What is flashover in insulator?

A flashover is an electric discharge over or around the surface of an insulator. In electric power transmission, a flashover is an unintended high voltage electric discharge over or around an insulator, or sparking between two or more adjacent conductors.

What are the different power frequency tests done on insulator mention the procedure of testing?

• Power frequency dry flashover test. The insulator to be tested is mounted in the same manner in which it is to be used.
• Power frequency wet flashover test (Rain test)
• Impulse frequency flashover test.
• Temperature cycle test.
• Puncture voltage test.
• Mechanical strength test.
• Electro-mechanical test.
• Porosity test.

What is the flashover phenomenon?

Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). When the temperatures of the evolved gases becomes high enough, these gases will ignite throughout their extent.

What happens in a flashover?

Flashover is a thermally-driven event during which every combustible surface exposed to thermal radiation in a compartment or enclosed space rapidly and simultaneously ignites. Flashover normally occurs when the upper portion of the compartment reaches a temperature of approximately 1,100 °F for ordinary combustibles.

What are the causes of failure of insulator?

Causes of failure of insulator:

• The main causes of failure of insulator is cracking.
• The problem with defective of material .
• The some porcelain is manufactured with low temperature so it will easily absorb the moisture from the air or cement.

What is flashover voltage of insulator?

The flashover voltage is the lowest when the insulator is polluted with metal pieces because metal is a good conductor. Hence, current can flow through the insulator surface easily. The flashover voltage is lower when the insulator is polluted with wet sand compared to dry sand.

What indication does flashover occur?

The most common signs of a flashover are high heat and rollover. The heat will be extreme so be on the alert for a severe and sudden change in temperature. This heat will be so intense it will be felt through your gear. Rollover is often confused with flashover.

How can flashover happen?

How fast can a flashover occur?

Knowing the warning signs are key in giving you the signal to get out immediately. Multiple sources average your time for a flashover to be from 7-10 seconds. So the best-case scenario is you have 10 seconds to react and get to safety. This is usually about 5′ of distance for the average firefighter.

What is flashover distance?

Flashover distance – It is the shortest distance through air between the electrodes of the insulator.

What is meant by insulation failure?

One of the main causes of failure of a transformer is the insulation failure. The purpose of the insulation is to prevent the flow of electric current between points of different potential in an electrical system. Failure of any of these insulating medium results in catastrophic damage to transformer.

What is a result of flashover?

A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases.

Why does the flashover voltage of insulators decrease with increasing insulator diameter?

The flashover voltage of insulators decreases with increasing insulator diameter. This was observed for 1.2/50 μs impulse, DC, and 60 Hz AC voltages [33 ], and probably occurs because the increasing length of the triple junction provides more relatively weak points for the initiation of surface flashover.

What are the countermeasures for insulator flashovers caused by contamination?

Contamination caused insulator flashovers produce frequent outages in severely contaminated areas. Lines closer to the ocean are in more danger of becoming contaminated. Several countermeasures have been proposed to improve insulator performance. 1. Increasing leakage distance

What are the flashover characteristics of V-shape insulators?

Pollution flashover characteristics of V-shape insulators. Under the same salt density, flashover voltage in unit leakage distance of V-shape insulators from different angles changes with the string angle. The closer two insulators, the severer the flashover between strings will be. 3.

Does string length affect pollution flashover characteristics of polluted insulators?

The effect of string length on pollution flashover characteristics. The relation between the pollution flashover characteristics of polluted insulators and string length or plate number was studied for a long time, but the results obtained by each country do not agree.