13-11-2012, 03:48 PM
basics of circuit breaker
Basics of Circuit Breakers.pdf (Size: 4.31 MB / Downloads: 41)
Introduction
Welcome to another course in the STEP series, Siemens
Technical Education Program, designed to prepare our
distributors to sell Siemens Energy & Automation products
more effectively. This course covers Basics of Circuit Breakers
and related products.
Upon completion of Basics of Circuit Breakers you will be able
to:
• Explain the need for circuit protection
• Identify various types of overcurrent protective devices
• Explain the basic electro-mechanical operation of a circuit
breaker
• Identify various types of Siemens circuit breakers
• Identify circuit protection ratings for various types of
Siemens circuit breakers
• Describe time-current characteristics on a time-current
curve
• Explain the benefits and function of circuit breaker
coordination
• Identify internal and external circuit breaker accessories
Need for Circuit Protection
Current and Temperature Current flow in a conductor always generates heat. The greater
the current flow, the hotter the conductor. Excess heat is
damaging to electrical components and conductor insulation.
For that reason, conductors have a rated continuous current
carrying capacity or ampacity. Overcurrent protection devices,
such as circuit breakers, are used to protect conductors from
excessive current flow. These protective devices are designed
to keep the flow of current in a circuit at a safe level to prevent
the circuit conductors from overheating.
Conductor Insulation
Motors,of course, are not the only devices that require circuit
protection for an overload condition. Every circuit requires some
form of protection against overcurrent. Heat is one of the major
causes of insulation failure of any electrical component. High
levels of heat can cause the insulation to breakdown and flake
off, exposing conductors.