Nowaday, the use of devices at the right voltage is an issue that users need to keep in mind. Current transformers are designed to change the amperage as desired. Let’s learn more about the characteristics of current transformers in the following article.
What is current transformer?
Current transformer is a type of voltage transformer commonly used to reduce an alternating current (AC). It produces a current in its secondary coil proportional to the current passing through it.
Structure of current transfomers
Current transformers consist of the following main parts:
- Primary Current
- Secondary Winding
- Hollow Core
- Ammeter
Characteristics of the current transformer
Unlike a potentiometer or a traditional power transformer, a current transformer consists of one or a few turns of wire.
Traditionally designed loops can be in the form of a flat piece of wire wrapped in a single loop or a coil of wire wound around the hollow core or directly connected to the circuit through the device with a central hole . And because of this design, the current transformer was often considered a “transformer chain” that functioned like a secondary winding.
The secondary coil may have a large number of inductors wrapped around the steel core to minimize the magnetic dipole consumption of the cross-section, so
the magnetic induction is used lower than that of the wire. This depends on how big the current needs to be reduced. Secondary winding is usually defaulted at 1A for low intensity or at 5A for high intensity.
The operation principle of the current transformer
Current transformers are based on electromagnetic induction. When alternating current flows through a wire, around it will appear an electric field, this electric field induces on the coil and an electric current will appear in it. This ratio of current is based on the number of turns of the winding in a current transformer.
Operation mode of the current transformer
CT series has two basic working modes: short circuit mode and open circuit mode.
Short-circuit mode of primary and secondary current with Z2 load
The ratio of the primary short-circuit current to the rated current is called the current multiple of the current transformer. When this multiple is large, the CT error increases and it depends on the secondary current or the load. Often with a protective circuit, the current multiple of the current CT must reach a value such that its error is less than 10%.
Secondary open circuit mode
When the secondary circuit is open, the secondary side will have inductive voltage with very high amplitude, endangering people and secondary equipment. To prevent saturation in the magnetic circuit, it is also made current transformers with air gap or linear current transformer.
CT has a current ratio inversely proportional to the number of turns. Therefore, it is possible to change the current ratio by changing the number of primary or secondary side windings.
Basic specifications of current transformers
What does the ratio 100/5A or 300/5A of the current transformer mean?
Most current transformers have a standard of 5 amps (5 A) and 1 amps (1 A). On CT models, there are usually parameters such as: 100 / 5A or 100 / 1A or 500 / 5A.
For example: 100/5. So, what does this odds ratio mean?
This means that when 100 amps running in the current transformer will turn into 5 amps (5 A) or at a ratio of 500/5 they will also result in a current of 5 amps for secondary winding and 500 amps for primary coil.
How to read the 5A value?
Most electrical cabinets use mechanical parameter that can read the value of 5A. Today with increasing demand, we need to transmit this 5A signal to the PLC or other devices for monitoring and control. However, PLC and other control devices cannot read this 5A directly.
The decoder for value 5A of Analog output current transformer 4-20mA | Z201-H
All control devices today come in the form of analog 4-20mA or 0-10V precisely because we have to use via a 5A value converter of CT series 5A or CT series 10A to form Analog 4-20mA .
Application
Current transformers are an indispensable device in power monitoring and measurement systems. In simple terms, a current transformer is an electrical device used to convert high-value current to standard 5A and 1A currents. To provide safe voltage for circuit measurement, control and protection.
In addition to the classical current transformer that works on the principle of electromagnetism, there are now new type transformers for ultra-high voltage grids to reduce the cost of insulation of classic current transformers.
Block type current transformers, used in cables and busbars of the main circuit, almost like primary windings, but with only one winding. They are completely separate from the high voltage source operating in the circuit system and are always connected to the amperage load in the electrical equipment.
There are a wide range of current measurement and measurement equipment, such as wattmeter, power factor meter, power meter, protection relays or examples the release coils in magnetic circuit breakers …
Common types of current transformers
Taiwan Meters manufactures industrial electrical equipment from Taiwan. With more than 50 years of experience, Taiwan Meters equipment has gained many certifications (UL, RoHS) from prestigious organizations around the world of product lines such as current transformers, Volt gauges, gauges. Ampere, Volt switches, Amp switches …
Here are the types of current transformers of Taiwan Meters, there are 3 types of ring transformers: ring, winding and block form.
Ring type current transformer
“Rings” will not be allowed to make on the primary winding. However, instead the current flowing in the circuit, it will flow and run straight through the gaps or holes of the “ring” in the current transformer.
Currently, some ring current transformers have been constructed with a “key”, which helps the loophole or gap of the current transformer to be opened, installed and closed and does not need to be disconnected the fixed circuit.
Square type current transformer
Tech specs:
Origin: Taiwan
Standards : CE, RU, RoHS, TUV
Measuring range: 50-5000 / 5A, class 1
Dimension: MFO 30 to MFO 130 mm from 30 × 10 to 130x20mm
Round type current transformer
Tech specs:
Origin: Taiwan
Standards : CE, RU, RoHS, TUV
Measuring range: 50-4000 / 5A, class 1
Dimension: RCT 15-1 to RCT 15-4 from phi φ35 to phi φ110
Taping type current transformer
For the primary winding of the current transformer, it will be connected directly to the conductors to help measuring the current flowing in the circuit. Usually the current in the secondary winding will depend entirely on the winding ratio of the current transformer.
Tech specs:
Origin: Taiwan
Standards : CE, RU, RoHS, TUV
Measuring range: 50-6300 / 5A, class 1
Dimension: from phi φ28 to phi φ125
Block type current transformer
This is one of the common current transformers used in cables as well as the busbars of the main circuit, it is almost like a primary winding, but there is only one coil. They are completely separated from the high voltage source, which helps to operate in the circuit system and is always connected to the load current in electrical equipment.
Removable current transformer
Tech specs:
Origin: Taiwan
Standards : CE, RU, RoHS, TUV
Measuring range: 100-6000 / 5A, class 1
Dimension: TS-23 to TS-816 from 20 × 30 to 80 × 160 mm
Protection type current transformer
Tech specs:
Origin: Taiwan
Standards : CE, RU, RoHS, TUV
Measuring range: 100-4000 / 5A
Dimension: PR1 to PR10
Conclusion
Currently, current transformers and ampmeter are used together as a pair, in which the design of the current transformer provides a standard secondary current, when this current even reaches its maximum level, it does not deviate from the allowed amperage range of the ammeter.
Hopefully this article has sent you the most necessary information. See you in the next article.
