Advantages of solidly grounded generators

In solid grounding, the generator neutral is connected directly to the station earth with no intentional impedance.

Advantages

• Neutral held at earth potential: during a line-to-ground fault the healthy phases stay close to phase voltage, so there are no high overvoltages.
• No arcing-ground problem: the fault current is large and the arc does not restrike, so transient overvoltages are eliminated.
• Reduced insulation cost: equipment and lightning arresters can be rated for phase voltage (about 80 % arresters).
• Simple and reliable protection: the large earth-fault current operates ordinary overcurrent/earth-fault relays quickly and selectively.
• Simple and cheap: no resistor, reactor or transformer to buy and maintain.
• Supports single-phase loads: a 4-wire LV supply (phase-to-neutral loads) is possible, which is why small LV diesel and micro-hydro sets are usually solidly grounded.
• Better personnel safety because faults are cleared quickly.

Limitation

For large generators the earth-fault current can exceed the 3-phase fault current (since $X_0$ is small), causing stator core burning and severe mechanical stress, so solid grounding is used mainly on small LV machines.