1 minute vs 1 second isolation voltage test for isolated offline SMPS transformr - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: August 11, 2019, 11:11:47 am
content: Some offline transformers are spec'd for 3750vac for 1second (3mA).Some are spec'd for 3750vac for 1 minute (3mA).It is strange to me that power integrations, on their design software, only ever design the isolated flyback transformers to 3000vac for 1 second (thats for 200-265vac input).(screenshot of design result attached)Do you know why this is?Why would anyone want to spec it for one minute?......no mains transient lasts for one minute?....they only last 50us

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 11, 2019, 11:37:56 am
content: May be to do with what's required by different standards. Some certainly call for breakdown tests over a period of time, presumably due to progressive breakdown of insulating materials.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2019, 03:02:44 pm
content: There may be some room for standards to accept a higher voltage (say, 3kV) for a shorter duration, instead of the nominal (say 2.5kV 1min) rating.Preference for manufacturers is shorter tests, for more production. I've read a lot of datasheets which note a more stringent 60s test done on a sampled basis, 1s at 100% full test rate. Some standards accept that too.But again, depends on the standard in question. RTFSTim

author: floobydust
author_rank: Super Contributor
timestamp: August 11, 2019, 07:26:53 pm
content: You can refer to relevant BS EN 61558 - Safety of power transformers, power supplies, reactors and similar products —Routine production tests are 3kV only for 1 second (two-layer insulation). Certification tests are much more demanding.From the IEC insulation coordination safety standards:a) The 1.2/50μsec impulse voltage withstand test is to verify the capability of the solid insulation to withstand the rated impulse voltage.b) The a.c. voltage test is to verify the capability of the solid insulation to withstand:– the short-term temporary overvoltage– the highest steady-state voltage– the recurring peak voltageIf the peak value of the a.c. test voltage is equal to or higher than the rated impulse voltage, the impulse voltage test is covered by the a.c. voltage test.Solid insulation has a different withstand characteristic compared to clearances if the time of stress is being increased. In general, the withstand capability will be decreased significantly. Therefore, the a.c. voltage test, which is specified for the verification of the withstand capability of solid insulation, is not allowed to be replaced by an impulse voltage test.c) The partial discharge test is to verify that no partial discharges are maintained in the solid insulation:– at the highest steady-state voltage– at the long-term temporary overvoltage– at the recurring peak voltaged) The high-frequency voltage test is to verify the absence of failure due to dielectric heating.The technical committees specify which tests are required.

author: ocset
author_rank: Super Contributor
timestamp: August 12, 2019, 07:31:35 pm
content: Thankyou very much...Interestingly, EN61558 isnt mentioned in the following power supply's datasheet...We are wondering what kind of isolation test the following power supply is spec’d to?…..It’s the Philips Xitanium Xtreme 75W LED driver…..AKA…“Xitanium 75W 0.35-0.70A GL Prog sXt” (datasheet below)The datasheet says it has “Basic” insulation.That is, how would they have carried out the hi-pot test on it? (voltage setting?, time duration?, current limit setting?)The following reveals that “basic insulation” means withstanding 1000V+2x(operating voltage)…however, I happen to know that Basic Insulation means 3750VAC for one minute for an isolated offline SMPS…..during that minute, the RMS current should not exceed 3.5mA.https://electrical-engineering-portal.com/what-is-hipot-testing-dielectric-strength-testWould you agree that at the Philips Approvals testing session for Dielectric withstand for this power supply…they would have set the Hi-pot instrument to 3750VAC for one minute and set a current limit threshold of 3.5mA?(the standards do not actually specify a current limit threshold)Philips Xitanium Xtreme 75W LED driver datasheet:https://www.docs.lighting.philips.com/en_gb/oem/download/xitanium/Xitanium_75W_0.35-0.70A_GL_Prog_sXt_929000702302.pdfHere is the product brochurehttps://www.docs.lighting.philips.com/en_gb/oem/download/xitanium/Xitanium-XtremeLED-brochure.pdf

author: floobydust
author_rank: Super Contributor
timestamp: August 15, 2019, 06:10:25 pm
content: There are dielectric strength tests for acomponentto the component standard, or dielectric strength tests for theproductto the product standard, or for complete equipment. You can be evaluating creepage/clearances, or solid insulation. They are not the same test voltages and conditions. I'm not sure which you're after.The dielectric strength test current is really to detect the spacing/insulation's outright failure. Once you get up to 3-5mA it's pretty much an arc and game over. Corona or a Y-cap leakage is say 1mA max. so they give some leeway for that. The test current is not critical.The Philips LED PSU can have isolation between many different ports- mains+LED, or DALI, the enclosure etc. For streetlights, I don't see a need for the LED to be isolated, as old magnetic ballasts are hazardous live for the bulb.Your 3,750VAC 1 minute test value depends also on the product's overvoltage category, and if it can be used for 3-phase systems. I think this is why it is higher than expected.I find it easier to get the values from the safety standards or the product's assessment report.

author: ocset
author_rank: Super Contributor
timestamp: August 16, 2019, 05:36:16 pm
content: Thanks, we wish to know what was the test they did on the main isolation transformer within the product?ie, voltage time and current limit