Electrical Failure
An Electrical Arc Furnace was facing Electrical Failure from power program harmonic resonance. Failure analysis simulation & electrical design and style for prevention.
Summary: An Electrical Arc Furnace near a hyperactive railway traction line was struggling with electrical failure from an unusual energy excellent harmonic distortion dilemma. The Gigantic 22kA copper bus bar accustomed to overheat visibly crimson-very hot, vibrate audibly loud loosening nuts and bolts and dress in out affected plates. In-addition, it usually encountered other harmonic complications like bulging and blasting of detuned capacitor, motor overheating and failures, HPMV lights ballast failures, 33kv fuse blowing and overheating of the Electric Arc Furnace transformer.
An on website electricity quality harmonic Evaluation revealed an unstable grid supply zone which was providing into the plant. It was tending in direction of a series resonance. A harmonic solution was intended. A 33kv harmonic filter was put in in the plant's 33kV grid incomer. Its functionality monitored for just a year and no electrical failure occurred. The set up passive tuned harmonics filter resoled all electricity high quality harmonic challenges because of energy technique resonance as well as associated electricity surge. It eliminated electrical failure and equipment tripping. In addition, the enhanced operative energy process ailments facilitated amplified productiveness, significantly, with congruous reduction in distinct energy usage (SEC) concerning kWh/ A ton of iron alloy generated.
Electrical Failure
Fig.one EAF Electrodes- six.5Ton, 6mva, 22kA
Index Conditions- ability high-quality engineering, harmonic review, root bring about analysis, grid stability, ability process resonance, harmonic Answer, harmonic filter.
I. NOMENCLATURE
EAF Electrical Arc Furnace
TRF Transformer
NLL Non Linear Load
THDv Complete harmonic distortions, voltage
THDi Complete harmonic distortions, present
In Person recent harmonic orders, like 3rd is I3
Vn Unique voltage harmonic orders, like fifth is V5
II. INTRODUCTION
The factory manufactures Pig Iron which happens to be an intermediate products made by smelting iron ore with significant carbon gasoline for instance coke typically with limestone as flux. As observed in Fig.2, the ingots are generated at quite a few a branching buildings which might be laid in sand at proper angles to its central channel called the runner whereby the liquid metal is poured straight from The underside of the EAF. This kind of configuration resembles, in overall look, to a litter of piglets suckling over a sow. As the metallic cools and hardens the branching ingots, the Pigs, only crack clear of the Substantially thinner runner, the Sow, for this reason the title Pig Iron.
Pig Iron from 6.5Ton EAF around the Casting Mattress
Fig.2 Pig Iron being tapped in a very Casting Mattress
The high carbon articles 3.5%-four.5% makes it brittle. Being an intermediate product it is intended for re-melting, and thus the uneven ingot size and inclusion of small degree of sand are usually not sizeable when compared to the ease of its casting and handling. Pig Iron is applied usually and mostly in foundry marketplace also to some extent in induction furnace sector for manufacturing unique quality of iron billets.
The EAF is powered from the 3ph, six.0mva, 33kv/160v, 22kA, 50Hz, transformer as shown in Fig.5, and connects it through a 3ph, 22kA, 160v, copper bus-bar that connects to its three electrodes. The electrodes are then submerged into the demand of iron ore and coke. Therefore the electrodes proficiently limited circuit by itself and that result in monumental latest (22kA) to stream throughout the charge. Its effect melts the demand as revealed in Fig.one.
The Heat control into your demand is finished by electrode positioning lowering it maximize, and raising it lower the heat and likewise the facility demand from customers. A Semiautomatic Manage process repeatedly positions the electrodes at an correct depth to the cost for your ideal warmth and power demand from customers. The charge is continually fed into the EAF from its prime hopper. The liquid metallic is however tapped from its bottom inside a batch method at just about every interval of about 3-one/2hrs as demonstrated in Fig.two, manufacturing six.5Tons per batch and summing as much as 45tons on a daily basis in 7 batches.
There nevertheless is a dilemma to overcome with EAF for iron ore melting. Iron ore fines and that specifically from Indian mines have about fifty six% Fe written content. It is far from plenty of a conductivity which can develop powerful short circuit amongst its a few electrodes, which requires a minimal 65% Fe articles.
33kv, three.80mvar Harmonic filter for 33kv Elecrtic Arc Furnace
Fig.4: 3.80mvar Harmonic filter for 33kv EAF
The situation is solved by pre-processing the iron ore and thus rising its Fe information; whereby it is blended with couple percentage of mill scales, and sintered inside a hydro cyclone. Sintering is really a means of welding with each other smaller sized particles of metal by applying heat below its melting stage. It is a straightforward approach that requires no direct electric power. The Original warmth is created by utilizing some squander resources like packaging waste, rice husk etcetera., then the flame is carried as a result of by oxygen lancing and that is realized by drawing ambient air throughout the sintered mixture employing ID Enthusiast.
Mill Scale is hardened oxidized surface area that will get designed about the steel surface when it can be scorching processed. It contains 98% Fe inside the types of iron and oxidized iron particularly Fe, FeO, Fe2O3 and Fe3O4. It is just a bye-item from sizzling rolled milling course of action. It will get formulated any time a heated steel ingot is very hot rolled into a prolonged sheet. Superior-stress h2o jets at about 70 bar descale it and fall it down from your steel surface. It's a scale and it peels off as flake off the hot rolled metal surface. Mill scale is really a squander that receives produced in huge built-in metal plants.
III. Scenario STUDY
A. Difficulty Assertion
First of all, very low fault level, because of its remote place around a forest land. Secondly, large electric power high-quality harmonic disturbances, from a hyperactive Howrah-Mumbai railway traction line that passes beside it and receives 25kv provide within the exact same close by 132/33kv Ghatsila Substation as proven in Fig.three (The very best caption photo).
Furthermore, the conventional engineering structure apply is restricted in setting up only power aspect compensation capacitors for linear masses, and capacitors with detuned reactors for non linear hundreds (NLL). The same style observe is additionally followed listed here Given that via the EAF as NLL.
6mva, 33kv/160v EAF transformer
Fig.5: EAF Transformer, 6mva, 33kv/160v
The factory receives electricity form a 50mva, 132/33kv, TRF at Ghatsila Substation that also supplies to numerous other bordering industries specifically, 2x Pig Iron vegetation, 1x Induction Furnace plant, 6x General public Distribution substations Each and every by way of a 33/11kv sub-distributions, 7x Rice Mills Every via a 33/11kv sub distributions and 2x Induction Furnace plants Each and every through a 33/11kv sub-distribution.
Should the NLL is existing in the facility program then connecting PF capacitors with current-restricting reactors or with detuned reactors, with out obtaining the minimum Look at on its resonance ailment, can be a recipe of a potential harmonic resonance trouble. It has become the main triggers that defines a stable grid in addition to a secure energy process in an industry. The resulting energy surge that predominantly manifest as voltage sags and fluctuations, as being the consequence of electrical power high-quality harmonic resonance, is the single most important cause that inflicts billions of dollar damages in terms of industrial devices failures and productivity losses on a yearly basis around the world. Electrical harmonics are unpredictable. Under favorable electricity technique impedance, the brought on harmonic resonance circumstance, magnifies equally the harmonics and the power fluctuations inside the grid offer. The factory was then hardly six-months from its startup commissioning and documented comprehensive electricity high quality disturbance and devices failures all through our onsite harmonic analyze.
one. 33kv capacitor failure: It had put in 1800+1200kvar capacitor financial institutions with detuned reactors from the MNC company for sustaining plant PF close to at UNITY level. The capacitors began bulging from all sides thereby reducing its powerful kVAr output along with the plant energy aspect, and inevitably it began blasting one by one with time. We observed that the smaller sized 1200kva bank experienced failed fully and the bigger 1800kvar bank partially.
two. HPMV ballast failure: Lighting ballasts were burning routinely.
EAF transformer, 6mva, 33kv/160v, 50hzFig.five EAF Transformer 6mva 33kv/160v 50Hz
3. 33kv HT Fuse failure: The EAF auxiliary load is run from a one.0mva, 33/0.415kv, 50Hz Transformer. It really is related on the upstream at 33kv main incomer PCC by way of a 33kv HT fuse as shown in Fig.4. The fuse was blowing routinely at typical intervals which consequently used to journey the electrical arc furnace.
4. AC Motor overheating and failure: The EAF auxiliary load contains a number of constant pace squirrel case induction motors, SQIM, for apps like in EOT cranes, cooling tower enthusiasts, condenser water pumps, air compressors and other utilities. Just about all 3ph, 50hz, 415v LT motors accustomed to overheat regularly and that finally used to burn off its stator winding insulation.
22kA copper bus bar of an Electric Arc Furnace
Fig.5a EAF TRF LV bus bar 3ph 160v 22kA
five. The Gigantic 22kA copper bus-bar utilized to overheat and vibrate: The 22kA copper bus-bar that connects on the 3phase electrodes of the EAF, accustomed to overheat visibly purple-warm and vibrate audibly loosening its nuts & bolts. The phenomenon utilised to happen in about after a month. The situation persisted even after ensuring that each one bus bar nuts & bolts ended up limited and thereafter even after changing those nuts and bolts, and brazing and solidly repairing the afflicted bus bar plates. The continued vibrations and rubbing among the bus bar plates wore out the influenced bus bar portion. These then have been changed with new bus bar plates, but the problem still continued. The 22KA bus-bar termination in the 160v, EAF transformer secondary facet is revealed in Fig.five and the 22kA bus bar in Fig.5a.
6. 6mva EAF TRF substantial winding temperature: The transformer winding temperature achieved as superior as 90oC While it couldn't be loaded further than 5mva mainly because of the existed issues. The prevailing situations were being ideal enough for a potential failure in the EAF transformer itself. Transformers are prone to present harmonic distortions that can melt open its HV winding and create a one or multiple phase faults generally an open circuit with or without having earth fault. Transformers will also be liable to voltage harmonic distortions and energy good quality harmonic resonance ailments which can melt away its winding insulation possibly at HT or LT or can cause an earth fault in between its winding and entire body or at OLTC terminals. Most weighty industries like steel have a record of these types of superior voltage transformer winding failures
Present-day harmonic distortion of an EAF with de tuned harmonic filter
Fig.6 Grid THD (Present) with De tuned HF
B. Harmonic Research and Root Result in Analysis
The Power High-quality harmonic measurements were being performed through Apr.2012 applying a top quality 3phase electric power top quality harmonic analyzer of type PowerPro which actions at a sampling amount of 256/cycle and calculates RMS value of all measured parameters at every single cycle basis. It actions all regular state energy parameters, energy high quality such as person phase and neutral harmonics up to 64th, THDi, THDv, Inrush present-day, waveform distortions and voltage and present-day spikes with 65uS precision. Further more facts in the instrument could possibly be acquired at www.candura.com.
It was noticed that the power process of the incoming grid offer was tending to a greater harmonic resonance affliction which was the primary cause for the about at the time a month runaway harmonic resonance that utilized to cause the large overheating and vibration of your gigantic 22kA copper bus bar from the EAF transformer. An electrical electric power system having an induced harmonic resonance situation might cause dissipation and/or oscillation of huge degree of Electrical power. This was the basis cause for your bus bar to get visibly pink very hot and vibrate audibly loud; mixture of which utilized to loosen the buts and bolts on the bus bar, Regardless of how tightly it absolutely was held The calculated harmonics of each present-day and voltage in conjunction with its distorted waveforms are proven in Fig.six and seven respectively.
Voltage harmonic distortion of an EAF with de tuned harmonic filter
Fig.seven Grid THD (Voltage) with De tuned HF
The present waveform at 33kv incoming grid PCC was really distorted with 14.8% THDi with 125A peak load latest and eleventh (I11) and 17th (I17) as key current harmonics as proven in Fig.six.
The voltage waveform within the 33kv incoming grid PCC was only moderately distorted and was well inside of IEEE 519 boundaries with 3.9% THDv at 47kv peak load voltage (RMS price of rated line voltage is 33kv) and 11th (V11) and fifth (V5) as significant voltage harmonics as revealed in Fig.7.
It had been obvious from these measured harmonic bar charts and waveform graphs that a Portion of the incoming grid which was provided in the 50mva Transformer feeder from the Ghatsila substation was beneath harmonic resonance issue. The 11th harmonic variety will not be a natural harmonic that an EAF of this specification could deliver. Its authentic cause was the capacitors with detuned reactors mounted from the manufacturing unit and may be by many other encompassing industries in the exact electrical energy method.
A combination of these was tending in the direction of a series harmonic resonance issue with the interaction With all the grid energy supply. When an electrical electrical power system will get subjected into a harmonic resonance issue it magnifies each the current and the voltage harmonics, cause voltage sag and fluctuations, and energy swings. The extent of it depends upon the circumstances which exist then within the effective zone of your electrical ability process and its then load ailments. These parameters range constantly, and so would be the circumstances, period and also the extent on the grid instability in addition to its harmonic magnifications.
Harmonic Filter at a 33kv Electrical Arc Furnace Substation
Fig.eight Harmonic Filter in a 33kv EAF SS (entrance)
This root result in prognosis derived through the onsite harmonic Investigation was further more cross checked Along with the failure records as in depth less than trouble assertion. The nature of electrical failures and the techniques All those have been going on ended up in consonance Along with the actuality of existence of the harmonic resonance situation Using the incoming grid offer.
C. The answer, Passive Tuned Harmonic Filter (HF)
The absolute best solution for solving harmonic resonance issue is to set up a passive tuned harmonic filter closer to the ultimate load level which In such cases was at the 3ph, 160v, 22kA, electric powered arc furnace transformer's secondary offer PCC. This 160v LT bus bar was connected to the 3phase electrodes on the EAF which was the final load level. Also, the 6mva, 33kv/ 160v EAF transformer would give an isolation between the grid as well as manufacturing facility. These types of an isolation causes it to be comparatively easier to tackle a possible sequence harmonic resonance phenomenon with lesser design complexities; than building it with out the advantage of possessing that isolation transformer, since it greatly isolated the manufacturing facility load from another loads throughout the same productive grid provide zone.
3800kvar Harmonic Filter at a 33kv EAF Substation
Fig.9 Harmonic Filter at a 33kv EAF SS (rear)
However 160v is too very low a voltage and 22kA is too high a load existing which would have rendered the LT passive harmonic filter project commercially unviable even after taking into consideration higher Electrical power performance and higher productiveness People normally accrue when harmonic filters are put in nearer to load issue, as compared with upstream at a higher bus voltage.
Basically the solution acquired limited to tuning and realigning the incoming grid's ability procedure impedance at its 33kv PCC starting from the 50mva grid Transformer offer at Ghatsila substation. It essential putting in the harmonic filter with the 33kv PCC which also happened to be the grid as proven in Fig.3., the top caption photograph.
The mounted harmonic filter would So not just cater to the manufacturing unit's have NLL but also to a bigger grid supply zone to the extent Individuals are linked With all the identical 50mva grid TRF. In-addition harmonics are identified as nonlinear masses for all The great causes. It does not want to incorporate by itself inside a transformer isolated zone and its transgression inside an effective and larger power provide zone are quite common. Its extent is again continually variable consistent with the associated electrical electricity system and its load circumstances.
We have now had previous experiences of hassle from this sort of installations. Which additional receives compounded a result of the insufficient motivation for harmonic suppression among the other neighboring factories. Presented nonlinear character of your harmonic resonance, it's very Considerably achievable that some factories get afflicted incredibly challenging and a few is probably Electrical Failure Analysis not as challenging to have taken a Be aware of it. The full voltage harmonic distortion (THDv) with the affected 33kV grid offer zone could attain intermittently as significant as 40% moreover beneath resonance with a favorable electric power method impedance at that prompt, and in combination with nonlinear loads and capacitor switching because of the surrounding factories.
THD Latest harmonics right after harmonic filter at 33kv EAF
Fig.10 33kv THD (Latest) following Tuned HF
The resultant resonance results in vibration sound overheat and occasional TRF HV winding failures. The recorded details of seriously distorted 33kv grid supply underneath this kind of harmonic resonance ailments might be attained from www.enconengineers.in. The harmonic filter was set up within the 33kv PCC on the manufacturing unit at its outside substation, and that is also 33kv grid supply, as proven in Fig.eight (entrance check out) and Fig.nine (rear see).
D. Benefits Realized.
Once the set up of 33kv harmonic filter at the grid incomer on the manufacturing facility's outside substation a couple of 12 months back, a repeat harmonic examine was completed.
The present waveform for the 33kv grid incomer PCC was managed in just 6% THDi, at 152A peak load present and I5 and I7 as key present-day harmonics as shown in Fig.ten. The unbalance in the 3ph waveforms in present magnitudes is a result of the unequal arcing Amongst the a few electrodes of the EAF.
The voltage waveform in the 33kv grid incomer PCC was controlled very well in just IEEE 519 norm at two% THDv at forty five.6kv-peak load voltage (RMS value of rated line voltage is 33kv) and V7 and V23 as significant voltage harmonics as proven in Fig.eleven.
THD Voltage harmonics following harmonic filter for electrical arc furnace
Fig.11 33kv THD (Voltage) right after Tuned HF
Thereafter the manufacturing facility general performance was noticed carefully for more than a calendar year. All power high quality harmonic disturbances and tools failure troubles all obtained settled and The bizarre resonance challenge Along with the gigantic 22kA bus bar overheating and vibration didn't come about thereafter indicating that the chances of a extreme electrical power top quality harmonic resonance is drastically lowered. Nonetheless, investigating the THDv waveform as in Fig.11 about the post harmonic Alternative scenario, there continues to be some probability to get a probable resonance and that's why it is claimed that resonance cannot be eradicated but can only be shifted away from a working frequency bandwidth.
The situation arose below weren't due to an ordinary electrical power excellent harmonic difficulty. The current harmonic distortions (THDi) were not superior enough to trigger this sort of an abnormal harmonic issue as well as the voltage harmonic distortions (THDv) had been very well inside IEEE 519 boundaries, as discovered in the course of the First ability high-quality harmonic measurement. A percentage of the grid provide zone ranging from the 50mva, 132/33 Transformer at the providing Ghatsila Substation was within the boundary traces of its electric power method's security.
IV. Summary
The enumerated case study and its yearlong efficiency verification report Obviously create all round advancement of main electrical power process parameters not merely In the plant but also inside the successful grid source zone.
Executing the ability high-quality engineering with the downstream of a plant with key NLL mirrors ideal grid problems. An engineering effort and hard work that will drastically avert electrical pollutions from coming into the electrical electricity system with the grid.
In-addition, it lessens carbon emission by maximizing productivity, getting rid of barriers to Vitality effectiveness, and marketing productive utilization of Strength all alongside. That begins from downstream plant to neighboring customers, and up towards the upstream electricity plant, the IPP electrical power provider and also the grid enterprise.
The associated fee saving when appeared narrowly compared with the electric power Monthly bill by yourself might seem average. But when put next holistically with significantly decreased financial investment Price tag, decreased carbon footprint, uninterrupted manufacturing, MTBF, stock price of parts and workforce enthusiasm coupled with ever rising cost of Power, the economic Advantages would much outweigh the expense of the solution.
EAF harmonics case analyze authorV. BIOGRAPHIES
Kanai Banerjee graduated in Electrical Engineering from Bengal Engineering and Science University, Shibpur, India in the yr 1983.
Labored at Bharat Weighty Electricals Restricted from 'eighty three to '95 and thereafter for a promoter at Encon Engineers nonetheless day.
His Unique fields of fascination include things like electricity quality engineering, harmonic remedies and manufacturing passive tuned harmonic filter and triplen harmonic filter of all measurement LV and HV, troubleshooting failures, Power conservation, electrical consultancy and HVAC engineering for starting genuinely green developing and retrofitting massive centralized HVAC initiatives.
He continues to be instrumental in increase the corporation's amazing growth and standing for a expertise-primarily based technologies Answer company on energy high-quality, energy efficiency, approach optimization and in Total Electricity Management fields.
An Electricity auditor Accredited via the bureau of Power effectiveness underneath the ministry of ability authorities of India, a member and chartered Specialist engineer While using the institute of engineers India, a member on the Indian Culture of heating, refrigerating and air-conditioning engineers, ISHRAE and a member in the Canadian and American EMTP-ATP consumer group.