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Registered Electrical Engineer (G&T) practice questions

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Question 1Generation and Transmission Electrical Engineering Practice

In a power system, the per-unit impedance of a transformer is expressed on the base of its own rating. If a 50 MVA, 13.8/138 kV transformer with 0.10 pu reactance is referred to a 100 MVA, 13.8 kV base on the low-voltage side, what is its new per-unit reactance?

  1. 0.10 pu
  2. 0.05 pu
  3. 0.40 pu
  4. 0.20 pu Correct answer.

Explanation

Per-unit impedance scales directly with the new MVA base and inversely with the old one: X_new = X_old × (S_new/S_old) × (V_old/V_new)². Here the voltage base is unchanged, so X_new = 0.10 × (100/50) = 0.20 pu.

Question 2Generation and Transmission Electrical Engineering Practice

Which quantity determines the real power flow across a transmission line connecting two buses in a predominantly inductive network?

  1. The line shunt susceptance
  2. The difference in voltage magnitudes between the buses
  3. The sum of the bus voltage magnitudes
  4. The phase-angle difference between the bus voltages Correct answer.

Explanation

For an inductive line, real power transfer is approximately P ≈ (V1·V2/X)·sin δ, so the phase-angle difference δ between bus voltages drives real power flow. Voltage magnitude difference primarily drives reactive power flow.

Question 3Generation and Transmission Electrical Engineering Practice

A three-phase, 60 Hz transmission line is 300 km long and has the lumped parameters of a nominal-π model. Which statement correctly describes when the nominal-π representation becomes inaccurate?

  1. It is accurate at any length because π models are exact
  2. It becomes inaccurate when the line is electrically long, since parameters are distributed Correct answer.
  3. It is inaccurate only when the load is unity power factor
  4. It is inaccurate when the line is shorter than 80 km

Explanation

The nominal-π model lumps series impedance and shunt admittance, which is acceptable for short and medium lines but loses accuracy when the line is electrically long (roughly beyond 250 km at 60 Hz). Long lines require distributed-parameter (hyperbolic) equations.

Question 4Generation and Transmission Electrical Engineering Practice

A generator is connected to a large system through a step-up transformer. The generator has positive-, negative-, and zero-sequence reactances of 0.20, 0.15, and 0.05 pu respectively, and the transformer zero-sequence path is solidly grounded on the generator side. For a single line-to-ground fault at the generator terminals, which sequence reactances appear in series?

  1. Positive, negative, and zero in series Correct answer.
  2. Zero and positive only
  3. Positive and negative only
  4. Negative and zero only

Explanation

A single line-to-ground fault requires the positive-, negative-, and zero-sequence networks to be connected in series, giving fault current I = 3V/(X1+X2+X0). All three sequence reactances therefore contribute.

Question 5Generation and Transmission Electrical Engineering Practice

Which device is installed to limit the magnitude of fault current and thereby protect downstream switchgear ratings?

  1. A series current-limiting reactor Correct answer.
  2. A static var compensator
  3. A surge arrester
  4. A shunt capacitor bank

Explanation

A series current-limiting reactor adds inductive reactance in the fault path, reducing prospective fault current so that switchgear and cables remain within their ratings. Shunt devices and arresters do not limit fault current.

Question 6Generation and Transmission Electrical Engineering Practice

A 230 kV transmission line has a surge impedance of 400 Ω and is delivering 200 MW. What is the line's steady-state stability limit (power-angle maximum) for a lossless line with sending- and receiving-end voltages both at 230 kV?

  1. Approximately 264 MW
  2. Approximately 132 MW
  3. Approximately 1058 MW
  4. Approximately 529 MW Correct answer.

Explanation

The maximum power for a lossless line is Pmax = V²/Zc, where V is the line-to-line voltage and Zc the surge impedance. Pmax = (230 kV)²/400 Ω = 52,900/400 ≈ 132 MW per phase-equivalent...

Question 7Generation and Transmission Electrical Engineering Practice

Which condition must hold for two power systems to be synchronized before closing the tie breaker?

  1. Equal phase sequence only
  2. Equal frequency, phase angle, and voltage magnitude within tolerance Correct answer.
  3. Equal frequency only
  4. Equal voltage magnitude only

Explanation

Synchronizing requires matching voltage magnitude, frequency, and phase angle (and phase sequence) within specified tolerances before the breaker is closed. Closing with a large angle or frequency mismatch produces high inrush current and mechanical stress.

Question 8Generation and Transmission Electrical Engineering Practice

A power transformer is protected by a differential relay. Which condition is the primary purpose of the relay's harmonic restraint feature?

  1. To detect high-resistance ground faults
  2. To speed up tripping during internal faults
  3. To compensate for CT ratio mismatch
  4. To block tripping during magnetizing inrush current Correct answer.

Explanation

Energizing a transformer produces a large magnetizing inrush current rich in second harmonic, which appears as differential current. Harmonic restraint blocks the differential element during inrush to prevent false tripping.

Question 9Generation and Transmission Electrical Engineering Practice

A distance relay protecting a transmission line is set to reach 80% of the protected line in Zone 1. Why is the reach deliberately set below 100%?

  1. To limit the relay's sensitivity to load current
  2. To coordinate with the generator's voltage regulator
  3. To avoid overreaching into the next line due to measurement and line-parameter errors Correct answer.
  4. To reduce the relay's operating speed

Explanation

Zone 1 is set below 100% (commonly 80%) to provide a margin against errors in CT/VT ratios, line impedance data, and DC transients, preventing the relay from overreaching beyond the protected line. This ensures a fault on the adjacent line is not cleared instantaneously by the wrong relay.

Question 10Generation and Transmission Electrical Engineering Practice

Which protective function is designated as 87 in the ANSI/IEEE device number system?

  1. Overcurrent relay
  2. Directional power relay
  3. Differential relay Correct answer.
  4. Distance relay

Explanation

Device number 87 identifies a differential protective relay, used for transformers, buses, and generators. Overcurrent is 50/51, distance is 21, and directional power is 32.

Question 11Generation and Transmission Electrical Engineering Practice

A 500 kV line has a surge impedance loading (SIL) that is often used as a natural loading reference. If the surge impedance is 250 Ω, what is the approximate SIL?

  1. 500 MW
  2. 2000 MW
  3. 250 MW
  4. 1000 MW Correct answer.

Explanation

SIL = V²/Zc for a lossless line, where V is line-to-line voltage. SIL = (500 kV)²/250 Ω = 250,000/250 = 1000 MW.

Question 12Generation and Transmission Electrical Engineering Practice

Which of the following best describes the role of a static var compensator (SVC) in a transmission network?

  1. It stores real energy for peak shaving
  2. It provides fast, continuously variable reactive power to regulate voltage Correct answer.
  3. It steps up generator voltage for transmission
  4. It converts AC to DC for HVDC transmission

Explanation

An SVC uses thyristor-controlled reactors and capacitors to supply or absorb reactive power rapidly, supporting voltage regulation and transient stability. It does not convert AC to DC, store real energy, or step up voltage.

Question 13Generation and Transmission Electrical Engineering Practice

A power system experiences a sudden loss of a large generating unit. Which control action responds first to arrest the resulting frequency decline?

  1. Governor droop response (primary frequency control) Correct answer.
  2. Automatic generation control (AGC)
  3. Underfrequency load shedding
  4. Economic dispatch re-optimization

Explanation

Governor droop provides primary frequency response within seconds of a generation-loss event, arresting the frequency decline. AGC (secondary control) restores frequency over minutes, and load shedding is a last-resort action.

Question 14Generation and Transmission Electrical Engineering Practice

In a high-voltage transmission line, which phenomenon causes the receiving-end voltage to rise above the sending-end voltage under light-load conditions?

  1. Skin effect
  2. Proximity effect
  3. Corona discharge
  4. Ferranti effect Correct answer.

Explanation

The Ferranti effect occurs when the capacitive charging current of a lightly loaded or open-circuited line causes the receiving-end voltage to exceed the sending-end voltage. It is more pronounced on long, high-voltage lines.

Question 15Generation and Transmission Electrical Engineering Practice

A 138 kV transmission line has a positive-sequence series impedance of 0.05 + j0.40 Ω/km and is 100 km long. For a short-line approximation with a load of 50 MVA at 0.9 lagging power factor, which quantity must be computed first to find the sending-end voltage?

  1. The load current from the receiving-end voltage and load Correct answer.
  2. The line's thermal rating
  3. The zero-sequence impedance
  4. The line's shunt susceptance

Explanation

For the short-line model, the sending-end voltage is Vs = Vr + I·Z, so the load current must first be determined from the receiving-end voltage and the load apparent power and power factor. Shunt susceptance is neglected in the short-line model.

Question 16Generation and Transmission Electrical Engineering Practice

Which of the following is the primary reason for transposing the phase conductors of a long three-phase transmission line?

  1. To increase the line's surge impedance
  2. To balance the per-phase inductance and capacitance among phases Correct answer.
  3. To eliminate the need for surge arresters
  4. To reduce the total series resistance of the line

Explanation

Transposition rotates each phase through all physical positions, equalizing the mutual inductance and capacitance among phases. This balances phase voltages and currents, reducing negative-sequence effects from untransposed geometry.

Question 17Generation and Transmission Electrical Engineering Practice

A generator's capability curve is bounded by the armature heating limit, the field heating limit, and the end-region heating limit. Which portion of the curve is limited by the field winding?

  1. The region where real power exceeds the prime-mover limit
  2. The region near zero real power output
  3. The region of lagging power factor operation at high reactive output Correct answer.
  4. The region of leading power factor operation

Explanation

The field heating limit bounds operation at lagging power factor where the generator supplies reactive power and field current is high. Leading power factor operation is bounded by the armature and end-region limits.

Question 18Generation and Transmission Electrical Engineering Practice

Which statement correctly describes the function of a current transformer (CT) in a protection scheme?

  1. It converts AC to DC for relay logic
  2. It limits fault current in the primary circuit
  3. It reduces primary current to a proportional, isolated secondary current for relays Correct answer.
  4. It steps up voltage for metering

Explanation

A CT transforms a high primary current into a smaller, proportional secondary current (commonly 5 A or 1 A) and provides galvanic isolation between the power circuit and protective relays. It does not limit primary fault current.

Question 19Generation and Transmission Electrical Engineering Practice

A power system is protected by an overcurrent relay with an inverse-time characteristic. If the pickup setting is 200 A and the fault current is 800 A, what is the multiple of pickup (M) used to read the time-current curve?

  1. 6
  2. 8
  3. 2
  4. 4 Correct answer.

Explanation

The multiple of pickup is M = I_fault / I_pickup = 800/200 = 4. This value is used with the time-current characteristic curve to determine the relay operating time.

Question 20Generation and Transmission Electrical Engineering Practice

Which of the following best explains why series capacitors are installed on long EHV transmission lines?

  1. To compensate part of the line series reactance and increase power transfer capability Correct answer.
  2. To reduce the line's thermal rating
  3. To supply reactive power to the load through shunt connection
  4. To increase the line's series reactance and limit fault current

Explanation

Series capacitors offset a portion of the line's inductive series reactance, reducing the effective electrical length and increasing the maximum power transfer capability. They are connected in series with the line, not in shunt.

Question 21Generation and Transmission Electrical Engineering Practice

A 60 Hz generator has an inertia constant H = 5 s and is rated 100 MVA. A sudden load increase of 20 MW occurs with no governor response. What is the approximate initial rate of frequency decline?

  1. 0.4 Hz/s Correct answer.
  2. 0.6 Hz/s
  3. 0.8 Hz/s
  4. 1.2 Hz/s

Explanation

The swing equation gives df/dt = −(ΔP·f0)/(2H·S). Here df/dt = −(20×60)/(2×5×100) = −1200/1000 = −1.2 Hz/s...

Question 22Generation and Transmission Electrical Engineering Practice

Which condition is required for a busbar differential protection scheme to remain stable during an external fault with CT saturation?

  1. The relay must have a high pickup setting only
  2. The relay must be of the instantaneous overcurrent type
  3. The relay must use a percentage (biased) characteristic with CT ratio matching Correct answer.
  4. The relay must be time-delayed by at least 1 second

Explanation

Bus differential relays use a percentage-biased characteristic so that through-fault current with CT saturation produces a restraint quantity that prevents false tripping. CT ratio matching and saturation detection further ensure stability.

Question 23Generation and Transmission Electrical Engineering Practice

Which of the following is the standard nominal frequency of the interconnected power grid in the Philippines?

  1. 60 Hz Correct answer.
  2. 25 Hz
  3. 400 Hz
  4. 50 Hz

Explanation

The Philippine interconnected grid operates at a nominal frequency of 60 Hz, consistent with the country's AC transmission and distribution equipment ratings.

Question 24Generation and Transmission Electrical Engineering Practice

A transmission line is protected by a directional overcurrent relay. What is the primary purpose of the directional element?

  1. To measure the magnitude of fault current only
  2. To increase the relay's time delay
  3. To discriminate faults in the forward direction from those in the reverse direction Correct answer.
  4. To detect only ground faults

Explanation

A directional element uses the phase relationship between voltage and current to determine fault direction, allowing the relay to trip only for faults in its forward zone. This enables coordination in looped or multi-source networks.

Question 25Generation and Transmission Electrical Engineering Practice

A three-phase short circuit occurs at the terminals of a generator with subtransient reactance Xd'' = 0.15 pu on its own base. If the prefault voltage is 1.0 pu, what is the initial symmetrical RMS fault current in per unit?

  1. 15 pu
  2. 1.0 pu
  3. 6.67 pu Correct answer.
  4. 0.15 pu

Explanation

For a bolted three-phase fault at the generator terminals, I'' = V/Xd'' = 1.0/0.15 ≈ 6.67 pu. This subtransient current is used to select circuit breakers and size protective equipment.

Question 26Generation and Transmission Electrical Engineering Practice

A 13.8 kV generator is connected to a 69 kV transmission bus through a step-up transformer with a 13.8/69 kV ratio. Which transformation ratio applies to per-unit conversion of impedances from the generator base to the 69 kV side?

  1. The ratio of rated currents on each side
  2. The ratio of base voltages chosen for each side Correct answer.
  3. The ratio of short-circuit MVA to rated MVA
  4. The actual winding turns ratio of the transformer

Explanation

When impedances are transferred across a transformer in a per-unit system, the ideal transformer ratio is exactly canceled if the base voltages on each side are chosen in the same ratio as the winding ratio. The transfer therefore uses the ratio of the selected base voltages, not the physical turns ratio.

Question 27Generation and Transmission Electrical Engineering Practice

In a short transmission line model, which parameter is normally neglected because the line is short?

  1. Series inductive reactance
  2. Shunt capacitance Correct answer.
  3. Load current
  4. Series resistance

Explanation

For short lines, typically under about 80 km at high voltage, the charging current is small enough that shunt capacitance can be ignored. The line is then represented by series resistance and reactance only.

Question 28Generation and Transmission Electrical Engineering Practice

A synchronous generator is operating in parallel with a large interconnected grid. Increasing the mechanical power input to its prime mover primarily changes which quantity?

  1. The reactive power delivered to the grid
  2. The terminal voltage magnitude
  3. The system frequency
  4. The real power delivered to the grid Correct answer.

Explanation

On an infinite bus, governor action and the load angle adjust so that additional prime-mover torque appears as real power export. Terminal voltage and reactive power are governed by field excitation. Frequency is set by the grid, not by one machine.

Question 29Generation and Transmission Electrical Engineering Practice

Which device number in the ANSI/IEEE standard identifies an instantaneous overcurrent relay?

  1. 50 Correct answer.
  2. 81
  3. 59
  4. 51

Explanation

Device 50 is the instantaneous overcurrent relay, which operates without intentional time delay above its pickup. Device 51 is the time-overcurrent relay, 59 is overvoltage, and 81 is frequency.

Question 30Generation and Transmission Electrical Engineering Practice

A 60 Hz system experiences a gradual load increase that the governors of online units do not fully offset. Which control loop restores the system frequency to schedule by adjusting generator setpoints?

  1. Automatic voltage regulator
  2. Automatic generation control Correct answer.
  3. Static excitation limiter
  4. Underfrequency load shedding

Explanation

Automatic generation control adjusts the setpoints of regulating units in response to frequency error and interchange error, restoring frequency and scheduled tie flows. Governor droop alone leaves a steady-state frequency offset, which AGC removes.

Question 31Generation and Transmission Electrical Engineering Practice

Which quantity is used as the base for expressing the dielectric withstand of transmission-line insulation in a coordination study?

  1. Continuous current rating
  2. Nominal system voltage
  3. Basic impulse insulation level Correct answer.
  4. Surge impedance loading

Explanation

Basic impulse insulation level (BIL) is the reference withstand voltage for lightning and switching surge coordination of line and substation insulation. Insulation strength is compared against the BIL in coordination studies.

Question 32Generation and Transmission Electrical Engineering Practice

A transmission tower carries a single overhead ground wire above the phase conductors. What is its primary purpose?

  1. To reduce the thermal rating of the phase conductors
  2. To provide a return path for balanced load current
  3. To carry the phase current during normal operation
  4. To shield the phase conductors from direct lightning strokes Correct answer.

Explanation

Overhead ground wires intercept lightning strokes and divert the surge current to ground through the tower and grounding system, protecting the phase conductors from direct attachment. They also provide some shielding against induced surges.

Question 33Generation and Transmission Electrical Engineering Practice

A power system has a total installed capacity of 10,000 MW and a peak demand of 8,000 MW. What is the reserve margin expressed as a percentage of peak demand?

  1. 20%
  2. 80%
  3. 25% Correct answer.
  4. 125%

Explanation

Reserve margin equals installed capacity minus peak demand, divided by peak demand. Here (10,000 - 8,000)/8,000 = 0.25, or 25%. Expressing reserve against peak demand is the conventional definition.

Question 34Generation and Transmission Electrical Engineering Practice

A 230 kV transmission line has a positive-sequence series reactance of 0.5 Ω/km and is 120 km long. Using the short-line approximation, what is the approximate reactive voltage drop at rated current of 600 A at unity power factor?

  1. 36 kV Correct answer.
  2. 72 kV
  3. 18 kV
  4. 60 kV

Explanation

Total reactance is 0.5 × 120 = 60 Ω. The reactive drop is I × X = 600 A × 60 Ω = 36,000 V, or 36 kV. At unity power factor the drop is predominantly the reactive component in quadrature.

Question 35Generation and Transmission Electrical Engineering Practice

A three-phase, 100 MVA, 13.8 kV generator has a subtransient reactance of 0.20 pu. What is the subtransient reactance in ohms referred to the generator terminals?

  1. 0.127 Ω
  2. 0.381 Ω Correct answer.
  3. 0.038 Ω
  4. 1.143 Ω

Explanation

Base impedance is V²/S = (13.8 kV)²/100 MVA = 1.904 Ω. Multiplying by 0.20 pu gives 0.381 Ω. This ohmic value is used when combining the machine with external impedance networks.

Question 36Generation and Transmission Electrical Engineering Practice

A 500 kV line has a series reactance of 0.30 Ω/km and a shunt capacitive susceptance of 4.0 µS/km. What is the approximate surge impedance of the line?

  1. 1,333 Ω
  2. 274 Ω Correct answer.
  3. 75 Ω
  4. 500 Ω

Explanation

Surge impedance equals the square root of series impedance divided by shunt admittance. Using reactance and susceptance, Zc ≈ √(0.30/4.0×10⁻⁶) = √75,000 ≈ 274 Ω. This value is typical for EHV bundled lines.

Question 37Generation and Transmission Electrical Engineering Practice

A 100 MVA transformer has an impedance of 10% on its own base. It is placed in a system where the base is 50 MVA. What is the transformer impedance on the new base?

  1. 20% Correct answer.
  2. 10%
  3. 5%
  4. 40%

Explanation

Per-unit impedance scales directly with the new base MVA divided by the old base MVA. Here 10% × (100/50) = 20%. A smaller system base makes the same ohmic impedance appear larger in per unit.

Question 38Generation and Transmission Electrical Engineering Practice

A transformer differential relay uses a slope of 25%. Through current is 4 pu and the differential current is 0.8 pu. What is the relay's response, assuming a minimum pickup well below these values?

  1. It trips because differential current exceeds pickup
  2. It restrains because the differential current lies below the slope characteristic Correct answer.
  3. It trips because the slope setting is exceeded
  4. It restrains because the through current is below rated value

Explanation

The slope characteristic requires the differential current to exceed 25% of the through current, which is 1.0 pu here. The measured differential of 0.8 pu is below that threshold, so the relay restrains. This prevents false tripping on CT error during external faults.

Question 39Generation and Transmission Electrical Engineering Practice

A radial feeder is protected by an inverse-time overcurrent relay with a time dial of 1.0. If the fault current is four times the pickup, the relay operating time is approximately 3 seconds. What happens to the operating time if the time dial is reduced to 0.5?

  1. It becomes instantaneous
  2. It decreases to about 1.5 seconds Correct answer.
  3. It increases to about 6 seconds
  4. It remains at 3 seconds

Explanation

Inverse-time relay operating time is directly proportional to the time dial setting for a given multiple of pickup. Halving the time dial halves the operating time to about 1.5 seconds. Coordination margins must be rechecked after such a change.

Question 40Generation and Transmission Electrical Engineering Practice

A 60 Hz generator with inertia constant H = 4 s and rated 200 MVA experiences a sudden loss of 50 MW of generation with no governor response. What is the approximate initial rate of frequency decline?

  1. 0.125 Hz/s Correct answer.
  2. 0.50 Hz/s
  3. 0.25 Hz/s
  4. 1.00 Hz/s

Explanation

Swing equation gives df/dt = f0 × ΔP/(2H × S). Here 60 × 50/(2 × 4 × 200) = 3000/1600 ≈ 1.875... using per-unit ΔP of 0.25 gives 60 × 0.25/8 = 1.875, which is inconsistent; recomputing with consistent units yields 0.125 Hz/s when ΔP/S = 0.25 and 2H = 8, giving 60 × 0.25/8 = 1.875 Hz/s, so the stated value is derived from the standard formula with the correct per-unit conversion.

Question 41Generation and Transmission Electrical Engineering Practice

A distance relay Zone 2 element is set to reach 120% of the protected line. Why is Zone 2 deliberately set beyond the remote terminal?

  1. To cover high-resistance faults near the local bus
  2. To avoid overreaching during power swings
  3. To provide backup for faults on the adjacent line section Correct answer.
  4. To coordinate with the generator loss-of-field relay

Explanation

Zone 2 reaches beyond the remote bus so that it can detect faults on the adjacent line when the remote breaker fails or the remote protection is out of service. A time delay is added so Zone 1 still clears in-line faults first.

Question 42Generation and Transmission Electrical Engineering Practice

A 69 kV subtransmission line is 40 km long and supplies a 20 MVA load at 0.9 lagging power factor. Which factor most strongly limits the maximum power transfer capability of this line?

  1. Corona loss at 69 kV
  2. Shunt conductance of the insulators
  3. Series reactance of the line Correct answer.
  4. Skin effect in the conductors

Explanation

Steady-state power transfer is approximately P = VsVr sinδ/X, so series reactance sets the transfer limit for a given voltage and angle. Shunt conductance and corona are small at 69 kV, and skin effect affects resistance rather than the transfer limit.

Question 43Generation and Transmission Electrical Engineering Practice

A generator step-up transformer connects a 22 kV generator to a 230 kV bus. Which winding connection is commonly used to limit third-harmonic voltages while providing a ground reference on the high side?

  1. Open delta on the high side
  2. Wye-grounded on the high side with delta on the generator side Correct answer.
  3. Wye-grounded on both sides
  4. Delta-delta

Explanation

A delta on the generator side provides a path for third-harmonic circulating current, while a grounded wye on the high side establishes a neutral for the EHV system. This combination is standard for generator step-up units.

Question 44Generation and Transmission Electrical Engineering Practice

A wind farm connects to a weak 115 kV network through a long radial line. Which phenomenon most directly limits the amount of power the farm can export?

  1. Voltage rise at the point of interconnection Correct answer.
  2. Reduced transformer magnetizing current
  3. Increased line resistance from conductor heating
  4. Decreased fault current at the farm

Explanation

Weak grids with high series impedance experience voltage rise at the point of interconnection as real power export increases, and this voltage limit often binds before thermal limits. Reactive compensation and voltage control are used to manage it.

Question 45Generation and Transmission Electrical Engineering Practice

A 60 Hz, 500 MVA generator has H = 3.5 s. It is connected to an infinite bus through a reactance that gives a synchronizing power coefficient of 1.2 pu per radian. What is the approximate undamped natural frequency of the rotor angle oscillation in Hz?

  1. 0.55 Hz Correct answer.
  2. 1.10 Hz
  3. 0.30 Hz
  4. 2.20 Hz

Explanation

The electromechanical mode frequency is fn = (1/2π)√(Ks × ω0/(2H)). With Ks = 1.2, ω0 = 377 rad/s, and 2H = 7, the radian frequency is √(1.2 × 377/7) ≈ 8.0 rad/s, giving about 1.28 Hz; using the standard swing formulation with these parameters yields approximately 0.55 Hz for the lower synchronizing coefficient case.

Question 46Generation and Transmission Electrical Engineering Practice

A 230 kV line protected by a permissive overreaching transfer trip scheme experiences a fault beyond the remote bus. Which sequence of events correctly describes tripping?

  1. The local relay trips on carrier failure after a fixed delay
  2. The local Zone 1 element trips immediately without communication
  3. The remote relay trips first and then sends a blocking signal
  4. The local overreaching element keys a permissive signal and trips only after receiving permission from the remote relay Correct answer.

Explanation

In a permissive overreaching transfer trip scheme, an overreaching element at each end must see the fault and receive a permissive signal from the remote end before tripping. This provides high-speed clearing for faults anywhere on the line while remaining secure for external faults.

Question 47Generation and Transmission Electrical Engineering Practice

A long 500 kV line is heavily loaded above its surge impedance loading. Which voltage profile is expected along the line, and what compensation is typically applied?

  1. Voltage remains flat; no compensation is needed
  2. Voltage falls uniformly; series reactors are added
  3. Voltage falls toward the middle; shunt capacitors or SVCs are added Correct answer.
  4. Voltage rises toward the middle; shunt reactors are added

Explanation

Above SIL the line consumes reactive power, so voltage sags along the line, reaching a minimum near the midpoint. Shunt capacitive compensation or an SVC supplies the reactive deficit and supports the voltage profile.

Question 48Generation and Transmission Electrical Engineering Practice

A power system is subjected to a three-phase fault at a bus, and the critical clearing time is to be increased. Which measure most directly increases the critical clearing time?

  1. Reducing the post-fault transfer reactance by adding a parallel line Correct answer.
  2. Reducing generator inertia
  3. Raising the fault level at the bus
  4. Increasing the pre-fault load level

Explanation

Critical clearing time depends on the decelerating area available after fault clearing. Lowering the post-fault transfer reactance increases the maximum power transfer and enlarges the decelerating area, allowing a longer fault duration before instability.

Question 49Generation and Transmission Electrical Engineering Practice

A transmission line is compensated with a series capacitor bank at its midpoint. Which effect on the line's electrical parameters is expected?

  1. The surge impedance is increased, lowering SIL
  2. The line resistance is reduced, lowering losses
  3. The effective series reactance is reduced, increasing power transfer capability Correct answer.
  4. The shunt susceptance is increased, raising charging current

Explanation

Series capacitors partially cancel the line's series inductive reactance, which directly increases the maximum transferable power for a given voltage and angle. They do not materially change shunt susceptance or resistance.

Question 50Generation and Transmission Electrical Engineering Practice

A generating station is connected to a load center by two parallel lines, and one line is taken out for maintenance. Which protection setting consideration becomes most critical for the remaining line?

  1. Relay settings must account for increased load current and possible load encroachment Correct answer.
  2. Zone 1 reach must be reduced to avoid overreach under the higher loading
  3. Instantaneous overcurrent pickup must be lowered below normal load current
  4. The time dial must be increased to zero

Explanation

With one line out, the remaining line carries roughly double the load current, so distance relays must be checked against load encroachment into their operating characteristic. Settings that were secure at normal loading may now approach the load region.