Power System Protection – Verified PYQ Authority Guide
Power System Protection 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
13 verified PYQs are currently mapped to this Sub Subject hub. The represented years include 2026, 2024. Exam coverage currently includes Additional Assistant Engineer (Electrical), Supervisor Instructor Electrical Group, Vidyut Sahayak (Junior Engineer - Electrical). 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.
- To prevent an alternator from operating in motor mode due to prime mover failure, a/an __________ relay is used.
Additional Assistant Engineer (Electrical) · 2026 · Reverse Power Relay
A — Reverse Power relay. It detects active power flowing from the energized system into the alternator when the prime mover can no longer… - Which protection is employed for generator rating from 1 MVA to 5 MVA?
Vidyut Sahayak (Junior Engineer - Electrical) · 2024 · Balanced Earth-Fault Protection for Small Generators
C — Balanced earth fault. This is the protection scheme associated with the 1–5 MVA generator range in the supplied paper. - In a Buchholz relay, what does the mercury switch attached to the upper float do?
Additional Assistant Engineer (Electrical) · 2026 · Upper Float Alarm
Slow internal faults generate gas that accumulates in the Buchholz chamber and displaces oil, causing the upper float to fall. The upper-float mercury switch… - What is the purpose of the Time Multiplier Setting (TMS) in an overcurrent relay?
Additional Assistant Engineer (Electrical) · 2026 · Time Multiplier Setting (TMS)
TMS scales the operating time of an inverse-time overcurrent relay without changing its pickup-current setting. A lower TMS gives faster operation for the same… - In a circuit breaker, current interruption is achieved when the arc is:
Additional Assistant Engineer (Electrical) · 2026 · Cooling and De-ionization
Successful interruption requires the arc path to lose conductivity around current zero. Cooling and de-ionization remove energy and charged particles, rapidly increasing dielectric strength… - What is the primary function of a protective relay in an electrical system?
Additional Assistant Engineer (Electrical) · 2026 · Fault Detection and Tripping
A protective relay continuously evaluates electrical quantities to recognize abnormal or fault conditions. When its operating criterion is met, it sends a trip command… - In an electric arc, since the arc path is purely resistive, the arc voltage is:
Additional Assistant Engineer (Electrical) · 2026 · Arc Voltage-Current Phase Relation
For a purely resistive arc path, voltage and current have no reactive phase displacement. Therefore the arc voltage is in phase with the arc… - In the context of transformer protection, which of the following protection schemes is precisely designed to distinguish earth faults within the transformer windings, mainly in the star-connected primary side?
Additional Assistant Engineer (Electrical) · 2026 · Restricted Earth Fault Protection
REF protection is a sensitive unit protection for earth faults within the defined zone of a star-connected winding and its neutral CT arrangement. It…
Formula & key-relationship bank from verified solutions
With export taken as positive: P_export > 0 during generation; P_export < 0 during motoring.KEY RELATION / LOGIC: Under healthy or external-fault conditions, the residual of the phase CT currents balances the neutral CT current; an internal earth fault produces differential relay current.I_sc ≈ V_th / Z_th
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
- A — Reverse Power relay. It detects active power flowing from the energized system into the alternator when the prime mover can no longer supply sufficient mechanical power.
- C — Balanced earth fault. This is the protection scheme associated with the 1–5 MVA generator range in the supplied paper.
- Slow internal faults generate gas that accumulates in the Buchholz chamber and displaces oil, causing the upper float to fall. The upper-float mercury switch then closes the alarm circuit; severe oil surge operates the trip element.
- TMS scales the operating time of an inverse-time overcurrent relay without changing its pickup-current setting. A lower TMS gives faster operation for the same multiple of pickup current.
- Successful interruption requires the arc path to lose conductivity around current zero. Cooling and de-ionization remove energy and charged particles, rapidly increasing dielectric strength between the contacts and preventing arc re-establishment.
Exam tips already validated in SRO solutions
- Reverse power protection is commonly associated with ANSI device function 32. Focus on the direction of real power, not the direction of reactive power.
- Generator protection questions often distinguish selective differential/earth-fault schemes from backup time-graded overcurrent schemes.
- Buchholz: upper float = alarm; lower/surge element = trip.
- Plug setting sets pickup; TMS sets time.
- Extinguish arc = cool + de-ionize + restore dielectric strength.
Common mistakes to avoid
- Do not interpret “reverse power” as reversed phase sequence, reverse rotor rotation or reactive-power reversal.
- Assuming ‘balanced earth fault’ means the fault itself is balanced; the word refers to the protection scheme’s current balance.
- Alarm operation is associated with the float falling as gas accumulates, not rising.
- Do not confuse TMS with current/pickup setting.
Topic and concept coverage
Mapped topic labels include Protective Relays, Circuit Breakers, Generator Protection, Transformer Protection, Fault Analysis, Overcurrent Protection. The concept trail includes Arc Voltage, Arc Voltage-Current Phase Relation, Balanced Earth-Fault Protection for Small Generators, Cooling and De-ionization, Directional Response of Relay, Electromagnetic Operating Principle, Fault Detection and Tripping, Impedance-based Transmission Line Protection. 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, Circuit Breakers, Circuit Breakers, Circuit Breakers, Circuit Breakers, Circuit Breakers, Protective Relays, Generator Protection, Transformer Protection, Arc Voltage, Arc Voltage-Current Phase Relation. 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.