Surge tank

sachin

I am working on the analysis of a 12km long Head Race Tunnel. I dont have any turbine characterstic data and I have taken 20sec time as shut down time. Can you please suggest me how can I take time schdule for approximate analysis for a 600MW project (500m net head) with 4 pelton turbines? I have modeled restricted orifice(dia 2m) type surge tank(dia 12m) for the analysis. I am getting 15 bars pressure near the surge tank. My problem is that at the distance of around 6km u/s side from tank the pressure is around 8 bars, can you please tell why pressure is not reducing even at such high distace? I have also modeled same problem without surge tank and for this I am getting pressure of 50 bars near tank

Please suggest me something about this.

Thanks

Sachin