Purpose and principle of operation of the current transformer
Humanity is largely dependent on current. But just because he does not obey, you need special devices. It acts as a current transformer. What is it and what is its purpose? What is the principle of the current transformer? And how important is it?
What is a current transformer?
Under TT understand the measuring apparatus, which is necessary to convert the current. Structurally, in the transformer the primary winding is connected to the circuit in series, while the secondary one has measuring instruments, as well as protection and automation relays. TT is the main measuring device in electric power industry. Both windings are isolated. Secondary during operation usually has a potential that is close to the “ground”, which is achieved by grounding one end.
Thanks to the transformer, it is possible to take into account and measure the high-voltage current using instruments for low.In the end, everything comes down to measuring the primary, the value of which is recorded in amperes. It is necessary to distinguish the measuring current transformer from the power one. So, in the first induction is non-permanent and directly depends on the mode of operation. Therefore, current transformers are considered universal.
Purpose and principle of action
How is everything going? What is the principle of the current transformer? Through the power primary winding, which has a certain number of turns, voltage flows, which overcomes the impedance. A magnetic flux arises around the coil, which can catch the magnetic circuit. It must be placed perpendicular to the direction of the current. Thus, the minimum of the electric power will be lost during its transformation to the electric. Intersecting perpendicularly arranged turns of the secondary winding, the magnetic flux activates an electromotive force, under the influence of which a current arises that overcomes the total resistance of the coil and the output load. At the same time, a voltage drop occurs at the terminals of the 2nd circuit.
Now a little about special cases:
- The principle of operation of the welding transformer is based on maximum power output. Its design must withstand high voltage.
- The principle of operation of a single-phase transformer is based on magnetic flux. So, if you close the secondary winding to some kind of resistance, then when a current appears, a driving force will arise. If we pay attention to the Lenz law, then we can conclude that the magnetic flux will decrease. But the principle of operation of a single-phase transformer provides for the connection of direct current to the primary winding, as a result of which the reduction of the magnetic flux does not occur.
All current transformers (both for measurements and for protection) can be classified according to the following criteria:
- By the nature of the installation.
- TT designed to work in the air.
- Current transformers for operation in indoor conditions.
- TT, designed for embedding inside electrical equipment.
Current transformers have a number of requirements. All necessary information should be specified in the passport or attached table.
Here is a short list of them:
- Rated voltage can be in a wide range.
- The rated primary current that goes through the 1st winding. Indicates the values for continuous operation of the equipment.
- The rated secondary current passing through the 2nd winding. Its quality is indicated by an indicator of 1 or 5 amps.
- The secondary load corresponds to the resistance in the external 2nd circuit and is expressed in ohms.
- I1т - designed for rated voltage above 330 kV.
- I3t - is used in the range of values of 110-220 kV.
- I4t - used at a voltage that does not exceed 35 kV.
The principle of operation of the transformer may depend on the material:
- In the manufacture of conductive parts of aluminum, the temperature should not exceed 200 ° C.
- If the parts that conduct current are made of copper or its alloys and come in contact with oil or organic insulation, then the limit is 250 ° C.
There are also requirements for mechanical loads that the current transformer must withstand at a wind speed of 40 m / s. The principle of the device may change slightly due to constructive additions:
- If the CT is up to 35 kV, then this value is 500 newtons.
- With values of 110-220 kV, a resistance of 1000 N is required.
- When 330 kV is exceeded, the requirement for mechanical loads increases to a level of 1500 newtons.
Hazardous factors when working with a current transformer
When working with TTs, it is necessary to be extremely cautious, since there are significant risks of suffering up to death. So, beware:
- Possibilities of damage by high voltage potential, which can happen in case of insulation damage. Since the current transformer magnetic core is made of metal, it has good conductivity and magnetically connects the separated TT windings (primary and secondary). Therefore, there is an increased risk that personnel will receive electrical injury, or equipment damage due to defects in the insulating layer. To avoid such situations, ground one of the secondary terminals of the transformer.
- The possibility of damage by high-voltage potential due to the break of the secondary circuit. Her findings are marked as "I1" and "I2". To the direction in which the current flows, was polar and coincided across all windings, they are always connected to the load during the operation of the transformer. This is necessary due to the fact that the current,passing through the primary winding, has a high potential power, which is transmitted to the secondary circuit with minor losses. With a break in such cases, indicators are sharply reduced due to leakage into the external environment. When such incidents significantly accelerated the voltage drop in this torn area. The potential that is formed on open contacts, with the passage of current reaches several kilovolts. Such a value is life threatening. Therefore, it is necessary to make sure that all secondary circuits on current transformers are reliably assembled. And upon failure, shunting shorts are set. The principle of operation of the transformer does not tolerate neglect of safety rules, and it is very easy to get an electric shock.
- Design solutions that were used in current transformers. Any TT, like all electrical devices, must solve certain problems that arise during the operation of electrical installations. Fortunately, the industry offers a significant range. But in some cases it is better to improve the existing structure from the point of view of the enterprise, than to produce something new than many use without having enough experience.Without knowing what the transformer principle is, the consequences of such an intervention can create life-threatening situations.
Within the framework of this article we discussed the purpose and principle of operation of a current transformer. As you can see, this device is very important for the normal functioning of society. But at the same time, it is also quite dangerous, so you should always be careful not to climb inside the device, especially when current transformers work. The purpose and principle of operation of such devices were considered by us as far as the size of the article allowed. However, we have studied all the most important things.