Voltage compensated protection-a new form of backup protection for use on distribution circuits

A new relay has been developed jointly by Manweb and GEC-Alsthom, the microprocessor protection relay. The version suitable for overhead line protection is denoted as MPR(OLP). This has been designed to utilise rented low grade variable frequency (VF) pilots to perform a unit protection function. It has been found that rented communication circuits whether DC or VF may fail coincident with power system faults. The practice of having back up protection at the BSP only, causes too much disruption. For this reason a back up protection was designed and incorporated into MPR(OLP). The in-built back up protection is called voltage compensated protection. This is a new protection but it has evolved from overcurrent relay principles. It uses sequence voltages to modify an IDMT characteristic