Electrical Failure Analysis

Electrical Failure
An Electrical Arc Furnace was going through Electrical Failure from electricity technique harmonic resonance. Failure Investigation simulation & electrical structure for avoidance.

Summary: An Electrical Arc Furnace near a hyperactive railway traction line was dealing with electrical failure from an abnormal electricity excellent harmonic distortion dilemma. The Gigantic 22kA copper bus bar accustomed to overheat visibly purple-incredibly hot, vibrate audibly loud loosening nuts and bolts and don out influenced plates. In-addition, it regularly encountered other harmonic difficulties like bulging and blasting of detuned capacitor, motor overheating and failures, HPMV lights ballast failures, 33kv fuse blowing and overheating of the electrical Arc Furnace transformer.

An on site electrical power high quality harmonic analysis exposed an unstable grid supply zone which was supplying to the plant. It was tending toward a collection resonance. A harmonic Alternative was developed. A 33kv harmonic filter was set up at the plant's 33kV grid incomer. Its performance monitored for your yr and no electrical failure transpired. The put in passive tuned harmonics filter resoled all energy high-quality harmonic troubles as a result of energy method resonance and also the involved electrical power surge. It eliminated electrical failure and equipment tripping. Also, the enhanced operative electrical power procedure problems facilitated improved productiveness, significantly, with congruous reduction in particular Power usage (SEC) with regard to kWh/ Tons of iron alloy developed.

Electrical Failure
Fig.1 EAF Electrodes- 6.5Ton, 6mva, 22kA
Index Phrases- electricity top quality engineering, harmonic examine, root cause Evaluation, grid stability, electricity procedure resonance, harmonic Option, harmonic filter.

I. NOMENCLATURE

EAF Electric powered Arc Furnace
TRF Transformer
NLL Non Linear Load
THDv Full harmonic distortions, voltage
THDi Overall harmonic distortions, present-day
In Person present-day harmonic orders, like third is I3
Vn Unique voltage harmonic orders, like fifth is V5

II. INTRODUCTION

The manufacturing unit manufactures Pig Iron and that is an intermediate merchandise made by smelting iron ore with large carbon gas including coke normally with limestone as flux. As witnessed in Fig.2, the ingots are produced at many a branching structures that are laid in sand at right angles to its central channel known as the runner whereby the liquid metal is poured directly from the bottom from the EAF. Such a configuration resembles, in appearance, to a litter of piglets suckling with a sow. Given that the metallic cools and hardens the branching ingots, the Pigs, basically split from the Considerably thinner runner, the Sow, consequently the title Pig Iron.


Pig Iron from 6.5Ton EAF about the Casting Bed
Fig.2 Pig Iron being tapped in a Casting Mattress
The significant carbon information 3.five%-four.5% makes it brittle. Remaining an intermediate product or service it is intended for re-melting, and thus the uneven ingot dimension and inclusion of small degree of sand are certainly not important in comparison with the ease of its casting and managing. Pig Iron is applied usually and primarily in foundry industry and to some extent in induction furnace marketplace for generating specific grade of iron billets.

The EAF is driven from the 3ph, six.0mva, 33kv/160v, 22kA, 50Hz, transformer as revealed in Fig.five, and connects it by way of a 3ph, 22kA, 160v, copper bus-bar that connects to its three electrodes. The electrodes are then submerged in the charge of iron ore and coke. So the electrodes properly limited circuit by itself Which bring about massive present-day (22kA) to stream with the charge. Its influence melts the cost as shown in Fig.one.

The Heat Manage into your demand is finished by electrode positioning reducing it improve, and boosting it lessen the heat as well as the power demand. A Semiautomatic Regulate method repeatedly positions the electrodes at an ideal depth to the charge with the ideal heat and ability demand from customers. The demand is repeatedly fed in the EAF from its prime hopper. The liquid metal is on the other hand tapped from its bottom in a batch system at each individual interval of about 3-one/2hrs as demonstrated in Fig.two, generating six.5Tons per batch and summing as many as 45tons each day in 7 batches.

There however is a challenge to overcome with EAF for iron ore melting. Iron ore fines Which specifically from Indian mines have about fifty six% Fe material. It isn't ample a conductivity that can generate effective shorter circuit among its a few electrodes, which needs a minimum amount 65% Fe content.

33kv, three.80mvar Harmonic filter for 33kv Elecrtic Arc Furnace
Fig.4: three.80mvar Harmonic filter for 33kv EAF
The problem is solved by pre-processing the iron ore and therefore expanding its Fe content material; whereby it's blended with handful of share of mill scales, and sintered in the hydro cyclone. Sintering is a strategy of welding with each other scaled-down particles of metal by making use of heat beneath its melting level. It is an easy procedure that needs no direct electrical power. The Original heat is produced through the use of some waste resources like packaging waste, rice husk and many others., and then the flame is carried by way of by oxygen lancing that is obtained by drawing ambient air throughout the sintered mixture utilizing ID Supporter.

Mill Scale is hardened oxidized area that receives created to the steel surface area when it can be scorching processed. It is made up of 98% Fe within the sorts of iron and oxidized iron specifically Fe, FeO, Fe2O3 and Fe3O4. It's a bye-product or service from warm rolled milling method. It receives developed whenever a heated metal ingot is hot rolled right into a extended sheet. Significant-pressure drinking water jets at about 70 bar descale it and fall it down within the steel surface area. It is just a scale and it peels off as flake off the recent rolled steel floor. Mill scale is really a squander that receives generated in substantial built-in steel plants.



III. Circumstance STUDY

A. Issue Statement

To start with, small fault level, because of its distant location close to a forest land. Next, significant ability quality harmonic disturbances, from a hyperactive Howrah-Mumbai railway traction line that passes beside it and gets 25kv source from the identical close by 132/33kv Ghatsila Substation as demonstrated in Fig.three (The top caption picture).

Moreover, the traditional engineering structure practice is limited in putting in only electricity issue payment capacitors for linear masses, and capacitors with detuned reactors for non linear hundreds (NLL). The exact same layout exercise can also be adopted listed here considering that because of the EAF as NLL.

6mva, 33kv/160v EAF transformer
Fig.five: EAF Transformer, 6mva, 33kv/160v
The manufacturing unit receives electrical power variety a 50mva, 132/33kv, TRF at Ghatsila Substation that also supplies to a number of other bordering industries specifically, 2x Pig Iron plants, 1x Induction Furnace plant, 6x Public Distribution substations Each individual through a 33/11kv sub-distributions, 7x Rice Mills Every through a 33/11kv sub distributions and 2x Induction Furnace crops Each individual via a 33/11kv sub-distribution.

In case the NLL is existing in the ability method then connecting PF capacitors with present-restricting reactors or with detuned reactors, without the need of getting the minimum Test on its resonance condition, is really a recipe of a potential harmonic resonance difficulty. It is probably the important results in that defines a stable grid along with a stable electricity procedure in an marketplace. The ensuing ability surge that mainly manifest as voltage sags and fluctuations, because the consequence of electrical power excellent harmonic resonance, is The one most big induce that inflicts billions of greenback damages concerning industrial machines failures and efficiency losses on a yearly basis all over the world. Electrical harmonics are unpredictable. Less than favorable power procedure impedance, the brought on harmonic resonance condition, magnifies both equally the harmonics and the ability fluctuations in the grid offer. The manufacturing facility was then barely 6-months from its startup commissioning and noted considerable ability excellent disturbance and products failures in the course of our onsite harmonic study.

one. 33kv capacitor failure: It had installed 1800+1200kvar capacitor banking companies with detuned reactors from the MNC firm for sustaining plant PF in the vicinity of at UNITY stage. The capacitors started out bulging from all sides thereby reducing its effective kVAr output as well as plant electricity aspect, and inevitably it started off blasting one by one with time. We noticed the lesser 1200kva financial institution had unsuccessful completely and The larger 1800kvar financial institution partially.

2. HPMV ballast failure: Lights ballasts had been burning consistently.
EAF transformer, 6mva, 33kv/160v, 50hzFig.5 EAF Transformer 6mva 33kv/160v 50Hz

3. 33kv HT Fuse failure: The EAF auxiliary load is run from a 1.0mva, 33/0.415kv, 50Hz Transformer. It is related with the upstream at 33kv primary incomer PCC by way of a 33kv HT fuse as proven in Fig.4. The fuse was blowing commonly at normal intervals which in turn utilized to excursion the electrical arc furnace.

four. AC Motor overheating and failure: The EAF auxiliary load consists of quite a few continual velocity squirrel case induction motors, SQIM, for purposes like in EOT cranes, cooling tower enthusiasts, condenser water pumps, air compressors and various utilities. Virtually all 3ph, 50hz, 415v LT motors utilized to overheat commonly and that eventually utilized to burn up 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 accustomed to overheat and vibrate: The 22kA copper bus-bar that connects to your 3phase electrodes from the EAF, utilized to overheat visibly crimson-incredibly hot and vibrate audibly loosening its nuts & bolts. The phenomenon employed to occur in about after a month. The problem persisted even soon after ensuring that every one bus bar nuts & bolts had been limited and thereafter even right after replacing Individuals nuts and bolts, and brazing and solidly correcting the impacted bus bar plates. The ongoing vibrations and rubbing concerning the bus bar plates wore out the affected bus bar part. Individuals then were replaced with new bus bar plates, but the problem however continued. The 22KA bus-bar termination within the 160v, EAF transformer secondary aspect is revealed in Fig.five and the 22kA bus bar in Fig.5a.


6. 6mva EAF TRF superior winding temperature: The transformer winding temperature achieved as higher as 90oC While it could not be loaded over and above 5mva due to existed complications. The prevailing situations were being perfect plenty of for a potential failure of your EAF transformer by itself. Transformers are liable to recent harmonic distortions which will melt open its HV winding and make a single or several section faults generally an open up circuit with or with out earth fault. Transformers can also be at risk of voltage harmonic distortions and energy excellent harmonic resonance circumstances which will burn its winding insulation both at HT or LT or could potentially cause an earth fault among its winding and system or at OLTC terminals. Most hefty industries like steel have a heritage of these kinds of high voltage transformer winding failures

Existing harmonic distortion of an EAF with de tuned harmonic filter
Fig.six Grid THD (Current) with De tuned HF
B. Harmonic Analyze and Root Result in Evaluation

The Power High quality harmonic measurements have been performed in the course of Apr.2012 working with a high quality 3phase electrical power top quality harmonic analyzer of form PowerPro which measures at a sampling fee of 256/cycle and calculates RMS worth of all measured parameters at every single cycle foundation. It steps all steady state electricity parameters, power good quality which include individual stage and neutral harmonics nearly 64th, THDi, THDv, Inrush present, waveform distortions and voltage and recent spikes with 65uS precision. Further more particulars with the instrument could be acquired at www.candura.com.


It absolutely was observed that the ability technique of your incoming grid supply was tending to a greater harmonic resonance ailment which was the main reason behind the about as soon as per month runaway harmonic resonance that accustomed to trigger the large overheating and vibration with the gigantic 22kA copper bus bar of the EAF transformer. An electrical electrical power process with an induced harmonic resonance situation can result in dissipation and/or oscillation of big amount of Vitality. This was the basis bring about to the bus bar to get visibly red scorching and vibrate audibly loud; mixture of which accustomed to loosen the buts and bolts of your bus bar, no matter how tightly it was held The calculated harmonics of both of those current and voltage together with its distorted waveforms are demonstrated in Fig.six and seven respectively.

Voltage harmonic distortion of the EAF with de tuned harmonic filter
Fig.seven Grid THD (Voltage) with De tuned HF
The current waveform at 33kv incoming grid PCC was extremely distorted with 14.8% THDi with 125A peak load recent and eleventh (I11) and seventeenth (I17) as major current harmonics as demonstrated in Fig.6.

The voltage waveform in the 33kv incoming grid PCC was only moderately distorted and was properly in IEEE 519 boundaries with three.nine% THDv at 47kv peak load voltage (RMS value of rated line voltage is 33kv) and 11th (V11) and 5th (V5) as significant voltage harmonics as proven in Fig.seven.

It had been obvious from these calculated harmonic bar charts and waveform graphs that a Element of the incoming grid which was supplied from the 50mva Transformer feeder of your Ghatsila substation was below harmonic resonance problem. The eleventh harmonic variety will not be a purely natural harmonic that an EAF of this specification could crank out. Its authentic induce was the capacitors with detuned reactors mounted through the manufacturing facility and should be by all kinds of other surrounding industries in the similar electrical power system.

A combination of these was tending in direction of a collection harmonic resonance ailment via the conversation with the grid power provide. At the time an electrical power program gets subjected to your harmonic resonance condition it magnifies the two The present and the voltage harmonics, bring about voltage sag and fluctuations, and Power swings. The extent of it is dependent on the circumstances which exist then in the effective zone on the electrical power program and its then load ailments. These parameters vary continually, and so are the problems, period as well as the extent with the grid instability along with its harmonic magnifications.

Harmonic Filter at a 33kv Electrical Arc Furnace Substation
Fig.eight Harmonic Filter in a 33kv EAF SS (front)
This root result in prognosis derived within the onsite harmonic Evaluation was even more cross checked with the failure information as specific less than issue statement. The character of electrical failures as well as methods People ended up going on were in consonance With all the actuality of existence of the harmonic resonance condition Using the incoming grid provide.


C. The Solution, Passive Tuned Harmonic Filter (HF)

The absolute best solution for resolving harmonic resonance problem is to install a passive tuned harmonic filter closer to the final load position which In such cases was within the 3ph, 160v, 22kA, electric arc furnace transformer's secondary supply PCC. This 160v LT bus bar was connected to the 3phase electrodes in the EAF which was the ultimate load place. Also, the 6mva, 33kv/ 160v EAF transformer would present an isolation between the grid and the factory. This kind of an isolation causes it to be comparatively simpler to tackle a potential series harmonic resonance phenomenon with lesser design and style complexities; than planning it devoid of the benefit of acquiring that isolation transformer, as it enormously isolated the manufacturing unit load from one other hundreds throughout the exact helpful grid source zone.

3800kvar Harmonic Filter in a 33kv EAF Substation
Fig.nine Harmonic Filter in a 33kv EAF SS (rear)
On the other hand 160v is simply too very low a voltage and 22kA is simply too significant a load latest which might have rendered the LT passive harmonic filter task commercially unviable even soon after taking into consideration increased Strength effectiveness and higher productivity those usually accrue when harmonic filters are installed nearer to load issue, compared to upstream at the next bus voltage.

Almost the answer acquired limited to tuning and realigning the incoming grid's power process impedance at its 33kv PCC starting from the 50mva grid Transformer supply at Ghatsila substation. It demanded putting in the harmonic filter in the 33kv PCC which also transpired being the grid as proven in Fig.three., the highest caption image.

The mounted harmonic filter would As a result not just cater to the manufacturing facility's very own NLL but also to a bigger grid provide zone into the extent Individuals are linked with the similar 50mva grid TRF. In-addition harmonics are referred to as nonlinear loads for all The great factors. It doesn't want to include alone inside a transformer isolated zone and its transgression within just a highly effective and bigger electricity supply zone are quite common. Its extent is once more continuously variable in keeping with the involved electrical electrical power procedure and its load problems.

We've experienced past activities of trouble from these kinds of installations. Which further more gets compounded a result of Electrical Failure Analysis the not enough inspiration for harmonic suppression between other neighboring factories. Given nonlinear nature on the harmonic resonance, it is vitally A lot attainable that some factories get afflicted very tough and many is probably not as difficult to have taken a Notice of it. The full voltage harmonic distortion (THDv) at the impacted 33kV grid offer zone could access intermittently as high as 40% in addition underneath resonance with a positive power program impedance at that fast, and together with nonlinear hundreds and capacitor switching from the encompassing factories.

THD Recent harmonics just after harmonic filter at 33kv EAF
Fig.ten 33kv THD (Current) following Tuned HF
The resultant resonance triggers vibration sound overheat and occasional TRF HV winding failures. The recorded facts of seriously distorted 33kv grid source under this sort of harmonic resonance situations may be received from www.enconengineers.in. The harmonic filter was mounted within the 33kv PCC of your factory at its outdoor substation, that is also 33kv grid provide, as proven in Fig.8 (front check out) and Fig.9 (rear see).

D. Final results Attained.

Following the installation of 33kv harmonic filter with the grid incomer with the manufacturing facility's outside substation a couple of yr in the past, a repeat harmonic examine was completed.

The present waveform on the 33kv grid incomer PCC was controlled inside of 6% THDi, at 152A peak load present and I5 and I7 as significant existing harmonics as proven in Fig.10. The unbalance within the 3ph waveforms in present magnitudes is because of the unequal arcing among the three electrodes of your EAF.

The voltage waveform within the 33kv grid incomer PCC was managed very well in just IEEE 519 norm at two% THDv at 45.6kv-peak load voltage (RMS worth of rated line voltage is 33kv) and V7 and V23 as main voltage harmonics as proven in Fig.11.

THD Voltage harmonics just after harmonic filter for electrical arc furnace
Fig.eleven 33kv THD (Voltage) immediately after Tuned HF
Thereafter the manufacturing facility functionality was observed closely for more than a 12 months. All electric power excellent harmonic disturbances and products failure troubles all received resolved and The weird resonance challenge Along with the gigantic 22kA bus bar overheating and vibration did not happen thereafter indicating that the probability of a intense ability good quality harmonic resonance is drastically diminished. Nonetheless, taking a look at the THDv waveform as in Fig.eleven about the submit harmonic solution state of affairs, there stays some opportunity for a probable resonance and that is why it is said that resonance cannot be eradicated but can only be shifted away from a Doing the job frequency bandwidth.

The situation arose listed here were not resulting from a normal power high-quality harmonic situation. The current harmonic distortions (THDi) weren't large more than enough to lead to this kind of an unconventional harmonic difficulty and the voltage harmonic distortions (THDv) ended up effectively in just IEEE 519 limitations, as found in the course of the initial electric power top quality harmonic measurement. A portion of the grid provide zone ranging from the 50mva, 132/33 Transformer with the providing Ghatsila Substation was to the boundary strains of its ability process's steadiness.

IV. Summary

The enumerated circumstance analyze and its yearlong general performance verification report Evidently build all spherical improvement of major energy program parameters not merely Within the plant and also in the efficient grid offer zone.

Doing the power high quality engineering on the downstream of a plant with major NLL mirrors ideal grid situations. An engineering hard work that should enormously stop electrical pollutions from moving into the electrical energy method in the grid.

In-addition, it lowers carbon emission by improving productivity, removing limitations to Electrical power effectiveness, and selling productive usage of energy all together. That starts from downstream plant to neighboring customers, and up to the upstream power plant, the IPP electricity supplier and the grid organization.

The price saving when looked narrowly compared Together with the electricity bill by itself might sound moderate. But when compared holistically with substantially diminished investment Price tag, reduced carbon footprint, uninterrupted manufacturing, MTBF, inventory expense of factors and workforce drive coupled with ever growing cost of Power, the financial Gains would considerably outweigh the price of the solution.

EAF harmonics situation study authorV. BIOGRAPHIES

Kanai Banerjee graduated in Electrical Engineering from Bengal Engineering and Science College, Shibpur, India from the year 1983.

Labored at Bharat Hefty Electricals Limited from 'eighty three to 'ninety five and thereafter as a promoter at Encon Engineers continue to day.

His Distinctive fields of desire include electrical power high quality engineering, harmonic solutions and producing passive tuned harmonic filter and triplen harmonic filter of all dimensions LV and HV, troubleshooting failures, Vitality conservation, electrical consultancy and HVAC engineering for establishing truly environmentally friendly constructing and retrofitting huge centralized HVAC tasks.

He has been instrumental in increase the business's extraordinary growth and reputation to be a expertise-primarily based technology Alternative company on ability good quality, Power performance, course of action optimization and in Whole Energy Management fields.

An Vitality auditor Licensed from the bureau of Electrical power effectiveness under the ministry of electrical power government of India, a member and chartered Qualified engineer Along with the institute of engineers India, a member with the Indian society of heating, refrigerating and air-conditioning engineers, ISHRAE and also a member within the Canadian and American EMTP-ATP consumer group.

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