A distribution transformer, also known as a “service transformer”, is a transformer that transforms the entire voltage in an electric power distribution system. It does this by lowering the voltage in the distribution lines down to the level applied by the consumer. Distribution transformers are the phase below transformers used for electric power delivery.
Many types of transformers are used in the distribution system. There are three-phase, single-phase, pad-mounted, pole-mounted, and underground transformers. Distribution transformers are usually smaller and less prone to clogging oil. There are many sizes and efficiency options available on the market for these transformers. The price and determination of the end-users will determine the distribution transformer that is purchased.
Distribution transformers can be found in nearly all sectors of the economy, including residential and commercial. There are many ways to classify distribution transformers:
- Types of insulation: dry-type or liquid-immersed
- Multiple phases: Single-phase or triple-phase
- Voltage level (for dry type): Low or medium
The Importance of Transformers
The distribution transformer is the most important piece of electrical equipment in an electrical distribution system. It can even have a significant impact on the system’s overall price, competence, and dependability. It is important to choose and obtain energy-efficient delivery transformers that are optimized for the following points:
- A particular distribution network
- Investment strategy for the utility
- Maintenance policies for the network
- Loading conditions and local service
Structure of Distribution Transformers
- The distribution transformer is the same as a normal transformer. The major parts of this transformer include the Oil Tank, Conservator Buchholz Relay and Breather Unit.
- By placing the coils in an oil tank, you can soak them.
- The conservator is located on the exterior of the transformer frame above the oil tank. The tube connects it to the main tank via a metal tube. It is possible to contact the oil in the tank and allow it to expand during loading. This allows the oil’s temperature to rise or fall.
- When using a conservator tank, the Buchholz relay should be used. It is used to indicate errors such as oil loss when the oil gets low.
- The oil in the breather unit contains desiccant silicon gel. It will not be hygroscopic if it changes colour from blue to rose.
- The oil indicator indicates the level of oil within the conservatory unit.
- The oil temperature is monitored by the temperature detector. The transformer will be removed from service if the oil temperature reaches a certain point.
- The transformer’s pressure relief device lowers the pressure to prevent an explosion.
- The thermal relay serves as an indicator of temperature during winding.
- Radiators can be used to increase the cooling efficiency of the transformer.
- With the help of an external electric network, bushes are used to connect inner windings to a transformer.
Distribution Transformer efficiency
The efficiency of a distribution transformer is the ratio of output power to input power at full load. However, in the case of distribution transformers, this concept is slightly different. A distribution transformer can only be run at its maximum load condition. The maximum efficiency of the transformer is at 50% full load.
There are two main types of losses in a transformer: iron losses and copper losses. Core loss is iron loss. It is made up of hysteresis and eddies current losses. These losses are constant once the transformer is charged. This means that the loss amount does not depend on the secondary load. These losses are fixed under all load conditions. The load I determine the copper loss, also known as I2R loss. Distribution transformers cannot be operated with constant loads for 24 hours. Its loading can be high during day peak hours, but it may be lower at night.
It is therefore not feasible and economically viable to choose a transformer based on its efficiency. The all-day efficiency of a distribution transformer was created to solve these problems. This efficiency is equal to the efficiency of the distribution Transformer.
This concept uses the ratio between the total energy supplied by the transformer and the total energy that is fed to it over a 24-hour period instead of the ratio between power output and input. The all-day efficiency is calculated as the sum of total KWh at secondary and total KWh primary for a specific time period, preferably 24 hours. This means that
This can be used to evaluate the performance of a distribution Transformer, whose primary load is connected to the system for life, but secondary loads fluctuate tremendously throughout the day.
The conventional effectiveness of distribution transformer manufacturers is not real-world and economical. These difficulties led to the development of the concept of all-day competence for delivery transformers. This effectiveness is equal to the efficiency of the distribution Transformer.
General Purpose Distribution Transformers
These are used to power electrical delivery system loads, lighting, motor machines, and supply appliances. They can be supplied with copper or aluminium windings, with an average rating of 50VA to 750kVA. As fewer distribution transformers won’t create much heat, a greater number of them will be dry-type. They are non-combustible and are therefore preferred when placed in restricted spaces within a client’s building.
Even in the case of electric power, distribution transformers can be used. Distribution transformers are the final part of the distribution system at an average voltage. This type of power distribution transformer is less impedance and can only stop short circuit currents if the secondary side is damaged. Therefore, it is a standard practice to test power distribution transformers for short-circuits conditions.
The power distribution transformers can be either dry-filled or oil-filled. Two primary components of distribution transformers are the Coil and Core. The coil is a conductor that winds around a core. It is usually made of copper or aluminum, but it can also be made from other less-resistant materials. To transform voltage from one to the next, copper or aluminium conductors will be wound around a magnet core.
To cool and insulate the transformer’s core, liquid insulation material (or dry-type air) is applied to the conductors and surrounds it with liquid insulation material. Nearly all energy is transferred from at least one distribution transformer, before it is expended by an item of equipment or an end-use device like a motor.