CENEVAL EGEL Plus Ingeniería Eléctrica (EGEL Plus IELEC)

A three-phase power transformer has a nameplate rating of 50 MVA, 115 kV / 13.8 kV, with a leakage reactance of X = 0.10 pu on its own base. If the power system base is chosen as S_base,new = 100 MVA and V_base,new = 110 kV on the high-voltage side, what is the new per-unit reactance of the transformer?

• A0.2186 pu
• B0.1830 pu
• C0.0457 pu
• D0.0547 pu

In an unbalanced three-phase power circuit, the phase currents measured at a bus are Ia = 120∠0° A, Ib = 90∠-100° A, and Ic = 80∠110° A. What is the zero-sequence current component (Ia0) of this set of currents?

• A26.06∠-9.9° A
• B78.17∠-9.9° A
• C96.67∠0° A
• D0.0∠0° A

Before closing the breaker to synchronize a generator to an energized grid, which set of conditions must be satisfied between the generator and the bus?

• AEqual voltage magnitude, equal frequency, the same phase sequence, and voltages in phase…
• BGenerator voltage at least 10% above bus voltage and generator frequency exactly 2 Hz abo…
• COpposite phase sequence and a 180° phase difference so that the machines lock together
• DOnly the frequency must match; voltage and phase angle are corrected automatically after…

A 115 kV substation bus has a positive-sequence Thevenin impedance of Z1 = j0.05 pu on a 100 MVA, 115 kV base. Assuming a prefault voltage of Vf = 1.0 pu, what is the three-phase bolted short-circuit current (Isc) in symmetrical kiloamperes (kA)?

• A10.04 kA
• B17.39 kA
• C5.80 kA
• D20.00 kA

For a single line-to-ground (SLG) fault on phase A through a fault impedance Zf, how are the positive-, negative-, and zero-sequence networks connected in the symmetrical component equivalent circuit?

• AAll three sequence networks are connected in series with an impedance of 3*Zf
• BAll three sequence networks are connected in parallel with an impedance of Zf
• CThe positive and negative sequence networks are in parallel, and the zero sequence is ope…
• DThe positive and negative sequence networks are in series, and the zero sequence is in pa…

A line-to-line (L-L) bolted fault occurs between phases B and C of an unloaded synchronous generator. If Z1 = j0.15 pu, Z2 = j0.15 pu, Z0 = j0.08 pu, and prefault voltage is Vf = 1.0 pu, what is the magnitude of the subtransient fault current in phase B?

• A5.77 pu
• B3.33 pu
• C6.67 pu
• D2.63 pu

For an unloaded power system with sequence impedances Z1 = j0.20 pu, Z2 = j0.20 pu, and Z0 = j0.10 pu, a bolted double line-to-ground (DLG) fault occurs on phases B and C. What is the total fault current entering the ground (If = 3*Ia0)?

• A5.73 pu
• B3.75 pu
• C2.50 pu
• D7.50 pu

What is the zero-sequence equivalent circuit representation for a three-phase Delta-Wye transformer bank whose Wye winding has a solidly grounded neutral?

• AThe secondary (Wye) terminal is connected to the reference bus through the leakage impeda…
• BBoth primary and secondary terminals are connected directly through the leakage impedance…
• CBoth primary and secondary terminals are completely open-circuited, blocking all zero-seq…
• DThe Delta winding permits zero-sequence current to pass into the external line, but the g…

A 1,000 kVA distribution transformer has a core (no-load) loss of 1.8 kW and a full-load copper loss of 7.2 kW. At what load does it operate at maximum efficiency?

• A250 kVA
• B500 kVA
• C1,000 kVA
• D2,000 kVA

A three-phase transposed transmission line has flat horizontal conductor spacing with distance D between adjacent conductors (D_ab = D, D_bc = D, D_ca = 2D). What is the Geometric Mean Distance (GMD) of this line configuration?

• A1.26 * D
• B1.00 * D
• C1.41 * D
• D2.00 * D

Under what operating conditions does the Ferranti effect occur on an AC transmission line, and what is its primary electrical manifestation?

• AOn long, lightly loaded or open-ended transmission lines, causing the receiving-end volta…
• BOn heavily loaded transmission lines operating near thermal limits, causing severe voltag…
• CDuring symmetrical three-phase short circuits, causing high DC offset currents in the gen…
• DDuring lightning strikes, causing traveling voltage surges that reflect negatively at an…

A 400 kV, 60 Hz three-phase transmission line has a series inductance of L = 1.0 mH/km and a shunt capacitance of C = 10 nF/km. What is the Surge Impedance Loading (SIL) of this line in megawatts (MW)?

• A506 MW
• B169 MW
• C316 MW
• D160 MW

Two buses are connected by a lossless transmission link with reactance X = 0.25 pu on a 100 MVA base. Both bus voltages are held at 1.0 pu and the voltage angle difference is δ = 15° (sin 15° = 0.2588). What active power flows over the link?

• A103.5 MW
• B400.0 MW
• C386.4 MW
• D25.9 MW

In a power flow study using the Newton-Raphson method for a system with N buses, 1 Slack bus, m PV (generator) buses, and (N - 1 - m) PQ (load) buses, what is the dimension of the Jacobian matrix?

• A[2*(N - 1) - m] × [2*(N - 1) - m]
• B2*N × 2*N
• C(N - 1) × (N - 1)
• D[2*N - m] × [2*N - m]

What primary engineering assumption enables the decoupling of the P-θ and Q-V equations in the Fast Decoupled Load Flow (FDLF) method?

• ATransmission lines have a high X/R ratio, phase angle differences between adjacent buses…
• BTransmission lines have zero capacitance and infinite shunt resistance
• CAll generators have identical inertia constants and droop coefficients
• DLoad impedances remain strictly constant regardless of voltage variations

A synchronous generator has direct-axis reactances X''d = 0.12 pu (subtransient), X'd = 0.22 pu (transient), and Xd = 1.20 pu (synchronous steady-state). Which reactance governs the initial peak short-circuit current used to rate circuit breaker interrupting duty at t = 0 to 2 cycles?

• AThe subtransient reactance X''d = 0.12 pu
• BThe transient reactance X'd = 0.22 pu
• CThe synchronous reactance Xd = 1.20 pu
• DThe average of subtransient and steady-state reactance (X''d + Xd) / 2

According to international standards (IEC 60076) and Mexican practice, what is the angular phase relationship between the secondary and primary line-to-neutral voltages in a Dyn1 transformer?

• AThe low-voltage secondary voltage lags the high-voltage primary voltage by 30°
• BThe low-voltage secondary voltage leads the high-voltage primary voltage by 30°
• CThe secondary voltage is in phase (0° phase displacement) with the primary voltage
• DThe secondary voltage is in opposite phase (180° phase displacement) with the primary vol…

In the transient stability analysis of a Single Machine Infinite Bus (SMIB) system using the Equal Area Criterion, what condition determines the critical clearing angle (δ_cr)?

• AThe accelerating area (A1) during the fault is exactly equal to the maximum possible dece…
• BThe electrical power output equals mechanical power input at the instant of fault incepti…
• CThe rotor speed deviation reaches its maximum possible angular velocity at clearing
• DThe post-fault electrical power curve reaches its absolute mathematical peak

What is the primary technical reason for using bundled conductors (conductores en haz) instead of a single large conductor in extra-high-voltage (EHV) transmission lines?

• AIt increases the effective Geometric Mean Radius (GMR), lowering the surface electric fie…
• BIt significantly reduces line mechanical tension, eliminating the need for steel reinforc…
• CIt eliminates the skin effect entirely across the copper or aluminum strands at 60 Hz
• DIt increases zero-sequence impedance to block ground fault currents from reaching adjacen…

What is the primary engineering purpose of including a Delta tertiary winding in a large high-voltage Wye-Wye (Y-Y) autotransformer or power transformer?

• ATo provide a closed circulation path for third-harmonic magnetizing currents, preventing…
• BTo step down transmission voltages directly to 120/240 V residential single-phase service
• CTo eliminate the need for primary surge arresters by absorbing lightning impulses interna…
• DTo act as a mechanical damper against low-frequency seismic vibrations

A 230 kV substation bus has an equivalent positive-sequence short-circuit reactance of X_th = 0.08 pu on a 100 MVA base. What is the symmetrical short-circuit power capacity (S_sc) at this bus?

• A1,250 MVA
• B8 MVA
• C2,165 MVA
• D125 MVA

In short-circuit calculations for sizing high-voltage circuit breaker interrupting capabilities, what is the role of the system X/R ratio at the fault location?

• AA higher X/R ratio increases the DC time constant (tau = L/R), slowing the decay of the D…
• BA higher X/R ratio causes faster decay of the DC component, reducing the stress on breake…
• CThe X/R ratio only affects the symmetrical AC component, leaving the DC component unaffec…
• DA high X/R ratio converts symmetrical three-phase faults into unsymmetrical single line-t…

A 400:5 A current transformer feeds a panel ammeter that reads 3.2 A on its secondary scale. What primary current is flowing in the feeder?

• A3.2 A
• B256 A
• C80 A
• D1,280 A

According to Peek's formula for visual critical corona voltage in transmission lines, how does an increase in altitude (lower atmospheric pressure) affect the corona inception voltage (V_c)?

• AHigher altitude reduces air density (delta < 1), which lowers the dielectric breakdown st…
• BHigher altitude increases the dielectric strength of air due to cooler temperatures, incr…
• CAltitude has no effect on corona because corona inception depends exclusively on conducto…
• DHigher altitude eliminates corona completely because cosmic radiation ionizes all surroun…

On the operational capability curve (P-Q diagram) of a cylindrical-rotor synchronous generator, what boundary limits machine operation in the underexcited (absorbing reactive power) region?

• AStator core end-region heating due to axial leakage flux and the steady-state rotor angle…
• BRotor field winding thermal heating limit due to high field excitation current
• CTurbine boiler steam valve mechanical stroke limit
• DArmature winding copper I^2*R stator thermal heating limit

Under NOM-001-SEDE-2012 Article 210-19(A)(1), a branch circuit supplies a continuous commercial lighting load of 48 A. What is the minimum required ampacity of the branch circuit conductors before applying any temperature or bundling derating factors?

• A48 A
• B60 A
• C72 A
• D96 A

Six current-carrying copper conductors of size 4 AWG THHN (base ampacity 95 A at 90°C per NOM-001-SEDE-2012 Table 310-15(b)(16)) are installed in a single conduit located in an industrial room with an ambient temperature of 40°C. What is the adjusted ampacity of each conductor?

• A95.0 A
• B86.5 A
• C69.2 A
• D47.5 A

A three-phase, 480 V, 60 Hz feeder delivers a balanced load current of 150 A at a power factor of 0.85 lagging over a distance of 120 meters. The copper conductor has an AC resistance of R = 0.16 Ω/km and inductive reactance of X = 0.12 Ω/km. What is the percentage voltage drop (%VD) at the receiving end of the feeder?

• A0.88%
• B1.29%
• C2.24%
• D2.59%

A feeder is protected upstream by a 400 A molded-case circuit breaker (MCCB). According to NOM-001-SEDE-2012 Table 250-122, what is the minimum size of the copper Equipment Grounding Conductor (EGC / Conductor de puesta a tierra de equipos) required for this circuit?

• A6 AWG
• B4 AWG
• C3 AWG
• D1/0 AWG

A new commercial service entrance has three paralleled sets of 500 kcmil copper conductors per phase (total 1,500 kcmil per phase). According to NOM-001-SEDE-2012 Table 250-66, what is the minimum required size for the copper Grounding Electrode Conductor (GEC / Conductor del electrodo de puesta a tierra)?

• A2 AWG
• B3/0 AWG
• C1/0 AWG
• D250 kcmil

During a predictive-maintenance infrared survey, a bolted bus connection runs 18 °C hotter than an identical connection on another phase carrying the same load. Using the widely applied NETA maintenance testing criteria for similar components under similar loading, how should the finding be classified?

• AMajor discrepancy: repair immediately
• BPossible deficiency: warrants investigation
• CProbable deficiency: repair as time permits
• DNo deficiency: differences under 20 °C are normal

In the design of high-voltage substation grounding grids according to IEEE Std 80, what is the primary technical function of spreading a 50 mm to 100 mm (2 to 4 inch) layer of crushed rock (gravel) across the substation surface?

• ATo prevent weed growth and provide a level foundation for heavy equipment vehicles
• BTo provide a high-resistivity surface contact layer (rho_s ≈ 2,000 to 5,000 Ω·m), substan…
• CTo lower the total ground grid resistance (Rg) by providing high electrical conductivity…
• DTo act as a mechanical thermal barrier against molten oil fires in transformer containmen…

When measuring the grounding resistance of an electrode system using the three-point Fall-of-Potential method, at what theoretical percentage of the distance to the current probe (C) must the potential probe (P) be placed to eliminate mutual resistance overlap in a homogeneous soil?

• A50.0%
• B38.2%
• C61.8%
• D75.0%

According to NOM-022-STPS-2015, what is the maximum resistance to earth permitted for the electrode(s) of a lightning protection system (sistema de pararrayos)?

• A25 ohms
• B10 ohms
• C5 ohms
• D50 ohms

In high-voltage transmission substation engineering, what is the primary operational advantage of the 'Breaker-and-a-Half' (esquema de interruptor y medio) bus configuration?

• AIt requires the lowest initial capital investment and smallest land footprint of all subs…
• BIt provides high operational flexibility and reliability by allowing any circuit breaker…
• CIt requires only one single busbar and eliminates the need for disconnect switches
• DIt guarantees that a fault on either main bus results in a complete blackout of all conne…

In a Ring Bus (esquema en anillo) substation layout, what is a significant operational limitation when one circuit breaker is racked out for maintenance?

• AAll transmission lines connected to the ring must be permanently de-energized
• BThe ring is opened into a radial bus structure, meaning that a subsequent fault on any re…
• CThe substation grounding grid resistance doubles instantaneously
• DTransformer secondary voltages increase by 73% due to ferroresonance

A three-phase, 460 V, squirrel-cage induction motor has a full-load current (FLC) of 40 A per NOM-001-SEDE-2012 Table 430-250. According to Table 430-52, what is the maximum standard rating allowed for an inverse-time circuit breaker used for branch-circuit short-circuit and ground-fault protection?

• A50 A
• B70 A
• C100 A
• D125 A

According to NOM-001-SEDE-2012 Article 430-32, what is the maximum trip rating for an overload thermal relay protecting a continuous-duty motor marked with a Service Factor (SF) of 1.15?

• A115% of motor nameplate full-load current
• B125% of motor nameplate full-load current
• C140% of motor nameplate full-load current
• D175% of motor nameplate full-load current

Under NOM-001-SEDE-2012 Article 500, how is a Class I, Division 1 hazardous electrical location defined?

• AAn area where combustible dusts are present continuously under normal conditions
• BAn area where flammable vapors or gases are present only under abnormal conditions such a…
• CAn area where ignitible concentrations of flammable gases, flammable liquid-produced vapo…
• DAn area where easily ignitible fibers or flyings are handled, manufactured, or used

In external lightning protection design according to IEC 62305-3, what rolling sphere radius (R) is specified for a Class I Lightning Protection System (LPS)?

• A45 meters
• B20 meters
• C60 meters
• D100 meters

An industrial plant draws P = 450 kW at a power factor of 0.70 lagging (tan θ1 = 1.0202) from a 480 V three-phase system. What capacitor bank rating is required to raise the power factor to 0.95 lagging (tan θ2 = 0.3287)?

• A459 kVAr
• B148 kVAr
• C311 kVAr
• D113 kVAr

NOM-001-SEDE-2012 (Article 450-23) permits less-flammable liquid-insulated transformers to be installed indoors under certain conditions. What minimum fire point must the insulating liquid have to be classified as less flammable?

• A300 °C
• B150 °C
• C500 °C
• D100 °C

A utility samples the oil of its large power transformers for dissolved gas analysis every six months, trends the results, and schedules an internal inspection only when the gas generation rates exceed its alert levels. Which maintenance strategy does this describe?

• APredictive (condition-based) maintenance
• BCorrective (run-to-failure) maintenance
• CTime-based preventive maintenance
• DDesign-out maintenance

When designing a four-wire three-phase branch circuit supplying heavy non-linear loads (such as switch-mode power supplies in a data center) where high third-harmonic (triplen) currents are anticipated, why does the neutral conductor carry significant current even when phase loads are balanced?

• AThird-harmonic currents are 120° out of phase with each other and cause circulating curre…
• BThird harmonics (and other odd multiples of the third harmonic) are zero-sequence in natu…
• CThird harmonics cancel out the fundamental 60 Hz current, converting the neutral conducto…
• DThe skin effect in the neutral conductor forces high-frequency currents into the earth el…

Two 500 kVA transformers with identical voltage ratios operate in parallel. Transformer T1 has a percent impedance of 5.0% and T2 has 6.0% (each on its own base). How do they share a total load of 900 kVA?

• AT1 ≈ 490.9 kVA and T2 ≈ 409.1 kVA
• BT1 = 450 kVA and T2 = 450 kVA
• CT1 ≈ 409.1 kVA and T2 ≈ 490.9 kVA
• DT1 = 500 kVA and T2 = 400 kVA

A balanced three-phase 13.8 kV distribution feeder carries a line current of 250 A at a lagging power factor of 0.82. What are the active power (P) and reactive power (Q) delivered by the feeder?

• AP = 2,829 kW, Q = 1,975 kVAr
• BP = 4,900 kW, Q = 3,420 kVAr
• CP = 5,975 kW, Q = 4,170 kVAr
• DP = 8,487 kW, Q = 5,925 kVAr

A 200 MW synchronous generator operating on a 60 Hz grid has a turbine-governor speed droop characteristic of R = 4% (0.04 pu). If the system frequency drops by 0.12 Hz due to a sudden load increase, what is the resulting increase in generator electrical power output (ΔP)?

• A5.0 MW
• B20.0 MW
• C10.0 MW
• D2.5 MW

In Automatic Generation Control (AGC) for an interconnected balancing authority, what does the Area Control Error (ACE) equation, ACE = ΔP_tie - 10*B*Δf, represent?

• AThe total fuel consumption rate of all operating gas turbines in the control area
• BThe instantaneous active power imbalance of the local control area, measuring deviation f…
• CThe reactive power mismatch needed to regulate transmission bus voltages to 1.0 pu
• DThe thermal loading margin remaining on the critical tie-lines connecting adjacent utilit…