eHam
eHam Forums => Amplifiers => Topic started by: VE7RF on March 01, 2023, 05:09:13 AM
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Here, 3 x paralleled 8 ga Teflon wires (silver plated, and stranded) are used to wire each side of the incoming 240 vac mains...to the pair of paralleled 3 pole contactors. A 3rd contactor (double pole) will be later installed for the HV step start. Right angle drive to be installed on the small 240 vac variac, through the rear panel, so fil V can be dialed in.
Incoming line cord is 3 ga....and is 10' long. Other end can be trimmed off as required, and will be hardwired into a small 125 amp sub panel, then off to main panel.
https://www.youtube.com/watch?v=OokpV9aEG9A
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Is the COM terminal on the transformer (neutral?) at ground potential? That would be the UK approach however I gather that US/NA is different.
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If he finds his primary at his particular location to be 240 volts then common will be 120 and and 120 on the 240 tap. Added. If his primary happens to be 250 then it will be 125 and 125 added. Measure it with a meter to get the desired secondary. The two primaries are equal more or less depending on the single pole loads at his location at the time.
There are only two wires feeding the transformer and they are equal and hot.
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If he finds his primary at his particular location to be 240 volts then common will be 120 and and 120 on the 240 tap. Added. If his primary happens to be 250 then it will be 125 and 125 added. Measure it with a meter to get the desired secondary. The two primaries are equal more or less depending on the single pole loads at his location at the time.
There are only two wires feeding the transformer and they are equal and hot.
There is NO neutral coming into the amp. Everything runs of 240 vac. There is only ONE primary on the plate xfmr. It can only be wired for 240 vac. It does NOT have dual 120 vac primaries.
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Is the COM terminal on the transformer (neutral?) at ground potential? That would be the UK approach however I gather that US/NA is different.
Nope. Here is NA, the 230 vac, both are hot leads. In NA, the pole pig in street has an UN-balanced 12.5 kv / 14.4 kv input ( one side grnded)..... and a BALANCED 240 vac output. In NA, the secondary of the pole pig has a grounded CT. That grounded CT is also looped back to the grounded side of the 12.5 / 14.4 kv. That's done for safety...in case of a 12.5 / 14.4 kv primary to secondary short.
There is 120 vac from either hot leg to the grounded CT. The CT is the neutral. In the main panel in the home, the Neutral buss and the ground buss are bonded inside the main panel. On any sub panel hanging off the main panel, the neutral and grnd buss are NOT bonded together. Reason for that is.... all fault current must flow through the ground wire.
In NA, BOTH sides of the 240 vac are hot, both must be fused (or a dual breaker, with tie-bar between em.... and both require a switch, like a DPST.
In the UK, and elsewhere, the pole pigs are UN balanced on BOTH the input HV side...AND the low 230 vac output side. In the UK, there is NO CT on the low V side. BUT, one side of the 230 vac is grounded / neutral. That grnded side of the 230 vac is also fed back to the grounded side of the HV input of the pole pig. Same deal, done for safety...if the HV side arced to the low V sec, inside the pole pig.
In the UK, only ONE side of the 230 vac requires a breaker / fuse / SPST switch.
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If he finds his primary at his particular location to be 240 volts then common will be 120 and and 120 on the 240 tap. Added. If his primary happens to be 250 then it will be 125 and 125 added. Measure it with a meter to get the desired secondary. The two primaries are equal more or less depending on the single pole loads at his location at the time.
There are only two wires feeding the transformer and they are equal and hot.
There is NO neutral coming into the amp. Everything runs of 240 vac. There is only ONE primary on the plate xfmr. It can only be wired for 240 vac. It does NOT have dual 120 vac primaries.
Not familiar with Canada. But, in the U.S. 240 volts is two 120 volt legs added. Period.
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There is 120 vac from either hot leg to the grounded CT. The CT is the neutral.
Thanks to both for your explanations. Presumably, even though outside the amp the grounded CT is the AC primary current return (and guessing the two 120 vac hot legs are 180 degrees out of phase)..
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Yeah, each leg will have opposite voltage relative to neutral at a point in time. That is the neutral in the utility service transformer. A typical 240 volt U.S. plate transformer only needs two wires in and two wires out to work.
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If he finds his primary at his particular location to be 240 volts then common will be 120 and and 120 on the 240 tap. Added. If his primary happens to be 250 then it will be 125 and 125 added. Measure it with a meter to get the desired secondary. The two primaries are equal more or less depending on the single pole loads at his location at the time.
There are only two wires feeding the transformer and they are equal and hot.
There is NO neutral coming into the amp. Everything runs of 240 vac. There is only ONE primary on the plate xfmr. It can only be wired for 240 vac. It does NOT have dual 120 vac primaries.
Not familiar with Canada. But, in the U.S. 240 volts is two 120 volt legs added. Period.
No, there is NO two 120 volts added . It's a straight 240 vac across the entire sec winding of the pole pig. For 240 vac applications, the CT doesn't enter into the equation, and not required. (not required in the actual HV supply, nor any other device that operates on 240 vac).
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If he finds his primary at his particular location to be 240 volts then common will be 120 and and 120 on the 240 tap. Added. If his primary happens to be 250 then it will be 125 and 125 added. Measure it with a meter to get the desired secondary. The two primaries are equal more or less depending on the single pole loads at his location at the time.
There are only two wires feeding the transformer and they are equal and hot.
There is NO neutral coming into the amp. Everything runs of 240 vac. There is only ONE primary on the plate xfmr. It can only be wired for 240 vac. It does NOT have dual 120 vac primaries.
Not familiar with Canada. But, in the U.S. 240 volts is two 120 volt legs added. Period.
No, there is NO two 120 volts added . It's a straight 240 vac across the entire sec winding of the pole pig. For 240 vac applications, the CT doesn't enter into the equation, and not required. (not required in the actual HV supply, nor any other device that operates on 240 vac).
Good Lord. What do you think every 120 volt appliance in the house runs on. It is one leg of it. The 240 volt appliances use both legs. They don't even break but one leg on a range. Take the rear cover off the back with the oven turned off put still plugged in and poke your finger on the bake or broil elements. There is 120 volts on one side as long as it's plugged in.
As soon as I turn my amp on there is 120 volts on one leg. The other 120 volts is not turned on until the timer turns the step start relays on.
You want to poke your finger on that leg of my transformer and see what's on it when there is nothing coming out the secondary ?
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Presumably the pole transformer takes any 2 hot lines from the HV 3 phase (120 degrees off phase with the other two pairs } and converts to balanced 240 (180 degrees out of phase). Then feed each property with a 240: 120-0-120 transformation with a CT?
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Presumably the pole transformer takes any 2 hot lines from the HV 3 phase (120 degrees off phase with the other two pairs } and converts to balanced 240 (180 degrees out of phase). Then feed each property with a 240: 120-0-120 transformation with a CT?
No, just one single phase and neutral. The separate 120's are reverse windings in the transformer in your yard or at the street. My sister across the creek can have power just fine in a storm when mine is out. All three phases come by here. Most neighborhoods geographically not necessarily population wise have only a single phase service provided.
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single phase and grnd coming down each residential street...which feeds a pole pig every few poles.
Only main streets have all 3 phases of the HV 3 phase. Apartment flats and condominiums have all 3 HV phases, since they are on main streets, or have had 3 phases installed. In those cases, the 3 phase xfmr outputs 208/120 vac . Each floor gets just 208 vac single phase, ( like legs A+B) and also 120 vac, also single phase. 1st floor gets legs A+B. 2nd floor gets legs B+C. 3rd floor gets legs A +C. Then the process just repeats as you go to floors 4 and higher.
The reason for the 208/120 is..... the 120 is just the sq root of 3 ( =1.732) . 208 / 1.732 = 120 vac.
Commercial buildings typ get 208/120 as well. In some cases, it's 360 / 208. In some cases it's 480/277 or 470/ 271. Some cases it's 600 / 346. The higher voltages are typ for light industry or heavier capacity.
99% of the telco offices I looked after were 208/120. Main office down town was 470/277 In those cases, we brought the 14.4 kv 3 phase right into the building, and used our own step down xfmr. We got a lot cheaper rate. Flip side is, the step down xfmr's cost money, and are big and heavy. Small sites like cell sites are just 240/120..same as residential.
Across the water, In the city of Vancouver, it's all 12.5 kv. Here in town, a lot of the 14.4 kv has been upgraded to 25 kv.
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Presumably the pole transformer takes any 2 hot lines from the HV 3 phase (120 degrees off phase with the other two pairs } and converts to balanced 240 (180 degrees out of phase). Then feed each property with a 240: 120-0-120 transformation with a CT?
No, just one single phase and neutral. The separate 120's are reverse windings in the transformer in your yard or at the street. My sister across the creek can have power just fine in a storm when mine is out. All three phases come by here. Most neighborhoods geographically not necessarily population wise have only a single phase service provided.
Do your xfmrs have 2 x separate 120 vac windings..... or is it one 240 vac winding...with one CT ?
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Presumably the pole transformer takes any 2 hot lines from the HV 3 phase (120 degrees off phase with the other two pairs } and converts to balanced 240 (180 degrees out of phase). Then feed each property with a 240: 120-0-120 transformation with a CT?
No, just one single phase and neutral. The separate 120's are reverse windings in the transformer in your yard or at the street. My sister across the creek can have power just fine in a storm when mine is out. All three phases come by here. Most neighborhoods geographically not necessarily population wise have only a single phase service provided.
UK has 11 kV three phase (divided by 1.732 single phase), which is stepped down to commercial/domestic 415v three phase/240 single phase, carried on wooden poles along the streets in rural areas and suburbs. Houses usually take in just single phase, rare to have three phase supplied to a house (they assume you want to run a business from home, which can cause some interesting issues..). In built up areas the domestic supply cables are buried under the roads and also run underground to houses.
Hong Kong and Macau have 380v three phase/220v single phase. It is common to find three phase as well as single phase supplied in apartment buildings, lifts and other machinery in the main buildings, also domestic users may fit large air-conditioning units which use three phase.
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Presumably the pole transformer takes any 2 hot lines from the HV 3 phase (120 degrees off phase with the other two pairs } and converts to balanced 240 (180 degrees out of phase). Then feed each property with a 240: 120-0-120 transformation with a CT?
No, just one single phase and neutral. The separate 120's are reverse windings in the transformer in your yard or at the street. My sister across the creek can have power just fine in a storm when mine is out. All three phases come by here. Most neighborhoods geographically not necessarily population wise have only a single phase service provided.
Do your xfmrs have 2 x separate 120 vac windings..... or is it one 240 vac winding...with one CT ?
It has two 120 volt windings with one center tap or neutral. I can't see how you could get your single pole 120 volt circuits any other way. Or, how you could get them 180 degrees out of phase. The potential difference between the two is 240 volts.
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Unfortunately my EE PE retired NASA engineer friend K5AL passed away on me a week short of 90 years old. He would have been a good person to ask.
I have found over the years that I am wrong about how I think things work a lot.
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If the sec of the pole pig has 2 x separate 120 vac windings, they would have to be connected in the middle to make the CT.
That was what was on my small, ancient pole pig. Dual primaries is what u typ see on a ham plate xfmr, so it can be used on 120 or 240..... but that's a totally different aapplication.
The other method is just one 240 vac winding, with a single CT dead center, in the middle of the winding..then only one winding, with a CT..... similar to a fil xfmr with a CT.
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What's the view on the single phase plate transformer choice for this power level? How much is the 240 going to dip at key down? (did he connect to the 250?)
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What's the view on the single phase plate transformer choice for this power level? How much is the 240 going to dip at key down? (did he connect to the 250?)
The new plate xfmr is fine. The main issue with this power level is the V drop, from the pole pig in the street...to the primary of the plate xfmr. It's one big loop. It's typ 3-000 CU wire from main 200 amp panel to the meter base, then more 3-000
CU up to the pothead, where it's crimp spliced into just 2-00 aluminum drop line. The other end of the aluminum drop line connects to more aluminum..that runs between utility poles. In my case, my drop line terminates across the street, dead center between 2 x poles.....(mid span drop) then down 1.5 poles to the rinky dink 50 kva xfmr..... that feeds 9 x homes...and we all have...'200 amp' service.
On buddy's HF 3x6 amp, his dropped 8 vac under a 90 amp load. 6 vac from street xfmr to his main 200 amp panel, then another 2 vac, from main 200 amp panel...over 20' to the HV supply. He used 2 ga from main panel to HV supply. In his case, he had 240 vac coming in, unloaded..... so we used the 230 vac tap on the xfmr. That's normal to use a tap that's a full 10 vac lower than the no load incoming vac.
Mine used to be 247.2 vac in spring + summer.... and 239.9 vac in fall / winter. I could set a clock by it. These days, it's all over the map, varying by the time of day, hr, week, never know what's it's gonna be from one day to the next. I check once or twice a week, and lately it's sitting around 234 vac... and once in a blue moon, as high as 236 vac.
My plate xfmr primary has taps for 198-208-218-230-240-250. Only options are the 230 tap..or the 218 tap. I don't like the idea of using the 218 tap...in case the incoming vac shoots back up to 240 +.
On SSB, it's really a non issue. When Rich Measures pulse tuned his 4x10, with 30 wpm dots... the old bitty next door left
her porch light on all night long. Her porch light would pulsate like a machine gun. You can see lights blink on CW with just a 3 vac drop. On SSB, you never get that effect. Rich used 150' of just 4 ga wire from his HV supply, to his main panel. His plate xfmr was puny at just 68 lbs (later switched to a slightly bigger 86 lb xfmr, still way too small). His no load B+ was 9900..which dropped down to 9 kv...sucking 500 ma of idle current ( which then maxed out the CCS rating of his 4.5 kv xfmr).... then while talking on SSB, it dropped a bunch more. With a cxr it dropped even more. This is what happens when stuff is not sized correctly.
On high C filters, you get this massive current spike every 8.3 msecs, when on 60 hz single phase power. W8JI measured 60 amps on peaks, every 8.3 msecs, just on an AL-1200, running 1.5 kw out. Scale that up to 10-15 kw out, and you can see that the peak currents on high C filters is just wicked. Issue then is, you also get wicked V drops everywhere, from Cu wire, AL wire, all connections and splices, breakers / fuses / cross connects, relay contacts, contactor contacts, etc, etc.
Then add in the 'normal drop' from the plate xfmr, + glitch resistor...and you further compound the issue. This is why you don't want a plate xfmr with a high secondary DC resistance, cuz it will kill V regulation every time.
In my case, I opted at the last minute, to locate the HV supply (HV supply is just the xfmr + FWB / contactors etc, no filter caps) very close to the main panel.... then ran Teflon 393 coax, to carry the B+ over 20', then down 5', to the HV filter box, then to both RF decks. Then used 1-0 cu wire from main panel to plate xfmr box. I can't do anything abt the drop from the street, except use more C filtering, which works good.... esp on dynamic loads, like SSB. On data modes, you get max static load drop, but nothing u can do about it...and for static loads, everything is in steady state anyway.
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I know several folks in the US, that have 250-252 vac coming in. Typ, the 240 vac tap is used. If the B+ is a tad high, the 250 tap can be used. You can only do so much. Again, SSB is a non issue, lights don't blink or anything. On CW they will, but that depends on cw speed, and filter C used.
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Here everything coming from the pole pig or pad mount to your residential meter base is 4/0 4/0 2/0 aluminum and has been for decades. I must have sold a million feet of it.
The utility transformer with a neutral and your plate transformer with or without one are two different stories.
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Here everything coming from the pole pig or pad mount to your residential meter base is 4/0 4/0 2/0 aluminum and has been for decades. I must have sold a million feet of it.
The utility transformer with a neutral and your plate transformer with or without one are two different stories.
Dunno what gauge Al is used between poles, I think it is 4-0, just looking where the 2-0 alum drop line splices into the line between poles. It all sounds wonderful, but we are being sold a bill of goods imo. 9 x homes hanging off the same 4/0 alum , and also hanging off the same rinky dink 50 kva xfmr...and we all have...'200 amp' service. I already have 2 x neighbours sucking 7 kw all night long with their stupid EV cars. 2 x cars per home around here. Imagine 18 x EV cars sucking 7 kw all night long. Then toss in thes silly heat pumps, and the load is gonna skyrocket.
I talked to the local power co. They said, just let it blow up / burn up..and they will install a bigger one. They make em in 75/100/125 kva. 125 kv is the biggest single phase 240/120 pole xfmr they can use. ( A 75 kva weighs 900 lbs).
If they are gonna use aluminum, it really should be 2 x sizes up from 3/0 cu, like 250 mcm. Alum only conducts 60% as good as cu.
Local ham buddy, who is also an electrical contractor, tells me the power company uses a 9-11 amp slow blow HV fuse, in the feed to the 14.4 kv top line. Around here, everybody has natural gas. Now the push is on to electric everything. That's ok, I can always use my 218 tap, and suck even more current.
To handle the fil current on the big tubes, I had to use a Sola constant V xfmr....that feeds the small Variac..that feeds the fil xfmr..that feeds the cathode. It's the only way to keep the cathode V constant.
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Fortunately, I don't have any neighbors. So, I have my very own pole pig. The power company put capacitors in for power factor correction in back in the summer and they were going to put it in my front yard. Of course, you have the contractor who decides where to place them, the contractor that places them ,and the utility. I explained to the gentlemen that I owned everything for 2000 feet up the road, why not move it up a couple of poles. They did. The next will be regulators I'm sure. And, I'll have that battle which is the disadvantage of owning property.
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What's the view on the single phase plate transformer choice for this power level? How much is the 240 going to dip at key down? (did he connect to the 250?)
The new plate xfmr is fine. The main issue with this power level is the V drop, from the pole pig in the street...to the primary of the plate xfmr.
Right, as long as the utility suppliers (usually not the energy producers) can still supply the power at the reduced voltage, which is likely de minimise in their books. We as hams, whether you are talking about 10 w ccs or 10 kw ccs, are in the same boat. Just like one or two more ev in the chain.
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Fortunately, I don't have any neighbors. So, I have my very own pole pig. The power company put capacitors in for power factor correction in back in the summer and they were going to put it in my front yard. Of course, you have the contractor who decides where to place them, the contractor that places them ,and the utility. I explained to the gentlemen that I owned everything for 2000 feet up the road, why not move it up a couple of poles. They did. The next will be regulators I'm sure. And, I'll have that battle which is the disadvantage of owning property.
Certiorari will be your sword in battle