For the low-voltage distribution lines with many feeders, the following methods are mainly used to realize system monitoring: 1. Multi-channel system monitoring is realized by using a current transformer connected to a multi-function power monitor plus a 485 communication meter; 2 using a current transformer to connect the transmitter To achieve; use the above two schemes with high cost and large investment.
Ordinary low-voltage current transformer has the characteristics of small size, light weight, high accuracy, large capacity, convenient installation, etc., and the measurement range is relatively large, the secondary output signal is 5A or 1A, but there is no remote transmission and system monitoring acquisition. The way to achieve information transfer must be through a transmitter or power meter. In response to market demand, Jiangsu Ankerui Electric Manufacturing Co., Ltd. developed AKH-0.66S series double winding current transformer, primary current measurement range 5-6300A, two sets of output, two sets of output 5A or 1A, another group The output is 0-20mA, and the primary current can be overloaded 8-10 times. It can be directly used for system acquisition and remote transmission. It can be used with ARTU-M32 to simplify system structure, reduce cost and improve system reliability.
1.1 Structural features
The product has a novel structure, beautiful appearance and a transparent flip cover with anti-stealing device and convenient wiring. The transformer housing material is made of PC/ABS alloy, which has the characteristics of high temperature resistance, high mechanical strength and environmental protection. The main winding core adopts oriented cold-rolled silicon steel sheet, and the secondary winding core adopts permalloy. The material has stable performance. The mechanical strength is high, the magnetic permeability is extremely high, and the enameled wire is made of high-strength enameled wire. The material has the characteristics of high insulation strength and high temperature resistance.
The two-winding current transformer is developed on the basis of the traditional low-voltage bus-type current transformer. It is compatible with cable and copper bus installation. According to the measurement range of primary current, 5A-1250A adopts integrated design scheme. The main specifications are S-30I. , S-40I, S-50II; 1250A-6300A adopts split structure design, the main specifications are S-60II, S-80II, S-100II, S-120II, S-200II as split type, product appearance and profile view Figure 1 and Figure 2.
Figure 1 AKH-0.66 S series double winding current transformer appearance
1-terminal 1S1; 2-terminal 2S1; 3-terminal 1S2; 4-terminal 1S2; 5-sub winding; 6-main winding
Figure 2 cross-sectional view
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 the P2 from the P1 end of the main winding, the number of turns of the primary winding is N1, and the secondary current of the main winding is I2. The terminal 1S1 flows out, passes through the ammeter to the terminal 1S2, the secondary winding secondary winding turns to N2, and the secondary winding output terminals 2S1 and 2S2 outputs AC0-20mA small current signal, which is supplied to the measurement and control device for collection. So have:
From the formula (1), (2) can be obtained:
In the formula, I0 is the excitation current of the main winding, and I0' is the excitation current of the secondary winding. I0 and I0' are the main factors affecting the accuracy of the two-winding current transformer. To improve the accuracy level, the primary and secondary windings must be compensated. The common methods of compensation error are: core compensation, integer åŒ compensation, fraction åŒCompensation and magnetic shunt compensation, because the double winding current transformer itself should consider overload, so the main winding error does not need to consider core compensation, integer åŒ compensation does not work on the phase difference, magnetic shunt compensation generally compensates for small current 10% And the following effect is good, and the fractional åŒ compensation is most ideal (the number of turns of the secondary winding of the main winding can be reduced by using multiple wires); because the primary current of the secondary winding is generally 5A, 1A, the output is a milliampere small current signal, The secondary winding has a large number of turns, and the secondary wire is wound by a single wire. Therefore, the most ideal compensation method is core compensation, and the core with high initial magnetic permeability (such as ultrafine crystal) can improve the accuracy level, and low cost. Therefore, the use of reasonable error compensation is the key to improving the accuracy of the two-winding current transformer.
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