Transformer Mixup

[mull982]

If you are given two 'line to neutral' sources of the same voltage but arbitrary phase difference (think 'wye' connection, but random angle rather than fixed 120 degree phase angle) and want to calculate the 'line-line' voltage, then you use 2*sin(angle/2). For small angles this value is pretty similar to sin(angle), but from 120 to 180 degrees (where the answer is that line-line = 2x line-neutral) you will see why you need 2*sin(angle/2)

-Jon

I'm not sure I follow this. Wouldn't you just subtract the two 230deg phasors seperated by 30deg similar to how you would phases of the same suource seperated by 120deg?

 

[winnie]

mull982:

You are exactly right. The general principal is 'You take two phasors representing the line-neutral voltages, and you subtract one from the other in order to get the line-line voltage.'

One method that can calculate the magnitude (but not the phase angle) of the above is to use 2*sin(angle/2). I focused on this method rather than the general principal because that was the calculation being discussed.

-Jon

 

[BJ Conner]

Couldn't you also just use sin 30deg. This results in 115V difference.

IT's close. The 30 degree triangle defined by the two voltage phasors is not a right triangle. It is an isosceles triangle with one 30 degree angle and two 75 degree angles. If you divide it in half you get two right trinagles of 15, 90 and 75 degrees.

 

[mull982]

IT's close. The 30 degree triangle defined by the two voltage phasors is not a right triangle. It is an isosceles triangle with one 30 degree angle and two 75 degree angles. If you divide it in half you get two right trinagles of 15, 90 and 75 degrees.

I see it now. I was assuming that a right triangle was formed with vectors but I see now that it is not a right triangle thus the need to split the 30deg angle to form 2 right triangles.

Thanks for pointing this out.

 

[SG-1]

The customer has replied that he will accept the transformers.

The syncronizing is done on the 6.9KV side. The new gear is providing most of the equipment for that.

The 83 transfer on the secondary side is always open transition.

The loads are mainly lighting.

No earth shattering KaBoom !!!

 

[hurk27]

No earth shattering KaBoom !!!

Oh darn, I was going to ask for you to get video of it being brought online:grin:

 

[mxslick]

The customer has replied that he will accept the transformers.

The syncronizing is done on the 6.9KV side. The new gear is providing most of the equipment for that.

The 83 transfer on the secondary side is always open transition.

The loads are mainly lighting.

No earth shattering KaBoom !!!

You're making me very angry, very angry indeed!!

There was supposed to be an earth-shattering kaboom!!

Get my pew-36 explosive space modulator!!

Oh darn, I was going to ask for you to get video of it being brought online:grin:

That may still be interesting anyways, as the inrush of some transformers sounds really cool..like THIS ONE and THIS ONE.

That user posts a lot of cool videos, including destruction of batteries, capacitors and the like.