For the NPAR, I recommend doing a test to find out the most efficient number. e.g. run a same calculations multiple times with different NPAR. Also, do the same for LPLANE parameter as well. The manual instructs to use the number of node as NPAR as each parallel calculation can be run at each node minimizing communication overhead between each node. If not optimized, VASP takes extra time to comminucate between nodes, eating up your computation time. However, I have found that this instruction does not always hold up, and, really, this parameter is heavily dependent on the batch server/ node configuration. So, it is wise to do your own test to optimize this parameter (and other parameters as well).

Dear Geun 

Thanks for your reply. My Basic concern was that whether NPAR relates to no of node or no of cores. I am doing the test calculations. 

Personally I've found that, with your same node/processors configuration, setting NPAR=4 and NSIM=2 gives the best performance.