Help in assessing the Input mains circuit integrity - Page 1
Forum section: electronics / beginners

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: March 30, 2021, 07:34:59 pm
content: Hello everyone ,I've been working on designing a (220V-380VAC) 3/4Wire phase energy meter and in terms of metrology operation , things were working very well quite similar in terms of metrology if compared to a commercial unit. Now I'm no expert in mains power electronics circuit design so I opted to integrate an off the shelf AC/DC fly-back power supply, which when integrated in the meter worked well in lab conditions. I've followed and implemented the mains Input protection circuit going into PSU which is specified by the PSU manufacturer but to be honest I feel helpless as I have no idea how to calculate/know how and why the values are specified in this stage , I need to be able to know how much energy/ voltage and the where bouts of the circuit operates in a surge , fast transient and ESD situation since I plan on doing a pre-compliance test and one of the tests I'm concerned with is if the input protection fails then I have not backup plan so I would really appreciate if someone would kindly share his insights and knowledge on how to pre-simulate or calculate the values of the input circuit below in order to pass the following test conditions below as well.Figure (1): Schematic of the Mains Input circuitry with the Power SupplyTest 1Test 2Test 3Some information on the MOV used on each Line (230VAC)Final Note : I come from an Electronics and Communications background and i have done a reasonable amount of work in Low voltage ( Analog , Digital and RF ) board designs but I'm no expert in this subject but I'm willing to learn. I know how to simulate how an AC signal going in to a bridge rectifier and analyze the output , you know basic stuff that most of us learned during undergrad , but the ( fast transients ,...etc) on an AC mains situation, I've never worked with such case. I'm having a hard time on how to figure out how to model and simulate the MOV in the simulation programs ( LTSpice , Proteus ISIS & TI TINA ).My Questions :1. How do you calculate the correct MOV model/value for the above application to pass the test conditions mentioned above ?2. Will the current Input stage of the Power Supply survive the Tests mentioned above ?BR

author: t1d
author_rank: Super Contributor
timestamp: April 01, 2021, 03:24:27 am
content: This is way above my level of education, but I thought that I would remind you that there are meters made for collecting AC data... They go by the name of "Kill-O-Watt" meter, etc. The individual DIY modules can often provide the same information at less cost.https://www.amazon.com/s?k=kill-o-watt+meter&crid=RGIFLP9A107T&sprefix=kill-o-%2Caps%2C223&ref=nb_sb_ss_ts-doa-p_2_7https://www.amazon.com/s?k=ac+volt+current+meter&ref=nb_sb_nossOne trick that I have noticed with the modules is that they only go so far down toward zero volts, so watch out for that.To increase the current sensitivity of the module type, you can loop on leg of the DUT power cable through the current coil 10 times and, then, divide the meter reading by 10. So, with a meter that can only read down to 20mA, you can read it down to 2mA, with a little math.Also, for the module type, make sure you are buying an AC unit, not DC. It is easy to mix them up.I hope that helps.

author: penfold
author_rank: Frequent Contributor
timestamp: April 01, 2021, 06:52:36 am
content: In 61000-4-5 there are some circuits that describe how the transients are coupled into the DUT, via coupling/decoupling networks etc, during the test. That's a good place to start, for three-phase mains they are pretty well defined. They are also in text-books such as "EMC for Product Designers" by Tim Williams... the section on test methods is okay, not definitive, but it will describe what you're looking for.The advantage of only having to worry about the mains side of things is that the coupling/decoupling networks are all nicely described by lumped circuit elements (rather than capacitive clamps/EM clamps etc), so it's pretty easy to simulate and get a reasonable idea of the energy dissipated in components.