A restricted ground fault is recommended for equipment that is grounded, irrespective of its method of grounding. Unless the protection is restricted, the equipment may remain unprotected. Generally, it is an equipment protection scheme and is ideal for the protection of a generator, transformer and all similar equipment or circuits, requiring individual protection.
Figure 1 illustrates the operation of the relay when the fault occurs within the protected zone. The scheme will prevent isolation of the equipment for faults occurring outside the restricted zone (Figure 2).
A delta-connected or an ungrounded star-connected winding should also be protected through a restricted ground fault scheme, otherwise it will remain unprotected. There is no zero sequence or residual current in such a winding to detect a ground fault. Therefore just one CBCT will be enough for resterction of protection zone in this case.