Apparatus and method for cooling power transformers

A combination comprising:

• a power transformer having a primary for the application thereto of input power and having a secondary for the connection of a load thereto;
• circuitry for sensing the amplitude of the load current in the power transformer including comparator circuitry for constantly comparing the load current with a predetermined threshold level and producing a first signal whenever the load current exceeds the threshold level;
• and
• circuitry for applying the first signal to a timing circuit for initiating a predetermined counting period;
• said timing circuit counting so long as said first signal persists, and said timing circuit if not reset before the end of the predetermined counting period, for producing a second signal for enabling a cooling system for cooling the power transformer.

A method for cooling a power transformer which may be subjected to a load condition causing the temperature of the power transformer to rise above a desired level, the method comprising the steps of:

• sensing the amplitude of the load current in the power transformer;
• constantly comparing the sensed load current with a predetermined threshold level;
• producing a first signal whenever the load current exceeds the threshold level;
• counting the length of time the first signal is present;
• where the first signal indicates that the load current exceeds the threshold level;
• and
• in response to the load current exceeding the threshold level for longer than a predetermined period enabling a cooling system for cooling the power transformer.