This simulator models a metal-oxide varistor (MOV) surge arrester protecting substation apparatus from a transient overvoltage impulse. Launch a double-exponential voltage impulse, adjust the source impedance, MOV characteristic, ground-lead inductance and ground-return resistance, and watch how much of the surge actually reaches the protected equipment terminal versus what the arrester diverts to earth.
• A real-time 3D scene of the impulse generator/source, equipment terminal (bus), the MOV arrester, the inductive ground lead, earth return and the protected apparatus, with home view, focus-selected-part, toggleable enclosure cutaway, auto-rotate, expand and show/hide labels controls. • A Surge workbench tab with a labeled parts index (impulse generator, equipment terminal, metal-oxide varistor, inductive ground lead, earth return, protected apparatus) and click-to-inspect component callouts. • Impulse & arrester fixtures: open-circuit impulse crest (40–250 kV), fast exponential time constant / front (0.5–5 µs), slow exponential time constant / tail (20–100 µs), source impedance (10–100 Ω), MOV voltage at 1 kA (20–60 kV), MOV nonlinear exponent (10–40), ground-lead inductance (0–20 µH), ground-return resistance (0–5 Ω), and an 'Arrester connected' checkbox to disconnect the arrester entirely. • Playback controls: pause/resume, single step, larger step, and four playback speeds (0.1×, 1×, 10×, 60× laboratory speed), plus a 'Launch impulse' action. • An Impulse & energy analysis tab with two live charts, the underlying model equations (MOV power-law V–I characteristic, source/lead/earth voltage summation, absorbed-energy integral) and snapshot measurements including open-circuit source impulse, equipment terminal voltage, MOV voltage, arrester current, MOV absorbed energy and peak equipment voltage. • An Experiments tab with four guided fixtures (connected arrester, disconnected arrester, long ground lead, ground resistance) and a Model verification bench that runs independent deterministic checks against a fresh model without disturbing your live experiment, plus a timestamped event log and a copyable trial report. • A Learn & assess tab with guided lessons, a knowledge-check quiz with reset, and a written model-scope statement referencing manufacturer surge-arrester documentation.
A metal-oxide varistor's voltage rises with current according to a nonlinear power-law characteristic, Vmov = Vref·(I/1000 A)^(1/α) — it is not an ideal constant-voltage clamp. At each simulation step the model solves this characteristic together with the source impedance, ground-return resistance and lead inductance to find the actual instantaneous current through the arrester.
Disconnecting the arrester in the simulator removes the diverted current path entirely, so the protected equipment sees the full open-circuit impulse. With the arrester connected, source impedance limits how much of the impulse reaches the equipment terminal, since Vequipment = Vsource − Zsource·I.
Two connection-geometry terms add directly to the voltage the protected apparatus actually sees: the inductive ground lead contributes L·dI/dt, which can add substantial terminal stress during the impulse's rapid front even while the MOV itself is conducting normally, and the ground-return resistance contributes an I·R drop, since the ground connection is not an ideal zero-voltage sink. The simulator lets you isolate each effect by adjusting lead inductance and earth resistance independently.
Absorbed energy is tracked as Emov = ∫Vmov·I dt — a distinct duty from peak voltage. This is a teaching model of one positive double-exponential impulse and a monotonic MOV law: it excludes the arrester's leakage region, equipment capacitance, traveling waves, thermal runaway and standardized arrester test duty cycles. A protective-level assessment requires actual equipment insulation withstand data and manufacturer arrester ratings.
A metal-oxide varistor (MOV) arrester provides a low-impedance path to earth once voltage exceeds its nonlinear threshold, diverting most of the surge current away from the protected equipment. Its voltage rises with current per a power-law characteristic rather than staying perfectly flat, so the protected equipment terminal still sees some voltage — governed by the MOV characteristic plus the source impedance drop.
The connecting lead between the arrester and ground has inductance, and during the impulse's fast front the rate of current change (dI/dt) through that inductance produces its own voltage, L·dI/dt. This adds directly to the voltage stress at the protected equipment terminal even while the MOV itself is correctly diverting current, which is why a long or poorly routed ground lead degrades protection.
With no arrester connected, no current is diverted to earth, so the protected equipment terminal sees essentially the full open-circuit impulse voltage minus only the source impedance drop under no-load conditions. The simulator's "Arrester connected" checkbox lets you compare this directly against the protected case.
No. It models a single positive double-exponential voltage impulse against a monotonic MOV voltage-current law. It excludes the arrester's leakage region, equipment capacitance, traveling-wave effects, thermal runaway and standardized test duty cycles, so it should not be used as a substitute for manufacturer arrester ratings or a certified protective-level study.