CN1029494C - A kind of AC and DC current comparator - Google Patents

Abstract

The invention belongs to a current testing device, which is a comparator and consists of a measuring head and an electronic amplifier, wherein the measuring head is in an annular opening shape and consists of an upper half ring and a lower half ring, and a half surface A and a half surface B are arranged in the diameter direction. The mutual inductance direct coupling circuit of the secondary alternating current in the electronic amplifier is composed of a secondary winding, a load resistor, an electrolytic capacitor and a diode. The device can measure direct current and alternating current, and can also measure alternating current and direct current simultaneously, the assembly and disassembly are very convenient in field test, and the power failure, the assembly and the disassembly of the tested bus and the assembly and the disassembly of the tested mutual inductor are avoided.

Description

The invention belongs to a current testing device, which is especially suitable for the mixed use of alternating current and direct current.

"Electronics and Power the Journal of the Instification of Electrical Enginers Vol.32 No.1 January 1977." Electronics and Power the Journal the Journal the Journ " and a.c.by Transformer) devices and circuits. Although this comparator is very attractive, it has at least two disadvantages as follows: (1) The measuring head of the comparator is a closed-loop structure, and the measured line must pass through the center of the closed loop, which is very important for industrial field testing. inconvenient. The material used in the measuring head is a high-permeability film alloy, which is expensive. Poor tolerance to electromagnetic and mechanical shocks. (2) The obvious disadvantage of the electronic amplifier circuit is that for a large overcurrent, it is impossible for this power amplifier to send a corresponding compensation current. In this case, due to the saturation of the iron core, the balance of the magnetic potential is destroyed. Otherwise, it is required It is uneconomical to make the power amplifier very large.

According to the disadvantages of the above-mentioned prior art, the present invention provides an open-type AC/DC current comparator.

In order to accomplish the above object, the present invention adopts the following technical measures. Fig. 1 is an outline view of the measuring head of an open-type AC/DC current comparator, Fig. 2 is a cross-sectional view of the measuring head Huff plane A, and Fig. 3 is a circuit diagram of the comparator of the present invention. This AC/DC current comparator consists of two parts: a measuring head and an electronic amplifier. The measuring head is in the shape of an annular opening, consisting of upper and lower half rings, and Hough surfaces A and B are set in the diameter direction. The AC main iron core T ₂ in the measuring head is wound into a ring-shaped iron core by a silicon steel sheet, and the AC detection winding W _D is wound on the outside, and then the monitoring winding level W _K is wound on the outside of the winding, and the W _K is wound on the outside of the winding. Two DC main iron cores T 3 are wound with AC zero-adjusting winding W _a , and the two DC main iron cores T ₃ are rolled into ring-shaped iron cores by silicon steel sheets, and the excitation winding W _a is wound on the outside respectively. Then, assemble the above-mentioned AC and DC winding cores, wind the electrostatic shielding E outside them, and place it in the magnetic shielding core _T1 wound by silicon steel sheets, and wind the AC _and DC windings outside T1 The secondary winding W _s is covered with electrostatic shielding F on the outermost surface. After the above structure is casted with epoxy resin, Huff faces A and B are opened in the radial direction. The mutual inductance direct coupling circuit of the secondary AC current I _sa in the electronic amplifier is that most (about 99%) of the AC current (I _sa -I _M ) in the secondary winding W _s is generated by the mutual inductance direct coupling circuit, The mutual inductance coupling circuit is composed of secondary winding W _s , load resistance B, electrolytic capacitors C ₁ , C ₂ , diodes D ₁ , D ₂ , where the anode of D ₁ is connected _to the cathode of D ₂ and connected to the non-identical terminal and the output terminal of DC power amplifier _A , the cathode of _D1 is connected to the positive pole of C1, the anode of _D2 is connected to the negative pole of _C2 , the negative pole of _C1 is connected to the positive pole of _C2 , and then connected to the load B and the amplifier The grounding point is connected, and the other end of the load B is connected to the same-named end of W _s . Figure 3 shows the electrical schematic diagram of the open AC/DC current comparator. When the AC and DC currents I _pa + I _pd pass through the measured primary winding W _p , for the AC component I _pa , based on the principle of AC magnetic potential balance, The secondary AC current I′ _sa will be induced in the secondary winding W _s , because there is a certain amount of magnetizing current error in this secondary current I _sa , that is, a certain amount of AC safety is applied to the main iron core T ₂ Turn difference I _pa W _p -I _sa W _s , the ampere-turn difference will induce a signal in the AC detection winding W _D , and the signal obtained by W _D will be amplified and fed back through the electronic amplifier to obtain the magnetizing current I _M for compensating the secondary AC current , so that the ampere-turn difference I _pa W _p -I _sa W _s in the main iron core _T2 is close to zero, thereby obtaining a high-precision turn ratio relationship between the secondary current and the primary current, I _pa = (Ws)/ (We) I _sa , the secondary AC current I _sa with high accuracy flows through the external load B, and I _pa can be determined through I _sa . In order to ensure the system works with high precision and high reliability, an AC zeroing winding W _a and an AC monitoring winding W _k are set up. W _a is connected in series with the parallel branch of secret potential source e, resistor R, and capacitor C. Reasonable selection of the values of R and C can obtain the best AC zeroing effect, thereby effectively suppressing the influence of the DC system ripple on the AC system zero point. Influence. The AC monitoring winding W _k is connected to the monitoring device K. Once the electronic part or other parts fail, the accuracy of the secondary current will change, and the AC magnetic potential in the neutralization of the main iron core _T2 cannot approach zero. At this time The monitoring winding has a relatively large signal output, thus constituting the self-diagnosis function of this open type AC current comparator. It can be seen from Fig. 3 that, for the DC component _Ipd in the primary winding _Wp , the magnetic modulation principle is used for testing. A pair of excitation windings W _s evenly wound on a pair of DC main cores T ₃ are connected to an AC power frequency transformer T ₄ after butt connection, and the paired pair of T ₃ will be affected by a power frequency AC magnetic field. When the measured DC component _Ipd exists in the primary winding, a corresponding DC magnetic field will act in the DC main core _T3 , and the DC magnetic field will be modulated by the AC magnetic field. The center tap M of the excitation transformer will output an AC signal dominated by the second harmonic. The amplitude and phase of the signal correspond to the magnitude and direction of the measured DC _Ipd , and the filtering, demodulation, and amplification links composed of electronic components A. Provide feedback DC current I _sd to the secondary winding W _s . Since the open-loop gain of the system is very high, when the closed-loop system is balanced, the ampere-turn difference between the primary and secondary DC approaches zero, that is, I _pd W _p -I _sd W _s =0, I _pd = (Ws)/(Wp) I _sd , so that the secondary direct current I _sd with high turn ratio accuracy can also be obtained in the load B.

Figure 1 Outline drawing of the measuring head of the open type AC current comparator.

Fig. 2 Cross-sectional view of Hough plane A of the measuring head.

Fig. 3 Open type AC and DC current comparator circuit diagram.

The invention has the following advantages: (1) The iron core of the measuring head is replaced by the low-cost common silicon steel sheet material, which is more than 10 times more costly than the film alloy high magnetic permeability material, which not only has low overall cost, is convenient to manufacture, and can Withstand strong mechanical and electromagnetic shocks, which is convenient for industrial promotion and use. (2) The measuring head is an open structure composed of upper and lower half rings, which is very convenient to assemble and disassemble for on-site testing, avoiding power failure, assembly and disassembly of the busbar under test and assembly and disassembly of the tested transformer. (3) The present invention breaks through that the AC secondary current is provided by the amplifier, which brings about a series of problems such as requiring the power amplifier to be sufficiently large, poor in reliability, and high in cost. (4) This device can measure both DC current and AC current, and can also measure AC and DC current at the same time. (5) The comparator is equipped with self-diagnosis function of running status.

After testing, the open-type AC/DC comparator, such as the rated current of AC and DC, is 4000A. When AC and DC are input into the primary winding W _p with different combinations of ampere-turns at the same time, the AC error is measured at 1% of the rated current (40A ) to 100% rated current (4000A), its relative error (including in-phase component and quadrature component) does not exceed 0.005% (ie 50PPm). The test data is shown in Table 1 as the AC error data table, in ppm . (See Table 1 at the end of the text)

Table 1

AC AC current

AC error 40 ampere-turns 400 ampere-turns 1000 ampere-turns 2000 ampere-turns 3000 ampere-turns 4000 ampere-turns

DC

Ampere-turn In-phase Quadrature In-phase Quadrature In-phase Quadrature In-phase Quadrature In-phase Quadrature In-phase

0 +18 +13 +16 +15 +13 +8 +7 +8 +6 +4 +5 +3

40 +18 +13 +16 +15 +13 +8 +7 +8 +6 +4 +5 +3

400 +20 +14 +15 +16 +13 +8 +7 +8 +5 +4 +5 +3

1000 +20 +13 +14 +17 +13 +8 +6 +9 +5 +4 -

2000 +12 +20 +12 +20 +12 +9 +5 +10 +4 +5 -

3000 +14 +20 +11 +20 +11 +9 +5 +11 - -

4000 +14 +20 +11 +21 - - - - - -

Claims (1)

1. An AC/DC current comparator, consisting of a measuring head and an electronic amplifier, characterized in that the measuring head is in the shape of an annular opening, composed of upper and lower half rings, and Hough surfaces A and A are set in the diameter direction. B. The measuring head consists of the following parts: a) After the AC main core T ₂ is wound into a ring-shaped iron core by silicon steel sheets, the AC detection winding W _D is wound on the outside, and then the monitoring winding W _K is wound on the outside of the winding, and the AC is wound on the outside of the monitoring winding W _K Zero winding W _a ; b) After the two DC main cores T ₃ are rolled into ring-shaped iron cores by silicon steel sheets, the excitation windings W _a are respectively wound on the outside; c) Assemble the windings described in a) and b), wind the electrostatic shielding layer E outside them and place it in the magnetic shielding iron core _T1 wound by silicon steel sheets, and wind an alternating current shielding layer E outside _T1 The DC secondary winding W _a is covered with an electrostatic shielding layer F on the outermost side; d) After the above structure is casted with epoxy resin, Huff faces A and B are opened in the diameter direction, The mutual inductance direct coupling circuit of the secondary alternating current I _5a in the electronic amplifier is composed of a secondary winding W _a , a load resistor B, electrolytic capacitors C ₁ , C ₂ , diodes D ₁ , D ₂ , wherein the anode of D ₁ is connected to The cathode of D ₂ is connected to the non-identical terminal of W _a and the output terminal of DC power amplifier A, the cathode of D ₁ is connected to the positive pole of C 1, the anode of D ₂ is connected to the negative pole of C ₂ , and the negative pole of C ₁ is connected to the negative pole of C ₁ After the positive pole of C ₂ is connected, it is connected to the ground point of load B and amplifier A, and the other end of load B is connected to the terminal with the same name of W _a .

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