According some technical recommendation, the source side of power system shall be grounded not load side. The primary side of a utility transformer is load side of a distribution system; therefore it must not be grounded.
Generally it is necessary to ground each voltage level to achieve the protection and advantages of neutral grounding. The ground connection should be at the neutral lead of the generator or the power transformer bank. In other words, ground at the power source, not at the load. The ground connection should always be on the secondary of the transformer. If we ground the load side equipments, the amount of system impedance will be conditional and will change with situation of load breakers (close/open), also path of grounding fault which is important in directional protection topics can be changed related to load breakers conditions.