Electrical safety testers (often referred to as hipot testers) are an integral part of electrical and electronic equipment manufacturing. The hipot tester takes its name from the high potential (high voltage) it generates to perform dielectric withstand voltage and insulation resistance tests. In addition to these tests, many hipot testers provide accurate low resistance measurements and low resistance/high current outputs to test ground resistance and ground bond integrity.
Production electrical safety testing
Electrical safety testing is the most important step in the production process of most electrical and electronic equipment. It is designed to ensure compliance with safety agency labeling requirements, detect defective components or assembly defects, and reduce potential field failure rates and consequent warranty costs.
After production, the product must be 100% tested to ensure compliance with relevant agency certification and safety standards. Production testing is not as rigorous as initially certified, but usually includes basic dielectric resistance and shock hazard (leakage) testing. The plugged device will also be tested for ground resistance and standard requirements. Electric motors, transformers, and other such equipment may undergo insulation resistance testing.
A basic hipot tester (also called an AC hipot tester) applies a high voltage from a conductor to the chassis of the device under test (DUT). This test is commonly referred to as dielectric withstand voltage. Its purpose is to confirm that there is adequate insulation and isolation between non-conductive surfaces and the operating voltage to avoid the risk of electric shock.
Both AC and DC hipot tests are possible. Typically, this test should use the same voltage type as during normal operation. However, if the DC withstand voltage test is used on an AC circuit, the withstand voltage should be twice the peak (2 x 1.4 x RMS) + 1,000 V.
Hipot tester features
High-precision current and power measurement
According to the market and technical research results, users have a great application field for low-current and low-power testing in the induction withstand voltage test, which improves the resolution of current and power measurement display. High-grade 30.0-300.0mA resolution 0.1mA, current high-grade and low-grade accuracy are ± (0.4% reading value + 0.1% range value), low-grade power 0.50W-20.00W resolution 0.01W, high-grade 20W~300W resolution 0.1W, The power level error is ±(0.8% of reading value + 0.2% of range value). Current and power can guarantee the accuracy of the range from 0.50mA-300.0mA, 0.50W-300W can meet the user’s requirements for measurement accuracy.
High-precision active power measurement
Hipot tester has high-precision active power measurement, which can more effectively assist in the judgment of inter-turn short circuit for some miniature electronic transformers.
In the miniature electronic transformer, due to the large number of turns (above thousands of turns) and the thin wire diameter (the diameter of the enameled wire is less than 0.1mm), in the case of a short circuit of several turns to dozens of turns, compared with the normal transformer, the The change of the test current under the frequency doubling voltage is not as obvious as the change of the active power (the short-circuit 10 turns generally change by about 50%).
The experimental results show that in the case of inter-turn short circuit, the power factor of the transformer increases and the active power increases. It can be used as the basis for the judgment of the inter-turn short circuit of the miniature electronic transformer, and the performance of the transformer can be judged more accurately. The following test report data of 5W small transformer primary short circuit can indicate this problem.
Therefore, the current, power and power factor indicators can be used as the basis for determining the short circuit between turns of the transformer, and the power measurement method can be used as the best basis for determining. Moreover, since the tester adopts the induction withstand voltage test method to perform non-destructive testing, it will not cause damage to the tested load. On the premise of ensuring better test quality, it can greatly improve the production efficiency and reduce the loss of raw materials.
Therefore, the transformer induction hipot tester can better and more effectively test the longitudinal insulation performance of the transformer based on ensuring non-destructive testing, and is more suitable for transformer assembly line and laboratory testing.
According to the applicable standard, a device passes this test if the measured leakage current is less than the maximum allowable current, or if no breakdown has occurred, i.e. no sudden, uncontrolled flow of current.
For double-insulated products, the test standard usually specifies a higher voltage. Additionally, such devices often require special fixtures to connect the non-conductive housing to the conductive element.
There are several features that an instrument designed to run a Hipot tester might come in handy for. The maximum output voltage is adjustable – for many applications a maximum of 5kV will suffice, but sometimes higher voltages (up to 30 kV) may be required. Both AC and DC outputs are desirable, with excellent regulation to both line and load. The ramp rate, dwell time and discharge characteristics should all be controllable, and the instrument should be able to measure the phase angle of the leakage current through capacitive coupling detection.
Some standards allow separate measurement of in-phase and quadrature currents. Leakage currents due to capacitive coupling may not be a safety issue. The instrument should also include a way to specify minimum/maximum pass/fail current limits, as well as individual limits during ramping and programmable multi-channel testing.
Defects frequently detected by withstand voltage tests include contamination (dirt, debris) and not proper spacing between components (creepage and clearing). Creep is measured over the entire surface, and clearance is the air gap between components. Contamination can result in unacceptable leakage current levels. Clearing the problem can cause a malfunction.
Motor windings, transformer windings, and other applications involving cables or insulated wires may require insulation resistance testing. Insulation resistance testing usually involves confirming that the resistance exceeds a defined high resistance value.
In many cases, insulation resistance must be measured between multiple conductors. Examples include cable/connector assemblies, multi-conductor cables and relays. To make this measurement, short all but one of the wires together and apply the test voltage from the remaining wires across the shortened harness. Then repeat the test for each wire in the harness.