Substation Transformers 

Substation Transformers 

Transformers are vital in the electrical grid, playing a crucial role in power distribution and transmission. By efficiently stepping up or stepping down voltage levels, they enable the safe and reliable delivery of electricity from power plants to end-users. Substation transformers, in particular, are key to maintaining stable and functional power systems, highlighting their importance in our energy-reliant society.

What is a substation transformer?

Designed for three-phase transmission and distribution systems, a Substation Transformer is tailored for either indoor or outdoor installation on a concrete base. These transformers are uniquely structured, with high and low voltage cables entering the operational compartments through enclosed bushings on the sidewall in unit-type transformers, or via cover or sidewall bushings in open-type transformers.

A substation forms a critical part of the electrical installation, encompassing the endpoints of transmission or distribution lines along with the necessary switchgear. It often includes transformers as well. Essential for controlling and protecting the flow of electricity, substations vary in function – they can be transforming, converting, transmitting, or distributing. Specifically, a MV/LV (Medium Voltage/Low Voltage) transformer substation is designed to convert medium voltage electricity from the distribution network (for example, 20 kV) into lower voltages (like 400 V) suitable for supplying low voltage lines.

Key components of substation transformers

Substation transformers are complex devices composed of numerous key components, each playing a crucial role in their operation and efficiency. The main components include:

  1. Windings: They are coils of wire, typically copper or aluminum, that conduct electrical current. There are primary and secondary windings; the primary receives high voltage electricity, and the secondary delivers the transformed voltage.
  2. Magnetic Core: This is the physical structure around which the windings are coiled. It’s typically made of laminated steel to minimize energy losses through eddy currents and to efficiently transfer the magnetic field from the primary to the secondary winding.
  3. Insulation: Insulation is critical in managing the high voltages that the transformer handles. It prevents short-circuits and electrical leaks between the windings and other parts of the transformer.
  4. Tap ChangersThese allow for the adjustment of transformer’s output voltage, commonly rated in kVA, to compensate for varying loads or input voltages. They can be on-load (OLTC) or off-load tap changers, depending on whether they can operate while the transformer is under load.
  5. Cooling System: Transformers generate heat, and thus require cooling systems to maintain operational temperatures. Cooling methods include air-cooled systems, oil-cooled systems, or a combination of oil and water cooling for larger transformers.
  6. Bushings: These are insulating devices that allow for the safe entry and exit of electrical connections (high and low voltage) into and out of the transformer. They prevent electrical discharges and contain the different voltage levels within the transformer.
  7. Conservator Tank: In oil-filled transformers, the conservator tank manages the expansion and contraction of the cooling oil due to temperature changes, maintaining the oil level and pressure within safe limits.
  8. Protective Devices: This includes pressure relief devices, temperature gauges, and oil level indicators, which protect the transformer from damage due to faults, overheating, and oil leaks.

These components work together to ensure that substation transformers function efficiently, reliably, and safely, playing a pivotal role in the transmission and distribution of electrical power.

Substation transformer classifications

Transformer substations can be categorized based on voltage levels and their position in the electrical grid, as follows:

Voltage-Based Classification

  1. Super High Voltage Substations: These handle voltages above 500kV.
  2. High Voltage Substations: Operating at voltages like 66kV, 110kV, 220kV, and up to 500kV.
  3. Medium Voltage Substations: These encompass stations with voltages such as 6kV, 10kV, 15kV, 22kV, and 35kV.
  4. Low Voltage Substations: Typically dealing with voltages around 0.4kV and 0.2kV.

Grid Position-Based Classification

Intermediate Transformer Stations

Intermediate Transformer Stations play a vital role in the electrical grid, converting power from 110V – 220V to 22kV – 35kV. These stations are usually located outdoors to accommodate their large transformers and switches, essential for handling such significant voltage transformations.

Distribution Substations

Distribution substations transform power from 22kV – 35kV to lower voltages like 0.4kV – 0.22kV. They are crucial in providing electricity to civil buildings and factories, adapting to the varying voltage needs across different countries.

Types of Distribution Substations

Pole Mounted Substation: This setup involves mounting both high and low voltage transformers on a column. Typically, these substations use either single-phase transformers or a combination of three single-phase transformers. Accompanying low-voltage cabinets are also mounted on the columns.

Gantry Transformer Substation: In this design, a transformer is positioned on a structure supported by two large pillars. They are commonly used for voltage levels like 35kV, 22kV, and down to 0.4kV.

Grounding Substation Systems: These are often situated in areas with varied terrain, such as rural regions, and serve small to medium-sized organizations. They feature high-pressure equipment mounted on poles, with low-pressure distribution cabinets indoors and transformers placed on concrete platforms. Fences typically surround these stations for safety.

Indoor Substation: Designed for indoor settings, these substations contain three separate rooms for high, medium, and low voltage equipment. They are prevalent in densely populated or newly developed urban areas, focusing on both aesthetics and safety.

Kiosk Substation: This type of substation is enclosed in a robust metal frame and divided into three sections for medium-voltage, low-voltage, and transformer equipment. Kiosk substations are widely implemented in medium voltage networks across industrial sectors, residential communities, and high-rise structures.

These classifications reflect the diverse roles and settings in which transformer substations operate, catering to different needs within the electrical distribution and transmission network.


Substation transformers are pivotal in the efficient and reliable operation of our electrical grid. Their diverse types and classifications cater to a wide range of voltage requirements and grid positions, ensuring that electricity is safely and effectively distributed from generation points to end-users.

At TTES, we have over 100 combined years of experience manufacturing, maintaining, and repairing transformers. If you’re looking for industry-leading lead times of just 20 weeks on average, don’t hesitate and reach out to us for a free quote!

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