1, directly grounded system; Advantages: high sensitivity protection Faults: short circuit current 2, no grounding system; Advantages: short circuit current is small, the system allows the short run when single-phase grounding Weakness: the low protection sensitivity, high demands on insulation 3, the arc suppression coil grounded system Advantages: small short circuit current Weakness: the protection sensitivity is low, may cause resonance my facebook:https://www.facebook.com/?sk=nf