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Bruce in Bangkok[_5_]

On 14 May 2008 01:35:23 GMT, wrote:

In alt.engineering.electrical Don Kelly wrote:
| ----------------------------
| "daestrom" wrote in message
| ...
|
| wrote in message
| ...
| In alt.engineering.electrical Michael Moroney
| wrote:
|
| | Are the load tap generators configured make-before-break?
| | Break-before-make would mean a (very short) power outage every
| activation
| | but make-before-break would mean a momentarily short-circuited winding
| and
| | the break would involve interrupting a large short circuit current.
|
| I wonder how much regulation could be managed through the use of variable
| leakage inductance in the transformer windings.
|
|
| I suppose you could, but increasing leakage inductance means you're
| increasing losses aren't you? Just a percent or two on a unit rated for
| 250 MVA can be too much to tolerate.
|
| daestrom
| -------------
| I don't see changing leakage inductance having much effect on losses ( a
| great effect on voltage regulation -likely all to the bad) but the problem
| is one of changing leakage inductance.
| Does this mean changing a gap in the core? Does it mean moving one winding
| with respect to another? In any case it does mean some fiddling with the
| core or winding.

The thought is to change the core in some way. Maybe that can be done in a
gradual way, as opposed to winding taps that have to be either BtM or MtB.

| This has been done for series lighting circuits where the load current was
| kept constant by using a transformer which balanced the forces between coils
| against a fixed weight. If the current changed the secondary coil moved so
| that there was more or less leakage. The units that I have seen were rather
| cumbersome.

I'm thinking more along the lines of a motor drive to move the coil, and
that be controlled by the same authority that would have controlled the
steppable taps.

Some years ago I worked at an Air Base in Northern Thailand. the
airfield lighting was a constant current series circuit and used
transformer as you describe - a movable core winding that was driven
in and out of the outer windings by a motor controlled by a current
sensing system.

I believe that street light systems are similar.

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)