I am making a project in which i need to turnoff the transformer when the load current exceed 4amperes. I need to impleent thyristor to turn off the connections. I need to know which thyristors should be used and how it be programmed like via arduino or resberry pi

 

See this for e.g. ACS712 ebay 281752324740.
Also Fairchild app note AN-3006 for interfacing a zero crossing MOC316x/MOC305x etc.
Also known as a Solid State relay.
Max.

 

See this for e.g. ACS712 ebay 281752324740.
Also Fairchild app note AN-3006 for interfacing a zero crossing MOC316x/MOC305x etc.
Also known as a Solid State relay.
Max.

We cannot use relay for zero crossing, we need to use a thyristor for turning off the connection.

 

That is what the app note shows, a Triac.
The fig 1 in the app note shows such a circuit.
Or SSR.
You also mention you have to monitor the current level?
Max.

 

You can't connect a single thyristor in series with the AC supply to a transformer as it will rectify the AC and pass DC through the transformer. You can use two thyristors so each one conducts in the opposite direction. You can also surround a single thyristor with a bridge rectifier but any of these solutions are more complex than Max's suggestion of using a triac.

Les.