פלדת סיליקון כמבודד לקרינה סלולרית

גרעין השנאי בנוי מדפים רבים של פלדה מיוחדת.

הפלדה נקראת פלדת סיליקון (silicon steel) ומה שמייחד אותה מפלדה רגילה הוא צורת גרעיני המתכת: בתהליך הנקרא CRGO – Cold Role Grain Oriented – מייצרים 'כיווניות' לגרעיני המתכת, כך שלשדה החשמלי הנוצר בה יש כיוון ברור מסוים.

עובי דפי הפלדה הוא דק במיוחד – בין 0.2 ל 0.3 מ"מ. בנוסף, מכניסים בתהליך הייצור של הפלדה אטומי סיליקון, ביחס של בערך 4%. הסיליקון בפלדה תורם אף הוא לכיווניות השדה האלקטרומגנטי.

מצאנו בניסויים שדפי פלדת הסיליקון המוצאים משנאי מתח גבוה בתהליך המיחזור מתאימים במיוחד לבידוד אלקטרומגנטי של חדרים ומחיצות. בידוד כזה נדרש במספר מצבים כגון:

בטיחות בעבודה: חדרים הנמצאים בסמוך לארונות חשמל – לפי התקן, הקרינה בחדרים מאוכלסים בקביעות צריכה להיות בערך של 2 מיליגאוס. סביב ארונות חשמל, ישנה קרינה היכולה להגיע בקלות לערך של 50 מיליגאוס ויותר. בניסוי שנערך לא מכבר, ציפוי פלדת סיליקון על הקיר שבין ארון החשמל לחדר הישיבות הורידה את ערך הקרינה מ 55 מיליגאוס ל- 2.5 מיליגאוס

חדרי ישיבות מאובטחים ואטומים לקרינה יוצאת או נכנסת: על מנת למנוע ציטוט אלקטרוני, וביצוע שיחות סלולריות מחדרי ישיבות – ניתן לצפות את הקירות, הרצפה והתקרה בפלדת סיליקון ולחבר את הציפוי להדק אדמה (המגיע לשקעי הכוח, או לצנרת המים). בצורה כזו, כל קרינה אלקטרומגנטית ממכשיר ציטוט, טלפון סלולרי וכו' תתאפס ע"י ציפוי פלדת הסיליקון בצורה יעילה ביותר.

לחברת מגוואט שנאים מלאי של דפי פלדת סיליקון בגדלים שונים. מכיוון שהדפים הוצאו משנאים בתהליך מיחזור, מחיר פלדת הסיליקון עומד ללא תחרות לעומת חומר חדש, ובאותה יעילות בדיוק.

לפרטים – צרו קשר

חדש! שנאים חדשים ומשוקמים

IEC 76 מגוואט שנאים חתמה על הסכם ידע והפצה עם חברת אלקימה, יצרנית שנאים בתקן

ניתן לרכוש או להשכיר שנאי מתח גבוה סטנדרטיים או להזמין שנאי מותאם בדיוק לדרישתכם

אנו מעניקים את האחריות והטיפולים השוטפים לשנאי החדש. ניתן גם לרכוש שנאים משוקמים במחירים אטרקטיביים במיוחד

לפרטים, צרו קשר.

Transformer Oil Interfacial Tension Test

I previously discussed transformer oil analysis through DGA .

Here, I'd like to discuss another test at the disposal of analyzing the condition of a transformer insulation system - the Interfacial Tension Test (IFT).

As transformer oil degrades via oxidation, it cannot efficiently perform its insulation, cooling and protection of the core functions. Oxydation can occur via a myriad of reasons - oxygen derived from air, degrading paper insulation, water entering the oil via leaks, and also heat, electrical stress and many other factors.

One way to detect oil degradation is through its change in acidity (neutral number - NN) and through its IFT.

Acidity is manifested by a visible change of color in the oil - the oil turns markedly darker. These acids, combined with water content will degrade the paper insulation and cause rusting.

Another manifestation is the reduction of the IFT of the oil. IFT is a powerful tool that helps determine the condition of the insulation oil. It is highly correlated to the NN as shown in the figure at left. It is an empirical graph showing the strong dependency between the neutral number and the IFT.

Among Megwatt Transformers services, we offer comprehensive tests of transformers. Our analytics lab offers transformer oil testing and among them, we provide DGA, IFT, Acidity and water content.

Contact us for more information.

Dissolved Gas Analysis in power transformers

Power transformers, being key components in any electrical network, require mindful operation and maintenance, in order to obtain safe and optimum working life. As transformers age, monitoring of their condition becomes more vital, with surveillance and diagnostic techniques being needed to prevent the possibility of surprise failures. Dissolved Gas Analysis (DGA) is a fundamental technique in establishing fault mechanisms in oil-filled power transformers. In its simplest form, DGA analyzes the relative amount of three gasses in transformer oil: CH4, C2H4 and C2H2 (methane, ethylene and acetylene ) These gases are discharged from the insulation system (paper, wire) to the oil under detrimental conditions. Empirical measurements of the relative percentage of these gasses in the oil have been mapped to specific problems in the transformer. So the first step is collection of oil and measurement of the content of the gasses in the oil. Next, these percentages are plotted on a triangular coordinate system, called Duval triangle, shown right. This triangle is (empirically) pre-divided into 'fault zones'. The PPM data is plotted as a point on the Duval triangle and (to a rough first degree), the zone in which it falls on indicates the faulty area. PD fault zone is the partial discharge. T1, T2 and T3 indicate a thermal fault. D1 zone indicates a low-energy discharge, such as hot spots in the paper and paper/oil insulation. D2 zone is the high-energy discharge zone. DT - is an indterminate zone, attributed to a thermal fault or electrical discharge. All in all, Duval mapped about 170 different faults into the fault zones, including application of the method to faults in the load tap changer. Today DGA is considered a comprehensive method of assesing the state of a transformer. Still, it has its share of problems, and is open for interpretation somewhat. Because of the relative inaccuracy of gas-in-oil concentration measurements at low concentrations, DGA diagnostic methods, including the Duval Triangle, should not be applied unless the gas concentrations are well above the detection limit. Megawatt Transformers performs DGA analysis in-house. We employ a veteran in the field with more than 20 years of field experience. This experience, combined with our advanced analysis lab allows us to assess the condition of a transformer beyond the mere threshold numbers given by the gas analysis. This is especially important when the numbers are inconclusive, as is sometimes the case with these measurements. Contact us with all your transformer maintenance and repair needs.

Power transformer tanks - a weak link

Often the damage we see in power transformers involves the tank itself. So in this post I'll describe the power transformer tank, and give some tips on maintaining it.

The transformer tank provides the containment for the core and windings and the dielectric oil. The tank acts as the vacuum vessel for impregnating the transformer with oil.

The tank has a removable cover so that core and windings can be accessed and removed. The cover is fastened by a flange around the tank and is bolted. It should be inclined at about one degree to help drain rainwater.

The cover holes are made oil tight using gaskets. These are normally rubber bonded cork or neoprene bonded cork or stiff rubber. The rubber is synthetic rubber, so to resist degradation by the mineral oil. These gaskets joints represent a potential leak, and often is the source of more serious problems that occur due to poor maintanance.

The main tank cover flange usually represents the greatest oil leakage threat, since being of large cross section, it tends to provides a path for leakage flux, with the resultant eddy-current heating leading to overheating and degradation of gaskets.

From our experience, oil leaks are the first visible signs of deeper trouble. Therefore, we highly recommend to visually inspect power transformers on a regular basis. These checks must be done by qualified personnel, as the voltages from power transformers are deadly. checks for leaks around the cover flange, insulator gaskets and other auxiliary equipment are done as part of a routine maintenance check. It is fairly important, as an early diagnosis can save A LOT of money resulting from damage to the transformer later on (due to overheating) and the equipment connected to it (due to shorting) or around it (due to exploding).

Megawatt Transformers provides transformer maintenance that includes thorough testing of the transformer tank's gaskets, transformer oil analysis and transformer repairs. Contact us for more details.

Top maintenance tips for power transformers

Power transformers are expensive machines, and they require regular maintenance like we all do. Here are the top tips to keep power transformers healthy and prolong their service life, roughly in order of importance:

1. Monitor the transformer oil and analyze it regularly: taking oil samples is an essential prerequisite to any maintenance. An oil sample is such an important source of information as to the transformer condition that it is essential that extreme care is taken in obtaining it in order to ensure that the information gained is not misleading. There are strict procedures on how to take a proper sample (e.g. British Standard 5263, or IEC publication 475), but as an owner - make sure that the oil is sampled and analyzed regularly by a professional. Megawatt Transformers has an oil analysis lab and offers oil sample collection and analysis with same day results.
2. Visual inspection: visual inspection of power transformers on a routine basis can provide clues to the condition of the transformer. 'Wet', slow leaking transformers with patches of oil on their exterior indicate a leakage in the seals, a crack in the insulators or damaged fins. Other visual inspection includes the condition of the silica gel aerator for change of color. All these may indicate an impeding problem with the transformer insulation system.
3. Keep clean: keeping the transformer exterior clean and its surroundings tidy facilitates quick spotting of oil leaks. In addition, it helps cooling the fins/cooling pipes. Keeping the surroundings tidy reduces the chances of fire damage should the power transformer overheats. Megawatt Transformers provides complete power transformer maintenance and repair.
4. Check operation of fault analysis devices: The gas and oil actuated relay (Buchholtz) is used extensively to disconnect a transformer from teh supply in case of an interturn (core related) fault or any other internal failure. These are extremely important safeguards, and their operation must be checked periodically. Dissolved gas analysis devices also fall into this same category.

What are power transformers

Power transformers are one of the key components in the electric distribution grid.

Electricity is generated at power stations (hydroelectric, coal, solar). That's easy.

The tough part is (and that's not commonly understood) - its extremely hard to store electricity in large quantities. In fact, it's downright impossible.

Unlike water, fuel or food - storing electricity in large quantities (enough to supply a town for a week, for example) is simply not economical. Yes, batteries and capacitors do just that, but nothing close to the relative quantities. The best electric car can do on a charge barely half a tank of gas. And it uses a very, very heavy set of batteries to store that charge.

So the tough reality is that electricity needs to be continually generated, day and night, and continually be supplied to its consumers. If the consumers do not use the generated electricity, the energy used to create it has gone to waste - again, because there's no known way to store electricity for the time when the consumer needs it.

Think of one of those portable generators. You fill it with fuel, start it and it promptly starts converting fuel to electricity, whether you plug an appliance to it or not. See my point?

Now, since electricity can't be stored efficiently, it needs to be continually transported to (often) great distances. That's the power lines hanging on poles everywhere.

That's where power transformers come in. For physical reasons, the most efficient way to transport electricity is for it to be at the highest possible voltage. The higher the voltage, the less electricity is wasted in the distribution grid.

Voltage, for the purpose of this blog, is just like water pressure. So lets just say that the higher the pressure, the less waste in the electric 'pipe'.

Power transformers convert one voltage for another. So there are (huge) power transformers to convert the generator voltage to high voltage, ready to be transported. High voltage means hundreds of thousands of volts (400,000 volts is common). Now, on the other end, power transformers convert that voltage down back to the consumer voltage - commonly 110v, 220v.

So there, power transformers are the 'pressure converters' from low voltage to high voltage and back to low. And they are critical in any power grid.

Transformers are everywhere, all around us. Wall adapters, chargers, inside every power supply. They all convert voltages (110v, 220v) to whatever voltage is needed by the electronic circuitry (5v, 9volts etc).
Power transformers differ from a wall wart mainly in that they deal with huge quantities of electricity compared to their dwarf sibling. So they need to be a lot more efficient and they are much, much more expensive.

For example, they need to be liquid cooled, and they use a special transformer oil for that.

And they are a dangerous device to deal with, because of the high voltages involved. Thus they are confined to cages and locked rooms and are serviced and maintained by professionals only.

Megawatt Transformers offers service and maintenance to power transformers. We have a power transformers analysis lab, we offer transformer oil analysis treatment and hold a large inventory of spare parts.

We also offer power transformer recycling, and sell the recycled cores. We are the first EPA approved power transformer recycling plant in Israel.