Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Chapter 11
Switching and Control Devices
Prepared by:
Lincoln A. Azupardo
BSEE 5B
Purpose
• To make, break or change the connections in an
electric circuit, under either normal or abnormal
conditions
Switches
a) Knife switches
b) Disconnecting switches
c) Air-break switches
d) Control switches
e) Auxiliary switches
f) Oi...
a) knife switches
• Used to open and close circuits of low voltage and
current capacity.
• Used extensively in lighting an...
b) disconnecting switches
• Should never be opened until the circuit breaker in
the same circuit has been opened, and shou...
c) air-break switches
• Designed to open circuits under load
• Used generally outdoors for circuits of medium
capacity
• S...
d) control switches
• Includes all switches that are used to control the
operation of other equipment.
• Designed for oper...
e) auxiliary switches
• Includes all switches or contactors that are actuated
by some other control switch or device.
• Co...
f) oil switches
• At high voltages and large current capacities it is
desirable to immerse the switch contacts under oil.
g) magnetic-impulse switches
• arc is extinguished by blowing it magnetically into arc
chutes where it is lengthened coole...
Fuses
• Used to protect circuits of small capacity against
abnormal currents such as overloads or short
circuits.
Types: a...
a) cartridge fuses
• Composed of a strong fiber casing inside of which is
enclosed a fuse wire, generally an alloy of lead...
b) transformer fuse block and cutout
• It is common practice to place these fuses in the
secondary of such transformers, t...
c) expulsion fuses
• For higher voltages such as found in power circuits or
main feeders.
• Consists of a hollow tube, mad...
Classification of Circuit Breakers
Interrupting medium - air, air blast, oil, magnetic blast
Service - indoor, outdoor
Ope...
Air Circuit Breakers
• “carbon circuit breaker” have 2 or 3 contacts
• Protect the main contacts against arcing or pitting...
Circuit Breakers
• Standard oil circuit breakers may be classified
according to their method of operation as
a) Gravity op...
a) gravity-opened type
• Most common type wherein contacts are operated
by an insulated rod which projects outside the tan...
b) gravity-closed type
• It will close under the action of gravity
• Terminals are at the bottom of the tanks, the circuit...
c) horizontal-break type
• In both of earlier types, the circuit is broken by
contacts moving in a vertical plane, however...
d) air-blast circuit breakers
• Introduced in the United States practice in 1939
• Blow out the arc with a jet of air that...
e) magnetic-blast circuit breakers
• Designed for 5,000V and less
• These are air circuit breakers that extinguish their
a...
f) impulse oil circuit breakers
• Arc is extinguished by an oil blast produced by a
spring-driven piston.
Contact Details
• simplest type of contact is using of either flat or
curved metal surfaces as terminals of CBs
• Butt con...
• Bayonet or rod type
– Arcing tips are connected to the contact arms through
heavy springs
– Essential when contacts be o...
Circuit Breaker Construction
Mechanical details of CB vary a great deal, depending
on the particular requirements that mus...
• For very low capacity and voltages all poles of a
polyphase circuit breaker are sometimes placed in
the same tank, but f...
Circuit Breaker Control
• Remote electrical control may be obtained by means
of an operating motor or solenoid
• Operating...
Application of Circuit Breakers
To apply CBs: normal current of circuit, rated voltage, &
the interrupting capacity in amp...
Distance above sea level, feet Current-rating factor Voltage rating
4,000 0.99 0.98
5,000 0.96 0.95
8,000 0.94 0.86
10,000...
switching & control devices
switching & control devices
switching & control devices
switching & control devices
Upcoming SlideShare
Loading in …5
×

switching & control devices

668 views

Published on

DONE BY MY COLLEAGUES IN COLLEGE BSEE-5

Published in: Engineering
  • Be the first to comment

  • Be the first to like this

switching & control devices

  1. 1. Chapter 11 Switching and Control Devices Prepared by: Lincoln A. Azupardo BSEE 5B
  2. 2. Purpose • To make, break or change the connections in an electric circuit, under either normal or abnormal conditions
  3. 3. Switches a) Knife switches b) Disconnecting switches c) Air-break switches d) Control switches e) Auxiliary switches f) Oil switches
  4. 4. a) knife switches • Used to open and close circuits of low voltage and current capacity. • Used extensively in lighting and small power circuit • To protect such low capacity circuits against overloads and short circuits, it is necessary that proper fuses be connected in series with the switch blades
  5. 5. b) disconnecting switches • Should never be opened until the circuit breaker in the same circuit has been opened, and should always be closed before the circuit breaker is closed • May be operated by hand, either directly or by means of a wooden pole, or through a set of levers and bell cranks; or in the case of high voltage switches the control may e done electrically
  6. 6. c) air-break switches • Designed to open circuits under load • Used generally outdoors for circuits of medium capacity • Special arcing horns are provided so that arc may rise and be ruptured. • Built for about 135,000 volts maximum but their use is confined to lower voltages • Not designed to open under abnormal conditions
  7. 7. d) control switches • Includes all switches that are used to control the operation of other equipment. • Designed for operating voltage less than 250 volts and very small current capacities
  8. 8. e) auxiliary switches • Includes all switches or contactors that are actuated by some other control switch or device. • Control circuits may be designed for very small currents, while the operating circuits as a general rule must handle much larger currents and very often at higher voltages.
  9. 9. f) oil switches • At high voltages and large current capacities it is desirable to immerse the switch contacts under oil.
  10. 10. g) magnetic-impulse switches • arc is extinguished by blowing it magnetically into arc chutes where it is lengthened cooled, and interrupted.
  11. 11. Fuses • Used to protect circuits of small capacity against abnormal currents such as overloads or short circuits. Types: a)cartridge fuses b)transformer fuse block and cutout c)expulsion fuses
  12. 12. a) cartridge fuses • Composed of a strong fiber casing inside of which is enclosed a fuse wire, generally an alloy of lead • Used as a protective device in low-capacity circuits, such as small lighting and power lines, and on the secondary of instrument-potential transformers, when used for metering or relay protection
  13. 13. b) transformer fuse block and cutout • It is common practice to place these fuses in the secondary of such transformers, thereby protecting the transformer against short circuits or overloads. • Two types, both include a porcelain housing, enclosing the fuse and contact points. In one type, the fuse is carried on a plug that is provided with an insulating porcelain knob in order that it may be removed for re-fusing. A second type consists of rectangular porcelain receptacle with a removable front door that carries the fuse.
  14. 14. c) expulsion fuses • For higher voltages such as found in power circuits or main feeders. • Consists of a hollow tube, made of some heat- resisting substance such as fiber with a lining of asbestos or some other material, through which is passed a fuse wire. One end of the tube is closed and connected to the line; the other end is opened and allows the fuse wire to project out and connect to the other terminal • For outdoor use only
  15. 15. Classification of Circuit Breakers Interrupting medium - air, air blast, oil, magnetic blast Service - indoor, outdoor Operation – gravity opened, gravity closed, horizontal break Contacts – butt, wedge, laminated-flat contact, bayonet, explosion chamber, deion grid Action – nonautomatic, automatic Mode of control – direct control, remote control (manual, electrical[motor/solenoid], pneumatic) Tank construction – all poles in one tank, one tank for each pole Mounting – panel mounting, rear of panel, remote, remote from panel (framework, cell, floor)
  16. 16. Air Circuit Breakers • “carbon circuit breaker” have 2 or 3 contacts • Protect the main contacts against arcing or pitting, secondary copper contacts and also carbon contacts are provided • Carbon contacts take most of the arcing, and since carbon is very refractory, the contacts are not damaged very much • In case of damage to either the secondary or carbon contacts, it is possible to replace these easily.
  17. 17. Circuit Breakers • Standard oil circuit breakers may be classified according to their method of operation as a) Gravity opened b)Gravity closed c) Horizontal break • But several variations of these types are nevertheless found
  18. 18. a) gravity-opened type • Most common type wherein contacts are operated by an insulated rod which projects outside the tank • Tendency is for the contacts to fall open due to gravity
  19. 19. b) gravity-closed type • It will close under the action of gravity • Terminals are at the bottom of the tanks, the circuit being completed through contact rods • Equipped with a set of main contacts located at the top of the tank which opens before the arcing-rod contacts are opened and, hence, are not subjected to arcing and can, therefore, be located outside the tanks
  20. 20. c) horizontal-break type • In both of earlier types, the circuit is broken by contacts moving in a vertical plane, however, this type has its contacts arranged for horizontal motion.
  21. 21. d) air-blast circuit breakers • Introduced in the United States practice in 1939 • Blow out the arc with a jet of air that is supplied from a pressure tank • Arc is blown into a set of arc chutes, where it is subdivided into several parts, making the task of extinguishing somewhat easier.
  22. 22. e) magnetic-blast circuit breakers • Designed for 5,000V and less • These are air circuit breakers that extinguish their arcs by blowing them magnetically into arc chutes where they are lengthened, cooled and interrupted.
  23. 23. f) impulse oil circuit breakers • Arc is extinguished by an oil blast produced by a spring-driven piston.
  24. 24. Contact Details • simplest type of contact is using of either flat or curved metal surfaces as terminals of CBs • Butt contact – when moving contactors are held firmly against the stationary terminals by means of heavy springs – For low voltages and capacity • Wedge design – Wedge-shaped terminal on the moving element, which when in the closed position is forced between spring jaws
  25. 25. • Bayonet or rod type – Arcing tips are connected to the contact arms through heavy springs – Essential when contacts be opened at very high speed • Oil-blast explosion chamber – Consist of an upper, an intermediate, and a lower element – In the closed position, these three elements are pressed together
  26. 26. Circuit Breaker Construction Mechanical details of CB vary a great deal, depending on the particular requirements that must be met •Indoor – In most cases, lower voltage ratings and therefore present a different appearance. Generally, they are mounted in cells •Outdoor – Must naturally be water and moisture proof, the bushings must be designed for all weather conditions and, as a general rule must be given greater clearance
  27. 27. • For very low capacity and voltages all poles of a polyphase circuit breaker are sometimes placed in the same tank, but for medium- and high-capacity units it is necessary to enclose the separate poles in individual tank
  28. 28. Circuit Breaker Control • Remote electrical control may be obtained by means of an operating motor or solenoid • Operating voltages used are either 125 or 250 volts • DC is generally obtained from storage batteries, which give continuous service w/ maximum possible reliability • Pneumatic method of CB control, owing to its positive and unusually fast action • relays are placed in ckt in order that CB may be opened automatically in case of abnormal condition.
  29. 29. Application of Circuit Breakers To apply CBs: normal current of circuit, rated voltage, & the interrupting capacity in amperes must be known •Interrupting capacity of circuit breaker is also affected by the frequency of the circuit, p.f. prior to the short ckt, the temperature, and also the altitude of the breaker above sea level •Stored electrostatic and magnetic energy of system has definite effects upon •also limited by the safe operating temperature •Up to an elevation of 3,300 ft above sea level ther is no perceptible decrease in rating
  30. 30. Distance above sea level, feet Current-rating factor Voltage rating 4,000 0.99 0.98 5,000 0.96 0.95 8,000 0.94 0.86 10,000 0.91 0.80 12,000 0.89 0.74 14,000 0.87 0.70 • duty cycle is another consideration Standard duty cycles for CBs is CO-15 sec-CO CB is closed, then opens due to relay action. It is then reclosed in 15s and then again reopens

×