Design and Application of Double Winding Current Transformer
For low-voltage distribution lines with many feeders, there are mainly the following methods to realize system monitoring: 1. Multi channel system monitoring is realized by using current transformer connected to multi-functional power monitor and 485 communication meter; 2. It is realized by connecting current transformer to transmitter Using the above two schemes has high cost and large investment.
Ordinary low-voltage current transformer has the characteristics of small volume, light weight, high accuracy, large capacity, convenient installation, large measurement range and secondary output signal 5A or 1a. However, there is no way to realize information transmission for remote transmission and system monitoring and acquisition, and it must be through transmitter or power instrument. According to the market demand, Jiangsu ankerui Electric Appliance Manufacturing Co., Ltd. has developed akh-0.66s series double winding current transformer. The primary current measurement range is 5-6300a, and the secondary has two groups of outputs, one group outputs 5A or 1a and the other group outputs 0-20mA. The primary current can be overloaded by 8-10 times, which can be directly used for system acquisition and remote transmission. It can be used together with artu-m32 to simplify the system structure, Reduce cost and improve system reliability.
1. Product design
1.1 structural features
The product has novel structure, beautiful and generous appearance, transparent flip design, anti-theft device and convenient wiring. The shell of the transformer is made of PC / ABS alloy, which has the characteristics of high temperature resistance, high mechanical strength and environmental protection; The iron core of the main winding adopts oriented cold rolled silicon steel sheet, and the iron core of the auxiliary winding adopts permalloy. This material has the characteristics of stable performance, high mechanical strength and extremely high permeability; Enamelled wire adopts high-strength enamelled wire, which has the characteristics of high insulation strength and strong temperature resistance.
The double winding current transformer is developed on the basis of the traditional low-voltage bus current transformer and is compatible with the installation mode of cable and copper bar. According to the measurement range of primary current, 5a-1250a adopts an integrated design scheme, with main specifications of s-30i, s-40i and s-50ii; 1250a-6300a adopts split structure design. The main specifications include s-60ii, s-80ii, s-100ii, s-120ii and s-200ii. The product appearance and section are shown in Figure 1 and Figure 2.
Fig. 1 appearance of akh-0.66 s series double winding current transformer
1 - terminal 1S1; 2 - terminal 2S1; 3 - terminal 1S2; 4 - terminal 1S2; 5 - secondary winding; 6 - main winding
Fig. 2 section
1.2 working principle
The working principle diagram of the double winding current transformer is shown in Figure 3. The primary current I1 of the new double winding current transformer flows into P2 from the P1 end of the main winding, the number of turns of the primary winding of the main winding is N1, the secondary current I2 of the main winding flows out from terminal 1S1, passes through the ammeter to terminal 1S2, the number of turns of the secondary winding of the auxiliary winding is N2, and the output terminals 2S1 and 2s2 of the auxiliary winding output ac0-20ma small current signal, Supply measurement and control device acquisition. So there are:
From equations (1) and (2):
Where I0 is the excitation current of the main winding and I0 'is the excitation current of the auxiliary winding. I0 and I0 'are the main factors affecting the accuracy level of double winding current transformer, and to improve its accuracy level, the main and auxiliary windings must be compensated. The common methods of compensation error mainly include iron core compensation, integer turn compensation, fractional turn compensation and magnetic shunt compensation. Because the overload of double winding current transformer itself should be considered, the iron core compensation is not required for the error of main winding, Integer turn compensation has no effect on phase difference. Magnetic shunt compensation generally has good effect when compensating small current of 10% or less, while fractional turn compensation is the most ideal (the number of turns of main winding and secondary winding is small, and multiple wires can be wound in parallel); Because the primary current of the secondary winding is generally 5A and 1a, and the output is a milliampere level small current signal, there are many turns of the secondary winding of the secondary winding of the secondary winding, and the secondary wire is wound with a single wire, the most ideal compensation method is iron core compensation. Using an iron core with high initial magnetic conductivity (such as ultramicrocrystalline) can improve the accuracy level and low cost. Therefore, using reasonable error compensation method is the key to improve the accuracy of double winding current transformer.
