Some of the faults are temporary and there is no need to activate distance relays or trip circuit breakers. These temporary disturbances are categorized as voltage fluctuations as shown in the figure. Some conditions need to be checked to detect voltage fluctuations listed below: 
against
- No earth fault detection (no zero current)
- No phase-to-phase error (no negative sequence current)
- The change in ohmic resistance (impedance) over time occurs in three phases and is less than a certain setting value (ΔR and ΔX).
- Principle and operation of differential relay
- What is impulsive transient
