2012 FIDVR Events Analysis: Valley Distribution Circuits
The majority of fault-induced delayed voltage recovery (FIDVR) events on the SCE system occur during summer monsoonal season. These weather conditions bring rain and thunderstorms to hot climate areas where high concentrations of residential air conditioners (RAC) are in use. During these conditions, lightning strikes to the distribution and sub-transmission systems may result in system faults. If these faults decay the voltage below a certain threshold, they can cause air conditioner motors to stall. As a result, the RAC stalling behavior prevents voltage from immediately recovering, provoking FIDVR events. FIDVR events have been typically recorded in the transmission system as shown in Figure 1-1. It shows the voltage being depressed to 79 percent during a system fault. The voltage is kept suppressed by the stalling of RAC and slowly recovers as the RAC’s thermal overloads start opening, disconnecting the RAC from the system. The voltage does not stop at pre-fault voltage, instead it keeps increasing. This incremental change is due to the high amount of customer load disconnecting from the system and system capacitors remaining online. The system voltage starts decreasing to pre-fault levels when the system capacitors disconnect due to the over-voltage and customer load starts coming back to the system.