Mapa mental
Electrical Supply
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Electrical Supply
Principle EM induction
- Permanent magnet is moved relative to a conductor/vice versa, an EM force is created.
- Wire connected through electrical load, current flow and EMF is generated.
- Form of alternating sinusoidal supply.
- 3 coil on same spindal apart to rotate 120degree will produce 3 phase alternating supply
Sinusoidal waveform
- Cycle
- Period (T)
- Frequency (f)
- Amplitude
AC & Voltage
- Effective voltage = 0.707peak voltage
- Peak voltage use to express potential difference across tube:
- same with photon energy emitted (keV)
- voltage rating HT cables with compare to kVp applied
- Vt=Vpsin2paift / lt = Ipsin2paift
4 principle components:
- generating system
- by TNB in its power stations
- from : coal, hydroelectric
- to rotate a turbine engine connected to alternating generator.
- transmission system
- Step up transformer
- long distance transmission
- High voltage, smaller current
- reduce of copper conductor cross section
- Step up transformer
- local distribution
- minimum power loss
- delta/star connection
- advantages
- cheaper, less liability
- 2 diffenrent voltage
- connecting of any xray unit
- Permantly fixed
- mains isolator
- Temporary connection for mobile unit
- socket in wards.
- Permantly fixed
- generating system
Changes in main supply
- needs stable in voltage and frequency.
- complete stability not archieved
- exposure draws a lot of current which produce fall in main voltage
- slow variations over long period due to differences in demand
- outside xray exposure
- rapid variation in short intervals time
Plug & Socket
- give maximum possible protection from electrical hazard.
Circuit breaker & fuse
- protect xray circuit from damage due to overload.
Electrical insulation
- protect against effect of electric shock
- amount insulation for cable depend on current
- Cable, xray tube, transformer
Earthing
- all electric equipment
- if breakdown in insulation the conductor will exposed
- short circuit would occur