60Hz US transformer on 50Hz UK supply? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: May 06, 2020, 03:39:08 pm
content: What might happen if I run a US sourced 240V primary 60Hz transformer (7.5V at 52 Amps secondary) on our 240V 50 Hz mains supply? Thanks.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 06, 2020, 03:42:39 pm
content: Depends on how much margin was built into the design - it may suffer from core saturation, which may or may not be an issue in practice.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 06, 2020, 03:47:27 pm
content: US mains voltage is usually 110V. Are you sure your transformer is for 240V/60Hz?If yes, the frequency difference shouldn't be a problem. 50Hz or 60Hz doesn't matter much, if the voltage is the same. The transformer itself should still work OK at 50Hz.

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2020, 05:03:11 pm
content: The US mains voltage is 240V split, with each side being 120V to a neutral bonded center tap. Large appliances are 240V so both 120V and 240V equipment is common here.Mike is right, saturation can be a problem, it really depends on the specific transformer. Using a 50Hz transformer on 60Hz is no problem but going the other way around can be. A 50Hz transformer needs more iron for the same capacity. Many transformers are built for a world market but many are not and are made with as little material as will do the job they are intended to do.

author: ArthurDent
author_rank: Super Contributor
timestamp: May 06, 2020, 05:03:51 pm
content: The previous replies are reasonable. One problem with one designed for 60Hz is if the transformer has somewhat marginal steel in the core, it may run warmer on 50Hz. At least some transformers in the past transformers were rated for both 50/60Hz. Here's what one site said."Operating a transformer at 50Hz generates 20% more flux lines than at 60Hz. ... This can result in a transformer that exceeds safe temperature levels. Therefore, a transformer designed to run at 50Hz will simply run cooler at 60Hz. But one designed only for 60Hz may overheat if subjected to 50Hz."

author: rstofer
author_rank: Super Contributor
timestamp: May 06, 2020, 05:07:39 pm
content: Quote from: RoGeorge on May 06, 2020, 03:47:27 pmUS mains hasn't been 110V since the 1930s and was changed to 115V during WW2. After WW2, it was changed to 117V and in 1967 became officially 120V. You can often date schematics by what they called the input voltage.That's 'nominal' of course and the actual voltage will depend on distance to transformer, wire size/length and current.Motors here are typically rated for 460V even though the supply is nominally 480V. The reason is that a 5% over voltage is easily tolerated and there is usually some drop between the transformer and the motor up on the roof (of a tall building?). We overcome that by setting the 480V 5% high or around 500V. That gives us an allowance for quite a bit of drop before we get to the motors. It's also a little hot for 277V lighting but tolerable. There is some debate about where to set the transformer taps. Never low, of course, but nominal versus 5% high comes up all the time.We have a similar problem with 12kV versus 12.47kV. Most sites are actually 12470 but it's just called 12 kV. Some people call 480V as 460 even though that change came way back it '67 as well. In older plants, the panels are probably still labeled 460V.ETA: Some folks are still calling it 440 which goes back to the 110V days. Names stick, standards change. Again, it's not unusual to see panels labeled 440V.Our tolerances are nominally +5%..-10%.The 60 Hz transformer probably doesn't have enough iron to run at full capacity on 50 Hz. Try it and see how hot it gets.

author: boB
author_rank: Frequent Contributor
timestamp: May 06, 2020, 07:27:39 pm
content: It will probably just run a bit warmer on 50 Hz than it would on 60 Hz..... if it isn't already running too warm on 60 Hz.

author: alm
author_rank: Super Contributor
timestamp: May 06, 2020, 10:27:24 pm
content: I've seen some old Lambda power supplies that have their maximum output current derated by 10% when used at 50 Hz. Similar to operation at 10°C higher ambient temperature. I figured that was also to reduce transformer core saturation.

author: Ian.M
author_rank: Super Contributor
timestamp: May 06, 2020, 10:59:30 pm
content: The length of each half cycle is stretched by 20% at 50Hz vs 60Hz. Therefore there's 20% longer for the flux to build up and you need to derate the input voltage by 20% to have the same margin before saturation. That's a problem in 240V 50Hz UK (who exploit the tolerance margins on the harmonised EU standard 230V 50Hz supply) but less so for transformers with at least 10% margin in parts of the EU with old supply infrastructure where their old 220V 50Hz supply hasn't been adjusted closer to the nominal post-harmonisation 230V.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 06, 2020, 11:31:17 pm
content: For many years, Western Australia used 250v as a standard,-vs- 240v in the rest of the country.This supposedly came about when we changed from 240v 40 Hz to 50Hz.The story, which may be just an urban legend, is that the distribution transformers were less lossy, hence the higher voltage with the higher frequency.In any case, prior to the changeover, much equipment with transformers designed for 240v, 50Hz survived on 240v, 40Hz.After the changeover, the only problem was the over voltage, which was small enough to ignore.All the 60Hz transformiers I have seen in use on 50Hz seem to have survived for years without any problems, but they were mainly used in good quality test & Broadcast equipment, so probably had a bit more iron than consumer stuff.One supplier of UHF linear amplifiers had two different transformer types for 60 & 50Hz, but that is the only place I have seen it "spelled out".

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: May 07, 2020, 03:12:35 am
content: From the voltage 7.5V at 52Amps that seems to me that is for a heater of a 3CX3000 tube for a Ham power amplifier.3CX300A7 <https://www.cpii.com/docs/datasheets/76/3CX3000A7.pdf>But I might be wrong.

author: Ian.M
author_rank: Super Contributor
timestamp: May 07, 2020, 04:44:35 am
content: Quote from: Chris Wilson on May 06, 2020, 03:39:08 pmIt would be prudent to bring it up gently on a Variac, (2A or higher), starting at 200V monitoring the no-load input current for non-linear accelerating increase indicating the onset of saturation. You'd ideally take it all the way up to 255V, to cover UK line voltage permitted variation, but I bet it will crap out before that. Worst case, you may need to permanently buck the input voltage - a 230V:18V 40VA or higher toroidal transformer isn't too large or expensive, and wired as a bucking autotransformer on the feed gets you back nearly 10% of safety margin, albeit with a 10% drop in output voltage.

author: Chris Wilson
author_rank: Super Contributor
timestamp: May 07, 2020, 08:17:05 am
content: Quote from: Nuno_pt on May 07, 2020, 03:12:35 amClose, but no cigar. Yes to 3CX3000 heater, but it's in an industrial glue dryer for curing compositesThanks for all the replies, I may be in contact with the manufacturers who can confirm or not whether the same transformer was used in UK and US gear.