Podcast
Questions and Answers
What primarily determines the resistance of steel rails?
What primarily determines the resistance of steel rails?
What happens to the screening factor if the track is well maintained?
What happens to the screening factor if the track is well maintained?
Which protective measure is used to limit the longitudinal build-up of emf in telecommunication circuits?
Which protective measure is used to limit the longitudinal build-up of emf in telecommunication circuits?
What is a consequence of using open-wire aerial communication lines in relation to induced voltages?
What is a consequence of using open-wire aerial communication lines in relation to induced voltages?
Signup and view all the answers
What should be the break down test voltage of a cable to withstand voltages induced by a short circuit?
What should be the break down test voltage of a cable to withstand voltages induced by a short circuit?
Signup and view all the answers
What is the rms value permissible for cables tested with dc after installation?
What is the rms value permissible for cables tested with dc after installation?
Signup and view all the answers
If no breakdown tests are performed, what is the acceptable rms value range for cables tested at the factory?
If no breakdown tests are performed, what is the acceptable rms value range for cables tested at the factory?
Signup and view all the answers
Under what condition may higher induced voltages be permissible on cable conductors?
Under what condition may higher induced voltages be permissible on cable conductors?
Signup and view all the answers
What is the maximum permissible capacitive coupling current through a conductor-to-earth contact?
What is the maximum permissible capacitive coupling current through a conductor-to-earth contact?
Signup and view all the answers
What types of coupling can occur between two circuits?
What types of coupling can occur between two circuits?
Signup and view all the answers
What precaution should be ensured when working on cables carrying significant telecommunications voltages?
What precaution should be ensured when working on cables carrying significant telecommunications voltages?
Signup and view all the answers
What must isolating transformers and other line apparatus achieve regarding dielectric strength?
What must isolating transformers and other line apparatus achieve regarding dielectric strength?
Signup and view all the answers
What does the formula for induced emf in an overhead line primarily depend on?
What does the formula for induced emf in an overhead line primarily depend on?
Signup and view all the answers
What is the role of the reduction factor Kr in the context of induced emf?
What is the role of the reduction factor Kr in the context of induced emf?
Signup and view all the answers
Which reduction factor accounts for the induced currents in a metal sheathed cable?
Which reduction factor accounts for the induced currents in a metal sheathed cable?
Signup and view all the answers
How does the mutual inductance M vary?
How does the mutual inductance M vary?
Signup and view all the answers
Under what conditions does the reduction factor Kc improve?
Under what conditions does the reduction factor Kc improve?
Signup and view all the answers
What is the purpose of earthed conductors such as cable sheaths and metal pipes?
What is the purpose of earthed conductors such as cable sheaths and metal pipes?
Signup and view all the answers
What does the parameter 'a' represent in the formula for mutual inductance M?
What does the parameter 'a' represent in the formula for mutual inductance M?
Signup and view all the answers
Which factor can lead to an appreciable reduction in electromagnetic interference?
Which factor can lead to an appreciable reduction in electromagnetic interference?
Signup and view all the answers
What impact does the total induced current flowing in the rails have on the induced current of the overhead line?
What impact does the total induced current flowing in the rails have on the induced current of the overhead line?
Signup and view all the answers
In terms of interference reduction, what is the effect of the catenary current?
In terms of interference reduction, what is the effect of the catenary current?
Signup and view all the answers
What effect does increasing the mutual inductance between the sheath and wires have on screening?
What effect does increasing the mutual inductance between the sheath and wires have on screening?
Signup and view all the answers
What is the screening factor for a lead sheathed cable?
What is the screening factor for a lead sheathed cable?
Signup and view all the answers
How does the presence of metal work connected to earth near the track affect cable screening?
How does the presence of metal work connected to earth near the track affect cable screening?
Signup and view all the answers
What is a characteristic of the rails as conductors in terms of current behavior?
What is a characteristic of the rails as conductors in terms of current behavior?
Signup and view all the answers
In what scenario will rail current divide equally between feeding and loading points?
In what scenario will rail current divide equally between feeding and loading points?
Signup and view all the answers
What happens to part of the current in the rails as it moves away from the feeding point?
What happens to part of the current in the rails as it moves away from the feeding point?
Signup and view all the answers
How does the load current interact with the rails in practice?
How does the load current interact with the rails in practice?
Signup and view all the answers
What phenomenon causes an induced voltage in the rails?
What phenomenon causes an induced voltage in the rails?
Signup and view all the answers
What effect does steel tape armouring have on the screening factor?
What effect does steel tape armouring have on the screening factor?
Signup and view all the answers
What is the formula for calculating the induced voltage to earth on overhead bare conductors?
What is the formula for calculating the induced voltage to earth on overhead bare conductors?
Signup and view all the answers
Which of the following factors does NOT affect the current to earth from an earthed line?
Which of the following factors does NOT affect the current to earth from an earthed line?
Signup and view all the answers
What happens to the induced voltage as the horizontal spacing between the contact wire and the overhead conductor increases?
What happens to the induced voltage as the horizontal spacing between the contact wire and the overhead conductor increases?
Signup and view all the answers
When bare conductors are earthed through a person's body, what is the resulting discharge current proportional to?
When bare conductors are earthed through a person's body, what is the resulting discharge current proportional to?
Signup and view all the answers
What is the approximate induced voltage at a separation of 6 meters from a 25 kV contact wire?
What is the approximate induced voltage at a separation of 6 meters from a 25 kV contact wire?
Signup and view all the answers
According to the properties of induced voltage, which statement is correct?
According to the properties of induced voltage, which statement is correct?
Signup and view all the answers
What is the breakdown voltage of the spark gaps in telephone circuits mentioned in the content?
What is the breakdown voltage of the spark gaps in telephone circuits mentioned in the content?
Signup and view all the answers
Which method is used to take the effect of earth into account?
Which method is used to take the effect of earth into account?
Signup and view all the answers
What condition leads to a continuous discharge across spark gaps?
What condition leads to a continuous discharge across spark gaps?
Signup and view all the answers
What is the permissible continuous induced voltage limit recommended for safe operation?
What is the permissible continuous induced voltage limit recommended for safe operation?
Signup and view all the answers
Under what condition can the permissible voltage limit be raised to 150 volts rms?
Under what condition can the permissible voltage limit be raised to 150 volts rms?
Signup and view all the answers
What is the maximum permissible induced voltage during a fault on a nearby inducing line that meets standard technical specifications?
What is the maximum permissible induced voltage during a fault on a nearby inducing line that meets standard technical specifications?
Signup and view all the answers
What must be done when the induced voltage exceeds 60 volts rms?
What must be done when the induced voltage exceeds 60 volts rms?
Signup and view all the answers
What is the primary precaution to protect operators from induced voltages?
What is the primary precaution to protect operators from induced voltages?
Signup and view all the answers
What is the permissible peak voltage during a contact to earth of one wire of a nearby electrified railway line?
What is the permissible peak voltage during a contact to earth of one wire of a nearby electrified railway line?
Signup and view all the answers
What method is suggested for reducing noise interference in overhead communication circuits?
What method is suggested for reducing noise interference in overhead communication circuits?
Signup and view all the answers
Which protective measure is recommended when working near areas with voltage exceeding 60 volts rms?
Which protective measure is recommended when working near areas with voltage exceeding 60 volts rms?
Signup and view all the answers
What is the permissible induced voltage on cable conductors during a fault on a high-reliability power line?
What is the permissible induced voltage on cable conductors during a fault on a high-reliability power line?
Signup and view all the answers
What aspect impacts the effectiveness of periodic transposition in reducing induced emf?
What aspect impacts the effectiveness of periodic transposition in reducing induced emf?
Signup and view all the answers
How can the magnetic coupling between sheath and conductors be increased?
How can the magnetic coupling between sheath and conductors be increased?
Signup and view all the answers
What is the approximate screening factor achievable with well-designed cable circuits near electrified sections?
What is the approximate screening factor achievable with well-designed cable circuits near electrified sections?
Signup and view all the answers
What is the recommended minimum separation between a 25 kV contact wire and a communication line to limit induced voltage to 300 Volts?
What is the recommended minimum separation between a 25 kV contact wire and a communication line to limit induced voltage to 300 Volts?
Signup and view all the answers
What is the effect of the reduction factor Kr on the induced emf in an overhead line?
What is the effect of the reduction factor Kr on the induced emf in an overhead line?
Signup and view all the answers
What happens to the induced voltage when the separation between the inducing line and the receiving line is increased to 40 m?
What happens to the induced voltage when the separation between the inducing line and the receiving line is increased to 40 m?
Signup and view all the answers
Which of the following factors contributes to the definition of mutual inductance M per unit length?
Which of the following factors contributes to the definition of mutual inductance M per unit length?
Signup and view all the answers
Which factor is mentioned as reducing the effective height of overhead conductors?
Which factor is mentioned as reducing the effective height of overhead conductors?
Signup and view all the answers
What impacts the reduction factor Kc when evaluating induced emf between a cable conductor and its sheath?
What impacts the reduction factor Kc when evaluating induced emf between a cable conductor and its sheath?
Signup and view all the answers
Which parameter is NOT associated with the screening effect in the context of earthed conductors?
Which parameter is NOT associated with the screening effect in the context of earthed conductors?
Signup and view all the answers
What effect does the roughness of earth's surface have on electric capacitances in overhead lines?
What effect does the roughness of earth's surface have on electric capacitances in overhead lines?
Signup and view all the answers
How does the frequency of the inducing current affect the reduction factor Kc?
How does the frequency of the inducing current affect the reduction factor Kc?
Signup and view all the answers
In practice, what is the relationship between calculated values of electric induced voltages and measured values?
In practice, what is the relationship between calculated values of electric induced voltages and measured values?
Signup and view all the answers
What does the parameter 's' represent in the context of mutual inductance M?
What does the parameter 's' represent in the context of mutual inductance M?
Signup and view all the answers
How does increasing mutual capacitance between conductors affect induced voltages?
How does increasing mutual capacitance between conductors affect induced voltages?
Signup and view all the answers
What is the relationship between the total induced current flowing in the rails and the catenary current according to the content?
What is the relationship between the total induced current flowing in the rails and the catenary current according to the content?
Signup and view all the answers
What formula provides a more conservative approach for calculating minimum separation distance in overhead lines?
What formula provides a more conservative approach for calculating minimum separation distance in overhead lines?
Signup and view all the answers
What impact do high harmonics have on electric induction in overhead lines?
What impact do high harmonics have on electric induction in overhead lines?
Signup and view all the answers
When does Kc tend to be smaller under heavy inductive conditions?
When does Kc tend to be smaller under heavy inductive conditions?
Signup and view all the answers
What can be concluded about the screening effects of earthed conductors?
What can be concluded about the screening effects of earthed conductors?
Signup and view all the answers
Which of the following conditions is most likely to be fulfilled in practical applications of these overhead lines?
Which of the following conditions is most likely to be fulfilled in practical applications of these overhead lines?
Signup and view all the answers
In what form is the function M, representing mutual inductance, expressed?
In what form is the function M, representing mutual inductance, expressed?
Signup and view all the answers
How does increasing mutual inductance between sheath and wires affect the screening?
How does increasing mutual inductance between sheath and wires affect the screening?
Signup and view all the answers
What happens to the rail current after a few kilometers?
What happens to the rail current after a few kilometers?
Signup and view all the answers
Under what circumstances does the return current split equally at feeding and loading points?
Under what circumstances does the return current split equally at feeding and loading points?
Signup and view all the answers
What effect does having several cables buried in the same trench have on screening?
What effect does having several cables buried in the same trench have on screening?
Signup and view all the answers
How is the induced voltage in the rails calculated?
How is the induced voltage in the rails calculated?
Signup and view all the answers
What is the effect of steel tape armoring on the screening factor?
What is the effect of steel tape armoring on the screening factor?
Signup and view all the answers
Which characteristic is NOT associated with the rails as conductors?
Which characteristic is NOT associated with the rails as conductors?
Signup and view all the answers
What causes the induced voltage in the rails from the overhead line?
What causes the induced voltage in the rails from the overhead line?
Signup and view all the answers
What is the primary consequence of the rail current's proximity to the earth?
What is the primary consequence of the rail current's proximity to the earth?
Signup and view all the answers
Study Notes
Interference Problems with 25 kV AC Traction
- Interference to line-side cables from an adjacent AC traction system is a specific case of interference between power and telecommunication lines.
- Interference can be caused by electric or magnetic fields.
- Strong coupling between power and communication circuits is not necessary for interference to occur.
- Power used in transmission lines varies depending on the voltage.
- 400 kV lines use 109 W.
- 132 kV lines use 108 W.
- 33 kV lines use 5 x 106 W.
- 11 kV lines use 106 W.
- 400/240 V mains use 104 W.
- Telephone lines have significantly lower power levels.
- Sending end: 10−3 W.
- Receiving end: 10−5 W.
- Power systems prioritize high efficiency, while telecommunication systems prioritize clear signal transmission.
- Interference in telecommunications can range from minor noise to significant signal distortion.
- Disturbance refers to perceptible noise.
- Danger is more critical and can cause equipment damage or risk to human life.
- Tolerable levels of interference depend on the specific communication system and operating conditions.
CCIT Directives
- The International Telegraph and Telephone Consultative Committee (CCITT) provides permissible induced voltage limits.
- Permissible continuous induced voltage is limited to 60 volts rms for screened or unscreened cables and open wire lines.
- Under specific conditions (e.g., difficult work operations), the limit may increase to 150 volts rms.
- Special precautions must be taken in these cases, including worker training and warning markings.
Permissible Voltage Levels During Fault
- During faults in nearby power lines, maximum permissible voltage levels on telecom lines are:
- 430 volts rms for power lines meeting standard construction codes.
- 650 volts rms for high-reliability power lines.
- 1000 volts peak for contact with earth on DC or electrified railways.
- Increased permissible voltage limits may apply to cables with earthed sheaths or lightning arrestors.
- For cables tested for breakdown strength
- DC: 60% of the test voltage
- AC: 85% of the test voltage
Conductive and Capacitive Coupling
- Conductive coupling occurs when circuits share a common branch.
- Capacitive coupling results in current flow through a contact between a conductor and earth or other metal. Up to 10 mA is considered permissible under this type of coupling.
Electrostatic Induction
- Electric fields induce voltage in parallel lines, with voltage inversely proportional to the separation distance.
Electromagnetic Induction
- The induced emf in an overhead line or cable parallel to an electrified railway depends on a number of factors:
- Mutual inductance per unit length
- Distance between the lines
- Supply frequency
- Catenary current
- Reduction factors (Kr, Kc, Km) for rail current, cable type, and the presence of earthed conductors or metallic pipework with high induced current.
Mutual Impedance M per Kilometer
- The mutual impedance and separation distance are expressed in a graph (Fig. 8.3).
Rail Currents
- Rail current is diverted into the earth at greater distances and higher frequencies due to the high attenuation and leakance of the rails.
- Rail currents often return to their origin points via alternative paths, including earth or other conductors.
Protective Measures
- Protective measures can be implemented in the low-current communication or at the source (the power supply).
- Protection involves use of isolating transformers, balancing circuits, and increasing signal-to-noise ratios.
- Methods for limiting the long-term effects from induced currents include voltage arrestors, protectors, and fuses.
- DC circuits and those containing operators should be replaced with AC or impulse circuits where possible, and safety procedures must be observed.
- Cabling overhead communication circuits or other measures can reduce interference.
- Screening is important in improving shielding effects.
- Steel tape armouring enhances magnetic screening.
Suppression of Interference at Source
- Booster transformers with a 1:1.1 ratio can significantly reduce interference.
- The booster transformer's secondary winding is connected to the rails in some systems to increase the current (e.g., to supply to rail circuits), decreasing noise on the telecom circuits.
- Additional limitations may occur if there is high impedance on the circuit, or harmonic components in the currents.
Booster Transformer System with Return Conductor.
- The return conductor method significantly reduces inductive interference.
- Booster transformer primaries are connected in series with contact wires, designed to withstand high voltages & endure any mechanical or thermal stresses.
AT System
- This 2x25kV overhead transmission and track alternating current (AT) system suppresses induction.
- Transformers (ATs) are placed along the track with the centre tap used for return current to avoid interference to the power feeding network.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the intricacies of interference between power lines and telecommunication systems, particularly focusing on the effects of 25 kV AC traction. This quiz covers various voltage levels, their respective power usages, and the impact of electric and magnetic fields on signal transmission. Delve into the challenges of maintaining efficient power systems while ensuring clear communication signals.
