Power transformer

Transformer Inputs

Supply voltage supply and load connection to the transformer are made using the so-called “inputs”. Inputs in dry transformers can be output to the terminal block in the form of bolted contacts or connectors with flat contacts and can be placed both outside and inside the removable housing. In oil (or filled with synthetic liquids) transformers, the bushings are located only externally on the lid or on the sides of the tank, and the transmission from the internal windings through flexible connections (dampers) to copper or brass studs with a thread cut into them. The isolation of the studs from the body is carried out using bushing insulators (made of special porcelain or plastic), inside of which the studs pass. The sealing of all the gaps in the inputs is carried out by gaskets made of special oil and petrol resistant rubber.

Inputs of power transformers by design are divided into:

• Porcelain tire insulation bushings
• Oil barrier bushings
• Capacitor bushings
• Paper Insulated Glands
• RIP-insulated bushings (with hollow insulator or direct cast insulator)
• Gas insulated bushings

Coolers

The cooling equipment collects the hot oil in the upper part of the tank and returns the cooled oil to the lower side. The cooling unit has the form of two oil circuits with indirect interaction, one internal and one external circuit. The internal circuit transfers energy from heating surfaces to oil. In the external circuit, the oil transfers heat to the secondary cooling medium. Transformers are usually cooled by atmospheric air.

Types of coolers:

1. Radiators come in many types. Basically, they are many flat channels in the plates with an end weld, which connect the upper and lower collectors.
2. Corrugated tank is both a tank and a cooling surface for distribution transformers of small and medium power. Such a tank has a lid, corrugated tank walls and a lower box.
3. Fans For large assemblies, it is possible to use suspended fans below or on the side of the radiators to provide forced air movement and natural oil and forced air (ONAF) cooling. This can increase the load capacity of transformers by about 25%.
4. Heat exchangers with forced circulation of oil, air. In large transformers, heat dissipation through natural circulation through radiators requires a lot of space. Space requirements for compact coolers are much lower than for simple radiator batteries. From the point of view of space saving, it may be advantageous to use compact coolers with significant aerodynamic drag, which requires the use of forced circulation of oil using a pump and powerful fans for pumping air.
5. Oil-water coolers , as a rule, are cylindrical tubular heat exchangers with removable tubes. Such heat exchangers are very common and represent a classic technology. They have diverse applications in industry. More modern designs, for example, flat membrane-type heat exchangers, have not yet entered into practice.
6. Oil pumps. Circulating pumps for oil cooling equipment are special compact, completely sealed structures. The engine is immersed in transformer oil; stuffing boxes are missing.

Voltage regulation equipment

Most transformers are equipped with devices for changing the transformation ratio by adding or disabling the number of winding turns.

Depending on the design, the voltage control of the transformer on the secondary windings can be done using the switch for the number of turns of the transformer or bolted connections by selecting the position of the jumpers or by connecting the corresponding output from the corresponding set with a de-energized and grounded transformer. With the help of such control devices, the voltage on the secondary windings varies within small limits.

Varieties of switches for the number of turns of the transformer:

1. No-load coil switches - Field-less switches (PBB)
2. Load Turn Switches - Load Control (on-load tap-changer)

Gas Relay

A gas relay is usually located in the connecting pipe between the tank and the expansion tank.

• The effect of gas protection is based on the fact that all sorts of damage, even minor ones, as well as increased heat inside the transformer tank (autotransformer) cause decomposition of oil and organic insulation, which is accompanied by gas evolution. The rate of gas formation and the chemical composition of the gas depend on the nature and extent of the damage. Therefore, the protection is carried out so that a warning signal is given during slow gas generation, and during rapid gas generation, which occurs during short circuits, the damaged transformer (autotransformer) is switched off. In addition, gas protection acts on the signal and the shutdown, or only on the signal in case of a dangerous decrease in the oil level in the tank of the transformer or autotransformer.

Temperature Display

To measure the temperature of the upper layers of oil, thermocouples are used that are built into the upper part of the tank in special pockets; To measure the temperature of the most heated point of the transformer, mathematical models are used to recalculate it relative to the temperature of the upper layers of the oil. Recently, sensors based on fiber optic technology are widely used to determine the temperature of the most heated point and other points inside the tank.

Built-in Current Transformers

Current transformers can be located inside the transformer, often near the grounded sleeve on the oil side of the bushings, as well as on low voltage buses. In this matter, price, compactness and safety play a role. With this solution, there is no need to have several separate current transformers in substations with external and internal insulation, designed for high voltage.

Moisture Absorbers

It is necessary to remove moisture from the air space above the oil level in the expansion tank to ensure that there is no water in the transformer oil.

Continuous Oil Regeneration Devices

During operation, water and sludge appear inside the oil transformer. Sludge is mainly obtained due to decomposition of oil, water - as a result of air ingress due to temperature changes in the oil volume of leaking tank structures (the so-called “transformer breathing”), and also as a by-product in chemical reactions of oil decomposition. Therefore, transformers of 160 kVA and more are equipped with continuous oil recovery devices. The latter are divided into thermosiphon and adsorption. Thermosiphon mounted directly on the transformer tank. Adsorption are installed on a separate foundation. The regeneration effect in both types of continuous oil regeneration devices is based on the use of a sorbent in them. Most often, silica gel is used as the latter in the form of granules with a diameter of 2.8 to 7 mm, which absorb moisture well. The difference between thermosiphon and adsorption is in the mechanisms of transporting filtered oil through them. In thermosiphon, natural circulation is used (when heated, the oil rises up, passing through the thermosiphon filter, then cooled, falls to the bottom of the transformer tank and again enters the filter, etc.). In adsorption filters, oil is pumped forcibly using a special circulation pump. Thermosiphon continuous regeneration devices are used on transformers of relatively small dimensions. With large dimensions, when the natural circulation cannot create the necessary performance, adsorption filtration is used. The amount of silica gel is calculated by the weight of the transformer oil (from 0.8 to 1.25%).

Oil Protection Systems

The most common oil protection system is an open expansion tank, in which air above the oil level is ventilated through a desiccant device. Silica gel granules with an average diameter of about 5 mm are filled in a desiccant device. At the same time, part of the moisture-absorbing device is located outside and has a transparent window, inside of which there is a so-called. indicator silica gel impregnated with cobalt salts. In normal condition, the indicator silica gel has a blue color, when wet, it changes its color to pink, which should be a signal to maintenance personnel to replace all silica gel in the desiccant device. Often at the top point of the expander a water-lock type device is installed, which is the first stage of draining the air entering the expander. Such a device is called an “oil shutter”. The oil seal is connected to the expander by its pipe, and in the upper part has a cup welded to the pipe. Inside the cup there is a wall separating the nozzle from the cup from the inside and forming the inner annular channel. On top of the cup is closed by a lid, also having a wall on the inside. The design prevents the cup from closing tightly with the lid and creates a gap between them, in addition, the internal wall of the lid, when fixed, also has a gap with the inner wall, i.e. a labyrinth system is created. In order to activate the oil shutter, pour cups of dry transformer oil into the annular channel to the level prescribed by the instructions, close the lid and fix the latter. The principle of operation of the device is as follows: air enters the gap between the lid and the wall of the cup, then passes through the oil in the annular channel partially giving moisture to the oil and enters the silica gel desiccant through the nozzle, and then into the expander. The expansion tank of the transformer can be equipped with an inflatable cushion. A synthetic rubber inflatable pillow is placed above the oil. The interior of the cushion is connected to the atmosphere, so it can inhale air when the transformer is cooled and the volume of oil is compressed, and exhale air when the transformer heats up.

Another solution is an expansion tank, which is horizontally divided by a membrane or diaphragm, which allows the oil to expand or contract without direct contact with outside air. Two of the above methods of oil protection are called “film protection”.

The space above the oil in the expansion tank can be filled with nitrogen. This can be done from a compressed gas cylinder through a pressure reducing valve. When the transformer inhales, the pressure reducer releases nitrogen from the cylinder. When the volume increases, nitrogen enters the atmosphere through the vent valve.

In order to save nitrogen consumption, you can set a certain pressure step between filling with nitrogen and the release of nitrogen.

Transformers can have hermetic execution. In small oil-filled distribution transformers, an elastic corrugated tank can compensate for oil expansion. Otherwise, it is necessary to provide a space above the oil inside the transformer tank filled with dry air or nitrogen, so that they act as a cushion when expanding or compressing the oil.

You can use a combination of different solutions. The transformer tank can be completely filled with oil, and at the same time have a large expansion tank of sufficient volume to expand the oil and the necessary gas cushion. This gas cushion may be continued in the next additional tank, possibly at ground level. To limit the volume of the gas cushion, you can open a message with the outside atmosphere at the specified upper and lower limits of internal pressure.

Oil Level Indicators

Oil level gauges are used to determine the oil level in the expansion tank, as a rule, these are devices with a dial, or a glass tube working on the principle of connected vessels installed directly on the expansion tank. The oil level indicator is located on the front side of the expansion tank.

Pressure relief devices

An arc discharge or short circuit that occurs in an oil-filled transformer is usually accompanied by overpressure in the tank due to the gas generated during decomposition and evaporation of the oil. The pressure relief device is designed to reduce overpressure due to internal short circuit and thus reduce the risk of tank rupture and uncontrolled oil leakage, which can also be complicated by fire due to short circuit. According to GOST 11677-75, oil transformers 1000kVA and higher must be equipped with a protective device in case of emergency pressure increase. Emergency pressure relief devices has two main versions:

• In the form of so-called. "Exhaust pipe" , installed with a slight slope on the transformer cover and connected by the lower part with its underwing space. The upper part of the exhaust pipe (the top of the pipe is located at a level above the top point of the expander) usually has a bend at the very end and is hermetically closed by a glass membrane, which breaks up with a sharp increase in pressure and produces an emergency discharge. When the transformers are located in the same switchgear and are not separated from each other by the wall, it is necessary to arrange the transformers in such a way that when the oil is ejected from the pipe, the latter does not fall on the adjacent transformer.

In addition, in the upper part, the exhaust pipe is connected to the expander using a special pipeline and has its own air dryer. The exhaust pipe is installed on transformers with an expander, although it should be noted that not all manufacturers install exhaust pipes on their transformers, considering them inefficient.

• In the form of various valve designs. The low weight of the valve disc and the low spring stiffness of the closing springs provide quick and wide opening. The valve returns to its normal closed state when overpressure is reset. Typically, valve designs are used in expansionless transformer designs.

The intermediate position between the above types of emergency pressure relief devices is the design used in transformers of the TMZ type. It consists of a glass membrane sealed in the transformer cover. Under the membrane is a steel spring-loaded striker with a latch and a hermetically sealed bellows. In the working position, the striker is cocked and fixed with a latch. With a sharp increase in pressure, the bellows contracts, breaking the retaining latch and thereby releasing the striker. Under the action of the spring, the latter splits the glass membrane, thus producing pressure relief. On top of this design is closed with a protective cap.

Sudden Overpressure Protection Devices

The relay for sudden pressure increase is designed to operate when an elastic oil wave occurs in the transformer tank in case of serious short circuits. This device is able to distinguish between fast and slow pressure build-up and automatically trips the switch if the pressure rises faster than specified.

Damage Protection Devices

Protection devices for power transformers are the elements of relay protection and automation equipment, fuses are often used on transformers 6 / 10kV.

Wheels / skids for transportation

In practice, large units are rarely delivered by crane to their installation site on the foundation. They need to be moved in some way from the vehicle to the base. If cast rails are laid from the place of unloading from the vehicle to the place of final assembly of the unit, then the unit can be equipped with rolling wheels. Rotation of 90 degrees for transport purposes is provided by wheels working in two directions. The unit is lifted by a lift and the wheels are turned. When the unit is installed in place, the locked wheels can be on it or removed and replaced with support blocks. You can also lower the unit directly onto the foundation.

If such a rail system is not provided, then ordinary flat guides are used. The unit is pushed along the greased rails directly to the installation site, or a track chain is used.

The unit can be welded to the foundation on which it is installed. The unit can also be placed on a vibration base to reduce noise transmission through the foundation.

Combustible Gas Detector

A combustible gas detector indicates the presence of hydrogen in the oil. Hydrogen is trapped through the dialysis membrane. Эта система даёт раннюю индикацию медленного процесса газогенерации ещё до того, как свободный газ начнёт барботировать в направлении газонакопительного реле.

Расходомер

Для контроля вытекания масла из насосов в трансформаторах с принудительным охлаждением устанавливаются масляные расходомеры. Работа расходомера обычно основана на измерении разницы давления по обе стороны от препятствия в потоке масла. Расходомеры также применяются для измерения расхода воды в водоохлаждаемых трансформаторах.

Обычно расходомеры оборудованы аварийной сигнализацией. Они также могут иметь циферблатный индикатор.

Согласно общепринятому ^[3] Общероссийскому классификатору продукции ОК 005-93

На сегодняшний день в России и странах СНГ и Таможенного Союза работает 25 завода по производству силовых трансформаторов I – III габарита, которые производят масляные и сухие трансформаторы различных типов, а именно:

Рынок силовых трансформаторов России объединяет совершенно разных по объемам и характеру производства предприятий – потребителей. Поскольку силовые трансформаторы относятся к товарам производственно-технического назначения (ПТН), то сегментирование рынка силовых трансформаторов целесообразно провести по производственно-экономическим признакам. В этом случае отчетливо выделяются следующие шесть групп потребителей:

1. Предприятия генерации (ГЭС, ТЭС, ТЭЦ, ГРЭС, ГАЭС, АЭС). Объекты Федеральной Сетевой Компании (подстанции магистральных электросетей).
2. Региональные распределительные электросетевые компании.
3. Промышленные предприятия разных отраслей (заводы, фабрики, комбинаты, др. предприятия, в т. ч., горнодобывающие, газодобывающие). Сельскохозяйственные предприятия и садоводческие товарищества. Объекты Министерства обороны РФ.
4. Нефтедобывающие компании.
5. Объекты жилищно-коммунального хозяйства, транспортной и социальной инфраструктуры (жилые микрорайоны, школы, торговые центры, больницы, аэропорты, автомагистрали, автовокзалы, речные и морские порты, речные вокзалы, водонасосные станции, станции очистки и т.п.). Муниципальные распределительные электросетевые компании.
6. Объекты железнодорожного транспорта (тяговые подстанции, станции, вокзалы).

Подобное сегментирование соответствует также схеме транспортирования электроэнергии от предприятий генерации к потребителям. Подробный анализ рынка изложен в книгах «Экспертный анализ рынка силовых трансформаторов России. Часть 1: 1-3 габарит» и «Экспертный анализ рынка силовых трансформаторов России. Часть 2; 4-8 габарит»

Структурная схема условного обозначения трансформатора ^[4]

Буквенная часть условного обозначения должна содержать обозначения в следующем порядке:

1. Назначению трансформатора (может отсутствовать)

   А — автотрансформатор

   Э — электропечной

2. Количество фаз

   О — однофазный трансформатор

   Т — трехфазный трансформатор

3. Расщепление обмоток (может отсутствовать)

   Р — расщепленная обмотка НН;

4. Cooling system
   1. Сухие трансформаторы

      С — естественное воздушное при открытом исполнении

      СЗ — естественное воздушное при защищенном исполнении

      СГ — естественное воздушное при герметичном исполнении

      СД — воздушное с дутьем

   2. Масляные трансформаторы

      М — естественное масляное

      МЗ — с естественным масляным охлаждением с защитой при помощи азотной подушки без расширителя

      Д — масляное с дутьем и естественной циркуляцией масла

      ДЦ — масляное с дутьем и принудительной циркуляцией масла

      Ц — масляно-водяное с принудительной циркуляцией масла

   3. С негорючим жидким диэлектриком ( совтолом )

      Н — естественное охлаждение негорючим жидким диэлектриком

      НД — охлаждение негорючим жидким диэлектриком с дутьем

5. Конструктивная особенность трансформатора (в обозначении может отсутствовать)

   Л — исполнение трансформатора с литой изоляцией;

   Т — трехобмоточный трансформатор (Для двухобмоточных трансформаторов не указывают);

   Н — трансформатор с РПН ;

   З — трансформатор без расширителя и выводами, смонтированными во фланцах на стенках бака, и с азотной подушкой;

   Ф — трансформатор с расширителем и выводами, смонтированными во фланцах на стенках бака ;

   Г — трансформатор в гофробаке без расширителя — «герметичное исполнение»;

   У — трансформатор с симметрирующим устройством ^[5]

   П — подвесного исполнения на опоре ВЛ ^[5]

   э — трансформатор с пониженными потерями холостого хода (энергосберегающий) ^[6]

6. Назначение (в обозначении может отсутствовать)

   С — исполнение трансформатора для собственных нужд электростанций

   П — для линий передачи постоянного тока

   М — исполнение трансформатора для металлургического производства

   ПН — исполнение для питания погружных электронасосов

   Б — для прогрева бетона или грунта в холодное время года (бетоногрейный) ^[6] , такой же литерой может обозначаться трансформатор для буровых станков ^[5]

   Э — для питания электрооборудования экскаваторов (экскаваторный) ^[5]

   ТО — для термической обработки бетона и грунта, питания ручного инструмента, временного освещения ^[5]

Для автотрансформаторов при классах напряжения стороны С.Н или НН 110 кВ и выше после класса напряжения стороны ВН через черту дроби указывают класс напряжения стороны СН или НН.

Note. Для трансформаторов, разработанных до 01.07.87, допускается указывать последние две цифры года выпуска рабочих чертежей.

France Transfo BEZ Transformatory SIEMENS IMEFY ABB