A reliable distributed temperature monitoring is very important for electric power systems because a power system failure will result in an enormous loss of life and property. Fiber Bragg grating (FBG) sensors, which have been studied intensively for last decade, can be very efficient tools for these applications because they are immune to EMI and can be highly multiplexed, which enables efficient quasi-distributed temperature sensing along tens of km range. We constructed a FBG sensor array system for temperature monitoring of power cables. For reliable sensor implementation, the FBG array is embedded in a metal tube which protects sensors from external disturbances and enables easy installment by soldering. The temperature-induced Bragg wavelength variations are accurately monitored by a scanned tunable wavelength filter. Differential measurement with a temperature stabilized reference grating and a curve fitting algorithm has been used to enhance measurement accuracy in temperature range of 25°C~70°C.