FAQ About Altitude Correction Factor Effect According to IEC Standard In High& Medium Voltage Switchgear

In general, the equipment-rated insulation level is specified at normal service conditions, among which the normal altitude is 1000m or below.

 For installations at an altitude higher than 1000 m, the insulation withstands the level of external insulation at the service location shall be determined by multiplying the rated insulation levels by a factor Ka in accordance with figure 1 of IEC 62271-1 standard.

For installations at an altitude higher than 1000 m from sea level, the required insulation to withstand the level of external insulation at the desired height must be calculated.

The basis of rating for switchgear is the standard reference known as sea level conditions.

For internal insulation, the dielectric characteristics are identical at any altitude and no special precautions need to be taken.

For external and internal insulation, refer to IEC 60071-2.

ka calculated in two standards as below:

• IEC 60071-2: Ka=e^[m × (H/8150)]
• IEC 62271-1:2011 : Ka=e^[m× ((H-1000)/8150 )]

m is taken as a fixed value in each case for simplification as follows:

•m= 1 for power frequency, lightning impulse, and phase-to-phase switching impulse voltages;

•m= 0.9 for longitudinal switching impulse voltage;

•m= 0.75 for phase-to-earth switching impulse voltage.

Please see an example in IEC 62271-1:2017 standard

Further the following graph if H=2000m and m=1:

Ka=e^[(2000- 1000 )/8150]=e^[1000/8150]=1.13

This factor must apply in the calculations to determine the amount of switchgear BIL.

What is the Basic Insulation Level (BIL) in switchgear?

The Basic Insulation Level (BIL) is a key parameter in both medium and high-voltage switchgear. It represents the maximum instantaneous voltage that a piece of electrical equipment can withstand without experiencing failure in its insulation. This parameter is crucial in ensuring the reliable operation of switchgear, as it helps engineers design equipment that can withstand transient surges without sustaining damage.

- BIL is a key parameter in switchgear design.

- It represents the maximum instantaneous voltage that the insulation can withstand.

- BIL helps in designing switchgear that can withstand transient surges.

How does the altitude above sea level affect the BIL of switchgear?

When designing switchgear, it's essential to consider the altitude at which it will be installed. As altitude above sea level increases, the air pressure decreases, which can reduce the insulating properties of air. Therefore, switchgear installed at higher altitudes may require a higher BIL to compensate for the reduced air insulation.

- Altitude affects the insulating properties of air.

- Higher altitudes may require a higher BIL.

- The altitude is a crucial factor in switchgear design.

What is the IEC 62271-1, and how does it relate to the switchgear and altitude factor?

IEC 62271-1 is a standard issued by the International Electrotechnical Commission (IEC) that provides guidelines for high-voltage switchgear and control gear. The standard includes a section specifically dedicated to the altitude correction factor. According to IEC 62271-1, for installations above 1000m, the dielectric tests should be corrected, considering the decrease in air density.

- IEC 62271-1 is a standard for high-voltage switchgear and control gear.

- It includes guidelines for the altitude correction factor.

- For installations above 1000m, dielectric tests should be corrected.

How does the altitude factor influence the BIL of high-voltage switchgear?

High-voltage switchgear typically requires a higher BIL due to the high voltage levels it must handle. When installed at high altitudes, the reduced air pressure can decrease the insulating properties of the air, potentially making the switchgear more susceptible to insulation failure. Therefore, when designing high-voltage switchgear for use at high altitudes, engineers must consider the altitude factor to ensure that the BIL is sufficient to prevent insulation failure.

- High voltage switchgear requires a higher BIL.

- Reduced air pressure at high altitudes can decrease air's insulating properties.

- The altitude factor must be considered in high-voltage switchgear design.

Does the altitude factor have the same effect on medium voltage switchgear BIL?

The altitude factor does indeed impact the BIL of medium voltage switchgear in a similar way to high voltage switchgear. However, the actual voltage levels and, therefore, the required BIL, are lower in medium voltage switchgear. Nevertheless, engineers must still consider the altitude factor when designing medium-voltage switchgear for installations at high altitudes.

- The altitude factor impacts the BIL of medium voltage switchgear similarly to high voltage.

- Medium voltage switchgear operates at lower voltage levels, and thus, its required BIL is lower.

- The altitude factor is crucial in the design of medium voltage switchgear.

What are some measures to mitigate the altitude factor's effect on switchgear BIL?

There are several ways to mitigate the effect of the altitude factor on switchgear BIL. One approach is to design the switchgear with a higher BIL to withstand the reduced insulating properties of the air at high altitudes. Another method is to use alternative insulation materials that are less affected by changes in air pressure. Lastly, adhering to the guidelines in IEC 62271-1 for altitude correction can also help ensure that switchgear performs reliably at high altitudes.

- Designing switchgear with a higher BIL can compensate for reduced air

insulation.

- Alternative insulation materials less affected by air pressure changes can be used.

- Adherence to IEC 62271-1 guidelines helps ensure reliable switchgear performance at high altitudes.

Source: Switchgear Content Website