[Amps] HV transformer and Variac

[Ros]

Semantic, Gary.  My e.e. school said it is not a transformer in the 
classic sense -"trans" as in transforming one voltage/current ratio into 
another with the added benefit of isolation which the autoformer does 
not provide.  The losses go up simply due to the fact that there is a 
greater potential difference.

On your last sentence, you say that if the input tap and the output tap 
is equidistant then, you have ordinary transformer action but not so.
Many other factors enter in.

Ros



On 7/23/2015 11:36 AM, Gary Schafer wrote:
> An autotransformer is in fact a transformer. It works just like a
> transformer with two windings (primary and secondary).
> The difference is the autotransformer shares the same winding for both
> primary and secondary. The core must be magnetized just as it is in a
> regular transformer. The core will have losses just like a common
> transformer.
>
> If of course the output tap on the autotransformer is set to the same place
> as the input tap then there will be little transformer action and mostly
> just core magnetizing loss.
> However the further away from the input tap the secondary tap is, the more
> transformer action there is and losses go up accordingly.
>
> If the output tap is halfway between the input tap then you have transformer
> action like you would have with a two winding transformer with different
> turns on each.
>
> 73
> Gary  K4FMX
>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Ros
>> Sent: Wednesday, July 22, 2015 10:15 PM
>> To: amps at contesting.com
>> Subject: Re: [Amps] HV transformer and Variac
>>
>> First, the Variac is not a transformer in the classical sense, it is an
>> autoformer or auto-trans-former.  It will not lose efficiency. Here is a
>> schematic of one and perhaps you can see why it won't lose efficiency.
>>
>> A common transformer has less efficiency than an autoformer due to core
>> loses, eddy currents, hysteresis, more heat (I2R losses), etc.
>>
>>
>>
>> Ros, W5BRY
>>
>>
>>
>>
>> On 7/22/2015 8:28 PM, Steve Bookout wrote:
>>> Hello all,
>>>
>>> Thanks to everyone for the informative responses.  Although I've now
>>> got more info to use in order to figure out what I am going to do, I'm
>>> not sure what that will be.
>>>
>>> It's really just a bit 'hot' for my needs and if I turn it down with a
>>> variac, regulation may suffer.  I do have a stack of two variacs on a
>>> common shaft, and although they are large, I don't know what their
>>> actual specs are.  Something for me to check.
>>>
>>> 73 de Steve, NR4M
>>>
>>> On 7/21/2015 03:03 , Steve Bookout wrote:
>>>> Hello all.
>>>>
>>>> Question for the experts.
>>>>
>>>> How does using a Variac to control the output of a HV transformer
>>>> affect things like efficiency?
>>>>
>>>> I think it would be reasonable to think that a transformer operated
>>>> at less than rated input voltage would be less efficient than one run
>>>> at full primary voltage.  I mean, it cost 'something' just to make a
>>>> transformer act like a transformer.
>>>>
>>>> I ask because I have a perfectly fine 'pole pig' transformer rated at
>>>> 5 KVA.  7200 AC volts on the output (reversed) is a bit much for my
>>>> needs, so was wondering what the trade-off would be if it were run at
>>>> considerably less than 220 input.
>>>>
>>>> I can see this is a better xformer for a 4cx10000, than anything I
>>>> would be using, but I have what I have.
>>>>
>>>> 73 de Steve, NR4M
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