The advantage is that the investment in insulation is reduced, because when single-phase grounding occurs, the neutral point voltage is zero and the non-fault phase voltage does not rise, so the voltage of equipment and lines to ground can be designed according to the phase voltage, thus reducing the cost and investment.
Neutral direct grounding system, also known as large grounding current system.
In this system, when one grounding point is grounded, another grounding point except the neutral point appears, which constitutes a short circuit.
The phase current of ground fault is very large. In order to prevent the equipment from being damaged, the power supply must be cut off quickly, so the reliability of power supply is low and power failure accidents are prone to occur. But when a single-phase grounding fault occurs in this system.
Because of the clamping effect of the neutral point of the system, the non-fault relative ground voltage will not increase obviously, which is beneficial to the system insulation.
References:
Baidu Encyclopedia Transformer Neutral Grounding System