Electric Transformers

[supersurgilator]

I don't know how many of you pay attention to the transformers on the utility poles in your area, but I was wondering if your part of town has any of the old black ones left? For some reason I have always liked those best, and noticed the other day that one near me was replaced last week.

 

[sudsmaster]

Probably for the better

The old ones probably contained toxic PCB's which are ok when contained but not so nice if and when the transformer leaks or explodes.

 

[qsd-dan]

What years do those black transformers date back to?

Sometime between 1968 and 1970 my town went from the overground poles and wires to underground wiring. It's weird; you drive south down one of the main streets in a residential area and to the left...poles and wires everywhere. Look to the right and nothing but trees in the air.

 

[supremewhirlpol]

I pay attention to them very often. There was a series of storms that came through the area about a month ago and took out the power. Power was out for a total of 8 hours. I was out on the porch cleaning bad adhesive off the keys of one of my synths when several utility trucks stopped in front of my house. The men got out and were looking at the Transformer on the pole, which is directly across from the house. One of the men got in the bucket and went up to it and was looking at what looked to be some sort of kick out fuse. He then lowers the bucket, pulls out a long stick with a hook on the end and puts the fuse back in place. As soon as he did that electricity for my street was back on with an added bonus. There was a frying type of sound coming from the transformer and the neutral line jumped. After about 5 seconds of hearing the frying sound the man pulled the fuse out with the hook and just as he did that there was a HUGE ARC of current that jumped from it(now that was just awesome!!!!). The man repeated this several times with the same result. A little down the power lines there were some wires that were touching as a result of tree branches falling on them(that was the real issue). But before they found that issue they replaced the transformer (50KVA) with a new one. After replacing it, the new transformer did the same thing(frying noise and arc). Then they decided to leave it on for a little longer to see if they could see where the issue was farther down the power lines. The issue was on a street a block over. After the lines were repaired no more arcing and frying noise. So what happened is that when the lines got crossed a short was created (on the secondary side) thus causing the transformer to heat up. The transformers on the poles consist of the primary and secondary windings submerged in mineral oil. The mineral oil dissipates heat. So if a transformer is put under a heavy enough load(like a short on the secondary side), the oil can come to a boil. The transformer was most likely replaced even though it probably still worked because it is unknown how long power had been applied to it while there was a short on the secondary side. Even though the oil is designed to dissipate heat it is not designed to preserve the windings during a long-term short. Also some oils can loose their cooling properties when they have been exposed to certain hot temperatures. So when metals heat up they expand a contract, same thing with windings. If windings used in both motors and transformers get hot enough over a period of time, it is possible that the windings will get thinner and longer, which means that they will be loose. Loose windings are BAD NEWS. Loose windings = reduction in EMF, Flux, etc. Which means weaker motor or transformer and the loss of insulation on the windings. When a winding set grounds itself or opens = lots of sparks, smoke, fire, and risk of electrical shock.

so, replacing the transformer in my case was a good call.

There are a few older black one here and there, but the city has upgraded a lot of them in the past year(most are gray now).

 

[tolivac]

Transformers-at the SW transmitter site where I work-we have LOTS of them-yes including the "pole pig" ones-they are used in some of the HV supplies in the transmitters.We have some "black" pole transformers-if at of any help they are Westinghouse units-75Kva-they are connected in a three phase stepdown bank-4160V 3ph primary to 230V sec.They run a 50Kw sideband transmitter.4160V used to be used by some utilites for power distribution.We use it as primary voltage for many of our tranmsitters.(GE) has the pole pig style transformers to step 4160V to 7Kv or 10Kv for 12Kv DC or 15KvDc.They feed three phase rectifier banks to convert the AC to DC for the power tubes.
On transformers that feed some of our HV rectifiers-they have to have their windings braced-primary and sec-because the power supplies have an ignitron tube crowbar to drain the supply capacitors in case of a fault-overload,arc,etc.sometimes when the crowbar trips the primary breaker doesn't trips fast enough.This puts a real stress on the windings of the transformer.The windings will actually twist on the core in the same manner as an induction motor will turn when turned on-An induction motor is nothing more than a transformer whose secondary is shorted and free to turn(rotor)Primay windings in the motor(stator)of course in a transformer we don't want the windings to move in case of faults.IE-short circuit--like the crowbar in the power supply-or a short in the electric power dist system.At our site we have medium voltager switchgear that contains circuit breakers with a 3 shot trip-the will try three times then lock off.same with your utility.If the power co has a fault and you see the your lights flash on and off three times--and no power-get out the candles.The breaker will have to be manually reset after the linemen have cleaned the fault.Oh yes in electric power utilty transformers-the neutrals on the sec are grounded in the transformer.This is to cause the primary fuse or breaker to remove the faulted transformer from the line-and to protect you from getting the primary voltage into your home wiring if the transformer gets a primary to sec short-this can happen!In one of our transmitters the HV transformer circuit breaker has backup fuse protection in case of a short-breakers may take a little time to trip in this case-the fuse blows instantly.It happened when the HV rectifier transformer failed in that transmitter!a new one had to come from Germany.Now we get them from Pennsylvania Transformer technologies co.They make transformers for power companies.Usually large ones found in substations.The substation at our site has three GE transmformers that step 115-138Kv to 4160V they are in a three phase bank.the substation is rated at 10Mva.10 megawatts.The Geerman transformer was made by Trafo Union-a German transformer co.The transmitter its used in is AEG-Germany's "General Electric".-a 250-500Kw shortwave transmitter.

 

[supremewhirlpol]

WOW !!!!! someone who actually services the power lines, boy do I have a boatload of questions for you. Exactly what are candles? What is the fuse like thing with a isolator on it that the guy would take in and out by a stick with a hook on it? Why the arc of current. Distribution power and three phase has not been covered yet in college. But I have done a little studying of three phase on my own. You mentioned High voltage rectifiers, transmitters, you also mentioned several transformers, What do all of these things do in regard to distribution of electricity. How does your power company keep the power factor up? You also mentioned several types of transformers, How are each type different? Where can I get a pole pig for cheap?

 

[tolivac]

I don't service power lines-but use utility grade equipment at my worksite-and have training on the med voltage circuit breakers and switchgear.Go to the Barnes and Powell website for excellent information on such equipment.They make all types of med and high voltage breakers for power companies and large power users-like where I work.The switchgear I use here is new BP.They gave us factory training on it.
The thing the lineman hooks with his linemans stick is the primary voltage fuse on the pole pig.Most new power co. dist systems use 13.8Kv as the primary voltage or phase to neutral it would be 7.4-7.8 KV.Ground mount (Underground residentual Distribution) transformers have similar fuses for their primaries-and the line man uses his hookstick to remove or apply them.
Oh yes-for candles-just that-actual candles or lanterns for light-if the 3 shot breaker has gone its three shots-you will be in the dark as long as it takes for the power company linemen to remove the fault-could be a branch across the lines blown down from a storm-or a metal roof panel as out my way.Oh yes-the breakers at my site are one shot-breakers for power companies are three shot.Three tries and they trip out and isolate the faulted section.On pole tops you can see these-reclosers-(breakers) sectionlizers(isolate)They are cylindrical shaped devices with line in and out-maybe a pole going to ground level at the base of the pole so a lineman can activate it manually.
the substation at our site does have power factor correction capacitors.Transfromer loads are usually pretty close to .8PF the usual standard..8PF is what most power company equipment is-generators,transformers,etc.
We have 4 diffrent types of high power(250Kw and above) transmitters at the site.3 are General electric 250Kw,3 Continental electronics 250-500Kw transmitters.The plant has one 50Kw sideband transmitter,one Brown Boveri 250-500Kw transmitter,and lastly tyhe AEG 250-500Kw transmitter.We no longer run 500Kw-too hard on the power bill.All program schedules are 250Kw.this is a Gov't SW transmitter site that broadcasts to other countries.Each transmitter uses different types of transformers.they are loaded with them.You have the HV rectifier transformers-they are used to develop the HV plate supplies for the power amp tubes-the HV is from 6Kv-28Kv DC.Filament transformers give a low voltrage but very high current secondary voltage to light tube filaments.And there are transfroemrs in the transmitters tyhat step the 4160 3Ph input power to 230V three phase to run blowers,pumps,and other power supplies and the filament supplies.In the AEG and BBC transmitters the 4160 is stepped down to 380V and 220V for the LV supplies.
If you want a pole pig to experiment with-try your areas power company salvage yard-don't know if they still sell old transformers.Keep in mind the hazards-LETHAL voltages if you try to connect the transformer and possible PCB in the oil filling.and these things are HEAVY!!!even a small 25Kva one can weigh several hundred pounds.Radio and TV statiuons used to use old pole pigs as transformers to power the HV supplies in old transmitters that parts were NLA.Same with radio amatuers.Just have to repaet if you want to experiement with these transfroemrs the power in them is LETHAL-BE CAREFUL!!!You might be able to get a 5Kva-10Kva transformer for your experiements-these would be easier to transport.And they may not trip your breakers or blow fuses if connected.If you were to connect the 220V winding of a 25KVA pole pig to your home wiring its likely the low internal impedence of the pig will trip your breakers.You have to limit the current.another transformer or inductive device connected in series with the transformer winding may limit the inrush current and prevent breaker tripping.please be very careful with these-we want you still around-leave the med voltage stuff to the experts-folks trained in it and who have the equipment to safely operate these transfromers.also folks who build giant Tesla coils like to use pole transformers for the coils power supply.

 

[supremewhirlpol]

I've seen on youtube were people have connected the secondary to the secondary of a microwave transformer, and use voltage from the primary of the polepig for a tesla coil, or Jacob's ladder. I think I've seen the sectionalizers, When you pull the handle power is cut off to a section of the powergrid, and as the poles pull back you see huge arcs of current until you hear a snap and power has been cut(lots of videos on youtube). I have done a little experimentation with microwave transformers, motor capacitors, and I successfully built a rotary phase converter to power my 3phase commercial front load washing machine. I've seen both step-up and step-down 3phase transformers, is it possible for them be used for the reverse purpose? What will happen if a 3phase step-down transformer is connected in such a way that power is applied to the secondary side? Can the transformer actually be used to power something else?

 

[tolivac]

A transformer can be connected in "reverse" power applied to the "secondary" and then the load connected to the "primary" as in connecting a pole pig in "reverse"-220V fed to its 220V winding and the HV taken from the HV winding.This is what was done when stations that have very old broadcast transmitter(they can't get the orig HV transfromer for its power supply)use a bank of pole pigs or a three phase transfromer connected "backward"many broadcast transmitters run from 3 phase 208V-220V power or larger models(50Kw AM,some television transmitters run from 480V 3 ph)In the transmitter HV application a bank of pole pigs with 2200V "primary" voltage hooked backward-220V connected to its "secondary" can then be used to feed a 5KvDC 3 ph rectifier.this is used in may types of transmitters.4160V transformers can feed 8Kv-10Kv DC rectifiers.You can also adjust the voltage from the transformer by adjusting the tap changer.
In the case of our station we have a 1.8MW generator-this can be used for load management-parralleled to the line or isolated(emerg power).Sometimes we get "Hot line tag" orders from the power co NOT to operate our generator.They want to eliminate the possibility of the gen feeding back into the line thru the substation transformers provided a hazard to their linemen.the gen could then feed into the substation transformers causing voltage to appear when it shouldn't.I have had to "lock out" our generator when a Hot line tag oreder has come to us.
Sounds great you are experimenting-you then know what you are doing and know the hazards of using HV transformers-in your 3 phase converot-did you use an old three phase motor as your convertor for the washer-this has been done on some farms.I can remember rotary convertors shown in old Sears farm catalogs.And I have delt with some radio stations that use the rotary convertors to run a transmitter that needs three phase power from a single phase powerline.The convertor sure makes a strange noise when it feeds an AM transmitter-AM transmitters draw more power as they are modulated by program material.
Oh yes there is a switch on the primary 115Kv side on our substation--It is in the locked power co side of the station.The switch has a warning sign on it to operate it no load only.So if the power co wants to use the switch-they have to ask us to turn off all transmitters and building loads.Another side of the station has access for our use to get to the line fuses that feed the main and spare lines for our transmitters.each transmitter has a main and spare 4160V feedline.the lines have their own fuses-and we have a long hookstick to change them.I have also rebuilt blown fuses-we use "renewable" ones-you can replace the blown element in the fuse cartridge with a new element.and you don't stand under the fuses-if they blow--the blown contents are blown thru the bottom of the fuse.

 

[supremewhirlpol]

The motor that I'm using for my rotary phase converter is used/old. I vibrates as the back housing that holds the rear bearing has bored out as the motor was originally used for a pump. It is 5 HP 230/460V 3PH 1800 RPM TEFC motor. The first motor is used and still have would work fine until it started to heat up. When this motor would heat up I my multimeter would read some very weird voltages coming from the three legs(1/2, 2/3, 1/3) and the voltage would be at times a little higher. My washing machine would react to the changes in voltage, for example, I would know when the motor was putting out weird voltages when the reversing timer in my washing machine would be out of sync with the cycle timer, and during the start of the extract cycle, the motor would sound louder and rushed. Voltages from one of the legs would be as high as 266V, and the other two would be around 238V and 244V. The phase imbalance would cause the motor in the washing machine to get hotter and after the cycle, I would smell the windings burning.
The motor that has the vibration issue provides voltages on the legs that are much more stable. I am currently using 2 line reactors that are connected in series to reduce the phase imbalance, so, my voltage average is about 233V and the volages that I get from the legs are 228V, 230V, and 232V. The washing machine likes this configuration a lot better. But, I still have the issue of the failing generator motor, I think I'm just going to have to fork over money and buy a new motor. They are a lot cheaper than a replacement motor for my washing machine. Maybe I will buy one for my birthday.

I was asking about reversing the transformer because I have a 460V 3ph motor that I would like to use for a project(maybe a washing machine) and the few step-up transformers on ebay are extremely expensive. I've seen some step-down transformers 460Vpri 3ph Delta/230Vsec 3ph Delta on there at prices that are within my reach.

Now for my next question:
Have you heard of a 3phase motor being used as a generator by itself? That is a 3phase motor in which the shaft is rotated to the nameplate RPM's by some other source and the leads of the motor being rotated are connceted to a machine to be powered. Is this possible?

The "Hot line tags": Are these used when the power company is doing maintenance to their substations or powerlines? When your company runs the 1.8MW generator, Does the some of the electricity from it go back into the powergrid? And if it does, does your company get paid for it?

 

[kenmoreforever]

a few years ago, like an idiot, I picked one up that had been left on the road by the power company. I did know it was ruined by the way.But I never saw such a mess of oil when i opened it up in hopes of coming up with a pile of copper to sell at scrap yard. it was not what i expected by the weight of that thing. I never did salvage any copper from it. just a mess. Never again. Stupidity at its finest that day i will admit.

 

[tolivac]

Rotary phase convertors-electricians usually call the phase created by the converer the "wild wire" becuase of the voltage variations.A good convertor doesn't have these problems-usually capacitors and reactors to stabilize the voltages.If you can try to shop for a used rotary convertor instead of using a 3 ph motor.A collegue who worked at the place I am working at has his own machine shop in his house.His lathe and milling machine required 3 phase power to work.He looked around-and low and behold he found a Phasemaster Convertor at of all places--one of the pawn shops.They sold it to him for only 5 bucks.Now he can run any of his machine tools with no problems.If you are getting wild voltages as you did-sure could cause damage to the load motor or device.
the 460V step down transformers should work fine if you need to use them in "reverse"-Ie to power a 460V device from 230V.And with convertors sometimes feeding the convertor output into a 3 phase transformer may straigten things out-IE weird voltages.
I have heard of "induction" generators-its a three phase,or single phase device with two stator windings-one in which you apply the DC excitation voltage-and the main winding you get the three phase of other output voltage (AC)these were used for induction heating generators.A standard 3 phase motor won't work becuasse of one winding.However a split phase motor with a start winding might work for induction generator experiments.You could apply a DC voltage to the start winding-say 12V or so at first.Then have another motor rotate the one you are using as a generator and then see if you get any output voltage on the run winding.You will need to disconnect the start switch and cap(if the motor you are using as a gen has one).If you can find a three phase motor with two three phase widnings-IE a two speed motor you can try experiments on that.Put DC into one set of windings and turn the motor and see if you can get an output on the other winding.Yes-the "hot line tags" are used when the power co is doing maintenance.they issue these tags to all customers like us and other who are on the same 115Kv line that have generators.Du Pont-another customer on the line that feeds us has gensets tour generator can be used in two modes-Load Management-the gen operates in parallel with the line-it is started and syncs with the powerline-and the gen absorbs most of our load-to 1.8Mw.the powerline takes the rest.We have to limit what the powerline takes when we are given a load management order from the power co.Typically we get them on the real hot or cold days.Then we have to use the generator in load mange mode.The gen can also be used in Emergency mode-Ie in a power failue at the line breaker to the gen stays open so no gen output feeds into the line-it is isolated from the line in that case.We can only run 1.8Mw-so we have to limit our load.Otherwise the gen will trip off.And then we are in the dark.If we fail to use our generator during a load mangement order from the power co-the penalty is VERY expensive.If the gen won't start or work we have to shut down as much of the load as we can-IE no transmitters running.And then notify the power co to repair our generator-it is provided by the power co.