rectifier transfomer connection of Battery charger

[zkz]

Sir,
Normally rectifier transformers used in Battery Chargers are found with Star-Delta configuration. Why secondary side is given as delta? What is the disadvantage if secondary side was Star?
Thanks in advance,
with regards
zkz

 

[Skogsgurra]

The rectifier in a battery charger works against a back-EMF. That means that output current is delivered in short pulses (low current angle) and that also means that triplene harminics are plenty.

A star/star transformer presents a very high impedance to triplene harmonics while a delta winding does not. You could have either primary or secondary delta connected - or both.

Google triplene harmonics and transformer windings to have a full explanation.

Gunnar Englund

http://www.gke.org

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

 

[zkz]

Hello,
Thanks for the explanation. I understood like this: Delta connection is provided for circulating the triplen harmonics produced by SCR rectification in short pulses within delta winding and not allowing those triplen harmonics back effected to supply system.
Please correct me if I am wrong.
regards,
zkz

 

[Skogsgurra]

What you say is true. But it sounds like you were reading a text on DC drives and SCR control.

Battery chargers (the vanilla variety) do not have thyristors. Current angle is small because the rectified voltage is below battery voltage most of the time. The diodes conduct only when rectified voltage is above battery voltage. A small current angle means a narrow and high current peak, which means lots of harmonics. As I said before, star windings show a high impedance for triplenes and that means that you can't get the desired charging current out of the charger. The delta winding circumvents the problem.

Is this a school thing?

Gunnar Englund

http://www.gke.org

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

 

[zkz]

It is not a school thing.
I have seen many battery chargers are with SCRs of which the rectifier transformers are connected in delta on secondary side. This is the reason for asking aboutit.

Thanks.
regards,
zkz