It is the second day I’m waiting here in a traditional coffee shop that we call as waroong kopee, this situation is so curing me from my feeling of homesick. As usual I drink my favorite coffee, a big cup of black java coffee and seeing green grass field on an electricity facility – a main substation – across the street and blue hills a distant apart. Actually, I am here for my old best friend who is really old now, a friend who had introduced me to a remarkable electricity equipment named Transformer.
Yeah, for years we meet at this waroong kopee starring out our beloved Transformer of my hometown, Pemalang. Now, I am starring out the Transformer alone. It’s been twenty five years since the Transformer erected in my hometown, the coat is getting fade because of weather and ageing, and some bird’s droppings “paint” it, but the reliability is only a little beat reduced from the first enegizing.
My mind gets back into twenty five years ago and memorizing when Pak Edi – my friend – introduced me all about transformer which made me so amazed. It was him from the transformer manufacture, to take care of guaranty for PLN (Perusahaan Listrik Negara, State Electricity Company) when some oil leakage happened on the Transformer. At that time I was a 17 years old naughty teenage boy who did not consider dangerous area around the main substation. He grabbed me and took me to security room, asking me hardly:”what are you doing here ? Don’t you know it is dangerous around here, high tension electricity everywhere !!”. I could not say anything, just shut my mouth up because I was shocked. Then, he spoke softer:”Do you know what is that ?”, he said, with pointing a very big-weird-tank by his finger, “nope”, I answered. “That is transformer”, he answered.
Then he pulled a fold of A3 paper from his bag and unfolded it. He shown me a drawing which was quite strange for me, then he explained how the core of a transformer was made. He explained how the silicon laminated steel sheet was arranged sheet by sheet and package by package to became a magnetic core for a transformer. He explained the function of yokes as a main reinforcement and mounting place for the core and any useful accessories. He explained to insulate electricity between yokes and core was using insulation tubes while the yoke’s rod pushed into yoke’s mounting holes and core’s mounting holes, because it is forbidden to let the short circuited electricity between core and yokes. Further, he extended the explanation that the bottom yokes were assembled with core by using mounting rods and some copper sheets because this assembly was used for grounding line.
Then, he pulled another A3 paper fold from his bag. He shown me a more strange pictures which was looked alike four baskets which was stepped on each other. I said, ”this is weird, I don’t understand what you are trying to say.” And I was trying to run away, but he hold and asked me,” do you know what transformer is ?”, “yes I do”, I answered, ”transformer is an equipment to rise up or stepping down electricity, that’s what my teacher said.” He asked, “Did he tell you further explanation?” “yes, he did; he said that the main components of a transformer are core and windings, the core is used to transform magnetic fields to become electric fields in each winding and split apart the electricity for stepping up or stepping down the voltage and current. The windings have two sided apart, primary winding and secondary winding.” I answered quite long to satisfy him and wish he would let me go. “Ha, ha, ha, ha.” he laughed quite loud and said,” Your teacher was correct, and you are clever since you understand what he told.” “Yeah, but I don’t know what you are trying to explain !!”, I cried out. He did not pay any attention to my wish and continue his lecture,” Now see this picture carefully, You see these ‘three baskets’ stepping over each other. These are not baskets, each ‘basket’ is a winding, the first is Low Voltage winding, the second is High Voltage winding, the third and fourth are auxiliary windings for stepping voltage by using on-load tap changer or widely known as automatic load tap changer. Perhaps you know that the primary winding would be High Voltage winding, and secondary winding is Low Voltage winding, that’s not so wrong or right since those windings can act as primary and secondary as well ”
I got headache for what he said, and getting worse and worse. Of course, I was a teenage high school boy who did pay much attention on play around, but what he explained echoed in my mind time to time and this motivated me to take electrical engineering education.
Now I memorize again for what he said years ago, even now I am working for the same transformer manufacture as quality assurance inspection engineer. My present job position forces me to understand transformer in widely range. I must understand how the windings assembled into core, by dismantling upper core package and then put each winding into each branch of core, every top and bottom of the winding must be hold and protected by press blocks.
The most complicated, risky and delicate are inter winding connection and OLTC (On-Load Tap Changer) connection to outer winding. There are many leads which look alike and high concentration and attention must be paid, specially the delta connection of auxiliary winding and OLTC, this is the most difficult because each phase indicates of currents superimpose which can lead to over-current in each tap or inside the OLTC mechanism. Further, if there would be a surge phenomenon due to switching between switch-gears it can ignite destructive currents with high density harmonics, and it can trigger imbalance phase currents and voltage. Since the absent of neutral line in delta connection, this type of connection is not regularly recommended for OLTC, except there is sufficient protection for this requirement.
My coffee is getting cold but Pak Edi is not coming yet, perhaps he will be late this time, or perhaps his grand children need him much, I don’t know.
Again, I memorize my job. Other critical problems are gaps between leads and gaps of cross sectional area between leads. The gap must be kept according to calculation, wider is better but it shall be bad for space availability mainly for the tank and upper cover of a transformer, then it must be strictly monitored. Thus, the gap is kept by using guider blocks, which is made according to gap calculation.
To be continued…