Transition Resistor/Reactor

The Transition Resistor/Reactor is a critical component of the Diverter Switch assembly in an On-Load Tap Changer (OLTC) for power transformers. Its primary function is to temporarily carry and limit the circulating current or manage reactive power when the switch moves between transformer taps under load, preventing arcing, reducing mechanical stress, and ensuring a smooth, safe transition without interrupting power supply. During a tap change operation, the diverter switch bridges two adjacent transformer taps. The transition resistor/reactor is inserted into the circuit to limit the circulating current (in the case of a resistor) or manage the phase shift and reactive power (in the case of a reactor) between the two voltage levels. This creates a temporary impedance path, allowing the main contacts to break and make connections with minimal arcing and electrical stress. Once the transition is complete, the component is bypassed, restoring the circuit to the new tap position. The component is available in resistor or reactor types, with materials such as Manganin or similar alloys for resistors, and grain-oriented silicon steel laminations with copper windings for reactors. Ceramic or mica insulation is used. Key parameters include rated voltage (10–35 kV), rated current (200–1000 A), transition time (30–60 ms), resistance (1–10 Ω) or inductance (0.1–1 mH), thermal time constant (5–15 min), operating temperature (-40 to 85 °C), insulation level (LI 75–200 kV), power frequency withstand voltage (28–95 kV), material grade Cu-ETP, weight (5–20 kg), and degree of protection (IP54–IP65). These values are reference ranges per IEC 60214-1 and other standards; verify model-specific values with the manufacturer. The component is designed for use in OLTCs for power transformers, ensuring reliable operation under load. It is not a standalone product but a part of the diverter switch assembly. For selection, consider system voltage, continuous current, transition time, and thermal requirements. Verification questions include confirming the rated voltage and current, transition time, insulation levels, and material grades with the supplier. Maintenance signals include increased arcing, abnormal heating, or insulation degradation. Failure boundaries include exceeding thermal limits or insulation breakdown, which can lead to transformer outage.

During a tap change operation, the diverter switch bridges two adjacent transformer taps. The transition resistor/reactor is inserted into the circuit to limit the circulating current (in the case of a resistor) or manage the phase shift and reactive power (in the case of a reactor) between the two voltage levels. This creates a temporary impedance path, allowing the main contacts to break and make connections with minimal arcing and electrical stress. Once the transition is complete, the component is bypassed, restoring the circuit to the new tap position.