Keywords: open-type current transformer, low-voltage distribution system, renovation project, working principle, application, construction details
1 Introduction
At present, most of the low-voltage current transformers in the market are mainly used for the construction of new projects. Due to the rapid economic development, enterprises' awareness of energy saving and emission reduction is gradually increasing, and many enterprises
The electrical characteristics of the industry are:
â‘ The operation time of the electrical cabinet is long;
â‘¡ Most current transformers only measure the system current, and there is no corresponding metering device and protection device. The metering device only has a master table of the power supply bureau.
However, the electrical energy of all workshops cannot be evaluated, and there is no system line protection device at all.
â‘¢ Provide the collected signal for APF active filtering in the occasions where the harmonic content is relatively large;
â‘£ Most of the line trunks are large-sized copper bars, and disassembly requires a lot of manpower and time, and it is not convenient to install conventional current transformers;
⑤The production time of the enterprise is urgent, and the power cannot be cut off for a long time.
Therefore, if you need to transform the above electrical, using an open-type current transformer can save a lot of investment for users.
2 Product design
2.1 Structural characteristics
This product has novel structure, beautiful appearance, and transparent clamshell design, which is convenient for wiring. The shell material adopts PC / ABS alloy, which has the characteristics of high temperature resistance, high mechanical strength, environmental protection, etc .; the iron core adopts oriented cold rolled silicon steel sheet, which has the characteristics of stable performance, high mechanical strength, and extremely high magnetic permeability; the enameled wire in the skeleton coil is adopted High-strength enameled wire has the characteristics of high insulation strength and strong temperature resistance. The specific structure is shown in Figure 1.
Open-type current transformers are developed on the basis of traditional low-voltage bus-type current transformers. They are compatible with cable and copper bar installation methods. According to the measurement range of primary current, 100A-5000A adopts a split design scheme. The main specifications are K-30 × 20, K-08 × 50, K-80 × 80, K-120 × 60, K-120 × 80, K-160 × 80, K-200 × 80.
figure 1
1-frame coil, 2-transparent flip cover, 3-mounting nut, 4-terminal, 5-core, 6-spring, 7-case, 8-mounting screw.
2.2 Working principle of open current transformer
The working principle of the open low voltage current transformer is shown in Figure 1. The primary winding of the open current transformer is connected in series in the line under test, and I1 is the line current, that is, the current transformer
Primary current, N1 is the primary turns of the current transformer, I2 secondary current of the current transformer (usually 5A, 1A), N2 is the secondary turns of the current transformer, Z2e is two
Impedance of secondary circuit equipment and connecting wires. When the primary current flows in from the current transformer P1 end and P2 end out, when the secondary Z2e is connected, according to the principle of electromagnetic induction, the current
In the secondary winding of the transformer, a current I2 flows from S1 and passes through Z2e to S2 to form a closed loop. It can be obtained that the current in the ideal state I1 × N1 = I2 × N2,
So I1 / I2 = N1 / N2 = K, K is the transformation ratio of the current transformer. However, since the core of the open-type current transformer is cut, the performance of the core will be better, so it is necessary
Increase the cross-sectional area of ​​the core of the transformer, and increase the number of ampere turns, so that I1 × N1 = I2 × N2≥100AN.
Figure 2 Figure 3
Note: In Figure 3, the upper body of the 1-open current transformer, the lower body of the 2-open current transformer, and the 3-mounting screws and nuts
2.3 Product installation
As shown in Figure 3, open the mounting screws and nuts of the transformer, remove the lower body of the transformer, install the upper body of the transformer into the primary busbar of the power distribution system, close the lower body of the transformer, and Install the screws through the fixing holes of the upper and lower bodies of the transformer, screw on the nuts to fix the upper and lower bodies of the transformer together, and then fix the transformer on the busbar through the mounting holes on both sides of the transformer. Complete the installation of the transformer. Then connect the secondary of the transformer to the measuring device. The whole process is relatively quick and simple.
3. Application
Open current transformers are mainly used in low-voltage distribution transformation projects. The output of open current transformers is the standard 5A or 1A like conventional closed-end transformers. It has high measurement accuracy and large capacity. It can be used with measuring instruments and instruments. The product has strong overload capacity and can be used with the device.
3.1 Application examples
Scheme (1) , taking the low-voltage feeder of a company in the semiconductor industry in Shanghai as an example, as shown in Figure 4, each feeder needs to measure the three-phase current and supply the current signal to the relay to prevent system current overload or short circuit. The primary busbar specifications of A, B, and C phases of each feeder are 120 × 10 × 3, the height of the copper bar is 1.5 meters, the rated current of each phase is 2500A, and the AKH-0.66 / 120 × 50II closed-mouth current transformer is used To collect current signals, each phase copper bar must be disassembled during construction. The weight of each phase copper bar is 480kg, so the installer needs at least 2 people and at least 3 hours to disassemble. The transformer installation wiring is 20 minutes, and it takes 3 hours to install the copper bars. Then each feeder needs at least 19 hours to complete the installation, and the factory must be powered off for about 20 hours.
Figure 4 Figure 5
Scheme (2) , taking the same low-voltage feeder of a company in the semiconductor industry in Suzhou as an example, as shown in Figure 5, each feeder needs to measure three-phase current and supply the current signal to the measuring instrument. The primary busbar specifications of A, B, and C phases of each feeder are 120 × 10 × 3, the height of the copper bar is 1.5 meters, the rated current of each phase is 2500A, and the AKH-0.66 / K-120 × 60 open-type current is used The current signal is collected by the transformer. During construction, there is no need to dismantle each phase of the copper bar. An installer only needs to open the transformer to install the screw \ nut, put the transformer on the bus bar, close the transformer, and then fix it with the screw \ nut Ok, then fix the transformer on the busbar.The entire process only needs 30 minutes to complete the installation and wiring to be disassembled, and the factory power outage only takes about 40 minutes.
Therefore, the cost comparison of each feeder in the above scheme is shown in table (1)
Table I)
3.2 Construction details
According to the parameters in the above product specifications of our company, and according to the actual situation of the user's site, select the appropriate open current transformer
Connect the relay or measuring instrument to the open current transformer for protection twice to ensure that the current transformer cannot be opened for the second time. Open the upper and lower parts of the open current transformer, and pay attention to the P1 surface and the lower side of the current transformer The two parts are the same, and the relays are installed on the site, all the sites are placed, and the large current once the bus bar passes through the copper bar occasions to wait for power outage, as shown in the following figure:
After the power failure, install the open current transformers of all circuits on the busbar at the same time, and install the upper and lower parts of the open current transformer through screws and nuts, as shown in the following figure:
Finally, the open current transformer is fixed on the busbar through our standard accessories, and the relay output signal line is connected to the auxiliary contact of the circuit breaker to complete the entire installation process. As shown below:
In summary, the use of open-type current transformers in the retrofit project has the highest cost performance, which can quickly realize intelligent low-cost multi-loop monitoring of low-voltage distribution, which is conducive to the further promotion and application of low-voltage intelligent distribution.
4 Conclusion
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