Different from precise power flow calculation， voltage adjustment induced by shunt VAR compensation can be estimated based on short calculation. Reactive power compensators in substation are generally connected in parallel to the low-voltage bus of a transformer and used to adjust the voltage of high-voltage or mid-voltage bus. While， the general estimation model of voltage adjustment by shunt VAR compensation can only be used to estimate the compensated bus voltage. In order to estimate voltage adjustment of a transformer's high-voltage and mid-voltage bus induced by shunt VAR compensation at its low-voltage bus， a corresponding expanded model is established and it can also be used to explain the mechanism of voltage adjusted by shunt VAR compensation as well as to estimate the requirement of substation shunt VAR compensation. The correctness， accuracy and practicality of the expanded estimation model are validated by the real experiments in Central China Power Grid and the corresponding simulative calculation.