How to Choose DC hipot test kit for transformers?

8) FAQ - Frequently Asked Questions.

Link to Hengfeng

8.1) I tested the same part with two ATs, both units read differently for the HPAC/HPDC

Unit 1 -   3.2 uA
Unit 2 - 10.0 uA

The ATs do not read the same small current, what should I do?

Answer:

As with any electrical  measurement, as the signal approaches zero, the potential error in the reading increases.
HI-pot measurements, by nature, monitor very small currents.
An ideal transformer would display a HIPOT current reading of zero.
It is a common misconception to equate these measurements with a typical DCR reading of around 2 ohms, where stability and repeatability are expected.

However, due to the very low current level, small readings can be influenced by the unit's inherent noise floor.
This might result in varying readings across different test equipment, but they should still remain well below the required limits.

Bad insulation (e.g., dead short, weak enamel between windings, etc.) would lead to excessive current readings that surpass your limits or potentially trigger a hard flashover/trip for genuinely faulty parts.

Some manufacturers opt to report results below a certain threshold (e.g., 20uA) as a hard &#;0.00&#;, but we prefer to report every measurement as proof, even when these results are subject to considerable error tolerances (e.g., + / - 100%).

Thus, obtaining slightly different HPAC/HPDC readings on various AT units is normal in cases where the part under test is a good insulator and the current measurement is exceedingly low.

8.2) My AT gives error codes even if I reduce the HIPOT requested voltage. 

What are the troubleshooting steps to fix this problem?

Answer:

Multiple factors could be causing the TRIP on the AT.

1. Fixture plate used - the fixture may be contaminated or lack sufficient clearance for the required voltage standoff (a general guideline is at least 1 mm minimum per volt standoff).
2. A genuinely faulty part.
3. Significant natural capacitance of the component (particularly for larger transformers - in these instances, lengthen the RAMP UP time).

The trip mechanism engages during the HIPOT test when a dead short or excessive current is detected.
If the trip occurs across multiple parts that you suspect are actually "good," check the fixture being used.
You can quickly evaluate the fixture and unit using the following two tests.

1. Run the program (ideally 4-5 times) directly from the AT Editor, with the fixture connected but NO DUT present.

Our company is the world’s best DC hipot test kit for transformers supplier. We are your one-stop shop for all needs. Our staff is highly specialized and will assist you in finding the right product.

You should anticipate failures on the measurement tests (e.g., R, LS, RLS, Z, MAGI, etc.) as no part is present.
However, programmed HPAC or HPDC tests should pass.
If the HPAC/HPDC tests fail without a DUT, then the fixture isn't properly isolating the nodes.

Inspect the fixture for 
A. Signs of contamination on the top surface.
B. The separation of the wiring within the fixture - wires should not cross, as this might result in "cross-talk."

2. Run the program on the unit with NO fixture and NO DUT connected.

This test checks the hipot integrity of the unit.
As before, you should expect to fail the measurement tests (e.g., R, LS, RLS, Z, MAGI, etc.) without a component present.
However, programmed HPAC or HPDC tests should pass.
If you experience HPAC or HPDC failure with no fixture connected, please contact us.

8.3) My AT Screen suddenly flickers during the HIPOT test, is my unit faulty?

Answer:

During any high voltage test (especially at voltages as high as 3-5kV), EMI emissions can occur through the air.
Due to the proximity of your DUT to the AT screen, the large screen may pick up this energy.

This can cause the screen to flicker during tests, but it is merely a visual effect and does not affect the unit's digital operation.
As long as the test remains controlled and the AT completes the test, this is expected behavior and should not raise concern.

This test applies a voltage to the DUT that is significantly higher than normal operating voltage, typically V AC plus twice the normal operating voltage. For appliances designed to operate at 120 or 240V AC, the test voltage usually rises to V AC.

A DC hipot test can typically substitute for an AC hipot test. The ideal voltage for a DC hipot is generally higher than the AC test voltage by a factor of 1.414. For example, a product tested at V AC would be assessed at V DC.

For double-insulated products, required test voltages may be considerably higher, such as VAC or even VAC for a 120 VAC power tool. The voltage is applied between the operating circuits and the chassis or ground, targeting the parts of a product that consumers might touch or come into contact with.

Refer to Figure 5 for a typical AC hipot test setup. The setup for a DC hipot test would be identical.

The purpose of the test is to prevent electrical shocks to consumers during product use, which can typically result from a breakdown in electrical insulation. The test also identifies potential design flaws or manufacturing defects that place components too closely together. There is a danger that dust, dirt, and other contaminants can accumulate in air gaps between conductors or circuit components over time in typical user environments. Inadequate design spacing poses a shock hazard after prolonged use. Subjecting the product to a very high voltage overstresses it to the point where arcing might occur if spacing is too narrow. If the product passes the hipot test, it is unlikely to pose an electrical shock risk during normal use.

Withstanding extremely high voltages ensures a substantial margin of consumer protection. Regulatory agencies typically mandate stringent hipot tests as a "type test" before products are released for public sale, with a less demanding test conducted on the production line. Testing laboratories regard the hipot test as the most crucial safeguard for consumers. While they may accept "design" or "type" tests for other tests, they always require hipot tests for 100% of the units on a production line.

Contact us to discuss your requirements for DC hipot test kit for capacitors. Our experienced sales team can help you identify the options that best suit your needs.