How to say no to more work as a PhD student so I can graduate I am entering my 5th year as a PhD student. The "understanding" with my advisor is that I need three journal papers accepted to graduate. I think I have enough material (designs/ measurements/ analysis) to write the three papers now, but so far have only written one. In a normal situation, my next step would be to write the other two papers. 

The issue is that my advisor received more short-term funding for my project, and he plans to ask me to do one more "design" before the grant expires. This "design" will extend my PhD by 1.5 years at the very least and I will have to delay my paper-writing to meet the incredibly ridiculous deadline associated with the short grant and design deadline. 

Naturally, my advisor being who he is, he will use the fact that I do not have the three papers to impose more work on me instead of allowing me to actually write the papers I need. He does not have a problem hitting the maximum duration allowed by the Institute to keep a PhD student (6-7 years), even when the student has done enough. 

This is further complicated by the fact that my advisor lacks experience in my specific field and only understand that "more designs = more papers". 

I need advice on how to address this. How can I make a compelling case that I have done enough and I just need to focus on publishing so that I can graduate? I would really appreciate realistic advice.  

Note: My advisor is very powerful in the department. This makes approaching the department unrealistic. I will be on the losing side if I approach the department. I am in a North American Institute.
I think your most realistic option is to have an honest discussion with your advisor about your goals and expectations. 

Tell them that you’d like to graduate by 20xx, and you think your work on A B C was fulfilling and interesting. You feel like you can really build a narrative around these projects that would culminate in a good thesis within the timeframe set above. Given your goal, you feel like starting a new project at this time will be detrimental to your progress.

Ideally your advisor would totally see it your way and you’ll graduate into the sunset. Realistically: advisors tend to be overzealous at times and can exert a lot of pressure over their students. A reasonable advisor would leave the choice to you; a clever one will make you believe that it’s a really good idea to start this new project (you don’t have enough material now, your CV will be amazing with the new project accomplished...). So a lot of this depends on the dynamics you have with your advisor.

I would not go over their head unless you’re willing and able to switch advisors. Its hard to get back to a good working relationship after something like that. 

I will try to establish my own independence and capacity to successfully graduate with a plan (by 20yy I plan to submit these results, draft by Jan 20zz and so on). 

Good luck!