What is a High Accuracy Current Transformer? Understanding Types, Working, and Applications

In electrical engineering, measuring the current flowing through a circuit is crucial for power systems’ safe and efficient operation. High Accuracy Current Transformer (HACT) is a device designed to measure high currents and transform them into low-level currents, suitable for measurement and control instruments. This article will explore the different types, working principles, and applications of HACT.

Introduction

A current transformer (CT) is a device used to measure electric current. It consists of a primary winding connected to the high-current circuit and a secondary winding connected to the measuring instruments or protective devices. CTs are widely used for metering, protection, and control applications in power systems. However, the accuracy of conventional CTs may be affected by several factors, such as temperature, saturation, and load, leading to errors in the measurement. To overcome this, high-accuracy current transformers (HACTs) are developed.

Understanding Current Transformer (CT)

A conventional current transformer is an instrument transformer used to step down high currents to a measurable level. It works on mutual induction between the primary and secondary winding. The primary winding of CT is connected in series with the high current circuit, and the secondary winding is connected to the measuring or protection devices. The ratio of the secondary current to the primary current is called the transformation ratio.

High Accuracy Current Transformer (HACT) Explained

High-accuracy current transformers (HACTs) are designed to overcome the limitations of conventional CTs in terms of accuracy and performance. HACTs can accurately measure various currents, from a few milliamperes to several kiloamperes. HACTs are used in applications where high accuracy is required, such as power quality monitoring, protection systems, and energy management systems.

Types of HACT

There are different types of HACTs based on their construction and application. Some of the common types of HACTs are:

Residual Current Transformer

A residual current transformer (RCT) is a type of HACT used to measure the residual current in a three-phase circuit. It consists of three primary windings connected to each phase and a secondary winding connected in a delta configuration.

Bar-type Current Transformer

A bar-type current transformer (BCT) is a type of HACT used for measuring high currents in a busbar. It consists of a primary winding, which is in the form of a bar, and a secondary winding wound around the bar.

Wound Type Current Transformer

A wound-type current transformer (WCT) is a type of HACT used for measuring high currents in a cable or conductor. It consists of a primary winding, a wound around the cable, and a secondary winding.

Multi-Ratio Current Transformer

A multi-ratio current transformer is a type of HACT used for measuring different current ratios. It consists of a primary winding and multiple secondary windings with different turn ratios.

Working Principle of HACT

The working principle of HACT is similar to that of a conventional CT. The primary winding of the HACT is connected in series with the high current circuit, and the secondary winding is connected to the measuring or protection devices. The current flowing through the primary winding generates a magnetic field, which induces a current in the secondary winding. The ratio of the secondary current to the primary current determines the transformation ratio of the HACT.

However, HACTs are designed with high-precision components to achieve accurate measurements. They are also insulated and shielded to minimize the effects of external factors such as temperature, humidity, and electromagnetic interference.

Advantages of Using HACT

The advantages of using HACTs over conventional CTs are as follows:

• High Accuracy: HACTs are designed to provide high accuracy over a wide range of currents, ensuring precise measurements.
• Compact Size: HACTs are designed with high-precision components, making them smaller and more compact than conventional CTs.
• Low Error: HACTs are insulated and shielded to minimize the effects of external factors, leading to low error in the measurement.
• Wide Range of Applications: HACTs are used in many applications, such as power quality monitoring, protection, and energy management systems.

Applications of HACT

The applications of HACTs are as follows:

Power Quality Monitoring

HACTs are used in power quality monitoring systems to measure the current and voltage harmonics, power factors, and other parameters that affect power quality.

Electrical Protection System

HACTs are used in electrical protection systems to measure the current flowing through the circuit and trigger protective devices in case of overcurrent or fault conditions.

Energy Management System

HACTs are used in energy management systems to measure the current and voltage of the power system, enabling effective control and management of energy consumption.

Smart Grids

HACTs are used in smart grid systems to measure the current and voltage of the power system, enabling real-time monitoring and control of the grid.

Arc Welding

High Current transformer using for arc welding.

HACT vs. Conventional CTs

The main differences between HACTs and conventional CTs are accuracy and size. HACTs provide higher accuracy over a wider range of currents and are smaller and more compact than conventional CTs. However, HACTs are more expensive than conventional CTs and require more complex design and manufacturing processes.

Factors Affecting HACT Accuracy

The factors affecting HACT accuracy are as follows:

• Temperature: The accuracy of HACTs can be affected by temperature variations, leading to errors in the measurement.
• Saturation: HACTs can saturate at high currents, leading to errors in the measurement.
• Load: The accuracy of HACTs can be affected by the load impedance, leading to errors in the measurement.
• Frequency: The accuracy of HACTs can be affected by the current’s frequency, leading to measurement errors.

Challenges in HACT Design

The challenges in HACT design are as follows:

• High Accuracy: HACTs require high-precision components and manufacturing processes to achieve high accuracy.
• Size: HACTs must be small and compact, which can be challenging to achieve with high-precision components.
• Cost: HACTs are more expensive than conventional CTs, which can challenge some applications.

Conclusion

In conclusion, High Accuracy Current Transformers (HACTs) are virtual devices used in power systems for measuring high currents accurately. They provide high accuracy over various currents and are used in various applications, such as power quality monitoring, electrical protection systems, energy management systems, and smart grids. Despite their advantages, HACTs have challenges in design and manufacturing and are more expensive than conventional CTs. However, with the increasing demand for high-precision and reliable measurements in power systems, HACTs are becoming more common and widely used.

FAQs

What is the accuracy of HACTs?

HACTs provide high accuracy over a wide range of currents, with typical accuracy values ranging from 0.1% to 0.5%.

What is the difference between HACTs and conventional CTs?

HACTs provide higher accuracy over a wider range of currents and are smaller and more compact than conventional CTs. However, HACTs are more expensive and require more complex design and manufacturing processes.

What are the applications of HACTs?

HACTs are used in various applications, such as power quality monitoring, electrical protection systems, energy management systems, and smart grids.

What are the challenges in HACT design?

The challenges in HACT design include:

Achieving high accuracy with high-precision components.

Designing a compact and efficient device.

Managing manufacturing cost.

3.How do HACTs improve power system operation?

HACTs provide accurate measurements of the current flowing through the circuit, enabling effective control and management of power systems and improving their efficiency and reliability.