[PSES] SPC component properties
Brian, I appreciate for your purposes the SPC component of choice is the MOV. Quite right too, if you are considering cost and device safety standards like UL 1449. SPC standards, which tend to be for component electrical and environmental performance, can only overlap the requirements of an Equipment/Device safety standard. Your perception of other protection technologies needs revision. True, PN junction zener breakdown diodes have a very soft clamping characteristic. NB The zener breakdown effect only occurs below about 7 V. To counter the poor zener clamping characteristic a multi-junction silicon semiconductor component using the punch-through effect can be used. This type of technology provides a sharp clamping characteristic from a few volts upwards. Punch-through voltage limiters can be found in Ethernet ports. These SPCs protect the Ethernet PHY chip against damaging overvoltages (even though 5-volts may not sound like an overvoltage) Above 7 V a different breakdown effect comes in -- the avalanche effect. Avalanche breakdown diodes have a good sharp clamping characteristic. You may see them referred to as SADs, Silicon Avalanche Diodes. The three-letter acronym powers that be in the IEC said they didn't want a sad component and so the ABD, Avalanche Breakdown Diode, acronym came into being. Unfortunately, many people, who don't know the difference between zener and avalanche breakdown, call ABDs zeners, which is totally wrong. All PN junction semiconductors have relatively low thermal capacity and energy absorption capability. These deficiencies can be countered by using series and parallel combinations of ABDs. There are several companies in the US making AC Power SPDs using this approach -- costly, but these have a better clamping performance than an MOV. The GDT uses gaseous discharge and the switching time from sparkover to the low-voltage arc can be in the tens of nanoseconds. The problem is that the sparkover voltage is dependent on the rate of voltage rise. This overshoot of surge sparkover to AC sparkover can be something like 2:1. This is not a firm ratio but dependent on the AC/DC sparkover voltage. An 80 V GDT will have a higher surge sparkover voltage than the sweet spot 250 V GDT. An interesting trend I've noticed is for GDT MOV series combinations where PLC is being used. Put MOV protection (read capacitance) on the AC supply and PLC reach and environmental pollution are reduced. Protect using a low capacitance GDT MOV series combination and PLC reach and environmental pollution are maximised. Regards Mick On 14/11/2011 21:04, Brian Oconnell wrote: o further abuse a meme - moar standards! [insert troll-face here] Another member has previously commented that there a several type of components used to arrest a surge. For the purpose of my OP, was focused on a MOV-type SPD as defined under UL CCNs VZCA2 and VZCA8, where the effective standards are UL1449 and CSA C233.1, and various CSA TILs. And of course, the wondrous IEC61051-2. This is another case where EMC requirements (61000-4-5,6) can affect product safety. Last year's update to the 2d ed of 60950-1 for my component power supplies was, for some models, quite an adventure. A problem NOT ADDRESSED by TC108 is the increased energy AFTER a surge, or during a SFC, due to the 120% rating requirement. Perhaps this was a principal intent of UL1449 3d ed - verify that the high E and I do not make the MOV puke it guts and start a fire. There are many sources of increased energy - my two problem children are the effects of an inductive kick to the circuit being 'protected' by the SPD*after* the current interrupt device has opened; and the higher voltage (CV^2), during a surge, at which the SPD will start conducting. As for GDTs - they take longer to get to low Z. And zener-type arrestors do not have a sharp knee at the conduction level. The ZnO MOV seems to be the best chance of survival, assuming the other circuit components can handle much higher coulombs running around before clamping. Moar standards! Moar unintended effects! Moarrr Brian -Original Message- From:emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of ralph.mcdiar...@schneider-electric.com Sent: Monday, November 14, 2011 11:31 AM To:EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] MOV requirements Does the industry really need another standard, I wonder? Ralph McDiarmid | Schneider Electric | Renewable Energies Business | CANADA | Regulatory Compliance Engineering From: John Woodgatej...@jmwa.demon.co.uk To:EMC-PSTC@LISTSERV.IEEE.ORG Date: 11/11/2011 06:48 AM Subject: Re: [PSES] MOV requirements In message4ebd2d05.5050...@ieee.org, dated Fri, 11 Nov 2011, Mick Maytumm.j.may...@ieee.org writes: MOV, Varistor, VDR; Metal-Oxide Varistor are all names for a voltage-limiting component using a particular technology. I think this 'particular technology' is an
Re: [PSES] SPC component properties
Mick, Good points, most of which are within the realization of my employer's designs. For example, for the automotive stuff, we tend to not use MOVs, but as you suggested, an avalanche diode(where our big concern is not surge, but ESD). But for component conversion devices, where the rated input will be up 1kV, we do the MOV and/or GDT dance. There are no normative safety requirements for the SELV/PELV input environment for our automotive toys, but for mains-connected stuff - you gotta dance with the component that can party until you puke. Have I used enough crass metaphors? Brian -Original Message- From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Mick Maytum Sent: Tuesday, November 15, 2011 6:15 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: SPC component properties Brian, I appreciate for your purposes the SPC component of choice is the MOV. Quite right too, if you are considering cost and device safety standards like UL 1449. SPC standards, which tend to be for component electrical and environmental performance, can only overlap the requirements of an Equipment/Device safety standard. Your perception of other protection technologies needs revision. True, PN junction zener breakdown diodes have a very soft clamping characteristic. NB The zener breakdown effect only occurs below about 7 V. To counter the poor zener clamping characteristic a multi-junction silicon semiconductor component using the punch-through effect can be used. This type of technology provides a sharp clamping characteristic from a few volts upwards. Punch-through voltage limiters can be found in Ethernet ports. These SPCs protect the Ethernet PHY chip against damaging overvoltages (even though 5-volts may not sound like an overvoltage) Above 7 V a different breakdown effect comes in the avalanche effect. Avalanche breakdown diodes have a good sharp clamping characteristic. You may see them referred to as SADs, Silicon Avalanche Diodes. The three-letter acronym powers that be in the IEC said they didnt want a sad component and so the ABD, Avalanche Breakdown Diode, acronym came into being. Unfortunately, many people, who dont know the difference between zener and avalanche breakdown, call ABDs zeners, which is totally wrong. All PN junction semiconductors have relatively low thermal capacity and energy absorption capability. These deficiencies can be countered by using series and parallel combinations of ABDs. There are several companies in the US making AC Power SPDs using this approach costly, but these have a better clamping performance than an MOV. The GDT uses gaseous discharge and the switching time from sparkover to the low-voltage arc can be in the tens of nanoseconds. The problem is that the sparkover voltage is dependent on the rate of voltage rise. This overshoot of surge sparkover to AC sparkover can be something like 2:1. This is not a firm ratio but dependent on the AC/DC sparkover voltage. An 80 V GDT will have a higher surge sparkover voltage than the sweet spot 250 V GDT. An interesting trend Ive noticed is for GDT MOV series combinations where PLC is being used. Put MOV protection (read capacitance) on the AC supply and PLC reach and environmental pollution are reduced. Protect using a low capacitance GDT MOV series combination and PLC reach and environmental pollution are maximised. Regards Mick On 14/11/2011 21:04, Brian Oconnell wrote: o further abuse a meme - moar standards! [insert troll-face here] Another member has previously commented that there a several type of components used to arrest a surge. For the purpose of my OP, was focused on a MOV-type SPD as defined under UL CCNs VZCA2 and VZCA8, where the effective standards are UL1449 and CSA C233.1, and various CSA TILs. And of course, the wondrous IEC61051-2. This is another case where EMC requirements (61000-4-5,6) can affect product safety. Last year's update to the 2d ed of 60950-1 for my component power supplies was, for some models, quite an adventure. A problem NOT ADDRESSED by TC108 is the increased energy AFTER a surge, or during a SFC, due to the 120% rating requirement. Perhaps this was a principal intent of UL1449 3d ed - verify that the high E and I do not make the MOV puke it guts and start a fire. There are many sources of increased energy - my two problem children are the effects of an inductive kick to the circuit being 'protected' by the SPD *after* the current interrupt device has opened; and the higher voltage (CV^2), during a surge, at which the SPD will start conducting. As for GDTs - they take longer to get to low Z. And zener-type arrestors do not have a sharp knee at the conduction level. The ZnO MOV seems to be the best chance of survival, assuming the other circuit components can handle much higher coulombs running around before clamping. Moar standards! Moar unintended effects! Moarrr Brian -Original Message- From: emc-p...@ieee.org
