Zero Sequence Current Relay:
This type of zero sequence current relay is similar to that of negative phase sequence relay as discussed in article Induction Type Negative Phase Sequence Relay.
The relay is made to respond to the flow of zero sequence currents also by providing another winding on the central limb of the upper electromagnet, connected in the residual circuit of three line CTs, as illustrated in Fig. 9.66.
Fig. 9.66. shows the arrangement for response to negative and zero sequence currents (only the central limb of the upper magnet has been Illustrated)