Practical voltage levels are termed medium voltage, which means the power transformer gets an incoming voltage in the range of 5 kV to 35 kV. High distribution voltages may cross 35 kV, but these are rare, and the distribution system is mostly within the medium power range. Today, distribution transformers are made as per standards such as the IEC (International Electrotechnical Commission) and IEEE (Institute of Electrical and Electronics Engineers).
In the U.S., the functionality and features of distribution transformers are built to adhere to the IEEE standard C57.12.00. However, a range of standards applies to particular uses and types of power transformers, including high temperature, generator duty, pole-mounted single-phase, compartmental pad-mount, and substation transformers.
Types of Medium Power Transformers
There are five types of medium power transformers, and we detail each below:
Ventilated Dry-Type Transformer
These transformers are isolation or voltage changing (step-down or step-up) devices that are cooled by air and not liquid. The case of the transformer has ventilation to permit air to move in and chill the coils. For outdoor use, dry-type transformers’ enclosure will typically have louvers to facilitate ventilation. These power transformers meet IEE standards C57.12.91 and C57.12.01, with ratings ranging from 15 kVA to 30 MVA, and main voltages greater than 601 V.
Pole-Mounted Single-Phase Transformer
These transformers are typically used in residential zones and small businesses needing three-phase electricity from a bank. Their size can vary from the small 5 kVA to the large 500 kVA, and voltages can go up to 35 kV. Pole-mounted power transformer banks permit the connection of three one-phase units to a three-phase platform for distribution via overhead lines. Overall functionality and layout, mounting standards, and winding connection types are built as per the IEEE standard C57.12.20.
Pad-Mounted Single-Phase Transformer
These transformers are commonly used in residential zones and distribute power via underground systems. Their layout and features adhere to the IEEE standard C57.12.38. The typical rating of these power transformers is 10-167 kVA (going up to 250 kVA according to IEEE standards scope) and primary of up to 35 kV.
Pad-Mounted Three-Phase Transformer
These power transformers are ground-mounted on concrete and placed in a tamper-proof steel cabinet. Generally, these transformers are smaller in size (45 to 5,000 kVA) but can be made in large sizes too (up to 10 MVA). They are installed in areas within or near public places.
Their pad-mounted, tamper-resistant, and compartmental design make them suitable for applications whose goal is to ensure public safety. The pad-mount power transformer’s overall functionality and design meet the IEEE standard C57.12.34, and its tamper-proof quality is built as per the IEEE standard C57.12.28. For coastal places, it is C57.12.29.
Substation transformers are the core of electrical substations. They alter the relationship between the incoming current and voltage and the outgoing current and voltage. Their rating is based on the relationship between their main and secondary voltage and their capability in carrying power.
Typically, substation transformers are rated 15, 25, 35, or 46 kV on the main at a power rating of around 5 to 20 MVA. The low or secondary voltage can be less than 600 V. The functionality and design of substation power transformers is as per IEEE standards C57.12.36 and C57.12.00.
In March 2007, European nations decided to reduce greenhouse gas emissions by about 20% from 1990 levels. To facilitate this, the European Commission (EC) issued guidelines to manufacturers of power transformers, including large and medium ones, to decrease CO2 emissions associated with this equipment.
Manufacturers are encouraged to minimize lifecycle costs and maximize efficiency over the average service life of a transformer, which is 40 years. We recommend that you talk to licensed professionals to get advice on electrical systems. They can suggest suitable solutions for your organization’s needs. Usually, CRGO materials are used in transformer