1. Why AC current is used for transmission?
Two wires are separated by insulators
5. What is Co-axial cable?
This consists of inner conducting copper wire surrounded by polyethylene. The outer surface is surrounded by plastic layer to prevent damage.
6. What is difference between co-axial and Balanced two wire system?
Fuse is a thin metallic strip which melts during fault or over current to prevent circuit from damage
11. What is difference between fuse and circuit breaker?
Relay prevents phase lines from fault where as circuit breaker prevents circuts from fault
13. What is corona?
Violet glow, hissing noise and ozone gas production around the transmission line is called corona
14. What causes corona loss?
Ionisation of atomospheric gas around the transmission line produces the corona loss. This reduces the current flow in the circuit
15. What is Skin effect?
The ability of AC current to concentrate near the surface of conductor is called as skin-effect. It reduces the conductor size
16. What is proximity effect?
Proximity effect are due to the interference of other electric signals with the transmission lines
17. What is Ferranti effect?
The Ferranti effect is an increase in voltage occurring at the receiving end of a long transmission line, above the voltage at the sending end. This occurs when the line is energized, but there is a very light load or the load is disconnected
18. How the corona loss can be reduced?
Corona loss can be reduced by increasing the diameter of conductor and increasing the distance between two conductors
19. How skin effect can be reduced?
To reduce skin effect the shape of the wire should be less for stranded conductor than that of solid conductor
20. What is Bus Bar?
A Bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. They form a link between the incoming and outgoing circuits. The size of the bus bar determines the maximum amount of current that can be safely carried
21. What is Arc Formation?
In circuit breaker when excess current flows the contact between electromagnet and fixed end begins to open when the distance increases arc will be produced due to high current which leads to increase in temperature
22. What are the factor that affects maximum current transmission?
Power delivered P = EVSin δ/X
Generally, δ is kept low (around 30°) because any disturbance can affect the stability of the system if δ value is high.
- AC current is used for transmission because it can be step up for transmission purpose and step down for distribution
- The output of rotating turbine is AC hence there is no necessary for convert into DC
- The losses and maintenance cost are high for DC then for AC
- To reduce the volume of conductor used
- To reduce the voltage drop and percentage line drop
- To reduce the loss and increase losses
- Balanced two wire
- Co-axial Cable
- Wave guide
- Micro strip
- Fiber optic
Two wires are separated by insulators
5. What is Co-axial cable?
This consists of inner conducting copper wire surrounded by polyethylene. The outer surface is surrounded by plastic layer to prevent damage.
6. What is difference between co-axial and Balanced two wire system?
- In co-axial cable the outer surface is grounded, hence the external interference is low while in two-wire outer surface is free hence the external interference is high
- In two-wire noise is high due to interference where as in co-axial cable noirse is absent as it is free from interference
- Co-axial cable is used for high frequency transmission and two-wire is used for normal frequency transmission
- Cost of co-axial cable is high where two-wire are available at low cost
- Primary transmission : 66 kv, 220 kv, 132 Kv, 440 Kv
- Secondary transmission: 33 Kv
- Primary Distribution : 11 Kv
- Secondary Distribution : 220 V or 230 V (for homes) and 440 V (for factories)
- Relay is a electromagnetic device which opens in the occurrence of fault. It is based on the principle of electromagnetic attraction and electromagnetic induction
- When the fault occurs supply to the relay will be lost hence the contact opens to prevent the line from fault
- Circuit Breaker is a device which opens when the fault occurs, the contact of the circuit breaker opens and separate the circuit from overcurrent
- It consists of contact lever with one end connected to electromagnet and other end connected to fixed contact if the current flow exceeds the safe operating range electromagnet gets energized and the contact opens from the fixed end thus separating the circuit
- Again if the current reduces the electromagnet get de-energized so contact will join to include the circuit again
Fuse is a thin metallic strip which melts during fault or over current to prevent circuit from damage
11. What is difference between fuse and circuit breaker?
- Fuse is a thin metallic strip where as circuit breaker is a electromagnet device
- Fuse needs replacement once fault occurs where as circuit breaker does not need replacement
Relay prevents phase lines from fault where as circuit breaker prevents circuts from fault
13. What is corona?
Violet glow, hissing noise and ozone gas production around the transmission line is called corona
14. What causes corona loss?
Ionisation of atomospheric gas around the transmission line produces the corona loss. This reduces the current flow in the circuit
15. What is Skin effect?
The ability of AC current to concentrate near the surface of conductor is called as skin-effect. It reduces the conductor size
16. What is proximity effect?
Proximity effect are due to the interference of other electric signals with the transmission lines
17. What is Ferranti effect?
The Ferranti effect is an increase in voltage occurring at the receiving end of a long transmission line, above the voltage at the sending end. This occurs when the line is energized, but there is a very light load or the load is disconnected
18. How the corona loss can be reduced?
Corona loss can be reduced by increasing the diameter of conductor and increasing the distance between two conductors
19. How skin effect can be reduced?
To reduce skin effect the shape of the wire should be less for stranded conductor than that of solid conductor
20. What is Bus Bar?
A Bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. They form a link between the incoming and outgoing circuits. The size of the bus bar determines the maximum amount of current that can be safely carried
21. What is Arc Formation?
In circuit breaker when excess current flows the contact between electromagnet and fixed end begins to open when the distance increases arc will be produced due to high current which leads to increase in temperature
22. What are the factor that affects maximum current transmission?
- Electrical Phase shift
- Thermal effect
- Voltage drop
Power delivered P = EVSin δ/X
Generally, δ is kept low (around 30°) because any disturbance can affect the stability of the system if δ value is high.
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