Explanation: The unequal potential distribution is undesirable and is expressed in terms of string efficiency. Impulse ratio is calculated during Impulse Frequency Flash Over Test. Impulse ratio is the ratio of impulse park over voltage to Spark over voltage at power frequency.

Explanation: Glass is cheaper than porcelain in the simplest shapes and if properly toughened and annealed gives high resistivity and dielectric strength. The main disadvantage of Glass is that moisture more readily condenses on its surface and facilitates the accumulation of dust deposit thus giving a high surface leakage. Hence, glass insulators can be used upto 25 KV under ordinary atmosphere and well upto 50 KV in dry atmosphere.

Explanation: Shackle insulator are almost universally used for low voltage lines. They can be used at all positions either intermediate terminal or angle where the angle exceed 60 degree deviation. They are generally used in conjunction with shackle sharps.

Explanation: Stay insulators are also called as guy insulators and are used in guy cables. Because it is necessary to insulate the lower part of the guy cable from pole for safety of people and animals on the ground.

Explanation: The capacitance due to two metal fittings on either side of insulator is known as the mutual capacitance and the capacitance between these metal fittings and earthed pole or tower is known as shunt capacitance. Due to shunt capacitance charging current is not the same through all the discs of strings. So voltage being directly proportional to the current flowing through them will be different.

Explanation: During flash over insulators are cracked or broken up due to the heat of Arc. Grading ring in addition to equalization of voltage distribution across the insulators unit when used in conjunction with Arcing horns protects the insulator string from flashover. It does so by keeping the arc away from the insulator string until it is interrupted by protecting devices.

Explanation: Due to rain insulators becomes wet and mutual capacitance increases while the shunt capacitance remains constant thereby decreasing the value of k. As k is inversely related to string efficiency so, string efficiency is improved. K is the ratio of stray capacitance to mutual capacitance.

Explanation: Voltage across whole string is equal to the sum of voltage across each unit. From this the voltage across middle unit can be calculated.

Explanation: Voltage across string is equal to the line voltage of conductor. So it is 100% of line voltage.

Explanation: 100% string efficiency can only be achieved by making voltage distribution across each unit of string equal. In practice it is impossible to attain such uniform voltage distribution. So 100% string efficiency cannot be achieved with any of the above methods.