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Messages - mahzuba

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দেশের বাজারে এসেছে আসুস ব্র্যান্ডের আরটি-এন১২ডি১ মডেলের ওয়্যারলেস রাউটার। একই সঙ্গে ডাটা ট্রান্সমিশন এবং ডাটা রিসিভের জন্য এতে রয়েছে মাল্টিপল ইনপুট এবং মাল্টিপল আউটপুট (মিমো) প্রযুক্তির ২টি শক্তিশালী অ্যান্টেনা।

ফলে বিঘ্নহীন ভাবে এইচডি ভিডিও স্ট্রিমিং, ভিওআইপি কল করা এবং অনলাইন গেম খেলা যায়। তার বা তারহীন নেটওয়ার্ক গঠনে এতে রয়েছে ১টি ওয়্যান পোর্ট, ৪টি ল্যান পোর্ট। এই ডিভাইসটিকে রিপিটার অথবা অ্যাকসেস পয়েন্ট হিসেবেও ব্যবহার করা যায়।

রাউটারটির মাধ্যমে ডায়নামিক ব্যান্ডউইথ অ্যালোকেশন এবং অ্যাকসেস কন্ট্রোল ব্যবহার করে ভার্চুয়াল ওয়্যারলেস রাউটার তৈরি করে ৪টি আলাদা নেটওয়ার্ক গঠন করা যায়। এছাড়া এতে রয়েছে ফায়ারওয়াল, লগিং, ফিল্টারিং, এনক্রিপশন, অর্থেন্টিকেশন প্রভৃতি নেটওয়ার্ক সিকিউরিটি ব্যবস্থা।

৩ হাজার ৫০০ টাকা মূল্যের এই অত্যাধুনিক রাউটারটি দেশের বাজারে এনেছে শীর্ষ প্রযুক্তি পণ্য ও সেবাদাতা প্রতিষ্ঠান গ্লোবাল ব্র্যান্ড (প্রা.) লিমিটেড।

পৃথিবীর উত্তর মেরু চৌম্বকত্ব হারিয়ে দক্ষিণ মেরুতে পরিণত হতে যাচ্ছে বলে জানিয়েছে, ইউরোপিয়ান স্পেস এজেন্সিং বিজ্ঞানীরা।

এরকম ঘটনা পৃথিবীর জীবনযাত্রায় এর আগেও ঘটেছে। বিজ্ঞানীদের মতে,  প্রায় ৭ লক্ষ ৮৬ হাজার বছর আগে উত্তর চুম্বক মেরু উল্টে গিয়ে আন্টার্টিকা চলে গিয়েছিল। মেরুদ্বয়ের এই চৌম্বকত্বের ‘পাল্টি’কে বলা হয়েছিল মাতুয়ামা-ব্রুণে ম্যাগনেটিক রিভার্সাল।

পৃথিবীর চুম্বক মেরু পরিবর্তনের কারণ হিসেবে বিজ্ঞানীরা মনে করছেন, যখনই কোনো মেরু চৌম্বক শক্তি হারায় পৃথিবীর মেরুর চৌম্বকীয় পরিবর্তন হবে। পরিবর্তন হওয়ার পর পৃথিবীর পুণরায় চুম্বক সমতা ফিরে আসে।

পৃথিবীর চুম্বকক্ষেত্র তৈরি হয় অন্তস্তলে গলিত লৌহের গতিবিধির ওপর। যদিও বিজ্ঞানীরা স্পষ্ট নন কখন কীভাবে পৃথিবীর চুম্বক পরিবর্তন হয়। তবে বিজ্ঞানীরা একমত, নিকট ভবিষ্যতের যে কোনো দিন ঘটতে পারে পৃথিবীর ভূচৌম্বকীয় পরিবর্তন।

Primacy of the research question

A good research paper addresses a specific research question. The research question—or study objective or main research hypothesis—is the central organizing principle of the paper. Whatever relates to the research question belongs in the paper; the rest doesn’t. This is perhaps obvious when the paper reports on a well planned research project. However, in applied domains such as quality improvement, some papers are written based on projects that were undertaken for operational reasons, and not with the primary aim of producing new knowledge. In such cases, authors should define the main research question a posteriori and design the paper around it.

Generally, only one main research question should be addressed in a paper (secondary but related questions are allowed). If a project allows you to explore several distinct research questions, write several papers. For instance, if you measured the impact of obtaining written consent on patient satisfaction at a specialized clinic using a newly developed questionnaire, you may want to write one paper on the questionnaire development and validation, and another on the impact of the intervention. The idea is not to split results into ‘least publishable units’, a practice that is rightly decried, but rather into ‘optimally publishable units’.

What is a good research question? The key attributes are: (i) specificity; (ii) originality or novelty; and (iii) general relevance to a broad scientific community. The research question should be precise and not merely identify a general area of inquiry. It can often (but not always) be expressed in terms of a possible association between X and Y in a population Z, for example ‘we examined whether providing patients about to be discharged from the hospital with written information about their medications would improve their compliance with the treatment 1 month later’. A study does not necessarily have to break completely new ground, but it should extend previous knowledge in a useful way, or alternatively refute existing knowledge. Finally, the question should be of interest to others who work in the same scientific area. The latter requirement is more challenging for those who work in applied science than for basic scientists. While it may safely be assumed that the human genome is the same worldwide, whether the results of a local quality improvement project have wider relevance requires careful consideration and argument.
Structure of the paper

Once the research question is clearly defined, writing the paper becomes considerably easier. The paper will ask the question, then answer it. The key to successful scientific writing is getting the structure of the paper right. The basic structure of a typical research paper is the sequence of Introduction, Methods, Results, and Discussion (sometimes abbreviated as IMRAD). Each section addresses a different objective. The authors state: (i) the problem they intend to address—in other terms, the research question—in the Introduction; (ii) what they did to answer the question in the Methods section; (iii) what they observed in the Results section; and (iv) what they think the results mean in the Discussion.

In turn, each basic section addresses several topics, and may be divided into subsections (Table 1). In the Introduction, the authors should explain the rationale and background to the study. What is the research question, and why is it important to ask it? While it is neither necessary nor desirable to provide a full-blown review of the literature as a prelude to the study, it is helpful to situate the study within some larger field of enquiry. The research question should always be spelled out, and not merely left for the reader to guess.

    Enlarge table

Table 1

Typical structure of a research paper
    State why the problem you address is important
    State what is lacking in the current knowledge
    State the objectives of your study or the research question
    Describe the context and setting of the study
    Specify the study design
    Describe the ‘population’ (patients, doctors, hospitals, etc.)
    Describe the sampling strategy
    Describe the intervention (if applicable)
    Identify the main study variables
    Describe data collection instruments and procedures
    Outline analysis methods
    Report on data collection and recruitment (response rates, etc.)
    Describe participants (demographic, clinical condition, etc.)
    Present key findings with respect to the central research question
    Present secondary findings (secondary outcomes, subgroup analyses, etc.)
    State the main findings of the study
    Discuss the main results with reference to previous research
    Discuss policy and practice implications of the results
    Analyse the strengths and limitations of the study
    Offer perspectives for future work

The Methods section should provide the readers with sufficient detail about the study methods to be able to reproduce the study if so desired. Thus, this section should be specific, concrete, technical, and fairly detailed. The study setting, the sampling strategy used, instruments, data collection methods, and analysis strategies should be described. In the case of qualitative research studies, it is also useful to tell the reader which research tradition the study utilizes and to link the choice of methodological strategies with the research goals [3].

The Results section is typically fairly straightforward and factual. All results that relate to the research question should be given in detail, including simple counts and percentages. Resist the temptation to demonstrate analytic ability and the richness of the dataset by providing numerous tables of non-essential results.

The Discussion section allows the most freedom. This is why the Discussion is the most difficult to write, and is often the weakest part of a paper. Structured Discussion sections have been proposed by some journal editors [4]. While strict adherence to such rules may not be necessary, following a plan such as that proposed in Table 1 may help the novice writer stay on track.

References should be used wisely. Key assertions should be referenced, as well as the methods and instruments used. However, unless the paper is a comprehensive review of a topic, there is no need to be exhaustive. Also, references to unpublished work, to documents in the grey literature (technical reports), or to any source that the reader will have difficulty finding or understanding should be avoided.
The basics

Having the structure of the paper in place is a good start. However, there are many details that have to be attended to while writing. An obvious recommendation is to read, and follow, the instructions to authors published by the journal (typically found on the journal’s website). Another concerns non-native writers of English: do have a native speaker edit the manuscript. A paper usually goes through several drafts before it is submitted. When revising a paper, it is useful to keep an eye out for the most common mistakes (Table 2). If you avoid all those, your paper should be in good shape.

    Enlarge table

Table 2

Common mistakes seen in manuscripts submitted to this journal
The research question is not specified
The stated aim of the paper is tautological (e.g. ‘The aim of this paper is to describe what we did’) or vague (e.g. ‘We explored issues related to X’)
The structure of the paper is chaotic (e.g. methods are described in the Results section)
The manuscripts does not follow the journal’s instructions for authors
The paper much exceeds the maximum number of words allowed
The Introduction is an extensive review of the literature
Methods, interventions and instruments are not described in sufficient detail
Results are reported selectively (e.g. percentages without frequencies, P-values without measures of effect)
The same results appear both in a table and in the text
Detailed tables are provided for results that do not relate to the main research question
In the Introduction and Discussion, key arguments are not backed up by appropriate references
References are out of date or cannot be accessed by most readers
The Discussion does not provide an answer to the research question
The Discussion overstates the implications of the results and does not acknowledge the limitations of the study
The paper is written in poor English

    International Journal for Quality in Health Care vol. 16 no. 3 © International Society for Quality in Health Care and Oxford University Press 2004; all rights reserved


    Huth EJ. How to Write and Publish Papers in the Medical Sciences, 2nd edition. Baltimore, MD: Williams & Wilkins, 1990.
    Browner WS. Publishing and Presenting Clinical Research. Baltimore, MD: Lippincott, Williams & Wilkins, 1999.
    Devers KJ, Frankel RM. Getting qualitative research published. Educ Health 2001; 14: 109–117.
    Docherty M, Smith R. The case for structuring the discussion of scientific papers. Br Med J 1999; 318: 1224–1225.
    FREE Full Text

Teaching & Research Forum / What’s a “research article,” anyway?
« on: November 03, 2014, 10:17:27 AM »
When scientists and other scholars want to make the results of their work public, they usually begin by publishing them in a scholarly journal with a title like New England Journal of Medicine, or Journal of Cell Biology.
What is and isn’t in a research article?

Research articles will usually contain:

    a summary or “abstract”
    a description of the research
    the results they got
    the significance of the results.

Research articles are not good places to find:

    basic summaries
    general introductions to a topic

They are the best way to access:

    The most recent, “cutting edge” research
    Authoritative information about older research

 রাসায়নিক এবং বায়োলোজিক্যাল (জীববিজ্ঞান) অস্ত্র নিষ্ক্রিয় করতে পারে এমন মাইক্রো-রকেট’র উন্নয়ন করেছেন বিজ্ঞানীদের একটি দল। খবর বিবিসির।
সমুদ্রপানির ক্ষমতায় অতি ক্ষুদ্র বস্তু মাপার যন্ত্র-রকেট ব্যাকটেরিয়া এবং অরগানফসফরাস নার্ভ (Sarin) গ্যাস’র মত অধঃপতিত প্রতিনিধিদের পরিমাপ করতে সক্ষম।
ক্ষদ্রাকার এসব রকেট পরিশেষে অস্তিত্ব হারানোর আগে আলো, বাতাস থেকে মূল উপাদানগুলো পৃথক করতে দুষিত নমুনায় সাতার কাটতে পারে।
এসিএস ন্যানোতে প্রকাশিত একটি নিবন্ধে দলটি বলেছে, প্রযুক্তিটি পরিবেশের বিষাক্ত গ্যাস ও তেজষ্ক্রিয়তা-সংক্রামিত বস্তু থেকে দুষণ নিষ্ক্রিয় করতে পারে।
 রকেটটি উন্নয়নের সঙ্গে জড়িত ক্যালিফোর্নিয়া বিশ্ববিদ্যালয়ের অধ্যাপক জোসেফ ওয়াং ব্যাখ্যায় বলেন, ‘বাহ্যিক কোন অনুপ্রেরণা দরকার নাই, শুধু সমুদ্রপানিকে পরিচয় করিয়ে দাও। পরে বুদবুদ তৈরি কর এবং চতুর্দিকে ঘুরাও। আগে মানুষের বাহ্যিক জ্বালানি লাগতো কিন্তু এখানে আমরা জ্বালানি হিসেবে সমুদ্রপানি ব্যবহার করছি।’
তিনি আরো বলেন, বায়োলোজিক্যাল অস্ত্র এবং অরগানফসফরাসের মতো নার্ভ প্রতিনিধি উভয়ই দুষণকেই রকেটটি অধঃপাতিত করতে পারে। যেগুলো সচরাচর মধ্যপ্রাচ্যে অস্ত্র হিসেবে ব্যবহৃত হয়েছে।
নিম্ন বিকারক ব্যবহার করে অল্প খরচে আমাদের রকেট এসবের বিরুদ্ধে দ্রুত প্রতিরক্ষা দিতে পারবে।

Teaching & Research Forum / Re: Another publication
« on: November 02, 2014, 12:50:56 PM »
Thank you.

EEE / Arriving at the scene of a power substation fire. What to do?
« on: November 02, 2014, 12:40:13 PM »
To contact utility personel

Power substations contain transformers, large quantities of oil, energized electrical equipment and, in some cases, cylinders of compressed gas. Some of the oil may contain polychlorinated biphenyls (PCBs).

On arriving at a substation fire, normally you should first call for firefighters and they should hook up and stand ready to protect adjacent properties. Utility personnel will tell firefighters when the substation has been made electrically safe. Firefighters can then proceed to put out the fire with conventional firefighting equipment.
Most substations are unattended, although an automatic signal system should summon a utility representative when an emergency develops. If a utility representative is not present when the firefighters arrive, the utility must be contacted to make sure one has been dispatched.

Most utility personnel are familiar with the substations they service. They are trained in the use of the specialized station firefighting apparatus and can identify the areas that are electrically safe.

Equipment in substation susceptible to fire:

Let’s go through the most common electrical equipment susceptible to the fire and see what happens:

    Explosion vents
    Porcelain bushings
    Overhead structures
    Control cables
    Cable trenches
    Circuit breakers
    Substation Ground Grids

1. Transformers
Flames shoot high out of a Georgia Power substation transformer

Flames shoot high out of a Georgia Power substation transformer

There are several hazards to be aware of when fighting transformer fires. As you already know, transformers are devices used to step-up or step-down voltages. They usually contain large volumes of insulating oil which, of course, is combustible and has a flash point of 145°C. Some of this oil may contain PCBs.

    A transformer consists of an iron core on which are placed two or three coils of conductors. By varying the number of turns on the coils, the voltage can be changed. The turns on the coils need to be insulated from each other to withstand the voltages. This insulation may be combustible.

For both cooling and insulating purposes, transformers are placed in large metal tanks. Further refinements can include pumps, fans, radiators or a large tank called a conservator, at the top of the main transformer tank which also contains oil.

Usually it is possible to extinguish transformer fires before all the oil has been consumed, thereby saving adjacent equipment from damage.

2. Conservators
Oil transformer conservator

Oil transformer conservator (photo credit: Tom Law via Flickr)

These are simply large tanks located at the top of transformers to allow for expansion and contraction of oil when the transformer is carrying electricity. There will be no large build up of pressure, but if one of these tanks were ruptured, it could release a large supply of fuel.

3. Explosion Vents

These are large vertical pipes with rupturable discs fitted to the transformer tops which are intended to vent pressure in the event of an internal transformer fault. They are unlikely to be a hazard to the people fighting a fire.

4. Porcelain Bushings
An oil-impregnated paper (OIP) bushing failure on the 400-kV, 100-MVAR reactor caused this reactor fire

An oil-impregnated paper (OIP) bushing failure on the 400-kV, 100-MVAR reactor caused this reactor fire (photo credit:

The function of these bushings is to let the high-voltage transformer connection pass through the grounded metal tank without energizing it. Typically they contain the same insulating material found in transformers – paper and oil.

    When subjected to high temperatures, the porcelain material can explode. This could result in flying projectiles and more oil as fuel for the fire. Be alert!

5. Overhead Structures
Overhead structure fire

Overhead structure fire (photo credit: Puget Sound Energy via Flickr)

Metal structures are often built over the top of electrical equipment to support insulators and high-voltage conductors. These structures will sag and eventually collapse when subjected to high temperatures.
Apart from the obvious hazards, such collapses could also result in breaking the transformer bushings with the consequences described above.

6. Control Cables

Control cables attached to large power transformers carry low voltage electricity for controlling cooling fans, pumps and motors. They usually become isolated if faulted.

7. Cable Trenches

Cable trenches carry the control cables mentioned above. In the event of a substation fire, cable trenches can carry transformer oil that may have leaked from a burning transformer or a broken porcelain bushing. Thus, a fire can be carried to adjacent equipment fairly readily.

8. Circuit Breakers
HV SF6 circuit breakers and current transformers

HV SF6 circuit breakers and current transformers (photo credit:

These are large switches. Some types of circuit breakers are equipped with porcelain bushings and combustible oil whose hazards are described above.

9. Capacitors
HV capacitor banks

HV capacitor banks (photo credit:

Capacitors are located in some, but not all substations. A capacitor bank is comprised of a number of small units measuring approximately 25 cm x 45 cm x 60 cm (10 inches x 18 inches x 24 inches).

There are three main hazards that firefighters should be aware of:

    The individual capacitors are sealed units which could explode when heated.
    Some of the capacitors contain polychlorinated biphenyls (PCBs) which can be hazardous to your health and the environment. In the event of a spill, extreme caution should be exercised. Provincial environmental guidelines must be followed.
    Capacitors can store lethal amounts of electricity even with the power off. In the event of a fire, utility personnel would, as soon as practicable, make them safe to handle.

Firefighters in such a situation must take every precaution necessary to protect themselves and all members of the public present. Again, all provincial environmental guidelines must be adhered to.

10. Substation Ground Grids

An extensive grounding grid system is located under the gravel in all utility substations. Its function is to protect personnel from high-voltage levels during fault conditions on the transmission lines outside the substations.
For example, should lightning strike one of the utility’s lines, it could cause an insulator flashover at the station which would raise the ground voltage several thousand volts. Under normal circumstances, personnel would not be exposed to any danger because the grounding grid would distribute the voltage over a wide area.

Metal ladders must not be placed against a substation fence or otherwise used in fighting substation fires. Metal tap rules, extension cords and other metal objects can also create a hazard and are not permitted in utility substations.

Faculty Forum / Re: বোকা বানাবে পাখি...!
« on: November 02, 2014, 12:34:53 PM »
This is an interesting post.

Faculty Forum / Re: top oil reserving countries
« on: November 02, 2014, 12:33:06 PM »
Informative post.

EEE / The most common accessories you can find on oil filled transformer
« on: November 02, 2014, 12:25:30 PM »
1. Liquid level gauge
Liquid Level Gauge

A liquid level indicator is provided to aid in the systematic inspection of the transformer under load. It consists of a float-arm inside the tank, an indicating pointer and a magnetic coupling between the two across a liquid-tight separation.

The gauge may be furnished with SPDT (Single Pole Double Throw) alarm contacts to give a remote annunciation of low liquid level. For contact wiring and terminal points, see the accessory connection diagram furnished with the transformer.

2. Liquid Temperature gauge
Liquid Temperature gauge

The temperature gauge is furnished to indicate the top liquid temperature in the tank in degrees Centigrade. The temperature-sensitive element is mounted in a leak-proof well, permitting removal of the thermometer without lowering the oil level.

The device is furnished with an additional red pointer to show the highest temperature attained since the last reset.To reset the maximum indicator, turn the knob in the center of the dial. The thermometer can be furnished with two SPDT contacts for a high temperature alarm, for energizing a fan circuit or for a low temperature alarm.

For wiring and contact settings, refer to the schematic furnished with the delivered transformer .

3. Pressure-Vacuum gauge
Pressure-Vacuum gauge

The pressure-vacuum gauge indicates whether the gas space in the tank is under positive or negative pressure. The pressure will vary depending on the transformer temperature. If the transformer is de-energized or operating under light load in low ambients, the pressure may be negative .

    Note: If the indicator reads zero and does not change under any load condition, the transformer should be checked for a possible leak in the seal. If sufficient air has been absorbed by the liquid during shipment or storage, the transformer may operate indefinitely in the vacuum range, depending upon the loading conditions .

This, in itself, is not cause for concern, provided the pressure vacuum gauge does not remain on zero for any length of time an indication of a leak. The unit may be equipped with pressure vacuum switches with two SPDT contacts for remote alarm on positive and negative pressure.

For wiring and contact ratings, refer to the schematic furnished with the delivered transformer .

When required, the pressure gauge is furnished with a pressure regulator that will automatically regulate the tank pressure between 7.0 psig positive and 3.0 psig negative. The pressure regulator is fitted with a valve and fitting to take gas samples.

4. Pressure Relief Device
Pressure Relief Device

All substation transformers are furnished with a:

    Mechanical pressure relief valve (PRV), or
    Pressure relief device (PRD).

The cover-mounted PRD consists of a selfresetting, spring-loaded diaphragm and a mechanical operation indicator. Should the tank pressure increase above that for which the device is set, the gas pressure will lift the diaphragm and let the gas escape quickly. Immediately after the pressure returns to normal, the diaphragm will reset and reseal the transformer.

A mechanical indicator will protrude vertically. This must be reset manually to indicate subsequent operations.

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5. Winding Temperature gauge
Winding Temperature gauge

Transformers may be furnished with a winding temperature gauge as optional equipment. A temperature sensitive stem is mounted in a leakproof well, permitting removal of both the instrument and stem without lowering the liquid level.
The well is heated by both the surrounding liquid and a heater element which is energized from a current transformer mounted inside the tank to simulate the hot spot winding temperature gradient.

The combination of the two temperatures is indicated on the gauge. An additional red pointer is furnished to show the highest temperature attained since the last reset.

    The maximum indicator is resettable by means of a pushbutton through the bottom of the dial bezel .

The gauge has three separate SPDT switches for fan control and alarm circuits. For wiring the contact settings, refer to the schematic furnished with the delivered transformer .

The equipment is calibrated to indicate the hottest spot of the transformer windings. All contacts are factory set to operate at the temperatures shown in the connection diagram. If readjustment of the contacts is desired, consult the manufacturer for detailed instruction.

6. Transformer Cooling Fans
Transformer Cooling Fans

In order to increase the transformer load without overheating the windings, a set of fans can be furnished as an optional item .Fan control consists of a contact on either the liquid temperature gauge or the winding temperature gauge (when furnished), and “Manual-Auto” control switch .

For continuous run, the switch is turned to the “Manual” position. In the “Auto” position, the fans are controlled by the contacts on the temperature gauge. For contact and temperature settings, refer to the schematic furnished with the delivered transformer.

Refer to wiring schematic for control equipment supplied.
Warning! Fan guards are furnished and installed for your protection. Do not remove fan guards or probe into the fan with long objects. Doing so can result in severe personal injury and equipment damage.

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7. High Voltage Bushings
High Voltage Bushings

High voltage leads for ratings 2 .4 kV and up are normally brought through the tank end wall using a porcelain bushing. To prevent excessive mechanical loading of the bushing, only flexible connections should be made to the bushing terminal.

The bushing should never be used as a structural member to support other current-carrying parts.

    Care must be taken in handling the bushing to avoid cracking the porcelain or damaging its surface.

Should it become necessary to replace a bushing or its gasket, proceed as follows:

    Vent the tank to the atmosphere until pressure is zero.
    Lower the liquid level to a point below the bushing level.
    Remove the nuts and washers used to clamp the flange of the bushing.
    Pull the bushing outward as far as necessary to replace the gasket and/or to unfasten the cable connection at bushing inner end.

Only in rare circumstances will there be insufficient slack in the cable leads to facilitate bushing replacement through the wall .The alternative means of gaining access to the connections is through the manhole.

When reinstalling the bushing, install a new gasket in the gasket recess on the underside of the flange to insure that the gasket is properly seated in the groove. A flat washer and lock washer should be placed between the mounting nut and the flange. After the nuts are finger tight, each one should be tightened to a torque of 60±5 inch pounds .

After completion, pressure test the transformer. When condenser-type bushings are used, supplementary leaflets forming a part of the complete instruction book will be provided.

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8. Low Voltage Bushings
Low Voltage Bushings

Low voltage leads for ratings in the 1 .2 kV Class are normally brought through the tank wall using an indoor bushing. This is a cast resin or porcelain bushing.

    The low voltage bushing should not be used as a structural member.

As a rule, only flexible connections should be made to any bushing. Avoid rigid connections between the bushing and other bus supports to eliminate thermal expansion forces to the bushing.

If a bushing is damaged and leaking transformer coolant, contact your factory representative for proper repair procedures.

9. De-energized Tap-Changer
De-energized Tap-Changer

Warning: Do not operate the tap-changer while the transformer is energized! Doing so can result in severe personal injury and equipment damage.

The tap-changer provides a means of changing the voltage ratio of a de-energized transformer without breaking the transformer seal. It is operated by means of a rotatable handle located on the side of the transformer. The tap-changer is normally provided with five or seven positions, as indicated on the tap-changer dial plate and transformer instruction nameplate.

10. Insulating liquid

The insulating liquid in substation transformers is either conventional transformer oil, R-Temp™ fluid or Envirotemp™ FR3™ fluid.When makeup liquid is required, use only approved fluid of the same type that is in the transformer.
It is important to check the proper liquid level in the transformer at all times by periodically observing the liquid level gauge.

In addition, the dielectric strength of the insulating liquid must be maintained at a high value. It is recommended that a sample be taken of the liquid and tested within one week after energization, and annually thereafter.

EEE / 6 Simple Rules to Ensure Substation Safety
« on: November 02, 2014, 12:20:37 PM »
Rule no. 1 (clearance)

Enough clearance from energized parts should be provided to avoid accidental contact with them. If that can’t be met, live parts should be guarded or enclosed.

Rule no. 2 (minimum height)

A minimum height from the ground to any ungrounded part of an electrical installation should be 8’-6”, so a person staying on the ground can’t touch a substation element or its part which may become energized accidentally. For example, the bottom of a post insulator supporting an energized bus does not normally have any potential.
However, if bus flashover to the ground over insulator occurs, touching the bottom of the insulator may become unsafe. That’s why an 8’-6” distance from the bottom of insulator to the ground should be provided.

Rule no. 3 (illumination…)

There should be sufficient illumination for personnel to clearly see their surroundings and perform any work safely. Required illumination levels are specified in NESC® [1].

Rule no. 4 (passageways…)

All passageways and stairs should be wide enough for personnel to navigate them safely, adequate railing should be provided, and floor openings should have guard rails.

Rule no. 5 (evacuation routes)

Exits should be clearly marked and evacuation routes should be free from obstructions. Depending on the function of the building (for example, control house), it may require several exits to avoid personnel being trapped during equipment fault, fire, etc.

Rule no. 6 (grounding, as always)

All substation metallic structures, fences, and equipment tanks should be connected to a station ground grid which should be designed to ensure that step and touch potential values are lower than the ones stipulated in the applicable standards.

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