Understanding Voltage Transformers: Types, Functions, and Applications in Electrical Engineering

When discussing transformers in the context of electrical engineering, it's important to understand that although there is no direct electrical connection between the primary and secondary sides, the primary and secondary coils conduct electricity through the principle of electromagnetic flux. Transformers can have multiple coils or windings on either the primary or secondary side, and in many cases, these transformers can have multiple primary sides connected in series (center-tapped), which can also be observed on the secondary side.

Transformers serve to convert the voltage level from the primary side to the secondary side. Based on the voltage level, transformers are classified into three primary categories: step-up, step-down, and isolation transformers. Each type serves a specific purpose in power distribution and management:

Step-Up Transformers

Step-up transformers increase the low voltage to a higher secondary voltage by maintaining a ratio of primary to secondary winding less than 1. The number of turns in the secondary windings is always higher than in the primary winding, which achieves the voltage increase.

Step-Down Transformers

Step-down transformers reduce the primary voltage to a lower voltage on the output side. This is achieved by a primary to secondary winding ratio greater than 1, thereby stepping down the voltage.

Isolation Transformers

Isolation transformers do not convert voltage from the primary to the secondary windings. The primary and secondary voltage remain the same, with their winding ratio always equal to 1. Isolation transformers are crucial in ensuring electrical isolation and reducing the risk of electrical shock in different applications.

Voltage Transformers (VT) and Potential Transformers (PT)

Voltage transformers, also known as potential transformers (PT), are a type of instrument transformer designed to measure high voltages. They present a negligible load to the supply being measured and maintain an accurate voltage ratio and phase relationship, allowing secondary connected meters to have accurate readings. These transformers are used to measure high voltages, which can be dangerous to measure directly using a multimeter. By stepping down the voltage, these transformers facilitate safer and more precise measurements.

Types and Circuit Representation of Voltage Transformers

Voltage transformers come in two basic solutions:

1. Simple Equivalent Circuit of Voltage Transformer: The voltage transformer can be represented by the equivalent circuit as shown in Figure 1 where all quantities are referenced to the secondary side. When the transformer is not in a 1/1 ratio, the equivalent circuit can be energized with an ideal transformer of the given ratio, but with no losses.

2. Electromagnetic Voltage Transformers: In shunt mode, the system voltage is applied across the input terminals of the equivalent circuit. As shown in Figure 2, the vector diagram for the circuit provides a visual representation of the voltage and current relationships within the transformer.

Understanding the intricacies of voltage transformers is crucial for engineers and technicians working in the electrical sector, ensuring reliable and safe power distribution and measurement in various applications.