Passing the Inrush Current Requirement
Passing the Inrush Current Requirement
For IEC 61000-4-11 Voltage Dips/Interruptions and Variations
By Jason H. Smith
Absolute EMC
November 14, 2020
The IEC 61000-4-11 has current inrush requirements that can not always be met by external power sources. There is a low-cost solution to this problem without having to purchase an expensive new power source. In the normative Annex, A of this standard lists out the requirement that the test generator must have the capability to drive 500A for 220V-240V mains. This requirement is mostly based on the power source, which is not always part of the IEC 61000-4-11 test generator. If the power source can not produce this 500A inrush current (through the test generator), there are some possible changes that need to be met for your testing.
- For each test, you need to measure the EUT’s inrush current and make sure it does not exceed your inrush capability as measured by the requirements of Annex A. This adds more steps to your testing and needs to be done for each EUT, adding cost.
- How is your setup's inrush limit measured? Can you just rely on spec-sheets of your power source? No.
- Inrush actually must be measured onsight in the test setup. It can only be done remotely at a calibration facility if the power sources and dips generator are sent together.
- Normally power sources are not sent or due to size and cost not recommended to ship. If using power mains of your facility which is possible in some cases inrush must only be onsite in the test setup.
- Use a more extensive AC power source that can handle the 500A inrush. It will increase cost if high current EUTs are never being tested.
- Use the CAB 1001 Inrush Compensator, which uses a unique trick with capacitors to deliver the inrush current to pass the 500Amp (900 Amps possible) requirement. The capacitance is switched in using a unique staggered and soft switch-in. This ensures that any down-line protection devices do not trip due to inrush.
