components.The results showed an interesting improvement with passive filters operation in THDV which decreases to 1.44% and 2.26% THDI without using complex and pricey methods like active filters 12, 18 … pulse rectifiers and variable frequency drives VDFs like active front end (AFE) drives.As a future work we propose a comparative study between the last cited mitigation techniques.

Fig. 3
Fig. 3 and 4 are describing voltage waveform and its spectrum at Al-Taba 220KV source bus.

Fig. 5
Fig. 5 and 6 are describing voltage waveform and its related spectrum at Al-Taba 30KV region after stepping it down with the transformer 220/30 KV.

Fig. 7
Fig.7 and 8show voltage waveform and their related spectrum at steel plant bus.We conclude subjectively from voltage curves that induction furnaces loads are mainly the issue maker.As well, Generated harmonics by the induction furnaces impact in turn neighboring grid.Table 4 mention the voltage distortion levels at the factory and grid buses compared to acceptable standard values.We notice that VTHD values are slightly out of accepted standard range values explicating waveforms distortions; Stills to essay current waveforms and spectrums for all buses.

Fig. 9
Fig. 9 and 10 are describing current waveform and its spectrum at Al-Taba 220/30 KV transformer.

Fig. 11
Fig. 11 and 12 are describing current waveform and its spectrum at steel plant 30/11 KV transformer.

Fig. 14
Fig. 14 to 19 below have shown the waveform and spectrum for the voltage at all buses after connecting the filters.

Fig. 20
Fig. 20 to 25 show the current waveforms and spectrums for all buses after connecting the filters.

TABLE I .
THE VOLTAGE LEVELS AT BUSES IN CASE THE FACTORY IS NOT LOADED

TABLE III .
SHORT CIRCUIT CURRENTS AT FACTORY AND NETWORK BUSES

TABLE IV .
VOLTAGE DISTORTION LEVELS AT THE FACTORY AND NETWORK BUSES

TABLE V .
CURRENT DISTORTION LEVELS AT THE FACTORY AND NETWORK BUSES

TABLE VII .
THE PARAMETERS OF THE FILTERS OF THE 5 TH , 7 TH AND 11 TH HARMONIC ORDER

TABLE VIII .
THE VOLTAGE LEVELS AT BUSES IN CASE THE FACTORY IS NOT LOADED AFTER FILTERS

TABLE IX .
BUSES VOLTAGE LEVELS AFTER IMPLEMENTING FILTERS

Table 10 is
the results comparison with standard limits after connecting the passive filters on PCC.

TABLE X .
THE VOLTAGE DISTORTION LEVELS AT THE FACTORY AND NETWORK BUSES WITH FILTERS

TABLE XI .
CURRENT DISTORTION LEVELS AT THE FACTORY AND NETWORK BUSES WITH FILTERS