What is a surge voltage? Choose the best description of a surge (impulse) voltage encountered in power and electronics systems.

Introduction / Context:
Surge (or impulse) voltages arise from lightning, switching transients, or electrostatic discharge. Correctly characterizing their polarity and time scale is critical for selecting surge protective devices and insulation coordination.

Given Data / Assumptions:

• Surges are brief events, typically microseconds to milliseconds.
• Amplitude can far exceed nominal system voltage.
• Both polarities are possible depending on source and coupling.

Concept / Approach:
Standards (e.g., 1.2/50 μs lightning impulse) define short rise time, short duration, and either polarity. Therefore, the most complete description must mention high magnitude, short duration, and bipolar possibility.

Step-by-Step Solution:
Assess duration → clearly very small relative to steady operation.Assess magnitude → significantly higher than normal line levels.Assess polarity → can be positive or negative based on event.

Verification / Alternative check:
Surge test waveforms used in EMC and insulation testing are generated with both positive and negative polarities to check equipment immunity.

Why Other Options Are Wrong:
Very long duration: Would describe an overvoltage swell, not a surge.
Only positive: Incomplete; negative surges are common.

Common Pitfalls:
Confusing ‘‘surge’’ with long-duration overvoltage or undervoltage events; surge protection must address both polarities and fast edges.

Final Answer:
has very high magnitude and very small duration and can be positive or negative