End fed track circuit

Railway Audio frequency jointless track circuit

Indian Railway Signalling Network Rail Thales

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Railway Audio frequency jointless track circuit

Why AFTC?

  • Jointless
  • Immune to traction voltages
  • Long length
  • Both rails available for traction currents
  • Broken Rail Detection in both rails
  • Superior Train Shunt Detection

End fed track circuit

End fed track circuit

 

Operating frequencies

Operating frequencies

 

Principle of operation

Principle of operation

 

“Electronic” separation joint

separation joint

 

TI21 Transmitter

TI21 Transmitter

 

Transmitter wave form

Transmitter wave form

 

TI21 Receiver

TI21 Receiver

 

Rail to rail audio frequency voltage

Rail to rail audio frequency voltage

 

Train Shunt

Train Shunt

 

Interface with non-track circuited line

Interface with non-track circuited line

 

Terminating with other TC’s

Terminating with other TC’s

 

Safety

     Design based on following assumptions:

  • Value of resistance can increase but not decrease
  • Capacitors can fail – open circuit, short circuit or leak
  • Semi-conductors can fail – open circuit, short circuit or leak at any or all of the terminals

          Transformers will provide reliable DC isolation

 

Safety in Transmitter & TU

  • Oscillator fails to oscillate, fails to modulate, oscillates at wrong frequency – will be detected by the receiver or the tuning unit
  • Component failure in tuning unit (TU) – will lead to reduction in voltage to receiver so that the output relay drops

 

Safety in Receiver

  • Receiver sensitive only to it’s own frequency
  • Failure of components will not lead to increase in receiver gain
  • Receiver gain does not increase with increase in power supply voltage
  • Receiver immunity to interference not jeopardised by component failure

Intermediate Receiver

Intermediate Receiver

 

Increasing Track Circuit Length by Addition of Compensating Capacitors

Increasing Track Circuit Length

 

 

Coded Track Circuit (AFTC) for Automatic Train Control

 

 

Automatic Train Control

Use of Line Matching Units (LMU’s) for Remote Housing of Active Units

Line Matching Units

 

Impedance Bond

  • Equalises the rail current
  • Limits the rail to rail voltage
  • Makes available both rails for traction return current
  • Provides means to connect return sub-station conductors

Impedance Bond

Impedance Bond

 

Allocation of Track Circuit Frequencies For 4 Lines (Eight Channels  A to H)

 

Allocation of Track Circuit Frequencies

 

Test Instruments

  • General instruments
  • Frequency selective voltage meter
  • Shunt box

TI21 in Automatic Signalling

  • Safe & efficient Train Detection for all types of traction territory
  • Efficient utilisation of costly assets
  • Increased line capacity particularly for mixed traffic
  • Increased safety – less accidents from human error
  • Automatic road barrier control
  • Coding can be added later when ATP introduced
  • Immune from effects of 3 phase traction systems

 

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