Overcurrent Protection Relay, How do I simulate it with Raspberry Pi?
How do I get the values needed from the table below (specifically
  TMS)?


TMS is short for Time Multiplier Setting. On an electromechanical overcurrent relay this may be set using a calibrated dial with numbers on it, called the Time Dial Setting (TDS). A TMS value of 1 represents the relay's normal operating time. Higher or lower values increase or decrease the operating time proportionally.  


  Do I need current sensor for this?


If you just want to simulate an overcurrent relay then you don't need any extra hardware since the Pi can do it all in software. But if you want to emulate it (ie. replace a physical relay with your Pi) then you will need to measure current.


  is there any easy explanation or can anyone link me to any easy
  books/websites for this?


Here's a good article describing how these relays work and explanation of the timing equations:- 

Overcurrent Protective Relays