Patent Number: 
Section: claims

1. A diagnostic system for protecting a tap-changer comprising:a sensor, positioned to detect temperature changes;an initial measured temperature, indicating an initial temperature measured by said sensor prior to initiating a tap change;a calculated temperature value, calculated according to the particular tap change to take place;a threshold value determined based on said initial measured temperature and said calculated temperature value, at which an alarm is generated;a second measured temperature indicating an actual temperature measured by said sensor after a tap change has been initiated;said alarm generated by the diagnostic system if said second measured temperature exceeds said threshold value. 2. The diagnostic system according to claim 1, further comprising a second threshold value above which, flow of electrical power through said tap-changer will be interrupted. 3. The diagnostic system according to claim 2, in which said second threshold value is higher than said first threshold value. 4. A diagnostic system for preventing degradation to electrical contacts in a tap-changer comprising:a contact measurement device for measuring a contact position;a contact signal generated by said contact measurement device, indicative of whether the contact is open or closed;a threshold time value related to a maximum amount of time that the contact may be in the contact position;a controller for receiving the contact signal and generating a closed time value based on the contact signal;said controller comparing the closed time value to said threshold time value to determine if the closed time value exceeds said threshold time value;a warning message generated by the diagnostic system indicating that said threshold time value has been exceeded. 5. The diagnostic system according to claim 4, further comprising a temperature sensor located in the vicinity of the contact to measure temperature and generate a temperature signal, said controller receiving the temperature signal and determining whether the warning message should be generated based on both the threshold time value and the temperature signal. 6. The diagnostic system according to claim 5, wherein the higher the temperature signal, the shorter the threshold time value must be for the system to generate the warning message. 7. The diagnostic system according to claim 4, further comprising a current sensor to measure current through the contact and generate a current signal, said controller receiving the current signal and determining whether the warning message should be generated based on both the threshold time value and the current signal. 8. The system according to claim 7, wherein the higher the current signal, the shorter the threshold time value must be for the system to generate the warning message. 9. The diagnostic system according to claim 4, further comprising:a temperature sensor located in the vicinity of the contact to measure temperature and generate a temperature signal;a current sensor to measure current through the contact and generate a current signal;said controller receiving the temperature signal and the current signal and determining whether the warning message should be generated based on, the threshold time value, the temperature signal, and the current signal. 10. The system according to claim 9, wherein the higher the temperature signal and/or the higher the current signal, the shorter the threshold time value must be for the system to generate the warning message.