HV Circuit Breaker Operating Mechanisms - Pneumatic and Compressor Systems

Technology Training that works

HV Circuit Breaker Operating Mechanisms – Pneumatic &

Compressor Systems

Technology Training that Workswww.idc-online.com/slideshare

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


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


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


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


Air as pneumatic medium• Benefits

– Cheap, available at no cost– Compressible like any gas

• Drawbacks– 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)

COMPOSITION OF ATOMOSPHERIC AIR

Nitrogen78%

Oxygen20%

Other Gases2%


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


Units used

• SI system of units is used as shown below

QuantityUnit of

measurementSymbol

Length Metre m

Mass Kilogram kg

Time Second s


Derived unit-Force

• Force = Mass x Acceleration

• Units– Mass in kg– Acceleration in meters/second/second– Force in Newtons


Derived unit-Pressure

• Pressure = Force/Area

• Units– Force in Newtons– Area in square meters– Pressure in Pascals

• Pressure can be Atmospheric, Gauge or Absolute


Pressure-Force-Area relationship


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


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


Relationship explained

• Pa is the atmospheric pressure

• Pgauge is the gauge pressure

• Pab is the absolute pressure

• Pvacuum is the vacuum pressure


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


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


Force multiplication principle


Pressure intensification

Explanation in the next slide


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 2

112 *

A

APP


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


Pressure acting on different areas


Annular area

D: Diameter of larger piston

d: Diameter of smaller piston

Shaded portion is the annular area


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


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


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


Combined gas law

• The laws seen earlier can be combined as follows:

2

22

1

11 **

or

constant a is *

T

VP

T

VP

T

VP


Units and conversion factors

From To Multiply byInches mm 25.4Feet Metres 0.3048

Square Feet Square Metres 0.0929Cubic Feet Cubic Metres 0.02832

Pounds kgs 0.4536

PSI ( lb/inch2 ) Bar 0.06895

Conversion Table


Dangers of high air pressure


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


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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HV Circuit Breaker Operating Mechanisms - Pneumatic and Compressor Systems

Engineering

Transcript of HV Circuit Breaker Operating Mechanisms - Pneumatic and Compressor Systems