{"id":6204,"date":"2013-01-29T08:00:19","date_gmt":"2013-01-29T12:00:19","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=6204"},"modified":"2023-04-08T20:13:39","modified_gmt":"2023-04-09T00:13:39","slug":"series-surge-suppressor","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2013\/01\/series-surge-suppressor\/","title":{"rendered":"Series surge suppressor"},"content":{"rendered":"\n

Radio facilities, particularly mountaintop transmitter sites, are prone to power transients. The causes can be varied, but most often, lightning is the culprit.\u00a0 Long power transmission lines to the site are vulnerable to direct strikes and EMF-induced spikes from nearby strikes.\u00a0 Other issues, such as switching transients, load fluctuations, and malfunctioning equipment can lead “clear weather” outages.\u00a0 Of course, the best way to deal with such things is through prevention.<\/p>\n\n\n\n

Power line surge suppressors have been around for quite some time.\u00a0 They usually take the form of a MOV (Metal Oxide Varistor) connected between the hot leg and neutral or ground.\u00a0 There are a few differences in designs, however.\u00a0 Typically, most facilities employ a parallel surge suppressor.\u00a0 That normally takes to form of an enclosure hung next to the main power panel with a group of MOV modules in it.\u00a0 The MOVs are fed from a circuit breaker in the panel.\u00a0 Like this:<\/p>\n\n\n\n

\"LEA
LEA parallel or shunt surge suppressor<\/figcaption><\/figure>\n\n\n\n

This is an LEA three-phase 208-volt shunt surge suppression unit, which has MOVs between all phases to ground and each other.\u00a0 That is connected in parallel to the electrical service with the circuit breaker disconnect.\u00a0 These function well enough, provided there is a good bit of series inductance before the unit and also, preferably after.\u00a0 The series inductance can come from many sources, including long secondary leads from the utility company transformer or electrical conductors enclosed in metal conduit, particularly rigid (verses EMT, or FMC) metal conduit.\u00a0 The inductance adds a bit of resistance to the transient voltages, which come in higher than 50 or 60 Hz AC waveform.<\/p>\n\n\n\n

A better method of transient protection is the Series Surge Suppressor.\u00a0 These units are installed in line with the incoming service and include an inductor to add the required series resistance coupled with MOVs and capacitors.\u00a0 Most series surge suppressors also filter out harmonics and RF by design, something desirable, particularly at a transmitter site.\u00a0 Series surge suppressors look like this:<\/p>\n\n\n\n

\"LEA
LEA DYNA systems series surge protector<\/figcaption><\/figure>\n\n\n\n

This is an LEA three-phase 240-volt unit.\u00a0 As in the other example, all phases have MOVs to neutral and each other.\u00a0\u00a0 There are MOVs and capacitors on the line and load side of this unit (the line side is the bottom of the inductor).\u00a0 A basic schematic looks like this:<\/p>\n\n\n\n

\"Series
Series surge suppressor basic schematic<\/figcaption><\/figure>\n\n\n\n

A few things to note; MOVs have a short circuit failure mode and must be fused to protect the incoming line from shorts to the ground.\u00a0 MOVs also deteriorate with age, the more they fire, the lower the breakdown voltage becomes.\u00a0 Eventually, they will begin to conduct current at all times and heat up, thus they should also be thermally fused.\u00a0 MOVs that are not properly protected from overcurrent or over-temperature conditions have the alarming capacity to explode and\/or catch on fire.\u00a0 From experience, this is something to be avoided.\u00a0 Matched MOVs can be paralleled to increase current handling capacity.<\/p>\n\n\n\n

The inductor is in the 100 \u00b5H range, which adds almost no inductive reactance at 60 Hz.  However, it becomes more resistive as the frequency goes up.  Most transients, especially lightning, happen at many times the 60 Hz fundamental frequency used in power distribution (50 Hz elsewhere unless airborne, then it may be 400 Hz).<\/p>\n\n\n\n

Capacitors are in the 1-10 mF range and rated for 1 KV or greater as a safety factor.\u00a0 The net effect of adding capacitance is to create a low-pass filter.\u00a0 Hypothetically speaking, of course, playing around with the capacitance values may net a better lowpass filter.\u00a0 For example, at 100 uH and 5 mF, the cutoff frequency is 225 Hz, or below the fourth harmonic.\u00a0 Care must be taken not to affect or distort the 60 Hz waveform or all sorts of bad things will happen, especially to switching power supplies.<\/p>\n\n\n\n

These units also need to have a bypass method installed.\u00a0 If one of the MOV modules needs to be replaced, power to the unit has to be secured.\u00a0 This can be done by connecting it to the AC mains before any generator transfer switch.\u00a0 That way, the main power can be secured and the site can run on generator power while the maintenance on the surge suppression unit is taking place.<\/p>\n","protected":false},"excerpt":{"rendered":"

Radio facilities, particularly mountaintop transmitter sites, are prone to power transients. The causes can be varied, but most often, lightning is the culprit.\u00a0 Long power transmission lines to the site are vulnerable to direct strikes and EMF-induced spikes from nearby strikes.\u00a0 Other issues, such as switching transients, load fluctuations, and malfunctioning equipment can lead “clear … Continue reading Series surge suppressor<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[18,152,215,5],"class_list":["post-6204","post","type-post","status-publish","format-standard","hentry","category-tech-stuff","tag-am-transmitter-site","tag-emergency-power","tag-fm-transmitter-site","tag-lightning"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/6204","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/comments?post=6204"}],"version-history":[{"count":15,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/6204\/revisions"}],"predecessor-version":[{"id":11457,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/6204\/revisions\/11457"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=6204"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=6204"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=6204"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}