Can I replace my charger twice if its under warranty? I have a problem: due to high power electricity my charger was damaged and I had to replace it - an Apple 13 inch MacBook Air charger. This has happened already once before, a month ago, and now it has happened again.

I want to know if, having replaced the charger previously one or two months ago, and now that the replacement charger has been damaged via the same issue (i.e. high power electricity), can I replace it again under warranty without any cost? What can I do if the Apple Care Centre in my city refuses to replace my charger the second time around?
I have no idea what you mean by High power electricity, but generally Apple will replace something as many times as necessary while it's under the warranty period so long as you haven't damaged it in some way. 

Your question implies that your chargers were not faulty, so if Apple determines that they've been damaged, you may be out of luck. However, if the chargers are supposed to be able to manage whatever it is you mean by High power electricity, then they should still be covered as something isn't working properly.

Of course, this assumes that by damaged you mean it no longer works, rather than just some sort change in cosmetic appearance.

Regardless, the only way to find out is to ask Apple. If you get no joy and feel that a replacement is honestly warranted, then your local consumer laws may offer a process you can avail yourself of.