Abstract: Introduces the application of open type current transformer in the renovation project, as well as the role of open type current transformer with switching quantity, and the advantages of comparison with conventional open type current transformer, and analyzes with engineering examples.

Keywords: low voltage distribution system, switching, open type current transformer, anti-theft, working principle

1.Introduction

With the transformation of urban and agricultural networks in China's power industry and the increasing automation of low-voltage distribution systems, open type current transformers, as an important electrical component in low-voltage distribution systems, have become more and more obvious in the transformation of power grids and have been widely used in measurement, metering, relay protection, system monitoring, grounding protection and various power system analysis.

However, the open type low-voltage transformers on the market at present may be installed with snaps that are not tightened to cause the core to be not completely closed; or during operation, the transformer shell is subjected to great stress and the shell hinge breaks, resulting in the upper and lower cores not being closed, affecting the accuracy of the transformer or no current output. The open type current transformer with switch can effectively feedback the above situation to the instrument or the background, and has a broad application prospect in power monitoring projects.

2.Working Principle of Current Transformer

Figure 1

The working principle of the open-ended low-voltage current transformer is shown in Figure 1. The primary winding of the open-ended current transformer is connected in series with the line under test, I1 is the line current, that is, the primary current of the current transformer, and N1 is the primary turns of the current transformer. I2 is the secondary current of the current transformer, N2 is the secondary turns of the current transformer, and Z2e is the impedance of the secondary circuit equipment and connecting wires. 

When the primary current flows in from the P1 end of the current transformer, and the P2 end goes out, in the case that the secondary Z2e is turned on, according to the principle of electromagnetic induction, the secondary winding of the current transformer has a current I2 flowing from S1, through Z2e to S2, form a closed loop. It can be obtained that the current is I1×N1=I2×N2 in the ideal state, so there is I1/I2=N1/N2=K, and K is the transformation ratio of the current transformer. However, after the iron core of the open current transformer is cut, the performance of the iron core will be worse, so the cross-sectional area of the iron core of the transformer must be increased, and the number of ampere turns must be increased, and I1×N1=I2 ×N2≥100AN.

In addition, the transformer on the switch, when the transformer snap did not card or the transformer aging caused by the rupture of the shell, the switch button pops up, normally closed to normally open, the signal termination transmission, the transformer no signal output; when the transformer snap is normal, the switch state is normally closed, the transformer works normally.

3.Open Type Current Transformer

Open type current transformers are mainly used in industrial city network and agricultural network renovation projects. Features are easy to install, no need to remove the primary busbar, and can also be operated with electricity. However, the current low-voltage open type transformers on the market have the following drawbacks.

(1) Open type current transformer on the market may not be installed when the clasp is not tight or the core is not closed, the risk of the transformer falling off or disconnected during operation.

(2) Open type current transformer will have no signal and other problems if it is artificially opened twice after installation. AKH-0.66/K-SW series current transformer can solve the above problems. This transformer has a beautiful appearance and is easy and simple to install and maintain. As shown in Figure 2, the transformer has the following advantages.

Figure2

(3) AKH-0.66/K-SW series current transformer, installation without disconnecting the electricity, you can operate with electricity, close the direct use of the site installation is simple, reducing labor costs.

(4) AKH-0.66/K-SW series current transformer, there are four leads in the module, two to transmit the current signal, two to transmit the switching signal.

(5) AKH-0.66/K-SW series current transformers, when the buckle is not locked or the transformer is aging, the casing is broken, the upper and lower casings pop open, the iron core is in poor contact, and the switch stuck on the lower casing of the transformer protrudes. The button will pop up, the switch will be disconnected, and the switching signal will terminate the transmission, which will prompt the open-type low-voltage transformer to stop working.

(6) AKH-0.66/K-SW series current transformer, the upper and lower shells with lead seal holes, once the installation is completed immediately lead seal.

4.Parameter Comparison Table

4.Conclusion

The emergence of AKH-0.66/K-SW series current transformer, with abnormal open alarm, stop on the power event reporting and other functions, but also for the enterprise to reduce the cost of human and material resources, due to the huge market, once the formation of production capacity, but also can drive the rapid development of other industries.