This is determined by the physical characteristics of the GDT and its different roles in the circuit.

Impulse breakdown voltage (e.g., for a rise rate of 1 kV/μs): This parameter characterizes the response speed of the GDT to fast transient overvoltages. Standards require high stability (low dispersion) because GDTs are often used as primary protection and need to operate quickly and predictably to discharge large lightning currents (e.g., 10/350 μs). If the impulse breakdown voltage has excessive dispersion, it may lead to failure to operate when needed (protection failure) or premature operation (increasing maintenance costs).

DC Breakdown Voltage: This parameter characterizes the activation threshold of the GDT under slowly changing or continuous voltage. The standard allows for a large degree of variability in this parameter because the GDT is in a high-impedance state before conduction.  Its DC breakdown voltage only needs to be significantly higher than the system's maximum continuous operating voltage to ensure that it does not malfunction. Its core value lies in its low residual voltage and high current handling capability after conduction. In a circuit, the GDT relies on its impulse breakdown voltage to quickly respond to lightning strikes, and on its DC breakdown voltage, which is much higher than the operating voltage, to remain inactive under normal power grid fluctuations.

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