Synchronous generators are run at a speed in synchronism with grid frequency and are used to convert mechanical energy to AC electrical energy. The generator is synchronised onto a large interconnected grid thus operating in unison or in parallel with all other generators of the overall system supplying energy to all the loads connected to it. It is essential to study the effect of the load variations on the voltage magnitude and the frequency. This paper studies the effect of load variations on the voltage magnitude and the frequency of an isolated three-phase synchronous generator. The three-phase synchronous machine has been modelled in the MATLAB Simulink environment. Separate PI controllers have been developed for keeping the magnitude and frequency of the terminal voltage constant. The simulation has been done in MATLAB Simulink environment. It can be concluded from the simulation results obtained that the magnitude and frequency of the terminal voltage of the synchronous generator remain constant at their rated values irrespective of variation in connected load (both real power and reactive power). These simulation results show the proper functioning of the proposed PI speed regulator and PI voltage regulator in this paper.