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Questions and Answers
What is the maximum allowable rail-earth voltage when measured across a 9 ohm relay?
What is the maximum allowable rail-earth voltage when measured across a 9 ohm relay?
What is the purpose of disconnecting existing track circuits before testing for stray direct current?
What is the purpose of disconnecting existing track circuits before testing for stray direct current?
How many times should stray current measurements be recorded each day during testing?
How many times should stray current measurements be recorded each day during testing?
What is the maximum stray current allowed for track circuits that are less than 100 meters in length?
What is the maximum stray current allowed for track circuits that are less than 100 meters in length?
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What type of voltmeter and ammeter should be used for conducting stray current tests?
What type of voltmeter and ammeter should be used for conducting stray current tests?
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What is the resistance value that a suitable earth must not exceed during stray current tests?
What is the resistance value that a suitable earth must not exceed during stray current tests?
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How should the length of the track to be tested be insulated?
How should the length of the track to be tested be insulated?
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How many days should the stray current tests be extended for?
How many days should the stray current tests be extended for?
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Study Notes
Stray Current Measurement Before DC Track Circuit Installation
- Purpose: Measure stray direct current before installing a DC track circuit in areas slated for AC electrification. This ensures DC track relays won't activate due to stray currents.
- Testing Locations: Tests are conducted only on non-electrified sections.
- Existing Circuits: If existing track circuits are present, disconnect them to prevent false readings caused by block joint leakage.
- Insulated Track Length: The length of the track that will be part of the track circuit needs insulated block joints at each end. These joints may or may not be electrically bonded during these tests.
- Earth Resistance: Select a suitable earth with resistance no more than 5 ohms.
- Equipment: Use a millivoltmeter and milliammeter for voltage and current measurements.
- Data Recording: Measurements must adhere to the diagram in Figure 1 (Measurement of Stray Current).
- Stray Current Measurement: Follow the circuit diagram in Figure 2 (Measurement of Rail-Earth Voltage) to measure current simultaneously.
- Relay Resistance: Use resistance values (9 ohms, 4 ohms, or 2.25 ohms) corresponding to the relays being installed.
- Test Duration: Consecutive measurements should occur throughout the day (morning, afternoon, evening) over three days.
- Maximum Stray Current Limits: The length of the direct current (DC) track circuit should be limited if stray current/voltage is detected. Acceptable voltage limits measured across specific resistances (9 ohms, 4 ohms, or 2.25 ohms) are 0.1V. The total stray current measurement should not exceed 100mA. For track circuits less than 100 meters, the maximum acceptable stray current is 10mA.
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Description
This quiz focuses on the procedures and principles of measuring stray direct current before installing a DC track circuit. It covers testing locations, equipment necessary, and precautions to take to ensure accurate readings. Ideal for those involved in railway electrification projects.
