In this paper the optimal placement of phasor measurement units to maintain the network observability in normal mode and considering the constraint installed on some buses has been studied. In addition to providing a suitable use of phasor measurement units, buses with high sensitivity have been considered, and optimal placement of the units considering the direct observability sensitive bus, observability with double redundancy for sensitive buses and direct observability sensitive buses with the double redundancy sensitive buses has been done. Also to minimize these meters to reduce costs, is considered effect meters presence power flow and power injection in the network. In this paper, the integer linear programming in MATLAB software environment for the implementation of 230 and 400 KV network in Khouzestan province has been used. Results, suggest the increases to observability reliability of the network.