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  • GE VERNOVA | HIGH IMPEDANCE BUS DIFFERENTIAL RELAY | MVAC

GE VERNOVA | HIGH IMPEDANCE BUS DIFFERENTIAL RELAY | MVAC

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GE VERNOVA | HIGH IMPEDANCE BUS DIFFERENTIAL RELAY | MVAC

MFAC relays provide high-speed differential protection for various types of power system plants including generators, reactors, busbars, motors and the individual windings of power transformers. MFAC relays are fast and reliable due to simple electromechanical construction and operate as a high impedance unit protection scheme with a wide range of setting.

Application

When circulating current protection schemes are subjected to through faults, the sudden and often asymmetrical growth in the system current can cause the line current transformers to reach saturation. In this condition, variation in transformer magnetising characteristics can cause large ratio errors with a consequent circuit imbalance and maloperation of the protective relays. To ensure stability, it is common practice to employ high impedance relays set to operate at a slightly higher voltage than that developed in the worst theoretical case of this condition for a given through fault current. On a balanced earth fault system for example, this is when one current transformer of a group is saturated whilst the others remain unaffected. The saturated transformer presents a low impedance path in parallel with the relay and limits the voltage applied. On internal faults this limitation does not exist and voltages of twice the setting are easily reached.

Key Benefits

  • High speed operation
  • Wide range of settings
  • Simple application technique
  • High stability for through faults
  • Compact robust design

MFAC Types

  • Type MFAC 14, is applied when protection is required for earth faults only. Applications for protecting power transformer windings are shown in Fig. 1
  • The three element version, Type MFAC 34, provides both phase and earth fault protection. A typical application for generator protection is shown in Fig. 2.
  • An external Metrosil unit having a non-linear resistance characteristic is recommended for each relay element, to limit the peak voltage appearing across the secondary differential circuits under internal fault conditions.
GE VERNOVA | HIGH IMPEDANCE BUS DIFFERENTIAL RELAY | MVAC

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