Learn the basic operating principles of circuit breakers as well as the different types. Review the range of operating mechanisms with a focus on pneumatics and compressors. MORE INFORMATION - http://www.idc-online.com/content/hv-circuit-breaker-operating-mechanisms-pneumatic-compressor-systems-25

1. HV Circuit Breaker Operating
Mechanisms – Pneumatic &
Compressor Systems
Technology Training that works

2. Topics
• What is Pneumatics?
• Units of Measurement
• Pascal’s Law
• Force Multiplication
• Pressure Intensification
• Pressure Acting on Different Areas
• Gas Laws
• Pneumatic Symbols
• Safety with Pneumatics
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3. Fluid and fluid power
• Any material capable of flowing is
a fluid
• Fluid can be a liquid or gas
• Fluid power systems involve
– Power transmission
– Control of power
• A fluid power system uses a fluid
under pressure
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4. Typical applications
Electricity Supply Circuit Breakers
Manufacturing Handling, Mixing, Lifting
Mining Continuous miners, Pit props, Drills
Agriculture Farm Equipment
Aircraft Undercarriage, Flight controls
Marine Steering, Stabilizers, Winches, Cargo doors
Forestry Earth moving equipment, Tree loppers, Tree strippers
Transport Automatic doors of trains, Brakes and Lifting equipment
Entertainment Amusement park rides
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5. What is Pneumatics?
• Pneumatics is the transmission and control of
power, using gas as the power transfer medium
• In most cases, air is the medium used
• Inert gases (ex: Nitrogen) used only in special
cases)
• When a liquid is used as the medium, it is known as a
HYDRAULIC system
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6. Air as pneumatic medium
• Benefits
– Cheap, available at no cost
– Compressible like any gas
• Drawbacks
COMPOSITION OF ATOMOSPHERIC AIR
Nitrogen
78%
Other Gases
2%
Oxygen
20%
– Contains moisture
– Can cause corrosion in system components in the
presence of oxygen
– Oxygen present in air can also aid combustion
– Needs external lubrication (unlike hydraulic fluids)
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7. Advantages of pneumatics
• Light weight equipment
• No return lines for the used fluid
• Infinite control of speed and pressure
• Faster speeds possible
• Instant stopping starting and change of direction
• Transmission of large forces
• Easy installation of lines at any desired angle
• Cheaper system as air is free
• Storage facilities required only for compressed air
• No environmental impact and safe to use in explosion prone areas
• No effect due to temperature variations up to 120 deg C
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8. Units used
• SI system of units is used as shown below
Quantity
Unit of
measurement
Symbol
Length Metre m
Mass Kilogram kg
Time Second s
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9. Derived unit-Force
• Force = Mass x Acceleration
• Units
– Mass in kg
– Acceleration in meters/second/second
– Force in Newtons
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10. Derived unit-Pressure
• Pressure = Force/Area
• Units
– Force in Newtons
– Area in square meters
– Pressure in Pascals
• Pressure can be Atmospheric, Gauge or Absolute
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11. Pressure-Force-Area relationship
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12. Alternate units for pressure
• Pressure can be expressed in ‘bar’ which is roughly
equal to atmospheric pressure with a value of 105
N/m2
• In the USA the unit used is Pounds per square inch
(psi)
• 1 psi =0.0703 kg/cm2
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13. Ways of expressing pressure
• Pressure can be expressed as
– Absolute pressure
– Gauge pressure
• A pressure gauge reads the pressure with respect to the
atmosphere
• This value is called gauge pressure
• Absolute pressure = Gauge pressure + Atmospheric pressure
• When Absolute pressure < Atmospheric pressure the
gauge pressure becomes negative
• In this case, the pressure is termed as vacuum pressure
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14. Relationship explained
• Pa is the atmospheric pressure
• Pgauge is the gauge pressure
• Pab is the absolute pressure
• Pvacuum is the vacuum pressure
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15. Pascal's Law
• Pressure applied to a confined static fluid is
transmitted equally and undiminished in all
directions throughout that fluid and acts with equal
force on equal areas
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16. Force multiplication
• Force = Pressure x Area
• Force applied at one point in a hydraulic system
can be multiplied by several orders of magnitude
• Force is applied to a cylinder with a small cross
section
• A cylinder of larger section in the same system
will multiply this force
• The factor of multiplication = The ratio of cross-sectional
areas
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17. Force multiplication principle
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18. Pressure intensification
Explanation in the next slide
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19. Pressure intensifier
• The device has two pistons coupled mechanically
• Inlet port creates a force F = P1 * A1
– Where
• P1 is the inlet air pressure and
• A1 is the large piston area
• F is transmitted to the smaller piston
• It can exert a pressure = F/A2 at the outlet port
• Outlet port pressure is given by
A
1
A
2
P  P
2 1*
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20. Pressure acting on different areas
• The same pressure acting on two pistons of
different sizes will produce different forces
• The net force is the difference between the two
• Net force=Pressure x Difference of piston area
• The difference in area is called annular area
• See the next slides
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21. Pressure acting on different areas
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22. Annular area
D: Diameter of larger piston
d: Diameter of smaller piston
Shaded portion is the annular area
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23. Double acting linear actuator
When air pressure in port 1 and port 2 is the same, the force on the left side of
the piston is higher
This is because the right hand side piston area is lower due to the presence of
the piston rod
The net force will move the piston from left to right
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24. Gas Laws
• Boyle’s law
– Product of pressure and volume of a given mass of a
gas will be constant at a constant temperature
– P x V is a constant
– P is measured as Absolute pressure
– Means that higher the pressure, lower is the volume in
inverse proportion
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25. Gas Laws
• Charles’ law
– At a constant pressure, volume of a given mass of gas is
proportional to the temperature
• Note: Temperature refers to absolute temperature
• (V/T) remains constant at a given pressure
• Gay-Lussac’s law
– At a constant volume, pressure of a given mass of gas is
proportional to the temperature
• Note: Temperature refers to absolute temperature
– (P/T) remains constant at a given volume
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26. Combined gas law
• The laws seen earlier can be combined as follows:
P *
V
T
or
is a constant
P V
P V
1* 1 *
2 2
2
1
T
T

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27. Units and conversion factors
Conversion Table
From To Multiply by
Inches mm 25.4
Feet Metres 0.3048
Square Feet Square Metres 0.0929
Cubic Feet Cubic Metres 0.02832
Pounds kgs 0.4536
PSI ( lb/inch2 ) Bar 0.06895
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28. Dangers of high air pressure
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29. Dangers of compressed air
• Flying particles while cleaning can cause injury
• Unrestrained hoses can whip around and cause
injury
• Compressed air can enter into the blood stream
when directed at the body
• Exhaust air from pneumatic equipment can blow
dust and dirt
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30. Prevent dangers by:
• Danger tags on the controls of equipment that is being
worked upon
• Depressurizing the system before you start to work on
it
• Ensuring that there is no trapped pressure in a system
before opening it
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31. DO YOU WANT TO KNOW MORE?
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