(Low Voltage Electrical Test + Hi pot/ Insulation Test + Impulse Test)
All-In-One Low Voltage Electrical Test
Inductance (L)/Leakage Inductance/Turn Ratio/Resistance (DCR)/Resistance (R)/Balance/Capacitance (C)/Short Circuit.
Automatic Balancing Bridge & 4-Wire DCR Test (DC Resistance)
Check if the winding tension is improper for Transformer.
Turns ratio is an important parameter in transformer.
Ideally, we can get the turns ratio by compare the input and output voltage. However, there are many parameters that might affect. So, there are some different ways to detect turns ratio.
TR Voltage Put a AC voltage on primary coil, and detect the voltage on secondary coil. Compare the turns ratio and phase
TRL Inductance Detect the inductance on each coil, and calculate the turns ratio. The turns ratio is more accurate on transformer with bigger leakage inductance.
Detect capacitance to make sure the insulation between winding position and winding coil is enough
The winding coil on the transformer include distributed capacitance, it usually distribute between winding coil.
Capacitance is usually represented by the capacitance by one winding to another winding in an equivalent circuit.
Cs and Cp is an equivalent capacitance in series or parallel in equivalent circuit.
D value is the ratio with AC resistance and capacitance, The lower the D value, is better.
Test leakage by LCR balance bridge
When the instrument connect a primary coil with the transformer and the secondary coil is under open status, the test result L= Lp on primary coil + Leakage Current.
→The leakage inside the instrument must short the secondary coil in the transformer.
A ideal secondary coil’s voltage will be 0V in short status. The voltage on both side of primary coil will be 0V. The inductance from primary coil will be the real leakage current.
The transformer may have partial discharge under high voltage/current that could penetrate the insulation cover.
Short time hipot testing is not able to detect the real life time of transformer, so, the impulse test is necessary.
Recently, the voltage on the electronic product is increasing. The partial discharge may happen under instant high voltage/current leaking. This may cause the penetration on the wire.
Short time withstanding test is not able to detect the product life of transformer. So, the inspection of impulse test is necessary.
MICROTEST use the non-destructive testing technology
Charge the inner capacitor until the setting voltage level, and discharge on the coil of the transformer. During this process, capacitor and inductor will create a set of amplitude-decreasing waveforms, and the instrument will analyze the pulse.
Safety Certification Testing Items
AC Hi pot
DC Hi pot
AC/DC Withstanding Voltage Test
Difference between AC and DC
AC Hi pot Test
Most DUT have parasitic capacitance. With AC test, might not able to charge the parasitic capacitance. Therefore, this will create constantly current go through.
DC Hi pot Test
The parasitic capacitance will be charged under DC hi-pot test. Therefore, the current will reduce to almost 0.
Advantages for AC Test
AC Hi pot Test
AC test is same as our normal usage electricity. Also, AC is able to do positive and negative polarity test.
AC test won’t charge the parasitic capacitance on the DUT, so it won’t create instantaneous peak current. Do not need to discharge the DUT after testing.
DC Hi pot Test
The parasitic capacitance on DUT has been charged under DC test, so the rest leakage current is the real current from DUT.
Disadvantage of AC/DC Hi-pot Test
AC Hi pot Test
If the DUT has huge parasitic capacitance, the current we detect will bigger then the actual current.
To fulfill the necessary current for the capacitance of the DUT, the output current is much more than DC test. This is danger for the operator.
DC Hi pot Test
Testing Voltage has to increase from 0.
The higher parasitic capacitance has, the more time it needs for DC voltage to increase. The voltage increase slower when it goes up. However, if the charging current is too high, it may cause the misjudgment for the instrument.
The discharge process is necessary after DC hi-pot test.
DC test can only do the single polarity test.
Hi-pot Test Time
The testing voltage is refer to the condition of DUT while doing Hi-pot test. If the voltage setting is too low, the insulation material defect might not be detected. If the voltage setting is too high and the testing time is too long, it may cause the permanent damage for the material.
Normally setting for the safety standard.
Formula →Testing Voltage= DUT recommend voltage × 2+1000V
EX : DUT standard :240V →Setting test voltage:1480V
Common way to safe time for testing
Testing time for most products is 60s. If there are more than one test on one item, it will cost a lot of time. This will lower the efficiency og the product line.
Therefore, the product line usually shorter the testing time to 1~2 sec. and higher 10%~20% testing voltage.
What is Insulation Resistance Test
VDE and TUV safety standard request insulation resistance test for some specific product before hi-pot test. The reason is to make sure the insulation will not be damaged while doing hi-pot testing. Insulation resistance test is the key item to evaluate the material.
Hi-pot test is judge by leakage current, but IR test is judge by resistance, and usually it’s higher than 1 MΩ. It tests the DUT’s resistance between both terminal.
Why Do We Need To Do IR Test
Confirm the performance of the structure of the insulation.
The insulation structure should have higher insulation resistance rate by using better material.
For the insulation material, the protection against electric shock of the switch must be guaranteed.
Confirm the insulation structure can pass the reliability test(heat durability, insulation)
The importance of insulation resistance.
Before assemble the product, IQC has to do the IR test for every components, such as switches, transformers, resistors, capacitors, inductors, PCB, wire or cable to make sure the quality.
Leakage Current Test
→Measuring Tiny AC Leakage Current
DUT has tiny parasitic capacitance. This characteristic will create leakage current by resistance. Capacitor is a resistance component under AC voltage. This may cause the test result include the leakage current inside the instrument. If the DUT has low leakage current, we must consider capacitance , frequency, and the voltage we put.
The surface or interior of the insulation material might discharge under high voltage test. Because of the lost of insulation performance, DUT may have temporary of discontinuity discharge.
Because that temporary discharge can’t be judge by leakage current, so Hi-pot tester will judge the defect product by the changing rate of testing voltage or leakage current.
Arc test is a geometric not a constant test. Also, the detection will be affect by the wire’s impedance or capacitance between the detectors. The rate of change of the current will be affect in the Arc detection.
|Low Voltage Electrical Test|
|Hi pot/ Insulation Test|
|Impulse Test (Layer Short Circuit)|
|AC Voltage Output||5000V|
|DC Votage Output||6000V|