Engineer Electric Railway flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

12-pulse rectifier

A traction rectifier using two six-pulse bridges fed by transformer secondaries displaced 30 degrees; series connection cancels the 5th and 7th harmonic currents on the AC side.

Traction voltage classes

Common nominal systems are 750 V DC, 1500 V DC and 3000 V DC, plus 15 kV 16.7 Hz AC and 25 kV 50 Hz or 60 Hz AC; voltage tolerances are defined by standards.

Rectifier no-load voltage

For a three-phase full bridge, ideal average DC voltage equals 1.35 times the secondary line-to-line RMS voltage; a 12-pulse series arrangement doubles that value when both bridges have equal input.

Regenerative receptivity

The ability of the traction supply to accept braking energy; it depends on nearby train load, reversible substations or energy storage, and catenary voltage limits that trigger brake resistors.

Contact wire stagger

A deliberate horizontal zigzag, typically plus or minus 200 to 300 mm, that spreads pantograph carbon wear across the strip and avoids a fixed contact point on the wire.

Catenary sag formula

For a level span with uniform weight w and tension T, midspan sag D is approximately w times span squared divided by eight times T; pre-sag compensates live load.

Neutral section

A short de-energized catenary section separating adjacent feeding zones; trains coast through it, and the pantograph must not bridge both sides unless the design permits.

Pantograph contact force

The vertical force between pantograph and contact wire, commonly 60 to 120 N static; dynamic variation must remain bounded to prevent contact loss and arcing at speed.

Constant flux region

Below base speed, traction inverters keep voltage-to-frequency ratio approximately constant, producing high torque; above base speed field weakening reduces flux and available torque.

Regenerative braking

Traction motors act as generators, and the inverter returns energy to the DC link; energy is reused, stored, or dissipated in brake resistors when the line cannot accept it.

Auxiliary static inverter

Converts the DC link or battery voltage to three-phase AC for cooling fans, compressors, lighting and control loads; redundant modules and battery backup preserve essential functions.

Brake blending

Coordination of regenerative or dynamic braking with friction brakes so total braking effort meets the demand while respecting adhesion limits and minimizing pad wear.

Track circuit

A failsafe train detection circuit using running rails as conductors; train axles short the rails, dropping a relay or receiver and indicating occupancy to the interlocking.

Approach locking

Interlocking protection that prevents a signal from being cancelled after a train has passed the approach track, forcing the route to be completed or timed out.

Movement authority

Permission for a train to proceed to a defined limit, issued by ATP or the signaler; ATP enforces braking curves so the train stops before the limit.

Grade of automation

GoA 1 to 4 classify train operation from manual driving with ATP supervision to unattended automatic operation, covering door control, departure and obstacle detection.

GSM-R

A railway mobile radio standard based on GSM, providing voice and data for train control and operations; it is being succeeded by FRMCS in new deployments.

SCADA RTU

Remote terminal unit at a substation or facility that acquires status and analog measurements, executes commands, and exchanges telemetry with the control center.

IEC 60870-5-104

A telecontrol protocol that carries SCADA messages over TCP/IP, commonly used between railway control centers and remote terminal units for monitoring and control.

Telecom ring protection

A fiber transmission ring that reroutes traffic after a link failure, typically within 50 ms, preserving signaling, radio and SCADA communications.

Stray current corrosion

DC traction current returning through earth instead of rails causes electrolytic corrosion at buried metal; mitigation uses insulated rails, return bonding, drainage and potential monitoring.

Surge arrester

A voltage-dependent device, commonly zinc oxide, that clamps transient overvoltages and diverts surge current to ground, then reseals after the impulse.

Rail potential

The voltage between running rails and earth; it must be limited because touch voltages endanger people and elevated potentials drive stray current into buried structures.

EN 50121

The European railway electromagnetic compatibility standard series, covering emissions and immunity for rolling stock, infrastructure and signaling equipment.

Protection selectivity

Coordination so the protective device nearest a fault trips first, isolating the smallest possible section while upstream devices remain closed for downstream faults.

DC feeder di/dt protection

A traction protection that detects the rapid initial current rise of a short circuit; it trips faster than overcurrent thresholds that must ride through train starting current.

Earth fault protection

Detection of current flowing from live conductors to earth through insulation failure; it trips the circuit breaker or alarms, depending on system earthing and safety policy.

Breaking capacity

The maximum short-circuit current a circuit breaker can interrupt safely at its rated voltage; it must exceed the calculated prospective fault current at the installation point.

Condition-based maintenance

Maintenance triggered by measured condition such as wear, temperature, or partial discharge, rather than fixed intervals, reducing unnecessary work while preventing failures.

Contact wire wear measurement

Periodic measurement of remaining contact wire cross-section, often by laser or mechanical gauge, compared with limits to schedule renewal before tensile strength is lost.

Insulation resistance test

A DC voltage test measuring leakage current to derive insulation resistance; results are compared with minimum values and previous trends to detect moisture or degradation.

ISO 55000

An international standard for asset management, defining principles for aligning asset portfolios with organizational objectives, risk, lifecycle cost and performance.