run 50Hz 20kv power trans on 60Hz 23kv?

[tjg124]

My first post in Eng-Tips and it's a toughie for me. Greetings 50/60 and 60/50 hertz experts! I can get a surplus 50 HZ 8 mva furnace rectiformer from a closed factory of ours in Europe for just the cost of transporation to the US. It comes with an autotransformer with a 20 KV primary input. I've read a lot of the postings on running 50 Hz equipment in 60 Hz systems, and I still am confused. I'm making two big changes. 1) frequency going from 50 to 60 Hz. by itself is OK, or so it seems. Losses are less, therefore heating is less, right? But then 2) I increase voltage at the primary of the system by 15%. I'd like to evaluate each issue separately then look at the net effect of both. I'm trying to get exact nameplates from Italy but don't have exact numbers such as Z yet. Is there a definitive resource of information on the 50 to 60 and 60 to 50 Hz subject?

 

[davidbeach]

Run at the same voltage, a 50Hz transformer will work just fine at 60Hz. Run at a voltage not exceeding 120% of the 50Hz voltage the magnetics will work just fine but the electrical insulation will need to be evaluated for the overvoltage.

Current/MVA ratings will need to be evaluated. Maximum current ratings should not be exceeded, higher voltage will result in a higher MVA at the same current. Constant MVA loading will result in lower current at a higher voltage. Core losses will increase with increasing voltage, although there is some decrease with increasing frequency. Load losses are generally proportional to load current squared. Make sure that the transformer cooling system can handle the new conditions, may require changing out the transformer fans.

 

[itsmoked]

In your case, except for any axillary equipment, the 60Hz on a 50Hz transformer is a non-issue. The voltages? Require scrutiny as David suggests.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

The reactive component of the impedance will increase with the increased frequency. This will tend to lower the available short curcuit current. For estimation of the available current, assume a simple proportion of 50hz./60hz. This assumes the impedance is 100% reactive and the error is small for high X/R values.
If the voltage is then raised 15% the available short curcuit current will increase 15%.
You will need to know the X/R ratio to calculate the new impedance precisely.
respectfully

 

[tjg124]

Hi guys,

Thanks for the rapid response.

About that 50/60 HZ book or paper. Does it exist? What's the definitive guideline for this?

OK, 50 Hz device is OK to run on 60 Hz magnetically. We will figure out some de-rate to run conservatively and not over amp the unit. But the voltage thing is still a big question mark to me. This regulator/rectiformer combo was manufactured in 1968 in Italy at the Brown Bovert factory that is now closed, so getting design info is unlikely. I'd doubt if power factor testing was ever performed on it, and to do PF testing now will yield little immediate results other than a good benchmark. My inclination is to get megger P/I test results, gas in oil, furans, Karl Fisher and evaluate it from that. If it looks OK at this point, use it.

Your thoughts?

 

[itsmoked]

What if this thing just doesn't work out? How much will it cost you, your organization? If it is sort of a, "dang I wish it had worked", kind of thing you could 'try it'.

If it's going to leave 10k customers in the dark maybe you should just find a used one locally... Maybe 'one in the local bush' is better than 'one in the hand' in another country across thousands of miles of water?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[tjg124]

Keith et. al,

I appreciate your thoughts of which I've had similar ones myself. Now I've changed my mode to deciphering Italian and European tap changer nameplate standards.

I just got a copy of the nameplate in Italian from our European staff. It says the "Volt A Vuoto" is 5682 <divided by> 23088. The <divided by> is the division symbol that does not exist on a QWERTY keyboard. My assumption is the 23088 is the primary voltage for the transformer, but I'm not sure what the 5682 is. Z (Tensione Di c. c.) is "7% a 22784/145.1" so this pretty much confirms that the rated incoming volts will work on our 23KV nominal system here at our plant.

The other thing the Europeans like to do is give the primary and secondary their own KVA ratings. Primary KVA is 10,200. Secondary KVA is 14,400. To me there is only one KVA rating of value, and that's the usable KVA from the secondary. My company calls this unit an 8.6 KVA unit in it's records. So now the new confusion factor is the real size of the unit. How can the primary have a smaller KVA rating than the secondary? If anything, because of efficiency losses, the secondary KVA should be less than the primary, right?

 

[ScottyUK]

The [&divide;] symbol can be obtained using the (&divide syntax but enclosed with [ ] instead of ( ). Click the Process TGML link below the text box you write your post in. There's a good selection of mathematical operators and other stuff in there.

Can you post an image of the nameplate? faq559-1100 gives you some hints on the way to do this.

I've never seen different VA ratings on a European transformer unless it is a multi-winding type with a rating on each winding. Damned strange. Incidentally, "volt a vuoto" translates as "volts to empty" in Babelfish, so could that be 'line - neutral' in more familiar terminology?

----------------------------------

Sometimes I only open my mouth to swap feet...

 

[Skogsgurra]

What worries me more than volts/Hz is the "furnace rectiformer" part of your post.

Is this furnace rectiformer controlled? Are there thyristors involved? If that is the case, you need the documentation to be able to adjust firing to the new timing that 60 Hz brings with it.

If not controlled (simple rectifiers), forget this post.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[tjg124]

Gunnar,

Good question about rectifier vs. thyristors. Our two existing rectiformers have 12 pulse rectifiers. I know our small one (6 mWe) has 360 rectifiers.

I'll e mail my contact in Europe and find out for sure that this is the same. I'm betting it is, but it sure is a good idea to check this ahead of time.

Thanks for the question!

Tom Graf

 

[davidbeach]

6 milliwatts needs 360 rectifiers???? I think you probably meant 6MW.

 

[itsmoked]

Very tiny rectifiers? Ow ow stoppit!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com