What is a medium voltage transformer?
The safe, measurable, and controllable management of electrical energy depends not only on the transmission lines but also on the proper functioning of the entire infrastructure. One of the invisible but indispensable components of this infrastructure is the voltage transformer. Particularly used in medium-voltage (MV) systems, the MV voltage transformer plays a critical role in protection and measurement applications.
What is a voltage transformer?
A voltage transformer is a type of transformer that reduces the electrical voltage in high-voltage lines to a measurable and safe level, providing suitable signals for measurement and protection systems. While the primary winding is directly connected to the MV busbar or phase line, the secondary winding typically produces a standardized low voltage, such as 100 V or 110 V. This allows electricity meters, energy analyzers, and protection relays located in MV switchgear to take measurements without being exposed to high voltage.
What is the purpose of an MV voltage transformer?
In systems operating at medium voltage levels, direct measurement is both dangerous and technically impossible. Medium voltage transformers reduce high voltage levels to values suitable for measurement and control, ensuring both reliable operation of measuring devices and accurate and rapid response of protection relays. In addition, energy monitoring, reporting, and billing processes are carried out uninterruptedly. Furthermore, they provide early warning by triggering alarm systems in case of overvoltage.
Where are MV voltage transformers used?
Medium voltage transformers are used in substations up to 36 kV and therefore within medium voltage switchgear. The most common application areas are:
In medium voltage switchgear (in the measurement and protection compartment)
In substations
In power generation plants
Inside medium voltage switchboards
At measurement points before metering systems
Used in conjunction with compensation systems and power quality energy analyzers.
MV Voltage Transformer Technical Specifications
Primary voltage: 3.6 – 36 kV (nominal MV level)
Secondary voltage: 100 V / 110 V (standard)
Frequency: 50 Hz
Insulation type: Epoxy resin, oil-filled, gas-filled (depending on application)
Installation: Indoor or outdoor, horizontal or vertical
Note: For indoor applications, epoxy resin voltage transformers compatible with compact MV switchgear are preferred. For outdoor conditions, oil-filled voltage transformers, known for their durability, are more commonly used.
The Difference Between MV Voltage Transformer and Current Transformer
Although both are used for measurement and protection purposes, the fundamental difference between them is this: A voltage transformer reduces the voltage and provides voltage information. A current transformer reduces the current value and provides current value information to the connected device. When used simultaneously in medium voltage measurement cells, both allow monitoring of all system parameters.
Why is Choosing the Right Voltage Transformer Important?
Medium voltage transformers are manufactured in accordance with international standards such as IEC 61869-3 and IEC 60044-2. Transformers used in TEDAŞ (Turkish Electricity Distribution Company) projects in Turkey are tested and certified according to TEDAŞ’s relevant specifications. Incorrect transformer selection can lead to measurement errors, delayed response of protection systems, and deterioration in power quality. This reduces system performance and shortens equipment lifespan. For correct transformer selection, the following parameters should be considered:
Voltage level
Class (measurement/protection)
Accuracy class (e.g., 0.5, 1, 3P, 6P)
Environmental conditions
Mounting type
Although often overlooked, medium voltage transformers play an indispensable role in the safety and operation of medium-voltage systems. When correctly selected, they directly affect not only measurement quality but also the effectiveness of protection systems, the accuracy of power monitoring, and system safety. The robust and sustainable operation of electrical grids depends on the equipment used being both high-quality and compatible with the system. Therefore, when selecting a medium-voltage transformer, thoroughly analyzing the technical requirements and choosing solutions that comply with standards is a critical step.