MICROTEST Impulse Winding Tester 7750

The MICROTEST 7750 Interlayer Short Circuit Tester is designed for reliable insulation quality testing of high- and low-winding components. It utilizes non-destructive pulse voltage for waveform sampling and comparison, effectively detecting insulation issues in motors, transformers, BL inductors, and other components.
It supports pulse voltage outputs of 1200V, 5200V, and 10000V respectively, and employs 200MHz high-speed sampling technology to analyze subtle discharge faults. It offers six analysis and comparison modes, including total area comparison, area difference comparison, corona number comparison, jitter number comparison, second derivative comparison, and waveform comparison mode. With a testing speed of up to 10 times per second, it is the optimal choice for automatic production lines of winding components.

By applying a pulse voltage to the terminals of the winding coil, a damped oscillation waveform is generated through L/C resonance without damaging the test object. This allows for the comparison of instantaneous waveforms between a standard reference and the test object, enabling the early detection of faults such as interturn short circuits, internal coil defects, or insulation flaws in the magnetic core. This method ensures the quality and longevity of the product.

_The internal capacitor Cs of the instrument is connected in parallel with the external test object inductance Lr.

_The instrument outputs a set of high-speed pulse voltages to the parallel circuit.

_This generates a resonance between the inductance L and the capacitor C

The following electrical characteristics
have changed as a result of the defective product
_Inductance of the coil
_Quality factor (Q value)
_Difference in coil turns (voltage difference)
_Variations in magnetic core material
_Short-circuits between windings inside the coil

It supports six analysis and comparison modes, enabling the analysis and detection of insulation short-circuit issues in different winding components.

_Total area comparison

In the range from 1 to 2 as shown in the diagram, a comparison of the waveform area of the test coil is performed. When an interlayer short-circuit occurs in the test object, the energy loss of the coil increases, causing the damping coefficient of the resonance to increase. As a result, the resonance amplitude decreases, and the total area also decreases. This is the fundamental parameter for detecting interlayer short-circuits.

_Differential area comparison

The difference between the point-to-point waveform areas of the standard sample and the test product is referred to as the “area difference.” When an inter-turn short-circuit occurs in the test object, the inductance decreases (similar to when the secondary winding of a transformer is short-circuited, the inductance of the primary winding decreases),resulting in a change in the oscillation frequency of the latter part of the waveform and a shift in the phase of the resonant waveform. Consequently, the area difference also changes.

_LAPLACIAN Comparison

In the case of poor insulation quality of the coil, discharges occur under high-voltage impulses, causing rapid changes in the oscillation waveform. By utilizing the second-order differentiation algorithm of the MICROTEST 7750, the highest discharge level can be obtained.

This effectively detects quality issues such as leakage due to faulty solder joints in integrated molded inductors.

_COMP Comparison

By setting an allowable waveform range for the standard wave, this feature can simultaneously determine the amplitude and phase of the resonant wave. It enhances the detection capability of inter-turn short circuits.

_FLUT Comparison

When there is inter-turn discharge in the winding coil, the waveform will exhibit tremors or fluctuations. Therefore, the instrument quantifies the degree of waveform tremors into numerical values for comparison.