Definition of Static Electricity
Static electricity is electricity that does not move. The word “static” comes from the Greek word “statikos”, meaning the act of making something stand still. Static electricity consists of electrical charges that remain unmoving on an object.
Static electricity is usually generated by the physical contact and separation of different kinds of materials. Various effects result from the formation of positive and negative charges. Static electricity cannot be avoided, because electric charges are naturally present in all objects.
Static electricity can cause problems in industrial equipment. It can interfere with the operation of electronic equipment, and it can cause sparks that ignite flammable liquids and vapors. In order to prevent these problems, you must understand the nature of static electricity
Electrical charges themselves cannot cause a fire or explosion. In order for static electricity to cause ignition, four conditions must exist.
- There must be a means of generating static charges.
- There must be a means of maintaining a potential difference.
- The potential difference between the charges must be great enough to cause breakdown of the resistance of the air between them.
- The spark must occur in a flammable atmosphere.
Some of the most common causes of static electricity in an industrial plant are listed below.
- pulverized materials passing through chutes or pneumatic conveyors
- Steam, air, gases, or nonconductive liquids discharging from a pipe or hose
- Nonconductive powered conveyor belts in motion
- Moving vehicles
- People walking on nonconductive carpeting or waxed floors.
Generating of Static Electricity
When two unlike materials are pressed together, some of the electrons at the surfaces transfer from one material to the other. When the two materials are then separated, more of the electron remain with one material than with the other. As result, the material having more electrons has a negative charge. The other material has an equal positive charge, because it lacks the same number electrons.
If a conductive path becomes available, the extra electrons on one material will rush to the other material. Then both materials will become electrically neutral again, or nearly so. If there is no conductive path between them, the two materials may remain charged even if the potential difference between that builds up to several thousand volts.
On some materials, for example concrete and asphalt, the charges are somewhat mobile. After these materials become charged, they will slowly discharge until they become electrically neutral again.
On insulating materials, for example plastic or rubber, the charges are unable to move freely. These materials can remain charged for a long time, even if the potential difference becomes fairly high.