In the open circuit test of transformer, the instruments are placed on the LV side, while in the short circuit test, these are placed on the HV side

In the OC test of transformer, the instruments are placed on the LV side because if measurements are made on high voltage winding, the current would be inconveniently small and the applied voltage inconveniently large. While in short circuit test the instrument is placed on the HV side just for the reverse case, i.e. if the instrument is placed in the LV side the current produced will be inconveniently high and the voltage inconveniently low.