Advantage of 12kV Impulse withstand Voltage over 8 kV Impulse withstand Voltage

Electrical assemblies and plants are susceptible to various types of over voltage, including temporary over voltage from the supply line and more severe transient non-linear overvoltage caused by atmospheric events such as lightning. These transient over voltages can occur directly when lightning strikes the structure or indirectly through electromagnetic fields induced around the impact point.

The capability of the assemblies to withstand such stresses depends all on the dielectric strength of the air between the two live parts carrying the impulse.

To assess the capability of electrical assemblies to withstand transient overvoltage, a specific test is conducted. This test involves applying an impulse withstand voltage of 1.2/50 μs, as illustrated in Figure 1, following a detailed procedure.

T1: peak time = 1.2 μs

T2: time at half value of U = 50 μs

The impulse voltage shall be applied five times at intervals of 1 second minimum between:

• All the circuits connected together and the enclosure connected to earth.
• Each pole, the other poles and the earthed enclosure connected together.

The test is passed if no discharges are detected.

This test is performed according to Table 10 of the IEC 61439-1, (shown below) which suggests the alternative between effective impulse, alternating voltage (r.m.s. value) and direct voltage, with the value defined as a function of the altitude and consequently of the quality of the ambient air around the assembly under test.

Verification by assessment (as an alternative to testing) prescribes to verify that clearances between all live parts with risk of disruptive discharges shall be at least 1.5 times the values specified in Table 1 of IEC 61439-1 as shown below. The 1.5 safety factor takes into consideration manufacturing tolerances.

In the context of busbar trunking systems, the choice between an 8 kV and a 12 kV impulse withstand voltage significantly impacts the system’s ability to withstand lightning surges and switching surges. A 12 kV rating offers more robust protection compared to an 8 kV rating, which is particularly beneficial in areas prone to severe electrical storms or with higher voltage requirements.

While 8 kV may be sufficient for some applications, 12 kV provides a higher margin of safety and can prevent potential damage or outages caused by transient voltage spikes.

Benefits of a 12 kV Impulse Withstand Voltage

• Higher Protection Level: A 12 kV rating indicates that the system can withstand higher voltage spikes without failure, which is crucial in areas with frequent lightning strikes or prevalent switching surges.
• Enhanced Safety: By providing a greater margin of safety, a 12 kV impulse withstand voltage reduces the risk of insulation breakdown or equipment damage due to transient overvoltages.
• Increased Reliability: A higher withstand voltage contributes to the overall reliability of the busbar trunking system, ensuring it operates properly under various electrical conditions.
• Potential for Higher Voltage Applications: 12 kV systems are suitable for a wider range of applications and higher voltage levels, whereas 8 kV might be limited to lower voltage applications.

While an 8 kV impulse withstand voltage can be adequate for certain applications, a 12 kV rating provides a more robust and reliable solution for busbar trunking systems. The higher rating offers enhanced protection against transient over voltages, ensuring better long-term performance, especially in areas with higher voltage requirements or severe electrical conditions. Therefore, choosing a 12 kV impulse withstand voltage can be a prudent decision for ensuring the resilience and reliability of electrical systems against transient over voltages.