Heat run test is similar to that of back to back test which can be conducted on the transformers. In heat run test, the watt meters are not required which are used in back to back test. Only a voltmeter is used to measure the primary applied voltage and ammeter to measure current in the secondary side. The arrangement of the transformers in connection for heat run test is shown in the Fig.1.
The primary side is excited at normal voltage and frequency. The secondary side is connected in open-delta. It is provided with a circulating current from an auxiliary single phase supply of any convenient frequency. The method gives the same results as that of back to back connection without the requirement of two identical transformers. It is possible to apply the method whatever the normal internal connections if temporary alterations can be made where necessary.
The heat run test is continued until the windings and the oil in the tank attain a steady temperature. This temperature rise must be within permissible limits which is set by designer.
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