O-Engineers Jan 2018
Short Description
Magazine for Engineers by Engineers...
Description
O-Engineers 6th issue, Jan 2018 Learning and Guiding
DISTANCE RELAY INTERVIEW QUESTIONS
(Page-15)
CONENS
PAGE E
PAGE 1
LET'S TALK
FEEDBACK
PAGE 2 FIELD DRYING OF OIL FILLED TRANSFORMER
PAGE 8 RESTRICTED EARTH FAULT RELAY
PAGE 15 DISTANCE RELAY INTERVIEW QUESTIONS
PAGE 23
PAGE 28
BREAD WITHOUT BUTTER
PAGE 31 FINAL SEMESTER
PAGE 35 BOOK FOR THIS MONTH
E-QUOTES
PAGE 34 ENGINEER MAKING DIFFERENCE
CONENS
PAGE E
PAGE 1
LET'S TALK
FEEDBACK
PAGE 2 FIELD DRYING OF OIL FILLED TRANSFORMER
PAGE 8 RESTRICTED EARTH FAULT RELAY
PAGE 15 DISTANCE RELAY INTERVIEW QUESTIONS
PAGE 23
PAGE 28
BREAD WITHOUT BUTTER
PAGE 31 FINAL SEMESTER
PAGE 35 BOOK FOR THIS MONTH
E-QUOTES
PAGE 34 ENGINEER MAKING DIFFERENCE
Editorial Let's talk Te year 2017, what a year? we did a lot, we got a lot, we lost a lot, we moved ahead a lot, we read a lot, we araid a lot, we eel job insecurity a lot, we did everything a lot,but the but the journey still not not ends and and still a lot is ahead o us. Te world is changing in seconds, not in hours or days, daily new android apps are amazing us, Artificial sofwares are playing with our mind in hidden robes, the terminology o the Sof-knowledge worker is at the mirage o all time, everywhere there is the race o knowledge gaining, one laptop with good wifi connection can make you the brilliant online consultant, tutor, engineer, manager etc. old technologies are replaced by new technologies, Universities are upgrading their educational system and companies are upgrading their expectations rom degree holders. we Engineers need to be prepared or this up-gradation i we are on another side(which is still stuck up with old thoughts and technologies) then we Engineers will lose this race, final year students need to be more brilliant in simulation sofware i they want to be an integral part o uture Sof-Knowledge based Organizations.
E
Feedback
Add mechanical engineering topics also in coming editions. (Engr. Naja ali)
Improvement is there, but need more efforts in developing a trend in engineering (Engr. Sumaiyya Wajih)
I liked the article "I Quit", yes it is quite an issue nowadays, lot o consultants and individuals are making money rom Jobless and On-job proessionals, and in many countries, there is no such law to grab such raudulent companies, good work team O Engineer, keep it up (Engr. Mukesh Narayan) It is great to see Engr. Irn Akhter's Going good article about guideline or Chinese (Engr. Zain EPC in Dec edition, a good learning Noor) (Engr. Fatah Ali Pasha) 1
Field Drying of Oil Filled Transformers
Engr. Iran Akhter
2
Haven’t written anything
in a while. In this short article, I have chosen an important subject or clarity or my ellow engineers esp in Pakistan. Why this subject now? Well, part o the reason is that we bought a new oil treatment machine and the other part is our interaction with clients during the marketing o our service. Tere are ew things which are not normally clear to people working at the plants. I will address those issues here. Question: Should I do dehydration at an interval or on the need basis? Well, you have to consider your maintenance strategy
or your transormers. I your oil breakdown voltage and moisture contents are within limits, you may not need dehydration o your transormer or a while. Some people don't like doing it or the ear o losing DGA history. Tey are not wrong. You need a resh sample aferward to establish a baseline. Te presence o moisture in a transormer deteriorates transormer insulation by decreasing both the electrical and mechanical strength. In general, the mechanical lie o the insulation is reduced by hal or each doubling in water content. 3
Remember the main insulation and one that defines the lie o a transormer is its solid insulation: mostly paper and some wood. So you don't want to operate your transormer near limits o moisture content. Limits are defined in IEC 60422 or both moisture content and relative saturation (or the degree o wetness or oil and paper). Water saturation o insulating oil is also very useul or trending. Saturation is the ratio o the water content present in a mineral oil at a certain temperature to the solubility o water in mineral oil at the same temperature, expressed in percent. It can be calculated rom known values, obtained by Karl Fischer titration or by on-line moisture sensors. Te amount o moisture in the paper is an important Water saturation parameter to measure as it o insulating oil is affects the ollowing: also very useul or 1. Aging rate o winding insulation. trending 2. Bubbling emperature which limits the loading o the transormer. 3. Te dielectric strength o the barriers at the bottom o the winding. Question: Afer ew hours/days o dehydrat4
-ion moisture content is again high and BDV has gone low? Tis happens a lot in the field. Te major issue is in understanding where is moisture is present. Most engineers think that moisture is in oil only. Tis concept is not only wrong but dangerous or your transormer. Moisture in transormer gets distributed in oil and solid insulation i.e., paper and wood. Under lower operating temperatures, it could be that 95% or more o the moisture is in the paper/wood. Water saturation solubility in oil increases with temperature. So the solution is to look at a moisture content in addition to BDV and calculate relative saturation and bring it below 5% as mentioned in the above table. It requires more time and good vacuum with heating o oil in the machine. A newer machine with no leaks and presence o a moisture sensor helps. As it takes more time, hence it is expensive as compared to usual 2 or 3 passes based on improvement in BDV alone. Te efficiency o dehydration regardless o method depends on a number o actors, including the oil temperature and the degree o vacuum pulled. Te challenge is to use a system that avoids use o excessive temperature, which promotes degradation o the cellulose, yet brings about the removal o the maximum
5
a degree o moisture rom the insulation. For efficient dry out, a vacuum in excess o the equilibrium values is required. Te drying operation occurs when the oilcellulose equilibrium condition is disturbed avorably. Other actors that determine the efficiency o water removal include, an initial water content in the oil and in the cellulose, oil film thickness, time o exposure to vacuum and accelerators, such as agitation. In the case o just wet oil, or wet oil and wet windings, a couple o recirculations o the oil through a vacuum dehydration system will dry the oil. Te dry oil will be contaminated by the wet windings as they seek equilibrium condition, repeating this cycle many times can correct the situation. Question: Can an old, leaking and contaminated machine poses a risk to my ransormer? It surely poses a big risk. You can aerate your transormer which will be cause o oxidation and hence reduce the lie o your transormer. A poorly maintained machine might introduce contaminants carried rom other jobs like PCB or as worse as traces o Cu2S. Question: I there is no leakage rom my transormer, where does the water come rom? 6
Well, water in the transormer can come rom outside which remains the biggest source. It enters during transormer manuacturing and transportation. In ree breathing transormer, a small amount o water enters into the transormer during breathing. But once you take a transormer in service, water is created as transormer ages as a by-product. Presence o high amount o water (moisture) accelerates urther production. It is a result o Pyrolysis, Hydrolysis, and Oxidation going on the oil/paper o transormer. Question: Will the dehydration process improve out o limit Oil power actor, IF and Acid Number? End o lie (EOL) or transormer oil is based on the limits o Oil Power Factor, Interacial ension and Acid Number. Once these values crossed the final limits, no amount o dehydration can help restore oil insulation properties. One may consider regenerating oil or replacing it altogether. Question: I have a leakage where oil is seeping out o transormer body, outside moisture cannot go in? Tis is a wrong concept. I you have leaked rom where oil comes out, moisture has a path to enter the transormer. So attend a leak as soon as possible. 7
Restricted Earth Fault Relay
Engr. Qazi Arsalan Hamid
8
Objective: o understand the working principle o REF Relay Power Equipment to be Protected: Power ransormer Relay Used: 7PG23 Discussion: REF is employed basically on transormer with vector group delta star, it is usually like Differential Protection o ransormer
In this we employed 1 Current transormer at star point o star-secondary point o ransormer, three current transormers with ring type connection is employed 9
as per figure below.
In Ring Connection, the Principle o Current circulation is applied Ia+Ib+Ic=0 and in star point o ransormer will be zero. Te concept o high impedance and low impedance: in high impedance REF relay, the star point o the transormer must be equipped with internal or external resistor, the internal resistor must be located in high impedance relay and external resistor will be
10
provided outside relay. in high impedance REF relay the ratio o Phase and neutral Cs must be same, but in low impedance REF relay it is not necessary, knee point voltage o high impedance REF relay Cs must be same, stabilization the voltage o high impedance relay is another deciding actor in relay operation when a setting voltage is equal to stabilization voltage relay not operate, but when stabilization voltage will higher than setting voltage the relay operates. in high impedance REF relay, we must provide Metal oxide varistor(MOV) or protection rom high voltages surges, and i C ratios are different then we employees the interposing Cs(auxiliary Cs) to prevent spill current, in low impedance no such thing as interposing Cs required. stabilization voltage=(Maximum ault current relay*Ct secondary resistance * lead resistance)/C urn ratio saety actor recommended is 2, Vk=2*Vsetting Minimum primary operating current o Relay=C turn ratio*(Relay operating current*no: o Cs*magnetization current o Cs*Varistor Current at Setting voltage) 11
when the ault occurs outside the restricted area, the zero sequence o Red phase to earth still flows through Red and neutral Ct so new Relay not operates.
12
in case o the internal ault, the equilibrium disturbed, and abnormal current o red to earth flows through C-neutral also, this result in relay operation.
13
Example Working:
8 MVA transormer with Z=0.0835p.u,ap=+/10%,CR=800/1 Location: Confidential Solution: Fault MVA=8MVA/0.0835=95.8084 Fault Current Primary=(Fault MVA/ (1.732*6.6KV))*1000=8281.06A in secondary, CR=800/1 and Fault Secondary Current=Fault maximum/C Ratio=8281.06/800=10.4763A Vs=Fault Secondary current*(Rct+RL) since Rl we consider 1 ohm with two leads, Rct is usually 4ohms Vs=10.4763*(4+2)=65.8579V Relay will be set 0.1In or maximum sensitivity Stabilizing Resistor=Rs =(Vs/0.1)-(AC burden/0.1 sqr) AC burden setting in 7PG23 relay is given as Vs*20mA=65.8579*20mA=1.317158VA Rs=(65.8579/0.1)-(1.317158/0.01)=526.8632ohms Cs must have Knee point voltage = 2*Vs=131.7158( i.e. saety actor=2) Operating time o Relay= 45ms at 3*Vs
14
Distance Relay interview Questions?
Engr. Qazi Arsalan Hamid
15
1. Te high-voltage power transmission line protection. ypically which type o relay protection used?
Answer 1: Voltage Relay Answer 2: Overcurrent Relay Answer 3: Differential Relay Answer 4: Distance Relay Answer is 4; Distance relay is continuously measuri-ng. the impedance o line by taking current and Distance relay is voltage line in the account. continuously measuring As Warrington stated in the impedance o line his book “Protection relays Teir Teory and Practical” i we use the differential relay or Voltage relay on transmission line it is principally uneconomical. Distance relay works on very simple law, that at any point in line when ault occurs the Voltage drop at ault will be V=IZ,it Follows that Voltage to current ratio will be Impedance, When ault occurs inside the designated relay ransmission line the V/IZ and Designated relay will not Operate. 2. Input signals are ed to the distance relay (Distance Relay) rom any o the ollowing devices.
Answer 1: C Answer 2: V Answer 3: Instrument Answer 4: C and V. Answer is 4; as we stated in Distance relay description given above, Distance relay will measure the Voltage to current ratio, so We must give Voltage via V and Current via C in Distance Relays. 3. Analysis o the perormance o the distance relay is generally used to analyze the diagram (Diagram) ormat.
Answer 1: R-X Diagram. Answer 2: V-I Diagram. Answer 3: P.F. Diagram Answer 4: I- Diagram 17
Answer is 1; Distance relay is dealing with Impedance, impedance is the vector sum o Resistance and Reactance o Line. R-X Diagram is the good tool or setting Fault Zone Limits, in any distance relay, three actors are important Current, Voltage and the Phase angle between Current and Voltage. From Voltage and current we can race Impedance, angle between voltage and angle is, or plotting it on R-X diagram, remember R= Z cos(angle) , X=Z sin(angle) . 4. Setting the Ground Fault Distance Relay or protection when used in Single Line to Ground Fault (SLG), we have to take into account include any parameters.
Answer 1: Power Factor Answer 2: Compensation Factor Answer 3: Full Load Current. Answer 4: Frequency Factor Answer is 2; For Ground, Fault Distance relays, the aulty phase Voltage and compensated aulted current must be used i.e
18
here m is the constant , I0 is Zero sequence Current
5. Set a distance relay Step Distance Protection Relay Zone 1, we will have to adjust working time as any.
Answer one: a 0.3-second delay. Answer two: a 0.5-second delay. Answer 3: a 1.0-second delay. Answer 4: Adjust to work immediately. (Instantaneous) Answer is 4.
19
6. Setting a distance relay Step, Distance Protection Relay Zone 1 should be set to prevent transmission distance estimation.
Answer 1: 40-50% o the length o the transmission line that needs protection. Answer 2: 50-60% o the length o the transmission line that needs protection. Answer 3: 80-90% o the length o the transmission line that needs protection. Answer 4: 120% o the length o the transmission line that needs protection. Answer is 3; Alstom book “Network Protection and automation guide “stated that 85% o ransmission line must be set to protect in Zone 1, we kept our distance relay under reach in 1st Zone to kept Saety margin, C Errors must be kept in View. 7. Te relay suitable or protection o long power transmission lines is
Answer 1: Te Impedance Relay. 20
Answer 2: Lenticular Relay. Answer 3: Te Quadrilateral Relay Answer 4: Te Mho Relay. Answer is 4; the long transmission lines are reactive in nature , that is why we can use mho relay in ransmission relay , but i arcing ault occurs at transmission line then we can implement Quadrilateral Relay on transmission line 8. Review Below Mention Distance relay (Distance Relays) o any type. Which type's property eatures a direction on its own.
Answer 1: Mho Relay Answer 2: Impedance Relay Answer 3: Reactance Relay Answer 4: 1 and 2 are correct. Answer is 4; MHO relay is Directional in nature 9. Reactance relay (Reactance Relay) is the distance relay to work on.
Answer 1: Relay or the impedance box below the set 21
value. Answer 2: Relay or the impedance room above a preset value. Answer 3: Relay sees an instance under the tree configuration. Answer 4: Relay sees an instance higher than the pre-set value. Answer is 2:Relay or the impedance room above a preset value.
10. Te high-voltage power lines with impedance per phase is 1 + j10 ohm Max / Phase Determine the size and angle o impedance respectively are.
Answer 1: 10.00 ohm, 90-degree phase angle/phase. Answer 2: 10.05 ohms, 84.29 ° phase angle/phase. Answer 3: 1.00 ohm, 10-degree phase angle/phase. Answer 4: 10.00 ohm, 10-degree phase angle/phase. Answer is 2; Z per phase= Sqrt((Sqr o 1)+(Sqr o 10))=10.05 ohm, and Phase angle per phase is atan(10/1)= 84.29 ° phase angle
22
Momtaz Alsolh Writer, Philanthropist and Consultant Saudi Arabian 23
O ver the past year, I have been sharing with everyone my memoir called “Bread without Butter.” My memoir is mainly about my experiences in the construction industry in the GCC region and this afer having worked or the Private sector. I have done my best to highlight crucial matters that are affecting employees and laborers and I have written about what should be the rights o GCC national employees, expatriate employees & oreign laborers and I have done my best to dissect sections o the Labor Law in the GCC region as well so that there is more awareness. I have also offered corrective actions on all the matters that required improvement or corrections and this to any employer or to any party that cared to read what I wrote. I have also shared my memoir with several influential individuals and I are hoping that positive changes shall see the light very soon. Other than the above, I have also shared several articles to promote peace in the Arab world. I am praying every single day or all the wars all around the world to end on urgent basis. I am one who believes that peace on earth is achievable shall we all believe that we are one big amily. o date, I have only shared 50 % o what I need to share. Tere are still several crucial matters that I need to
24
Initially, I thought that it would be best to remain silent. Ten I thought again and again. Ten I realized that i I kept silent the GCC region would remain in the dark and that it was wrong not to voice out. In the coming articles, I shall be dissecting construction contracts in a way that was never done beore. I shall be revealing the darkest secrets o the construction industry.I shall be dissecting the complete construction contract awarding process, the construction contract preparation, the Bill o Quantities,the Contract Specifications and much more. I shall be writing mainly about the misuse and I shall be revealing the abuse o the FIDIC orm o construction darkest secrets o the contracts. construction industry FIDIC stands or the International Federati-on o Consulting Engineers. Te biggest mistake in the GCC construction industry was to depend on a oreign orm o contract that only a ew knew the secrets. Te FIDIC orm o contracts have done the GCC region very wrong due to the individuals that knew the secrets and that took advantage o those that didn’t know the 25
the secrets. What a great world that we live in! Te strict majority o those that knew the secrets o the FIDIC orm o contracts and that have abused and misused such contracts are not GCC nationals. Our dependence on expatriates to handle construction contracts and to finalize mega deals was our biggest mistake which has led to several raudulent practices and several malpractices as well. Te reality is that there is more money that can be saved out o managing correctly the construction contract than the actual savings that can be done through the procurement process or through the savings on proper project management. Once again, I shall be discussing the absence o honest and appropriate internal and external auditing in the construction industry. I believe that auditors themselves need to be audited and they also need to be certified by local GCC governments as many are not qualified enough to conduct their jobs and this in an ethical, proessional or correct manner. Mainly, auditors lack the investigative sense. Auditing is a skill that is innate and it is an art that not many possess. Ten comes the quality management system certiying bodies who certiy construction companies blindly. 26
I shall be explaining everything in detail. I shall also be discussing the importance o having a localized orm o the construction contract that I have called “Te Unified GCC Form o Construction Contract.” “Te Unified GCC Form o Construction Contract” shall be what the GCC region actually requires to be protected against those that have outsmarted the FIDIC orm o contracts and that have done the FIDIC orm o contracts very wrong. I personally believe that FIDIC is not suitable any longer or the GCC region and I shall, later on, explain why. I am one who shall always believe in honesty and justice. I am also one who shall always believe in innovation and continuous improvement and or these reasons, the time has come to make drastic changes. I have always believed that what is wrong will never be right. Tat is all that I am willing to share or now. Important hope: I am still praying to Almighty Allah (God) to see the light o the air and just 2016 Labor Law in all GCC countries. Important reminder: Tere is a saying that goes like this: “Forgiven is the one that has warned!” 27
E-QUOES "Quotes Wall For Engineers" Carpediem Research Desk
28
“But remember this, Japanese boy... airplanes are not tools or war. Tey are not or making money. Airplanes are beautiul dreams. Engineers turn dreams into reality.” Hayao Miyazaki
“Engineers like to solve problems. I there are no problems handily available, they will create their own problems.” Scott Adams
29
“One man’s “magic” is another man’s engineering. “Supernatural” is a null word.” Robert A. Heinlein
30
Final Semester
Engr. Qazi Arsalan Hamid
31
Last month I was in Pakistan, I arranged sittings with
different universities students to dig out that what are they thinking about Post degree scenario or uture, Hammed rom UI told me “I am exciting about the ascination o my education curriculum, but most o the proessor style o delivering lectures are boring and they always paint any o our requirement in terms o exams marks”. anveer rom Mehran university told, “ most o the lecturers are threatened us in the classroom while we asked questions that i you want to knew it read it by yoursel, we are bound to deliver as per curriculum”. Ms. Anum rom Mehran University inormed that afer degree program she wants to do masters and Ph.D., but the issue is that most o the scholarships are reserved or University lecturers, these lecturers take lion share rom the allotted scholarships and other deserving candidates are out o the picture due to other commitments. Hassan rom Nust told “We are araid afer aizaz’s suicide, 1st we have thoughts that we will be engineers we will be fixed anywhere, but due to aizaz’s death now we have parallel thoughts, in our universities there is no career consultation group or advisor, senior engineers are busy in their work they are even not ready to come to our university or ready to allow us in their offices or 32
career advice”, usee rom Ned university told “ 1st I am planning to launch my final year project in the market with a bank loan, but on peers pressure I am dropping this idea as no one is ready to buy my idea, everyone in my group and my internal advisor is advising me that it is not possible” , Raheel rom Quaid e Awam told “ I am ed up with LinkedIn and Facebook job groups, most o the posted jobs are raud and most o the overseas recruiters asked money or visa processing and job allotment”. I talked with One university Proessor, I promised to not disclose his name in this article, he inormed” look we are tasked to deliver lecture as per the approved curriculum, we also try to give some extra inormation but tight schedule and limited resources are not permitting us to go beyond our aligned virtual boundaries” One oversea recruiter inormed me “look Arsalan, most o these resh graduates are willing to pay money and they offered us first, and rom us some recruiters accepted their offers, but most o us denied these offers, because we have to deliver best human resource to our client else they will not come to us again, or us our client is main source o business not applicant” 33
Engineer Making difference Edvard Csanyi, he is ounder and electrical engineer at EEP. Love in electrical engineering moved and motivated him to create all-in-one handy place like EEP and to share all his knowledge and experience, as well as to attract other electrical engineers to do the same. He is highly specialized or design o low voltage high power busbar trunking (
View more...
Comments
