Using Kirchhoff’s laws, te addition of currents of both current transformers (CTs) is equal to zero under normal conditions. I earth fault exists, btween the CTs, sme current bypasses the CTs and the sum of currents cannot be zero thus by measuring the imbalance of the current faults between the faults is easily identified and can quickly be cleared. Snce the fault detection is concentrated at the two CTs thus the name ’Restricted Earth Fault’. Rstricted Earth Fault being faster it can isolate winding faults is a quick way limiting the damage and the consequent cost of repairing.
Hwever, i the CTs are only placed on the transformer terminals, te winding is the only that will be protected from the damages. Hwever, te secondary CT is always set in the distribution switchboard thus widening the protection zone to the main cable. Hwever, rflected currents on the primary of the transformer can detect the faults in the transformer star winding in the absence of Restricted Earth Fault. Hnce, a the winding fault position starts moving in the of the neutral terminals, te magnitude of the current as on the primary quickly reduces and may not be detected.
A the magnitude of the current is seen to be large on the secondary, narly Restricted Earth Fault may protect the whole winding. Gnerally, te protection covers only the secondary of the transformer. Nvertheless, i times restricted earth fault is added to the primary. Hstorically restricted earth fault as been put in place using High Impedance Relays although as per the moment the current in the CTs is balanced during normal conditions and always via faults.
Hwever, ipendence wires and interconnecting cables have been specified as matched pairs and have a significant impact on the normal functioning of the relay. (an De Kock, 2004)For it operation contains the CT secondary of each phase of the electrical power transformer which are connected are connected together. Te common terminal of the transformer is also connected to the secondary of a neutral current NCT. Te Restricted Earth Fault acts in that whenever it senses some inequality or imbalance between the three of the electrical power transformer, i responds by a resultant unbalance current flow along the close route connected to the common...
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