The Functions and Working Principles of Current Transformers

Current transformers or CTs are primarily utilized in electrical power systems to measure current and to offer electrical isolation between the high voltage circuits and measurement equipment. They are widely used in protection, metering, and control applications in both industrial and commercial electrical systems. 

In this article, current transformer manufacturing companies will discuss the operations, structure, and the various categories of current transformers comprehensively.

Functions of Current Transformers

1. Current Measurement: The fundamental role of current transformer is to generate a secondary current proportional to the primary current in power system. Devices like the ammeters and wattmeters cannot directly work with high current flows, firstly owing to the fact that they are usually designed to work with low current. These high currents that flow through CTs are reduced to a level that is manageable thus making it possible to measure them effectively.

2. Protection: Current transformers are employed in protective relays, to measure abnormal quantities in electrical circuits to include overloads, short circuits or even fault currents. Since CTs are able to demagnetize high currents into a safer level relays are able to trigger circuit breakers to protect electric networks from destruction.

3. Isolation: CTs isolate the high-voltage systems from the low voltage measuring instruments through its galvanic isolation property. This isolation is important in order to safeguard the measuring devices and the operator from the high voltage side of the circuit to avoid danger on the life of the individuals and the damage on the instruments.

4. Energy Metering: In energy metering systems high currents are converted by current transformers to levels which can be easily measured and then logged, for billing or energy controlling. Together with potential transformers (PTs), they are used for the measurement of both current and voltage in electrical networks.

Working Principles of Current Transformers

Current transformers work on the fundamental concept of the electromagnetic induction. Similar to voltage transformers, CTs have two windings: namely the primary winding and the secondary winding. The first winding is connected in series with the high current circuit while the second winding is connected to measuring or protective devices.

Here’s how a current transformer works:

1. Primary Winding: The primary winding of the CT consists of one or only few turns of a conductor or any sub micron conductor. As the CT is connected in series with the high current circuit, the entire current of the load passes through the primary winding.

2. Magnetic Core: Anytime an electric current has to pass through the primary winding, then this induce a magnetic field in the CT. This magnetic field’s strength is directly proportional to the current within the primary winding. The magnetic core is used to couple the magnetic flux from the primary side to the secondary side.

3. Secondary Winding: Another is that the secondary winding of the CT has many turns of fine wire. The magnetic field in the core creates a current in the secondary winding according to the current turns established in the transformer between the primary as well as secondary windings. The secondary current is found to be in the ratio of 1: 10 with the primary current.

4. Turns Ratio: It is the turns ratio that got a specific impact on current as it affects how much is it is stepped down. For example, let the primary have one turn and let the secondary have 1000 turns; then, the secondary current is one/thousand of the primary current. For primary current of 1000 A, its value in secondary side will be 1 A.

5. Load on the Secondary Side: The secondary winding is connected to the sharing of the measuring instrument or relay. The secondary circuit should be kept closed or loaded with the right burden in order to yield accurate electrical measurements. When the secondary side is open some of the high voltages may build up causing all sorts of hazardous conditions and possibly even the destruction of the transformer.

6. Accuracy and Burden: It has been found that the performance of a current transformer is influenced by the burden, or the impedance appearing across the secondary winding. A high burden can result into wrong output being generated by the CT. Indeed to ensure the burden gauge is accurate it has to be ensured that the burden does not reach beyond the limits of the CT’s design.

Types of Current Transformers

1. Wound-Type Current Transformers: In this type, further coil the primary winding is wound around the core and is electrically connected to the principal current conductor. This design yields more accurate measurement of current and is applied where intense determination of the current is necessary.

2. Bar-Type Current Transformers: In bar-type CTs, the basic winding is either a solid or a hollow bar which is invariably the current carrying conductor in the case of bar type CTs. The bar runs through the middle of the core while the secondary winding is essentially around this bar. This type is used often in high current circuits such as the electrical substations.

3. Toroidal Current Transformers: One important feature of toroidal CTs is their absence of primary winding. However the conductor which is charged with current goes round a circular core. These CTs are small and are commonly utilised for the measurement of earth leakage currents or any protective objectives.

Applications of Current Transformers

1. Power Distribution Systems: The most usual application of CTs is in the electricity generation and transmission field to measure and regulate the electric current. They help in issues to do with metering, energy and even system protection.

2. Substation Equipment: Current transformers play a crucial role in substations particularly where protective relays are involved, where they assist in making sure that circuit breakers operate in instance of faulty conditions such as short circuits or situations where average currents are higher as compared to normal current.

3. Industrial Automation: CTs are widely used in industrial systems for monitoring and other protection purposes since they are important members of the automation systems where accurate current measurement is important.

4. Energy Metering: Energy metering systems used in billing employ currents transformers. ITH through CTs, the current flow through the network contributes appropriate measurement of energy used.

Conclusion

Current transformers are one of the most important instruments used in today’s electric power grid, offering a safe and precise means of measuring current. These features of the transformers help to stabilize electrical networks, isolate high currents and interact with protective relays and metering devices safely and efficiently. Knowledge of the functions and operating characteristics of CTs is particularly important for employees of electrical and energy companies, electrical engineers, and power system operators.