Title: Readingl Assignments
Course: WGF 107 DEVELOPMENT > Section: Content

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Sub-Title | Circuit Breakers: Diagramming, Types, and Their Role in Circuit Protection
Content
A circuit diagram (also known as an electrical diagram, elementary diagram, or electronic schematic) is a simplified conventional graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while a schematic diagram shows the components of the circuit as simplified standard symbols; both types show the connections between the devices, including power and signal connections. Arrangement of the components interconnections on the diagram does not correspond to their physical locations in the finished device.^[1]

Unlike a block diagram or layout diagram, a circuit diagram shows the actual wire connections being used. The diagram does not show the physical arrangement of components. A drawing meant to depict what the physical arrangement of the wires and the components they connect is called "artwork" or "layout" or the "physical design."

Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment.

In computer science, circuit diagrams are especially useful when visualizing different expressions using Boolean algebra.^[2]

Organization of drawings [edit]

It is a usual although not universal convention that schematic drawings are organized on the page from left to right and top to bottom in the same sequence as the flow of the main signal or power path. For example, a schematic for a radio receiver might start with the antenna input at the left of the page and end with the loudspeaker at the right. Positive power supply connections for each stage would be shown towards the top of the page, with grounds, negative supplies, or other return paths towards the bottom. Schematic drawings intended for maintenance may have the principle signal paths highlighted to assist in understanding the signal flow through the circuit. More complex devices have multi-page schematics and must rely on cross-reference symbols to show the flow of signals between the different sheets of the drawing.

Detailed rules for the preparation of circuit diagrams (and other document kinds used in electrotechnology) are provided in the International standard IEC 61082-1.
Image | Inside of a circuit breaker
Content
Operation[edit]

All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.

The circuit breaker must detect a fault condition; in low voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with protective relay pilot devices to sense a fault condition and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays and an internal control power source.

Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. Small circuit breakers may be manually operated, larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs.

The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current. Miniature and molded-case circuit breakers are usually discarded when the contacts have worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.

When a current is interrupted, an arc is generated. This arc must be contained, cooled and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas or oil as the medium the arc forms in. Different techniques are used to extinguish the arc including:

- Lengthening / deflection of the arc
- Intensive cooling (in jet chambers)
- Division into partial arcs
- Zero point quenching (Contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening. The zero crossing occurs at twice the line frequency, i.e. 100 times per second for 50 Hz and 120 times per second for 60 Hz AC)
- Connecting capacitors in parallel with contacts in DC circuits.

Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.

Types of circuit breakers[edit].

Many different classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features.

Low-voltage circuit breakers[edit]

Magnetic circuit breakers[edit]

Thermal magnetic circuit breakers[edit]

Common trip breakers[edit]

Medium-voltage circuit breakers[edit]

High-voltage circuit breakers[edit]

Sulfur hexafluoride (SF_6) high-voltage circuit breakers[edit]

Disconnecting circuit breaker (DCB)[edit]

Carbon dioxide (CO_2) high-voltage circuit breakers[edit]

Other Breakers
Links/Uploads
Circuit Diagram – Wikipedia http://en.wikipedia.org/wiki/Circuit_diagram

See also[edit]

- Electronic symbol
- Pinout
- Schematic capture
- Schematic editor
- Wiring diagram

Schematic-capture software[edit]

- AutoTRAX
- DesignSpark PCB
- DipTrace
- EAGLE (program)
- Edwinxp
- gEDA
- KiCad
- NI Multisim
- OrCAD
- Zuken

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Circuit Breakers – Wikipedia http://en.wikipedia.org/wiki/Circuit_breakers

See also[edit]

 | Electronics portal

- Arc-fault circuit interrupter
- Circuit breaker panel
- Circuit Total Limitation (CTL)
- Earthing system
- Hybrid switchgear modules
- Insulation monitoring device
- Network protector
- Power system protection
- Remote racking system
- Sulfur hexafluoride circuit breaker
- Motor control center (MCC)
- Power distribution center (PDC)
Attributions | Images and Content courtesy of Wikipedia – The Free Internet Encyclopedia