1. Principle of coil pulse test

Coil pulse test schematic

In the above picture: C1: storage capacitor

C2: Resonance capacity

Cp: ​​equivalent parallel capacitance at both ends of the coil

R: energy consumption equivalent parallel resistance

Lx: coil equivalent inductance

The storage capacitor C1 is charged in advance, the charging voltage is the maximum voltage set by the instrument, the switch SW1 is closed for a short period of time, and the device is closed at SW1. Since C1 ≥ C2, C1 quickly charges C2, after a period of time. After SW1 is disconnected. At the same time, the excitation pulse is simultaneously applied to a measured coil Lx, C2, Rp, Lx will exhibit a free-attenuation oscillation, which is exponentially decreasing and modulated with a sinusoidal signal. According to the damped oscillation condition of the resonant capacitor C2, the internal state of the coil is known to judge the quality of the winding component (including the insulation of the coil itself, the winding inductance).

Attenuation curve of the coil

Coil products (such as transformers, motors, etc.) due to factors such as winding materials, magnetic materials, skeletons, processing techniques, etc., can cause insulation performance degradation between coil layers, turns and pins.

The pulse test of the coil can test its electrical performance without damaging the device under test. This test method can judge the quality of the coil in a short time. When measuring, the same pulse as that measured by the standard coil is applied to the coil under test through capacitor discharge. Due to the presence of coil inductance, stray capacitance and Q value, a voltage attenuation waveform corresponding to the discharge pulse is compared, and the attenuation is compared. Some characteristics of the waveform can be used to detect the difference between the turns and inter-layer shorts and the number of turns and the magnetic material. If a high voltage pulse is applied, the insulation is judged based on the appearance of corona or interlayer discharge.

2. Brief description of the pulse test scheme

In general, there are two test schemes for coil pulse testing, analog and digital. Tonghui provides the analog TH2881 inter-turn insulation tester and the digital TH2882 series pulse coil tester.

(1) Analog coil pulse tester: TH2881A turn-to-turn insulation tester. The pulse test of the instrument is a traditional test method. The instrument provides two high-voltage pulse output ports H1 and H2. The tested coil is tested simultaneously with the standard coil, and the attenuation resonance waveform of the measured coil and the standard coil waveform are observed on the CRT. The difference is used to judge the quality of the coil under test.

The following is an example of the TH2881A test of the coil: there is no significant difference between the standard part and the attenuation oscillation waveform of the device under test. The measured winding between the measured windings is not faulty; the measured part does not match the waveform of the standard part, indicating that the measured winding is inter-turned. The insulation is faulty. The display of the fault waveform can be accompanied by a discharge sound, or the discharge spark can be seen and the ozone is smelled, and the display waveform exhibits a discharge glitch and a waveform jump.

Poor insulation of normal waveform

Short circuit waveform disconnection waveform

The winding of the device under test is broken, that is, the open circuit, the displayed waveform is in an arc, and sometimes the discharge phenomenon occurs at the broken line; if the winding of the device under test is completely short-circuited, the displayed waveform is a horizontal line.

The advantages of the analog tester are: the observation waveform is relatively intuitive; the operation is convenient. The disadvantage is: it is greatly affected by human factors, and it is impossible to use data to judge the pros and cons of the product; it is necessary to add the standard parts to the test end for a long time, which will affect the test result due to the aging of the standard parts for a long time; the inductance is small. It is difficult to measure, generally suitable for coil products above 1mH, such as various motors; the test terminal outputs high-voltage pulses for a long time, affecting the life of the instrument, and outputting a pulse every 20mS during the test, so that the CRT can obtain a stable visible waveform. When the small inductance is tested, the display brightness is greatly reduced due to the short screen display time, which affects the observation.

(2) Digital storage coil pulse tester: H2882-3/TH2882-5/TH2882S-3/TH2882S-5, this series of products uses high-speed digital sampling method, the waveform of the standard coil is stored in the instrument, the test will The measured waveform is compared with the standard waveform, and the merits of the coil under test are determined according to the set criteria (area, area difference, zero crossing, corona, etc.).

The advantages of this method are:

High-speed digital sampling makes the discriminating process automatically completed by the instrument, which can eliminate human influence factors; it is not necessary to measure standard samples at the same time during testing; all tests use unified criteria, standard sample waveforms can be stored, recalled, transferred, shared by multiple machines, etc. It can test a wide range of inductance, the minimum testable 10μH coil, basically adapt to the test of various coil products; high voltage is instantaneous output, one test theoretically only needs to output a high voltage pulse, which greatly prolongs the life of the instrument; there is no display Brightness issues, waveforms can be selected for optimal display; due to the use of digitization and intelligent technology, many additional analysis functions can be performed, such as time and period measurement, voltage measurement, multiple averaging, continuous testing, and automatic output voltage Level control (ALC), PASS/FAILL sound mode selection, etc.; various forms of criteria can be used to distinguish subtle changes in the quality of the coil under test, such as area, area difference, zero crossing, corona, etc.; Interfaces for different purposes, such as USB interface for data and standard waveform transfer and save, IEEE488 interface and RS232 interface for Man-machine communication or component automatic test system, HANDLER / SCANNER interface for automatic mechanical processor and pulse transformer coil automatic test system.

Beijing Atlantic Instrument Engineering Co., Ltd., as a distributor of Tonghui products, has been adhering to the principle of “advocating test and measurement technology” for more than 20 years, and adheres to the quality policy of “the world of instrumentation and perfection, sincere and sincere service”. Actively provide customers with professional, convenient and thoughtful localization services, including installation and commissioning, calibration and maintenance, precision measurement, and fault diagnosis. Now it has become one of the well-known instrumentation product integrators, application solution providers and system engineering service providers in China. (http://)

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