For a SCADA system deployed on a Power Network, which communication protocol for data transmission to the SCADA Main Terminal would you prefer?

For me I prefer to use IEC6185 is new standard for compunction network and system in substation. it is very good to communicated and easy to use it. if you need any more infromation just eamil me

As Mr Alhmaili stated, there is a standard IEC61850, for the design of electrical substation automation. IEC61850 is a part of the International Electrotechnical Commission's (IEC) Technical Committee57.

This information has been obtained from Wikipedia.

As Mr Munis stated there are plenty of other protocols out there widely used and built into many devices as standard. BacNet, LON and Mod-bus being the most popular as they are open standards. Of course there are many others, often proprietry (meaning not open or accessable to all).

Care should be taken (as Mr Munis stated) that your equipment can support the protocols. Also extra care should be taken for security. For instance, BacNet has no security features and unless secured in another way (VLan for example), all devices can be seen and interacted with.

It has always been my recommendation that the BMS/BEMS/SCADA network should be separately cabled and kept away from IT and their own structured cabling systems. IT is only as good as it's worst employee. The extra capital cost will be worth it.

Mr. Yoqoub has referred to IEC standard. Please note that IEC is a standards organization setting best pracises and standards. Nothing to do with Communication protocol. 

Regarding the question: there are few factors which decide the appropriate protocol to be used. 

However if it SCADA to HMI of another SCADA, then you may use any OPC DA compliant. 

Elsewise if applicable, you may also use Modbus RTU (this is serial and can be slow), or Modbus TCP/IP.

There are other communication protocols as well, but all depends if the installed SCADAs support them or not. the examples are Bacnet and lonwork protocols. 

Thanks