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Examoogle • User • info@examoogle.com • EE-2024-8821
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Arc voltage is directly proportional to
Arc length
Current
Both A and B
None of above
Arc length
Quick Summary: Arc voltage is the potential difference across the plasma column of an electrical arc. According to the Ayres equation, this voltage is directly proportional to the arc length because the arc acts like a resistance that increases linearly as the physical length of the plasma gap increases.
Arc voltage is the potential difference across the plasma column of an electrical arc. According to the Ayres equation, this voltage is directly proportional to the arc length because the arc acts like a resistance that increases linearly as the physical length of the plasma gap increases.
Varc=a+bl — The Ayrton equation where a and b are constants and l is the arc length.
In circuit breakers, when contacts separate, an arc is formed. As the contacts move further apart, the arc length increases. The arc column contains ionized gas particles; a longer column requires a higher electric field intensity to maintain the ionization, thereby increasing the voltage drop across the arc (Varc=a+bl, where l is length).
The arc voltage is essentially the sum of the electrode voltage drops and the voltage drop in the arc column.
Increasing the arc length is a primary method for arc extinction in circuit breakers.
The arc behaves like a non-linear resistance.
High arc voltage helps in current limiting.
Predictable behavior for coordination studies.
Increases the energy dissipation (I2Rt) within the switchgear.
Thermal stress on contacts increases with higher arc voltages.
Arc welding processes.
Design of high-voltage circuit breakers (e.g., SF6, Vacuum, Air-break).
Option B is incorrect because current actually decreases arc voltage in many plasma conditions due to increased ionization (the negative resistance characteristic of the arc).
Typical arc voltage drop is approximately 20-30V per cm in air, though this varies based on medium and pressure.
A is correct — The voltage drop across an electrical arc increases as the arc length increases due to the increased resistance of the longer plasma column.
Always remember that while resistance R increases with length, the arc's V-I characteristic is non-linear and typically displays negative resistance properties; do not confuse this with linear Ohm's law.