TABLE OF CONTENTS A circuit breaker is a device that switches on and switches off electric circuits during normal as well as abnormal operating conditions. During the making or breaking of the switching contacts, there is a transition stage of arcing between the contacts. The study of this phenomenon is of great importance for understanding the design and operational characteristics of circuit breakers.
Discharge in ac circuit breakers, generally in the form of an arc, occurs in the following ways:
When the contacts are being separated, arcing is possible even when the circuit emf is considerably below the minimum cold electrode breakdown voltage, because of the large local increase in voltage due to the circuit self-inductance.
| Note | This way of drawing arc is common to both dc and ac circuit breakers. |
In an ac circuit breaker, the arc is extinguished every time the current passes through zero and can restrike only if the transient recovery voltage across the electrodes already separated and continuing to separate reaches a sufficiently high value known as the breakdown voltage.
The arc phenomenon depends upon
The nature and pressure P of the medium
The external ionizing and deionizing agents present
The voltage V across the electrodes and its variation with time
The nature, shape, and separation of electrodes
The nature and shape of the vessel and its position in relation to the electrodes
An ideal gas is a pure dielectric because it consists of molecules which are electrically...
