Wire-wound resistor FRD Series

insulationswitchingfor transformers

Ferroresonance is a nonlinear resonance phenomenon that affects power networks. Circuit must contain at least below circuit elements as it can be defined as ferroresonance: • Non-linear saturable inductance (example; transformer) • Capacitor • Resistor In a circuit consists of these elements; by changing the values of an electrical component, the values of current and voltage values on the terminals at other components change suddenly. Ferroresonance begins some switching events such as; load rejection, energizing or de-energizing of transformer, switching of circuit breaker. The causes risk to it can be listed as follows: • Idling or operation on low load on the systems grounded neutral point • Insulation faults, • Overloading or idling of voltage transformer • Switching one or two phases • Dissymmetry caused by connection errors • Switching transformers or capacitors • Connecting low load power transformers to network with short circuit load • Long and / or capacitive cable feeding a transformer • Streak of lightning on transmission lines When the ferroresonance occurs some of the below symptoms are accompanied: • Phase-to-phase or phase-to-neutral long-term over voltages • Long – term overcurrents • Distortion on the current and voltage waveforms • Displacement of the neutral point voltage • Transformer overheating (at no load) • Load noise in voltage transformers and overheating in core and primary windings • The failures cause of thermal effect or insulation breakdown on electrical materials (capacitor banks, current – voltage transformers etc.)