Also known as basic insulation level (BIL): A specific insulation level, expressed in kilovolts, in accordance with which the complete system (including the line pole insulation to earth at every pole, the switchgear, the line isolators and reclosers, and the substations connected to the system, including their Transformers) is designed and constructed. (NRS 039:1995)
BIL is basic insulation level as per you or in other words it would be "basic impulse level" which implies the limit up to which an insulator could withstand impulse due to lightning strikes. Impulse is generated on the insulation due to the high voltage surges and spikes due to lightning strikes. BIL is generally much higher as compared to power frequency withstand voltage. In other words BIL is lightning Impulse withstand voltage. Impulse withstand voltage is the voltage that is generated due to switching operation and it's much higher than power frequency withstand, but BIL or the lightning withstand voltage is a the voltage level that an insulation can withstand during surge or lightning strikes.
Lightning impulse withstand voltage
That is the voltage rating the product can stand up to. If the lightning withstand voltage was 100,000,000V, that means the item could get struck by lightning that is up to 100,000,000V without damaging it.
Sudden rise in Voltage is called Impulse voltage.
It is the rated test voltage that will not cause insulation breakdown.
Simply, the voltage which is withstand by the test object as an impulse is called as rated impulse voltage.
BIL is basic insulation level as per you or in other words it would be "basic impulse level" which implies the limit up to which an insulator could withstand impulse due to lightning strikes. Impulse is generated on the insulation due to the high voltage surges and spikes due to lightning strikes. BIL is generally much higher as compared to power frequency withstand voltage. In other words BIL is lightning Impulse withstand voltage. Impulse withstand voltage is the voltage that is generated due to switching operation and it's much higher than power frequency withstand, but BIL or the lightning withstand voltage is a the voltage level that an insulation can withstand during surge or lightning strikes.
Lightning impulse withstand voltage
That is the voltage rating the product can stand up to. If the lightning withstand voltage was 100,000,000V, that means the item could get struck by lightning that is up to 100,000,000V without damaging it.
The Basic impulse level is the maximum peak voltage that a piece of equipment can withstand. When you exceed this rating the insulation will break down and short out.
The distance between high voltage lines is governed by either a switching impulse voltage or lightning impulse voltage. The distance between lines, or lines and tower must have a high enough dielectric strength to avoid flashover at these voltage. Air can withstand a voltage of 3kv/mm.
Sudden rise in Voltage is called Impulse voltage.
The instantaneous voltage rating of a given insulation sytem. In the case of a lightning strike, it is very high voltage but only for a split second. The insulation is designed to handle this rated voltage for a split second without damage to the apparatus. Any longer, and damage would result.
Power frequency volatge is applied for a duration of one minute and as such there would be many cycles of sinusoidal wave form applied during the tets; hence, RMS value is considered. Whereas LI is a surge and is typically 1.20 micro sec. wave; hence peak is considered.
It is the rated test voltage that will not cause insulation breakdown.
A test done on a transformer. The voltage at the power frequency is ramped up to verify the transformer is capable of handling the stresses due to switching and natural phenomena (lighting strikes).Withstand Voltage:The voltage which has to be applied to a test object under specified conditions in a "withstand test" is called the "withstand voltage".
Please refer Chapter 1, Page 2 of "Insulation coordination for power systems" by Andrew R. Hileman that gives a good description of the term BIL and BSL (Basic Switching Impulse Withstand Voltage).