Transformers – Verified PYQ Authority Guide
Transformers is organised as a topic-level PYQ authority page. It brings together the strongest verified question clusters, exam/year coverage and concept-level practice so students can revise the topic without jumping through unrelated notes. 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
8 verified PYQs are currently mapped to this Topic hub. The represented years include 2025, 2026. Exam coverage currently includes Assistant Engineer (Electrical), Class-2, Road and Building Department, Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2,. 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.
- A transformer has core loss = 500 W and full-load copper loss = 500 W. 1. Maximum efficiency occurs at full load condition. 2. At half load, copper loss becomes 125 W.…
Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · Load for Maximum Efficiency
At x p.u. load, transformer output is proportional to x while copper loss is proportional to x² and iron loss remains approximately constant. The… - Consider the following statements regarding Transformer Efficiency: 1. The maximum efficiency of a transformer occurs when copper losses are equal to core losses. 2. Transformer efficiency remains constant irrespective of the load…
Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · Maximum and All-Day Efficiency
Transformer core loss is approximately constant at fixed voltage/frequency, while copper loss is I²R and therefore varies with the square of load. The competition… - Consider the following statements regarding Transformer Testing: 1. The open-circuit test is conducted to determine core losses and magnetizing current at rated voltage conditions. 2. The short-circuit test is used to determine…
Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · Open-Circuit and Short-Circuit Tests
OC and SC tests separate transformer loss components without loading the transformer fully. OC emphasizes shunt/core behavior; SC emphasizes series/leakage behavior. Key relation: OC:… - A single-phase transformer operates with primary voltage of 230 V and secondary voltage of 115 V. It supplies a load current of 4 A. Assume ideal conditions. 1. The turns ratio between…
Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · Turns Ratio Current and Power
An ideal transformer conserves apparent power and relates voltages, turns and currents inversely. Turns ratio a=230/115=2. Output power=115×4=460 W. Key relation: V1/V2=N1/N2=a; I1/I2=N2/N1=1/a; ideal… - Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Then __________
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Load Sharing and Power Factor
If two transformers have different impedance magnitudes but identical X/R ratios, their impedance angles are equal. They may share unequal magnitudes of load, but… - A 2000/1000/500 three winding transformer is to be used as auto transformer with supply of 3000V. Two loads of 1050 kVA at 3500 V and other one at 180 kVA at 1000…
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Three-Winding Autotransformer Loading
The two specified loads are 1050 kVA and 180 kVA. The total apparent power supplied to the loads is therefore 1050 + 180 =… - While conducting open circuit test and short circuit test on a transformer, status of low voltage and high voltage windings will be such that in ____________
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Test Connections
In the usual transformer tests, the open-circuit test is performed by energizing the LV side and leaving the HV side open. The short-circuit test… - What is the number of primary turns in a 200/1000V transformer if the emf per turn is 10V?
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Turns and Volts per Turn
The given transformer ratio is 200/1000 V and the emf per turn is 10 V. For the 200 V winding, N = E/(emf per…
Formula & key-relationship bank from verified solutions
Pcu(x)=x²Pcu,FL. Here Pcu(0.5)=0.25×500=125 W. Maximum η: x²Pcu,FL=Pi → x=1.At x p.u. load: Pcu=x²Pcu,FL. Maximum η when x²Pcu,FL = Pi. All-day η = output energy (kWh)/input energy (kWh).OC: P0 ≈ Pi(core). SC at rated current: Psc ≈ Pcu,FL; Zeq = Vsc/Isc; Req=Psc/Isc².V1/V2=N1/N2=a; I1/I2=N2/N1=1/a; ideal V1I1=V2I2.Z_A = |Z_A|∠θ Z_B = |Z_B|∠θ (same X/R ⇒ same θ) Current-sharing magnitudes differ, phase angles remain equal.S_total = S₁ + S₂ = 1050 + 180 = 1230 kVA
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
- At x p.u. load, transformer output is proportional to x while copper loss is proportional to x² and iron loss remains approximately constant. The given losses make the maximum-efficiency load x=sqrt(500/500)=1 p.u. Every statement follows numerically, so B…
- Transformer core loss is approximately constant at fixed voltage/frequency, while copper loss is I²R and therefore varies with the square of load. The competition between these losses creates a definite maximum-efficiency load point. Key relation: At x p.u.…
- OC and SC tests separate transformer loss components without loading the transformer fully. OC emphasizes shunt/core behavior; SC emphasizes series/leakage behavior. Key relation: OC: P0 ≈ Pi(core). SC at rated current: Psc ≈ Pcu,FL; Zeq = Vsc/Isc; Req=Psc/Isc².…
- An ideal transformer conserves apparent power and relates voltages, turns and currents inversely. Turns ratio a=230/115=2. Output power=115×4=460 W. Key relation: V1/V2=N1/N2=a; I1/I2=N2/N1=1/a; ideal V1I1=V2I2. Exam focus: Voltage ratio follows turns ratio; current ratio is inverse. Common trap:…
- If two transformers have different impedance magnitudes but identical X/R ratios, their impedance angles are equal. They may share unequal magnitudes of load, but the load-current phase angles are the same, so both operate at the same power…
Exam tips already validated in SRO solutions
- If core loss equals full-load copper loss, maximum efficiency is at full load—an instant result.
- Remember: power transformer → ordinary efficiency; distribution transformer → all-day efficiency is frequently tested.
- OC → rated voltage, small current, core loss. SC → rated current, small voltage, copper loss.
- Voltage ratio follows turns ratio; current ratio is inverse.
- Separate load-sharing magnitude from power-factor angle.
Common mistakes to avoid
- Scaling copper loss linearly with load instead of with load squared.
- Saying efficiency is constant because transformer has no moving parts.
- Confusing “rated voltage” in OC with “rated current”; the OC current is deliberately small.
- In an ideal transformer input power equals output power.
- Different percentage impedance does not automatically mean different power factor if impedance angles are identical.
Topic and concept coverage
Mapped topic labels include Transformers. The concept trail includes Load for Maximum Efficiency, Load Sharing and Power Factor, Maximum and All-Day Efficiency, Open-Circuit and Short-Circuit Tests, Test Connections, Three-Winding Autotransformer Loading, Turns and Volts per Turn, Turns Ratio Current and Power. 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 Machines, Autotransformer Applications, EMF Equation, Ideal Transformer, No-load Operation, OC and SC Tests, Electrical Engineering, Transformer Efficiency, Ideal vs Practical No-load Current, Load for Maximum Efficiency, Load Sharing and Power Factor. 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.