A system for cooling a power transformer which generates heat, when driving a load, includes cooling devices located about the transformer which are powered to remove excessive heat from the transformer. The cooling devices may include fans to blow air onto the transformer and pumps for circulating a coolant about the transformer. The cooling devices of interest have a motor (e.g., a fan motor or a pump motor) which is energized in response to given temperature (heat) conditions. In systems embodying the invention, the currents flowing through the motors of cooling devices are sensed and monitored to determine whether the cooling devices are functioning correctly and to substitute functional cooling devices for those which are malfunctioning. The importance of sensing the motor currents and substituting operational cooling devices for defective ones is that a temperature rise due to a failure of a cooling device is not immediately detectable due to the large thermal constants associated with the transformer assembly. Sensing the currents in the motors enables the early detection of fault conditions in the cooling system. It also enables the monitoring of operating conditions and running time of the cooling devices to aid in the maintenance and operation of the cooling system.