Power System – Verified PYQ Authority Guide
Power System is a sub-subject authority hub. It is designed to expose the important topic/concept clusters represented by verified SRO PYQs and guide students from broad revision into the exact solved questions that support each area. Every factual learning cue below is drawn from the existing verified, published and approved English PYQ corpus or from its Knowledge Graph relationships; the hub does not invent unsupported technical claims.
PYQ evidence snapshot
14 verified PYQs are currently mapped to this Sub Subject hub. The represented years include 2025. Exam coverage currently includes Assistant Engineer (Electrical), Class-2, Road and Building Department. Subject context includes Electrical Engineering. These values come from live mappings and can expand automatically when new verified PYQs are added.
Most useful verified PYQs to solve first
Start with the actual questions rather than memorising a generic note. The links below are ranked from the mapped corpus using repeat history and editorial quality, while the complete explanation stays on the individual question page.
- __________ is the normal length of the cable sample used for testing.
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Cable Sample Length for Tests
For laboratory/factory tests that require a representative cable section while remaining practical to handle, a normal sample length is in the range of about… - How the sag at higher stages can be reduced in a voltage multiplier circuit?
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Voltage Multiplier Sag Reduction
In a Cockcroft-Walton multiplier, voltage sag/ripple becomes more severe toward the higher-output stages because charging currents pass through preceding capacitors. Increasing capacitance in the… - HVDC LCCs have ______________
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Degrees of Freedom in LCC HVDC
A line-commutated converter is fundamentally controlled through its firing angle, giving one principal control degree of freedom per converter bridge for steady-state DC voltage/current… - If all the sequence voltages at the fault point in a power system are equal, then fault is __________
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Sequence Voltages for Fault Types
In a line-to-line-to-ground (LLG) fault, positive-, negative- and zero-sequence networks are all involved and their sequence voltages at the fault point are equal because… - An isolated generator is connected to a turbine with its continuous maximum power of 20 MW, 50 Hz. Generator is connected with two loads of 8 MW, each operates at 50 Hz.…
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Isolated Generator Frequency with Droop
The two existing loads total 16 MW. Adding 6 MW raises demand to 22 MW, but the turbine can continuously supply only 20 MW,… - A single−phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The additional reactive power (in VAR) to be supplied by…
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Reactive Power Compensation of Single-Phase Motor
The motor apparent power is S=VI=400×31.7=12.68 kVA. At pf=0.7, real power is 8.876 kW and reactive power is Q=S√(1−0.7²)≈9.06 kVAR. For full correction to… - The neutral of the three phase 20 MVA, 11 kV alternator is earthed through a resistance of 5 ohms. The relay is set to operate when there is an out of balance…
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Neutral Earthing Resistance and Relay Setting
First refer the relay setting through the CT ratio: 100/5 = 20, so a 1.5 A relay pickup corresponds to 30 A primary residual… - A three−phase transformer having a line voltage ratio of 400/33000 V is connected in the star-delta. The CTs on the 400V side have a CT ratio of 1000/5. What must be the…
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · CT Ratio Matching for Star-Delta Transformer
Transformer differential protection requires the CT secondary currents presented to the relay to compensate for the transformer ratio and phase-connection effects. Using the given…
Formula & key-relationship bank from verified solutions
Typical laboratory cable specimen: order of metres, not hundreds of metres.For multiplier ladders, load-dependent ripple/sag is approximately proportional to: I/(fC) Larger C ⇒ smaller ripple/sagIdeal 6-pulse bridge: V_d = V_d0 cosα − commutation drop Main controllable variable: αLLG fault condition at fault point: V₀ = V₁ = V₂ (with current relations determined by the fault impedance)5% droop span = 0.05×50 = 2.5 Hz Droop slope = 2.5 Hz / 20 MW = 0.125 Hz/MW Initial load = 8+8 = 16 MW New demand = 16+6…S = VI = 400 × 31.7 = 12.68 kVA P = S cosφ = 12.68 × 0.7 = 8.876 kW sinφ = √(1−0.7²) ≈ 0.71414 Q = S sinφ…
Use these as revision triggers and open the linked PYQ before applying a formula numerically; variable definitions and assumptions belong to the exact solved question.
Core ideas repeatedly reinforced by the solved corpus
- For laboratory/factory tests that require a representative cable section while remaining practical to handle, a normal sample length is in the range of about 50 cm to 10 m, matching the keyed option.
- In a Cockcroft-Walton multiplier, voltage sag/ripple becomes more severe toward the higher-output stages because charging currents pass through preceding capacitors. Increasing capacitance in the higher stages is one effective grading measure to reduce the voltage sag there, which…
- A line-commutated converter is fundamentally controlled through its firing angle, giving one principal control degree of freedom per converter bridge for steady-state DC voltage/current regulation. Unlike VSC converters, an LCC cannot independently control active and reactive power.
- In a line-to-line-to-ground (LLG) fault, positive-, negative- and zero-sequence networks are all involved and their sequence voltages at the fault point are equal because the three sequence networks meet at a common fault-point voltage.
- The two existing loads total 16 MW. Adding 6 MW raises demand to 22 MW, but the turbine can continuously supply only 20 MW, leaving a 2 MW deficit beyond its headroom. With 5% droop on a 50…
Exam tips already validated in SRO solutions
- Do not generalize this broad range to every IEC/IS test; specific standards can prescribe exact dimensions.
- Use the official final key rather than the provisional highlight for revised questions.
- Keep converter technology in mind before answering 'degrees of freedom'.
- Memorize network interconnections, not just fault names.
- An isolated governor with droop does not restore frequency exactly to 50 Hz without secondary control.
Common mistakes to avoid
- Choosing above 100 m as though a factory sample were an installed feeder length.
- Decreasing capacitance when trying to reduce sag.
- Assigning two independent P and Q controls to a thyristor LCC as if it were a VSC.
- Confusing equal sequence currents of an LG fault with equal sequence voltages of an LLG fault.
- Applying 5% directly to the 2 MW load instead of to rated power/frequency.
Topic and concept coverage
Mapped topic labels include High Voltage Engineering, Fault Analysis, HVDC Transmission, Protection, Load Frequency Control, Power Factor Correction, Transmission Lines. The concept trail includes Cable Sample Length for Tests, CT Ratio Matching for Star-Delta Transformer, Degrees of Freedom in LCC HVDC, Isolated Generator Frequency with Droop, Neutral Earthing Resistance and Relay Setting, Open-Pipe Node Spacing, Partial Discharge in Bushings, Reactive Power Compensation of Single-Phase Motor. Use these labels as a revision map: move from the broad area to the narrow concept, solve a verified PYQ, inspect the detailed reasoning, and then attempt another question from the same cluster.
Knowledge Graph navigation
Continue with Electrical Engineering, Fault Analysis, Fault Analysis, Fault Analysis, Fault Analysis, Fault Analysis, High Voltage Engineering, Cable Sample Length for Tests, CT Ratio Matching for Star-Delta Transformer, CT Ratio Matching for Star-Delta Transformer, Defect Localization in Cable Insulation. These are canonical SRO entity links based on the Knowledge Graph and shared question mappings, not keyword-stuffed tag pages.
How to revise this authority page efficiently
- Solve before reading: answer a mapped PYQ first.
- Read the exact explanation: verify the correct principle, formula, distractor logic and common mistake on that question page.
- Move one level in the graph: use the closest concept/sub-topic/topic link rather than opening unrelated content.
- Reattempt: solve another verified PYQ from this hub and check whether the same error repeats.
Quality scope: this page is automatically maintained from SRO’s verified mapped corpus. It enriches one canonical authority URL instead of generating multiple near-duplicate pages for keyword variants. Manual authority articles are never overwritten by the automated engine.