Application Cases

Experiment Name: Research on the Electromagnetic System of an Opto-Magnetic Cable Eccentricity Measuring Instrument

Research Direction: Electromagnetic Testing

Test Objective:
Compared with other cross-linking methods, the ultraviolet (UV) cross-linking method offers advantages such as the ability to optimize the selection of PE base resin to enhance insulation material performance, increase single continuous processing time, and improve the DC electrical properties of the insulation through chemical grafting modification. The "2+1" type cross-linking process has successfully applied this method to the production of medium and high-voltage cables. Improving this cross-linking process requires the ability to measure the position of the core wire. Based on the current development status and needs of domestic cable eccentricity measurement technology, this paper divides the measurement system into two parts: the signal generation end and the signal measurement end.

The signal generation end consists of a signal generator, a power amplifier, a magnetic induction coil, and a magnetic ring. The magnetic induction coil is wound around the magnetic ring, and the magnetic ring is fixed on the outside of the core wire. The signal generator produces a high-frequency signal, which is amplified by the power amplifier and output to the magnetic induction coil. Through the principle of electromagnetic induction, the required high-frequency current is generated in the core wire.

The signal measurement end consists of an inductive sensor with an insulating housing, an amplification circuit, and a host computer. The inductive sensor is fixed on its insulating housing, and the insulating housing is also fixed on the outside of the core wire. Through the principle of electromagnetic induction, the inductive sensor generates an induced electromotive force. This induced voltage is amplified by the amplification circuit, and after data processing by the host computer, the position of the core wire can be determined.

Testing Equipment: ATA-4051 high-voltage power amplifier, signal generator, digital oscilloscope, sensor, magnetic rings.

Experimental Procedure:

Figure: Physical Images of Four Sizes of Magnetic Rings

In the actual measurement, four different specifications of magnetic rings were selected, as shown in the physical image above. The induced current in the core wire corresponding to different air gap thicknesses for these four magnetic rings was measured. The physical wiring diagram is shown in the figure below. A single-turn coil was wound around the magnetic ring. A stable 17V, 200kHz voltage signal was provided to the target magnetic ring via the signal generator and the power amplifier. The core wire passed through the magnetic ring and was connected in series with a 1nF capacitor to form a closed loop. The capacitor voltage was read using an oscilloscope connected across the capacitor terminals, allowing the induced current in the core wire to be calculated. Changes in air gap thickness were achieved by clamping paper sheets of specified thicknesses into the gap of the magnetic ring.

1 – Sensor and its housing; 2 – Magnetic ring; 3 – Capacitor; 4 – Oscilloscope; 5 – Power amplifier; 6 – Signal generator; 7 – Amplification circuit

Figure: Physical Wiring Diagram of the Signal Generation End Experiment

Experimental Results:

Figure: Measurement Results of Core Wire Induced Current for Four Magnetic Ring Specifications with Different Air Gap Thicknesses

The measurement results for the four magnetic rings are shown in the figure above. From left to right in the physical image, they are magnetic ring No. 1, No. 2, No. 3, and No. 4. The specifications are as follows:

• No. 1: Thickness 15mm, inner diameter 88mm, length 18mm, material manganese-zinc ferrite.

• No. 2: Thickness 10mm, inner diameter 69.5mm, length 25mm, material nanocrystalline.

• No. 3: Thickness 12.5mm, inner diameter 52.5mm, length 40mm, material manganese-zinc ferrite.

• No. 4: Thickness 12.5mm, inner diameter 41.5mm, length 25mm, material manganese-zinc ferrite.

It can be observed from the figure that the most significant drop in capacitor voltage occurs when an air gap is first introduced. Subsequently, as the air gap thickness gradually increases, the rate of decrease in capacitor voltage slows down. This trend is generally consistent with the simulation results.

Figure: ATA-4051C High-Voltage Power Amplifier Specifications and Parameters