Ferroresonance phenomenon in CFE, its origin and effects

Technological improvements and energy exchange between and within electrical systems require more availability and reliability, and the use of communication channels and measuring devices helps to achieve this goal. Coupling Capacitor Voltage Transformers (CCVTs) traditionally have been essential for power systems communications using Power Line Carrier (PLC). Normally, CCVT devices have an adequate ferroresonance protection. However, CCVTs failures due to environmental conditions and their lack of accuracy for energy billing led some electrical companies like the Mexican company Comision Federal de Electricidad (CFE) to gradual replacement of CCVT devices by the Inductive Voltage Transformers (IVT), which are installed now in bus bars of electrical substations. In addition to satisfy communications needs PLCs were replaced by the optical fiber communications. As IVT devices do not have anti ferroresonance elements, ferroresonance phenomenon started to appear more frequently during operation maneuvers in several electrical substations. This paper presents background on CCVT explosions, patterns of behavior before failures, Phasor Measurement Unit (PMU) records for system effects, measurements and simulation of typical ferroresonance occurrences. Ferroresonance mitigation techniques and possible protection schemes are also discussed.