Control.com - Nerds in Control

Two CT secondaries, each rated to 5A secondary current are connected in series to a Relay or Meter, CT inputs, can someone explain me what will be the significance/technical requirement/consequences of this. Will there be change in the accuracy?

I can't immagine why you need to do this but depending on the primary it will have different effects.

If both were on different phases they would give less than the sum. On the same phase (same wire) the current should be the same but you would have double the voltage available for a load.
It could also be dangerious if one primary is not loaded, similar to open circuit.

I remember from my apprentichip days being told NEVER to open circuit a secondary or it could blow up. The ratio between primary and secondary is very high. e.g. a 1000:5 ct has a ratio of 200:1. In theory if you have a ct on 400V load the potential secondary voltage can be 400x200 or 80,000 volts

hope this helps roy_matson@yahoo.ca

Hi!

I have a similar question. I was browsing the net for information on having a series connection of electrodes for a welding transformer set-up that will be used for my thesis. Is it possible to achieve that kind of set-up? Like for example, 4 electrodes in series to a single transformer?

Best Regards,
carloalison @ yahoo. com

No.

Think about it, how would you start all four at the same time? And any that are not lit are an open circuit.

regards

cww

When you say 4 electrodes, is that 2 *pairs* of electrodes for resistance welding? If so, then yes I have seen that configuration. It isn't very common though. You would only ever want to attempt it if:

1) The welds are close enough together that you don't have long welding shunts.

2) The welds are far enough apart that the welding current doesn't shunt across the part without going through the weld zones.

3) The material is very easy to weld, as you can't adjust each weld independently. This problem is the main reason why this technique isn't very
common.

Since you have a higher total weld resistance, you may need a higher transformer voltage. You will probably want a transformer with multiple taps so you can select whatever voltage you need.

Another way to do multiple welds with one transformer and one weld controller is to connect them in parallel and do one weld at a time. You close one set of electrodes, weld, open them, close the second set of electrodes, weld, open them, etc. You normally would want to use a weld controller that has multiple selectable sequences for this though, so each weld can be adjusted
independently. This method tends to be slower (only one weld at a time), but allows more flexibility in adjusting the weld. The welds still need to be fairly well matched though, as obviously each weld has to work with the same
transformer size and weld voltage.

Responding to Sukumar's 20-Oct query... the short answer is, yes, connecting CT outputs in series could adversely affect accuracy!

However, there is at least one situation for which the series connection is justified. If you are interested in more information let me know!

Responding to Roy Matson's 21-Oct reply... I suggest you search the List Archives for material on the subject of inadvertent "opening" of a CT's secondary circuit while it is in operation!

Regards, Phil Corso (cepsicon@aol.com)