Doble TDR900 User Guide
72A-2612-01 Rev. A 09/06
11
Chapter 4
Breaker Operation and Testing Theory
This chapter gives some basic theory circuit for breakers in relation to their operation and
testing.
An ANSI definition, C37.100 states:
“A breaker is a mechanical device capable of making, carrying, and breaking current
under normal circuit conditions and also making, carrying for a specific time, and
breaking currents under specified abnormal circuit conditions such as those of short
circuit.”
4.1 The Role of a Breaker
From the ANSI definition it seems clear that there is a “mechanical
element” to a breaker, and that the breaker has three roles to perform:
• To interrupt (break) current which is flowing in a conductor when required
• To allow current to flow in a conductor when required to do so
• To carry current
The definition also states that these must be performed under:
• Normal conditions
• Specified abnormal conditions
4.2 Breaker Characteristics
An ideal breaker has certain characteristics:
• A perfect conductor in the closed position
• A perfect insulator in the open position
• Fast when closing
• Fast when opening
Speed of operation is required to ensure that transients and overvoltages are not
introduced into the system containing the breaker.
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