Abstract: A system (27) for reducing the temperature of cooling oil for a power transformer (12) includes a heat exchanger (44) interposed in the cooling oil system. The heat exchanger (44) relies upon a liquid-to-liquid exchange of heat from the heated oil to a coolant flowing through the heat exchanger. In one embodiment, the coolant provided to the heat exchanger is obtained from an absorption chiller (65). Heat energy is provided to the chiller (65) from a heat storage device (80). In a specific embodiment, the heat storage source (80) can be a phase change material device. In a preferred cooling system, a programmable controller (55) determines the activation and operation of the system. The controller (55) can sense transformer or cooling oil temperature to trigger activation. In a preferred embodiment, the controller (55) compares a current temperature history against a temperature profile to anticipate increased cooling requirements.