Vacuum Circuit Breaker (VCB) Switching Dynamics: Transient Recovery Voltage (TRV) and RC Snubbers

Contact separation dynamics in vacuum, current chopping (<3-5 A), Transient Recovery Voltage (TRV) per IEC 62271-100, inductive load multiple reignitions, and R

1. Vacuum Arc Interruption Physics

Vacuum Circuit Breakers (VCBs) interrupt current at zero-crossing within a sealed ceramic vacuum interrupter bottle (10^-5 to 10^-7 mbar).

2. Current Chopping & Surge Generation Mechanism

When interrupting small inductive currents (e.g. unloaded transformer magnetizing currents), the arc extinguishes prematurely before the natural AC zero-crossing at a chopping current level (i_chop = 2 to 5 A):

V_{peak_surge} = i_chop · √((L_load) / (C_circuit))

3. Transient Recovery Voltage (TRV) Parameters (IEC 62271-100)

Grid Class	TRV Peak Voltage (u_c)	Time to Peak (t₃)	Rate of Rise (RRRV = u_c / t₃)
12 kV Terminal Fault	20.6 kV	44 μs	0.47 kV/μs
24 kV Terminal Fault	41.2 kV	88 μs	0.47 kV/μs
36 kV Terminal Fault	61.8 kV	132 μs	0.47 kV/μs

4. RC Snubber Sizing for Dry-Type Transformers

To suppress multiple high-frequency reignitions and protect dry-type transformer insulation, RC Snubber Surge Suppression Circuits are connected line-to-ground at transformer terminals:

R_snub = 50 Ω (Non-inductive resistor)

C_snub = 0.25 μF (Surge capacitor)

*Reference: IEC 62271-100:2021; IEEE Std C37.011-2019; CIGRE TB 570.*

Scope