Potential transformer vs current transformer

Potential transformer vs current transformer

Current transformers and potential transformers (also known as voltage transformers) are indispensable. Current transformers specialize in measuring electric current, providing step-down currents crucial for precision in applications like power system metering. On the other hand, potential transformers measure voltage, producing step-up voltages proportional to the primary circuit—a key function in voltage measurement for power systems. Together, these transformers ensure accurate monitoring and control, playing pivotal roles in maintaining the efficiency and integrity of diverse electrical systems.

Primary and Secondary Winding

Potential transformer

The primary winding in the potential transformer is connected in parallel to the circuit under examination. Similar to the current transformer, the turns in the primary winding are determined based on the primary voltage and the desired transformation ratio. The secondary winding, however, typically has fewer turns than the primary winding. This design allows the potential transformer to produce a reduced voltage in the secondary winding, maintaining a proportional relationship with the primary voltage. The turns ratio between the primary and secondary windings determines the extent of this voltage reduction, providing a standardized and manageable voltage suitable for measurement instruments, relays, and control circuits. The configuration of primary and secondary windings in a potential transformer enables accurate voltage measurements without directly exposing the measurement instruments to the high voltages in the primary circuit.

Current transformer

In a current transformer, the primary winding is designed to be connected in series with the current-carrying conductor that carries the current to be measured. The number of turns in the primary winding is determined based on the primary current and the desired transformation ratio. The secondary winding, on the other hand, is typically wound with a much larger number of turns than the primary winding. This configuration allows the current transformer to produce a reduced current in the secondary winding, making it proportional to the primary current. The turns ratio between the primary and secondary windings determines the extent of this current reduction, providing a scaled-down current suitable for measurement by instruments or protective relays.

Cores and construction

Potential Transformer

Potential transformers often employ laminated iron cores, sharing similarities with current transformers in core construction. The laminated core is chosen for its magnetic properties that facilitate efficient voltage transformation. Additionally, potential transformers may feature toroidal or ring-like cores that form a complete magnetic circuit. This design minimizes magnetic losses and enhances the accuracy of voltage measurement. The closed-core configuration is particularly advantageous in potential transformers, where maintaining precision in voltage transformation is crucial for applications such as metering and protective relaying in power systems.

Current Transformer

Current transformers also commonly utilize laminated iron cores in their design. These cores are crafted from thin sheets of iron or steel that are insulated from each other, minimizing eddy current losses. The laminated construction enhances the magnetic properties of the core, ensuring efficient induction of current in the secondary winding proportional to the primary current. This design choice is critical for maintaining accuracy in current measurement while minimizing energy losses. The laminated iron core also provides a path of low reluctance for the magnetic flux, contributing to the performance of the current transformer in high-current applications such as power system protection.

Potential and current transformer types

Potential Transformer

Potential transformers exhibit diversity in their types, encompassing both electromagnetic and capacitor voltage configurations. Electromagnetic potential transformers, the conventional choice, utilize a primary winding wound around a laminated iron core to transform high voltages into standardized, lower voltage outputs. In contrast, capacitor voltage potential transformers employ capacitive coupling, incorporating a capacitor in series with the secondary winding. This design allows for galvanic isolation and is advantageous in applications where minimizing electrical interference is crucial. The choice between these potential transformer types depends on factors such as accuracy requirements, the need for isolation, and the specific demands of the electrical system.

Current Transformer

Current transformers come in distinct types, including wound and closed-core configurations. Wound current transformers feature a primary winding wound around a laminated iron core, providing an efficient means to measure high currents without directly exposing measuring instruments to the full current magnitude. Closed-core current transformers, on the other hand, employ a core that forms a complete magnetic circuit, minimizing magnetic losses and enhancing accuracy. Both types are crucial in applications where precise current measurement is essential, such as in power systems for metering and protective relaying. The choice between wound and closed-core current transformers depends on factors such as the required accuracy, the magnitude of the currents being measured, and the specific characteristics of the electrical system.


Potential Transformer

As mentioned above, potential transformers find a multitude of applications in power systems where accurate voltage measurement is paramount. These transformers play a crucial role in metering, providing a scaled-down representation of high voltages for voltage meters and other monitoring devices. Potential transformers are integral to protective relaying mechanisms, ensuring that voltage levels within the system are continuously monitored to trigger protective actions in the event of abnormal conditions. Moreover, potential transformers contribute to the safe and efficient functioning of electrical equipment by supplying control circuits with standardized voltage signals. From power distribution networks to industrial settings, potential transformers serve as indispensable instruments for maintaining optimal voltage levels and ensuring the reliability of electrical systems.

Current Transformer

Current transformers are pivotal for gauging and overseeing electric current, serving a wide array of sectors. In power systems, their significance emerges in the context of metering, offering precise and scaled-down representations of high currents for monitoring and billing purposes. Protective relays in power distribution systems rely on current transformers to detect abnormal current conditions and initiate protective measures to prevent equipment damage. Current transformers are also crucial in industrial settings, ensuring the precision control of machinery by providing real-time information about current levels. Whether in power generation, transmission, or industrial processes, current transformers are indispensable for maintaining the stability, efficiency, and safety of electrical systems through precise current measurement.


Potential and current transformers are an essential part of our infrastructure. They both have distinct use cases and without them, the modern would be significantly different.

At TTES, we have over 100 combined years of experience manufacturing, maintaining, and repairing transformers of all types. 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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