Transmission / AC/DC / Converter Stations/ Distribution

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Transmission / AC/DC / Converter Stations/ Distribution - Quiz

Questions and Answers
  • 1. 

    The sending end voltage is higher than the receiving end voltage on a transmission line and requirement is to transmit power out of the control area: What needs to happen with the generation?

    • A.

      Create a leading power angle

    • B.

      Increase the frequency

    • C.

      Increase the prime mover

    • D.

      Adjust the voltage

    Correct Answer
    A. Create a leading power angle
    Explanation
    When the sending end voltage is higher than the receiving end voltage on a transmission line and the requirement is to transmit power out of the control area, creating a leading power angle is necessary. This can be achieved by adjusting the phase relationship between the voltage and current waveforms, causing the power to flow in the opposite direction. By creating a leading power angle, the power can be transmitted in the desired direction, ensuring efficient power transfer.

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  • 2. 

    Which is best described as a machine that is operating and is creating the effect of generating +VARS onto a transmission line  ?

    • A.

      Induction motor

    • B.

      Rectifier

    • C.

      Add a reactor

    • D.

      Synchronous machine

    Correct Answer
    D. Synchronous machine
    Explanation
    • Reactive loads can be either inductive or capacitive requiring
    high magnetic or electric fields

    • Reactive load examples:
    - Motors
    - Shunt reactors
    - Loaded transmission lines
    - Static VAR compensators
    - Transformers
    - Underexcited generators

    • Inductive loads have a component (typically a conductor wound around an iron core) that produces a magnetic field. They require the production of VARS to maintain voltage with current lagging voltage


    • Capacitive loads store energy in an electric field and produce VARs; these loads usually have parallel conductors which support an electric field. VARs need to be absorbed for this type of load to maintain nominal voltage

    • For a capacitive load, current leads voltage

    • Capacitive load examples:
    - Shunt Capacitors
    - Synchronous condensers
    - Unloaded, overexcited generators
    - Static VAR compensators
    - Lightly loaded transmission lines

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  • 3. 

    The phase shift between the sending and receiving ends of a transmission line is due to 

    • A.

      Reactance

    • B.

      Resistance

    • C.

      Voltage at which the line is operated

    • D.

      Conductor size

    Correct Answer
    A. Reactance
    Explanation
    Transmission lines are characterized by a series resistance, inductance, and shunt capacitance per unit length. These values determine the power-carrying capacity of the transmission line and the voltage drop across it at full load
    • Size of the conductor, Distance between lines affects reactance of the line. Resistance does not cause a shift in phase, the voltage at which the line operates is

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  • 4. 

    To insure the greatest transient stability of a line, it is best to:

    • A.

      Maintain the balance the power into the line and the load

    • B.

      Add series reactors

    • C.

      Add resistance

    • D.

      Increase the voltage

    Correct Answer
    A. Maintain the balance the power into the line and the load
    Explanation
    To ensure the greatest transient stability of a line, it is best to maintain the balance of power into the line and the load. This means that the amount of power being supplied to the line should match the amount of power being consumed by the load. If there is an imbalance, it can lead to instability and potential issues such as voltage fluctuations or equipment damage. By maintaining this balance, the line can operate efficiently and reliably, minimizing the risk of instability during transient events.

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  • 5. 

    To increase the power handling stability capability in a long high voltage transmission line add_____

    • A.

      Series capacitors

    • B.

      Shunt capacitors

    • C.

      Series Reactor

    • D.

      Shunt reactor

    Correct Answer
    A. Series capacitors
    Explanation
    Adding series capacitors to a long high voltage transmission line increases the power handling stability capability. Series capacitors help to compensate for the inductive reactance of the transmission line, thereby reducing the voltage drop and improving the power transfer capability. This allows for a more efficient and stable transmission of power over long distances. Shunt capacitors, series reactors, and shunt reactors do not provide the same benefits in terms of power handling stability in a long high voltage transmission line.

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  • 6. 

    Transient stability on transmission lines is most difficult for

    • A.

      Line to ground fault

    • B.

      Line to line fault

    • C.

      Two-line to ground fault

    • D.

      Three-phase fault

    Correct Answer
    D. Three-phase fault
    Explanation
    Transient stability refers to the ability of a power system to maintain synchronism and continue to operate stably after experiencing a disturbance. A three-phase fault, where all three phases of a transmission line come into contact with each other, is the most severe fault condition in a power system. This fault causes a high magnitude of fault current to flow, leading to significant mechanical stresses on the system. The large fault current can cause severe voltage dips and disturbances, which can result in a loss of synchronism and instability in the system. Therefore, a three-phase fault is the most difficult condition to handle in terms of transient stability on transmission lines.

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  • 7. 

    The operation of steady state stability limit of a power transmission system depends on the system synchronous reactance in which the system is operating at 

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    The operation of steady state stability limit of a power transmission system depends on the system synchronous reactance in which the system is operating at. This means that the synchronous reactance, which represents the ability of the system to withstand disturbances and maintain stability, plays a crucial role in determining the maximum power that can be transmitted without causing instability. Therefore, it is true that the steady state stability limit of a power transmission system depends on the system synchronous reactance.

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  • 8. 

    The surge impedance of a transmission line is directly proportional to line impedance and inversely proportional to capacitance

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    The statement is true because the surge impedance of a transmission line is determined by the ratio of its line impedance to its capacitance. A higher line impedance or a lower capacitance will result in a higher surge impedance. Conversely, a lower line impedance or a higher capacitance will result in a lower surge impedance. Therefore, the surge impedance is directly proportional to line impedance and inversely proportional to capacitance.

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  • 9. 

    To counter the effects of charging current on a long transmission line (> 10 miles), charging current will be reduced if:

    • A.

      Add series capacitor

    • B.

      Add series reactor

    • C.

      Add shunt capacitor

    • D.

      Add shunt reactor

    Correct Answer
    D. Add shunt reactor
    Explanation
    Adding a shunt reactor can help counter the effects of charging current on a long transmission line. Charging current occurs due to the capacitance of the line, and adding a shunt reactor helps to compensate for this by providing inductive reactance. This helps to balance the system and reduce the charging current, improving the overall efficiency and stability of the transmission line.

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  • 10. 

    If power in a transmission line is exceeding the surge capacitance of the load what is the cause?

    • A.

      Charging current less than power transfer

    • B.

      Charging current higher than power transfer

    • C.

      Charging current is equal to the power transfer

    Correct Answer
    B. Charging current higher than power transfer
    Explanation
    When power in a transmission line exceeds the surge capacitance of the load, it means that the charging current is higher than the power transfer. This can occur when there is a sudden increase in power demand or a fault in the system. The surge capacitance of the load refers to the ability of the load to absorb and store electrical energy. If the charging current is higher than the power transfer, it indicates that the load is unable to handle the excess power, leading to potential issues such as overheating or damage to the transmission line.

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  • 11. 

    As a functional load, the most loss on a DC system is from

    • A.

      Reactor

    • B.

      Filter capacitors

    • C.

      Valves

    • D.

      Converter transformer

    Correct Answer
    D. Converter transformer
    Explanation
    The correct answer is Converter transformer. In a DC system, the converter transformer is responsible for converting the AC voltage to DC voltage. During this conversion process, there are losses that occur in the transformer, such as copper losses and iron losses. These losses can be significant and result in a decrease in overall system efficiency. Therefore, the converter transformer is the component that contributes the most to the losses in a DC system.

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  • 12. 

    Reactive compensation methods do not cancel line charging.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    Reactive compensation methods are used to cancel out the effects of line charging. These methods, such as using capacitors or inductors, are designed to counterbalance the reactive power flow in the transmission lines caused by the capacitance and inductance of the system. By doing so, they help reduce the line losses and voltage drops, improving the overall efficiency of the power system. Therefore, the statement that reactive compensation methods do not cancel line charging is false.

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  • 13. 

    Shunt capacitors supply VARS to the system

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    shunt capacitors are installed as close to the load as possible. SVCS or a static var compensator is also used to provide rapidly controlable var support. They are normally located at transmission substations to increase stability to the power system.

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  • 14. 

    In a distribution system that has both underground cables and overhead lines, to divide the load equally, what is added to the overhead lines?

    • A.

      Shunt Capacitors

    • B.

      Shunt Reactors

    • C.

      Series Capacitors

    • D.

      Series Reactors

    Correct Answer
    A. Shunt Capacitors
    Explanation
    Capacitance is far greater for underground cables, where the conductors and ground are very close. The capacitance produces reactive power. To balanace the load the underground and overhead lines Vars should be matched to balance the current flow thought the system.

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  • 15. 

    When running a neutral in an overhead distribution system

    • A.

      A neutral in the distribution system is continuous

    • B.

      The size of the neutral conductor is the same size as the other phase conductors

    • C.

      The neutral of all transformers in the system is grounded at the transformer poles

    • D.

      The neutral conductor is run in the secondary of the distribution system

    Correct Answer
    D. The neutral conductor is run in the secondary of the distribution system
    Explanation
    The correct answer is that the neutral conductor is run in the secondary of the distribution system. This means that the neutral wire is connected to the secondary side of the transformers in the distribution system. This is important because it allows for the safe and efficient distribution of electricity. By running the neutral conductor in the secondary, any imbalances in the load between the phases can be compensated for, ensuring that the distribution system operates properly and safely.

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  • 16. 

    The voltage spread (difference between the maximum and minimum voltage at a point in distribution system) between heavy and light loads is

    • A.

      Largest for the first customer

    • B.

      Smallest for the first customer

    • C.

      Independent of the location

    • D.

      Equal for both customers

    Correct Answer
    B. Smallest for the first customer
    Explanation
    The voltage spread, or the difference between the maximum and minimum voltage at a point in a distribution system, is smallest for the first customer. This is because the first customer is closest to the source of power, and therefore experiences less voltage drop compared to customers further down the line. As a result, the voltage variation between heavy and light loads is minimized for the first customer.

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  • 17. 

    What area is the smoothing reactor? 

    • A.

      A

    • B.

      B

    • C.

      C

    • D.

      D

    • E.

      E

    • F.

      F

    Correct Answer
    B. B
    Explanation
    The smoothing reactor is located in area B.

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  • 18. 

    What area designates the DC Filter?

    • A.

      A

    • B.

      B

    • C.

      C

    • D.

      D

    • E.

      E

    • F.

      F

    Correct Answer
    C. C
    Explanation
    The correct answer is C. The question is asking which area designates the DC Filter. Since the options are not provided, it is not possible to give a specific explanation for why C is the correct answer. However, based on the information given, it can be assumed that the DC Filter is designated by area C.

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  • 19. 

    What area designates the AC Filter?

    • A.

      A

    • B.

      B

    • C.

      C

    • D.

      D

    • E.

      E

    • F.

      F

    Correct Answer
    E. E
  • 20. 

    What area is the Electrode (Line)?

    • A.

      A

    • B.

      B

    • C.

      C

    • D.

      D

    • E.

      E

    • F.

      F

    Correct Answer
    F. F
    Explanation
    The Electrode (Line) is located in area F.

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  • 21. 

    What type of HVDC filter is this?

    • A.

      Single tuned filter

    • B.

      Double tuned filter

    • C.

      High pass filter

    Correct Answer
    A. Single tuned filter
    Explanation
    This HVDC filter is a single tuned filter. A single tuned filter is designed to attenuate a specific frequency while allowing other frequencies to pass through. It consists of a series resonant circuit that is tuned to the desired frequency. In this case, the filter is designed to filter out a specific frequency in the HVDC system.

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  • 22. 

    What type of HVDC filter is this?

    • A.

      Single tuned filter

    • B.

      Double tuned filter

    • C.

      High pass filter

    Correct Answer
    B. Double tuned filter
    Explanation
    This is a double tuned filter because it has two resonant frequencies, allowing it to filter out two specific frequencies from the high voltage direct current (HVDC) system. A single tuned filter would only have one resonant frequency, while a high pass filter would allow high frequencies to pass through and attenuate lower frequencies.

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  • 23. 

    What type of HVDC filter is this?

    • A.

      Single tuned filter

    • B.

      Double tuned filter

    • C.

      High pass filter

    Correct Answer
    C. High pass filter
    Explanation
    This filter is classified as a high pass filter because it allows high frequency signals to pass through while attenuating low frequency signals. A high pass filter is designed to block or reduce low frequency components of a signal, allowing only the higher frequency components to be transmitted. In this case, the filter is specifically designed for high voltage direct current (HVDC) systems, where it is used to filter out low frequency harmonics and disturbances from the power supply.

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  • 24. 

    During light load conditions power lines are primarily inductive

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    During light load conditions, power lines are primarily capacitive rather than inductive. This is because when the load on the power lines is low, the reactive power demand decreases, resulting in a shift towards capacitive power. Capacitive power helps to compensate for the inductive power factor caused by the transmission and distribution equipment. Therefore, the correct answer is False.

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  • 25. 

    During heavy load conditions power lines are primarily capacitve

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    During heavy load conditions, power lines are primarily inductive rather than capacitive. This is because the high current flowing through the power lines creates a magnetic field, which induces a voltage drop and causes the power lines to behave inductively. Capacitive behavior is more prominent during light load conditions where the voltage is higher and the current is lower.

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  • 26. 

    Which element enable more real power to transfer on a  transmission line?

    • A.

      Series reactance

    • B.

      Series capacitance

    • C.

      Shunt capacitance to ground

    • D.

      Shunt reactance to ground

    Correct Answer
    B. Series capacitance
    Explanation
    - The angle δ in a transmission line should typically be ≤ 30o to ensure that the power flow in the transmission line is well below the static stability limit.
    - Any of these limits can be more or less important in different circumstances.
    o In short lines, where series reactance X is relatively small, the resistive heating usually limits the power that the line can supply.
    o In longer lines operating at lagging power factors, the voltage drop across the line is usually the limiting factor.
    o In longer lines operating at leading power factors, the maximum angle δ can be the limiting f actor.

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  • 27. 

    Which one is used to stabilize a long transmission line voltage that is lightly loaded?

    • A.

      Series capacitors

    • B.

      Shunt Capacitors

    • C.

      Series Reactors

    • D.

      Shunt Reactors

    Correct Answer
    D. Shunt Reactors
    Explanation
    Shunt reactors are used in power systems to counteract the effect of the line parasitic capacitance, thereby stabilizing the system voltage within acceptable limits. For short lines, we can basically ignore the impact of capacitive current from a voltage regulation point of view, but medium and long lines can have voltages at their receiving end much higher than the sending end, thus creating issues such as over-fluxing of power transformers and over stressing of line insulators. Under light-load conditions, the line produces more VARs, resulting in receiving end voltage being higher than sending end voltage. In order to consume the excess VARs when system is lightly loaded, an inductor is added to the system. Since inductors absorbs VARs, a reactor is connected in parallel with shunt capacitance of the line known as Shunt Reactor, ......

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  • 28. 

    To improve voltage regulation and increase the stability of the line what can be added

    • A.

      Series and shunt reactors

    • B.

      Series capacitors and static VAR compensators

    • C.

      Resistance and capacitance

    • D.

      Resistance and reactance

    Correct Answer
    B. Series capacitors and static VAR compensators
    Explanation
    VOLTAGE REGULATION OF AC LINES USING STATIC VAR COMPENSATOR
    The Static Var Compensator (SVC) is a shunt device of the Flexible AC Transmission Systems (FACTS) family using power electronics to control power flow and improve transient stability on power grids [1]. The SVC regulates voltage at its terminals by controlling the amount of reactive power injected into or absorbed from the power system. When system voltage is low, the SVC generates reactive power (SVC capacitive). When system voltage is high, it absorbs reactive power (SVC inductive). The variation of reactive power is performed by switching three-phase capacitor banks and inductor banks connected on the secondary side of a coupling transformer. Each capacitor bank is switched on and off by three thyristor switches (Thyristor Switched Capacitor or TSC). Reactors are either switched on-off (Thyristor Switched Reactor or TSR) or phase-controlled (Thyristor Controlled Reactor or TCR).
    http://www.rroij.com/open-access/efficient-voltage-regulation-in-three-phaseac-transmission-lines-using-static-varcompensator.php?aid=41385

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  • 29. 

    Which of the following is used to neutralize the effects due to increased line charging in EHV transmission lines?

    • A.

      Decrease line reactance with series capacitors

    • B.

      Increase line reactance with series reactor

    • C.

      Use shunt capacitor to balance line inductance

    • D.

      Use shunt reactor to balance line capacitance

    Correct Answer
    D. Use shunt reactor to balance line capacitance
    Explanation
    Extra-high-voltage (EHV) transmission lines are employed to transmit power over vast distances; due to the long lengths, these lines have large shunt capacitances associated with
    them. Shunt capacitance exists between the individual phases of the transmission line and also between the phase conductors and ground. When a transmission line is energized, it draws a large charging current because of the large shunt capacitance of the line. This current is mainly capacitive, and as we see from (2), the voltage at the receiving end of the line can become greater than the voltage at the ending end. To avoid an overvoltage condition along the line and the possibility of damaging the line insulator, shunt reactors are installed at the terminals of the line. As shown in Section III, this brings the
    voltage levels along the line to within specified levels.

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  • 30. 

    The efficiency of an HVDC converter station when operating at its rated capacity is generally within the range of

    • A.

      55% or less

    • B.

      55% to 75%

    • C.

      75% to 95%

    • D.

      95% or high

    Correct Answer
    D. 95% or high
    Explanation
    A 2,000-km long HVDC line rated at 800 kilovolts loses about 5 percent of the electricity it carries to heat, while an equivalent AC line would lose twice that amount, or about 10 percent. Long-distance DC transmission also uses less space: a 2,000-km DC link rated at 6,000-megawatts needs just one power line, versus three lines for an AC link of equivalent power and length.

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  • 31. 

    Which of the following elements is not a source of capacitive reactive power?

    • A.

      Overexcited generators

    • B.

      Shunt Capacitor

    • C.

      A lightly loaded transmission line

    • D.

      Capacitor banks

    • E.

      Under excited generators

    Correct Answer
    E. Under excited generators
    Explanation
    Under excited generators are not a source of capacitive reactive power. When a generator is under excited, it means that the excitation system is not providing enough reactive power to the generator. In this condition, the generator acts as a consumer of reactive power rather than a source. Capacitive reactive power is supplied by capacitors or overexcited generators, while under excited generators consume reactive power.

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  • 32. 

    Which of the following elements does not absorb reactive power?

    • A.

      Under excited generators

    • B.

      Shunt reactors

    • C.

      Line transformers

    • D.

      Motor Loads

    • E.

      Overexcited generator

    • F.

      Synchronous Condensor

    Correct Answer
    E. Overexcited generator
    Explanation
    An overexcited generator is capable of supplying reactive power to the system, rather than absorbing it. When a generator is overexcited, the generated voltage is higher than the system voltage, causing the generator to act as a source of reactive power. This is in contrast to under excited generators, shunt reactors, line transformers, motor loads, and synchronous condensers, which all absorb reactive power to varying degrees.

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  • 33. 

    Shunt reactors absorb Vars from the system.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Shunt reactors are used to absorb reactive power, also known as Vars, from the electrical system. Reactive power is required to maintain voltage levels and stabilize the system, but excess reactive power can cause inefficiencies. Shunt reactors are connected in parallel with the system and help to absorb and balance the reactive power, improving the overall power factor and system performance. Therefore, the statement "Shunt reactors absorb Vars from the system" is true.

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  • 34. 

    The circuit has 500-KW load and power factor of 0.5. What is the capacitive KVAR required to improve the power factor to unity?

    • A.

      500 KVARs

    • B.

      750 KVARs

    • C.

      850 KVARs

    • D.

      900 KVARs

    Correct Answer
    C. 850 KVARs
    Explanation
    Papparent =500/.5 theta = cos -1 (p.f.) = Theta Q = P x Tan(theta)

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  • 35. 

    In the overhead distribution system, which factor limits the line from using the full capacity of the line?

    • A.

      Capacitance of the line

    • B.

      Low Voltage at end

    • C.

      Power

    Correct Answer
    A. Capacitance of the line
    Explanation
    The capacitance of the line limits the line from using its full capacity in the overhead distribution system. Capacitance refers to the ability of the line to store electrical energy, and it can cause power losses and voltage drops. This means that as the capacitance increases, the line's ability to transmit power efficiently decreases. Therefore, the capacitance of the line acts as a limiting factor in utilizing the full capacity of the line in the overhead distribution system.

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  • 36. 

    In overhead distribution system practice, the factor which usually prevents the use of all the conductors’ current carrying capacity is:

    • A.

      Allowable voltage drop

    • B.

      Ambient temperature

    • C.

      Melting point of the conductor

    • D.

      Corona loss

    Correct Answer
    D. Corona loss
    Explanation
    What is Corona? A condition that occurs on conductors when the conductor's surface potential gets so high that the dielectric strength of the surrounding air is exceeded and ionization occurs.
    
    Method of keeping corona at low acceptable levels? Use conductors with a diameter as large as possible. One method of doing this is by using bundled conductors which have two or more conductors per phase supported by a single insulator string..

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  • 37. 

    What is one advantage of using a DC intertie over an AC intertie in connecting two seperate power systems

    • A.

      The two systems need not be synchronized

    • B.

      Leads can easily be taken off the DC intertie

    • C.

      DC breakers are more efficent

    • D.

      DC converter stations are simpler to build

    Correct Answer
    A. The two systems need not be synchronized
    Explanation
    Using a DC intertie allows for the connection of two separate power systems without the need for synchronization. This means that the frequency and phase of the two systems do not have to match, making it easier to connect systems with different characteristics. In contrast, an AC intertie requires synchronization, which can be more complex and time-consuming. Therefore, the advantage of using a DC intertie is that it provides more flexibility in connecting different power systems.

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  • 38. 

    How are two single phase voltage regulators hooked into distribution lines?

    • A.

      Series

    • B.

      Two windings

    • C.

      Scott conecction

    • D.

      Open Delta

    Correct Answer
    D. Open Delta
    Explanation
    Two single phase voltage regulators are hooked into distribution lines using the Open Delta connection. In this configuration, two transformers are connected in a triangular shape, with one transformer serving as a common center point for the other two. This arrangement allows for the generation of three-phase power using only two transformers. The Open Delta connection is commonly used when a three-phase transformer is unavailable or when there is a need for a temporary or backup power supply.

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  • 39. 

    In a long AC transmission system, series synchronous capacitors are added to:

    • A.

      Increase the line impedance causing an increase in the stability of the system

    • B.

      Eliminate sub-synchronous resonance

    • C.

      Cause a direct current charge to the line

    • D.

      Increase the system capacity but can cause sub-synchronous resonance to occur

    Correct Answer
    D. Increase the system capacity but can cause sub-synchronous resonance to occur
    Explanation
    Series synchronous capacitors are added in a long AC transmission system to increase the system capacity. These capacitors help in improving the power transfer capability of the system by compensating for the reactive power. However, the addition of these capacitors can also lead to sub-synchronous resonance, which is a phenomenon where the system oscillates at a frequency lower than the synchronous frequency. Therefore, while series synchronous capacitors increase the system capacity, they also have the potential to cause sub-synchronous resonance to occur.

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  • 40. 

    In a distribution system that has both underground cables and overhead lines, in order to divide the KVA rating accordingly, which of the following is added?

    • A.

      Capacitor to underground cable

    • B.

      Capacitor to overhead lines

    • C.

      Reactor to underground cable

    • D.

      Reactor to overhead lines

    Correct Answer
    B. Capacitor to overhead lines
    Explanation
    In a distribution system that has both underground cables and overhead lines, capacitors are added to the overhead lines in order to divide the KVA rating accordingly. Capacitors are used to improve the power factor of the system, which helps in reducing the reactive power demand and improving the overall efficiency of the system. By adding capacitors to the overhead lines, the KVA rating can be divided appropriately between the underground cables and overhead lines, ensuring efficient distribution of power.

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  • 41. 

    The limiting factor in the stability of a high voltage transmission system is the maximum:

    • A.

      Current which the transmission line conductors can handle

    • B.

      Voltage the transmission system can take without the insulators or bushings flashing over

    • C.

      Power which can be transferred without the transmission line losing synchronism

    • D.

      Transmission line phase angle between voltage and current

    Correct Answer
    C. Power which can be transferred without the transmission line losing synchronism
    Explanation
    The stability of a high voltage transmission system refers to its ability to maintain synchronous operation. Synchronism is the condition where the voltage and current in the transmission line are in phase with each other. If the power transferred exceeds a certain limit, the transmission line can lose synchronism, leading to instability. Therefore, the maximum power that can be transferred without losing synchronism is the limiting factor in the stability of a high voltage transmission system.

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  • 42. 

    Which of the following is not installed at a DC converter station?

    • A.

      Smoothing reactor

    • B.

      DC breaker

    • C.

      AC filters

    • D.

      Capacitors

    Correct Answer
    B. DC breaker
    Explanation
    A DC breaker is not installed at a DC converter station. DC breaker is a device used to interrupt the flow of direct current in a circuit. At a DC converter station, the main purpose is to convert alternating current (AC) to direct current (DC) or vice versa. The other options listed, such as smoothing reactor, AC filters, and capacitors, are commonly installed at a DC converter station to regulate and filter the current. However, a DC breaker is not necessary as the main focus is on converting the current, rather than interrupting it.

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  • 43. 

    In a distribution system with underground cable and overhead lines, in order to divide the KVA rating accordingly, which of the following is added to the overhead lines?

    • A.

      Capacitor to underground cable

    • B.

      Capacitor to OH lines

    • C.

      Reactor to underground cable

    • D.

      Reactor to OH lines

    Correct Answer
    B. Capacitor to OH lines
    Explanation
    Underground cables have a very low impedance, almost a short circuit compared to over head lines. A series capacitor will decrease the impedance and cause the line to load up.

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  • 44. 

    When cable and overhead line are paralleled to deliver power what do you add? 

    • A.

      Reactor to cable

    • B.

      Reactor to overhead line

    • C.

      Resistor to cable

    • D.

      Resistor to overhead line

    Correct Answer
    A. Reactor to cable
    Explanation
    When cable and overhead line are paralleled to deliver power, a reactor is added to the cable. A reactor is a device used to control the flow of electricity by introducing inductance into the circuit. By adding a reactor to the cable, it helps to regulate and stabilize the power flow, ensuring efficient and reliable delivery of electricity.

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  • 45. 

    The feeder voltage regulators used on DWP's  4.8KV feeder lines are most common in construction of

    • A.

      Autotransformers

    • B.

      CP transformers

    • C.

      Capacitor banks

    • D.

      Rotary condenser

    Correct Answer
    A. Autotransformers
    Explanation
    Autotransformers are commonly used in the construction of feeder voltage regulators for 4.8KV feeder lines. Feeder voltage regulators are used to regulate the voltage levels in electrical distribution systems. Autotransformers are a type of transformer that have a single winding and can step up or step down the voltage levels. They are often used in situations where voltage regulation is required, such as in distribution systems. Therefore, autotransformers are the most common choice for construction of feeder voltage regulators on 4.8KV feeder lines.

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  • 46. 

    When series capacitors are installed on a long EHV line of 500kV which one of the following effects will normally occur assuming that the line is heavily loaded?

    • A.

      Phase shift between the sending and receiving ends is increased

    • B.

      Line is lengthened electrically

    • C.

      Receiving end voltage will increase

    • D.

      Line stability is degraded

    Correct Answer
    C. Receiving end voltage will increase
    Explanation
    When series capacitors are installed on a long EHV line of 500kV that is heavily loaded, the receiving end voltage will increase. This is because the series capacitors help to compensate for the reactive power in the line, which in turn reduces the voltage drop along the line. As a result, the receiving end voltage is boosted, allowing for a more stable and reliable power supply.

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  • 47. 

    What is the effect of adding a series capacitance to long HV 500KV transmission line:

    • A.

      Increase angle between the sending end voltage and receiving end voltage

    • B.

      Line becomes electrically longer

    • C.

      Offset line inductance for maximum power transfer

    • D.

      Stability is degraded

    Correct Answer
    C. Offset line inductance for maximum power transfer
    Explanation
    Adding a series capacitance to a long HV 500KV transmission line offsets the line inductance. This helps in achieving maximum power transfer. By offsetting the line inductance, the reactive power flow is minimized, resulting in improved power transfer efficiency.

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  • 48. 

    In a long AC transmission system, transient stability is best maintained by

    • A.

      Fast clearing of faults

    • B.

      The acceleration factor of the generators

    • C.

      Proper load balance

    • D.

      The installed capacity of synchronous condensers

    Correct Answer
    A. Fast clearing of faults
    Explanation
    In a long AC transmission system, transient stability refers to the ability of the system to maintain stable operation after a disturbance. Fast clearing of faults is crucial for maintaining transient stability because it allows for the quick removal of any faults or disturbances in the system. By clearing faults rapidly, the system can prevent cascading failures and maintain a stable operating condition. This ensures that the system can quickly recover from disturbances and continue to deliver power reliably.

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  • 49. 

    The surge impedance of a 50 mile long underground cable is 50 ohms. For a 25 mile length what will it be:

    • A.

      25 ohms

    • B.

      50 ohms

    • C.

      100 ohms

    • D.

      None of the above

    Correct Answer
    B. 50 ohms
    Explanation
    The characteristic impedance or surge impedance (usually written Z0) of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction. Characteristic impedance is determined by the geometry and materials of the transmission line and, for a uniform line, is not dependent on its length. The SI unit of characteristic impedance is the ohm. Applying the transmission line model based on the telegrapher's equations, the general expression for the characteristic impedance of a transmission line is:Although an infinite line is assumed, since all quantities are per unit length, the characteristic impedance is independent of the length of the transmission line.

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  • 50. 

    When running a neutral in an overhead distribution system

    • A.

      A neutral in the distribution system is continuous

    • B.

      The size of the neutral conductor is the same size as the other phase conductors

    • C.

      The neutral of all transformers in the system, is grounded at the transformer poles

    • D.

      The neutral conductor is run in the secondary of the distribution system

    Correct Answer
    D. The neutral conductor is run in the secondary of the distribution system

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