--- title: "Specification for procuring a generator" subject: "Power Plant Design" chapter: 4 key: "semester_8/power_plant_design:generator-specification" source: https://www.bctengineer.com/q/semester_8/power_plant_design/generator-specification site: BCT Engineering --- # Specification for procuring a generator Power Plant Design · Chapter 4: Electric System Design of a Power Plant - Asked in: 2070 Bhadra, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/generator-specification - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-4 ## Question Develop a typical specification while procuring a generator to be used in power plant design. ## Short answer A specification covers rating (e.g., 12.5 MVA, 11 kV, 0.85 pf, 600 rpm), standards (IEC 60034), electrical parameters (X''d ≤0.22 pu, SCR ≥1.0, efficiency ≥97.5%), mechanical design (enclosed cooling, bearings, RTDs), excitation (static with AVR, ceiling 1.6 pu), and required tests, documents, spares, and warranty. ## Answer A **generator specification** is the technical document, part of the tender (bid) documents, that tells manufacturers exactly what generator the project needs. It covers the rating, design, performance, standards, tests and supply scope, so that bids can be compared on equal terms and the delivered machine fits the plant. A typical specification for a hydro generator (example: a 12.5 MVA unit) is set out below. #### 1. General and standards - Scope: design, manufacture, testing at works, packing, transport to site, erection supervision and commissioning of **2 sets** of three-phase synchronous generators with excitation and accessories. - Standards: **IEC 60034-1** (rating and performance), IEC 60034-33 (hydro generators), IEC 60085 (insulation), IEC 60034-4 (test methods). - Site conditions: altitude (e.g. 1200 m above MSL), ambient temperature (0–40 °C), humidity, seismic zone (Nepal: horizontal acceleration about 0.3 g), indoor powerhouse. #### 2. Rating and electrical data | Item | Typical value | |---|---| | Type | 3-phase, salient-pole synchronous, vertical shaft | | Rated output | 12.5 MVA at 0.85 pf lagging (10.625 MW) | | Rated voltage / range | 11 kV ± 5% | | Frequency | 50 Hz ± 2% (Nepal) | | Rated speed / runaway speed | 600 rpm (10 poles) / withstand runaway for 15 min | | Connection | Star, neutral brought out | | Sub-transient reactance $X''_d$ | ≤ 0.22 pu (unsaturated) | | Short-circuit ratio | ≥ 1.0 | | Efficiency | ≥ 97.5% at rated load (guaranteed, with penalty) | | Insulation class / temperature rise | Class F insulation, Class B temperature rise | | Inertia constant H / GD² | As required by governor stability, e.g. H ≥ 2.5 s | | Capability | Continuous at rated MVA from 0.85 lag to 0.95 lead pf | | Overload / unbalance | 10% for 1 h; $I_2$ continuous ≥ 10%, $I_2^2t$ ≥ 20 s | | Harmonics, TIF | THD of voltage < 5%, TIF as per IEC | #### 3. Mechanical and construction - Stator: laminated low-loss steel, class F VPI insulated winding, RTDs (6 per phase) in slots. - Rotor: salient poles with damper winding, designed for runaway speed. - Bearings: thrust and guide bearings with oil coolers and RTDs; insulated against shaft currents. - Cooling: closed-circuit air with air-to-water coolers (one spare cooler), or open ventilation for small sets. - Brakes and jacks, space heaters, fire protection (CO₂ or water spray), vibration probes. - Noise ≤ 85 dB(A) at 1 m. #### 4. Excitation and auxiliaries - Static (or brushless) excitation with digital AVR, PSS, limiters (OEL, UEL, V/Hz), field flashing, field breaker. - Ceiling voltage ≥ 1.6 pu, response time < 0.1 s. - Neutral grounding equipment (NGT with resistor), surge arresters and surge capacitors, CTs and PTs, terminal and neutral cubicles. #### 5. Tests, documents and commercial items - **Type and routine tests** at works: winding resistance, insulation resistance and PI, HV withstand, open- and short-circuit characteristics, reactances, heat run, overspeed, vibration. - Site tests: dry-out, polarisation index, HV test, commissioning tests (load rejection). - Documents: guaranteed technical particulars (GTP), drawings, O&M manuals, capability curve, test reports. - Spares (one spare pole, a set of bearing pads, one cooler), tools, training. - Delivery period, warranty (e.g. 24 months after commissioning), guaranteed efficiency with **liquidated damages** for shortfall, payment terms and price (FOB/CIF). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the purpose of a generator specification in tender documents? A. To fix the price B. To tell manufacturers exactly what is needed so bids can be compared equally C. To list only the spares D. To describe the site only Answer: B. It defines rating, design, performance, standards, tests and scope. (Key point: Purpose of specification) 2. Which standard is cited for rating and performance of rotating machines? A. IEC 62271-100 B. IEC 60034-1 C. IEC 60076 D. IEEE 485 Answer: B. IEC 60034-1 covers rating and performance; 60076 is transformers, 62271 breakers. (Key point: Standards) 3. For a 50 Hz hydro generator of 10 poles, what is the rated speed? A. 300 rpm B. 500 rpm C. 600 rpm D. 750 rpm Answer: C. N = 120f/p = 120 x 50 / 10 = 600 rpm. (Key point: Speed calculation) 4. What is the purpose of guaranteed efficiency with liquidated damages? A. To pay bonus always B. To penalise the supplier if the delivered efficiency falls short C. To fix the delivery date D. To set voltage Answer: B. Shortfall in guaranteed performance leads to a penalty. (Key point: Liquidated damages) ## Close variants set in other exams - [Specification for procuring a power transformer](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Apower-transformer-specification) — Power Plant Design, chapter 4, asked 4× ## Related in Power Plant Design - [Design: 245 m head plant, standby generator](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2073-245m-standby) — Power Plant Design, chapter 4, asked 14× - [Design: 260 m head plant, generator lead](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2078-260m-generator-lead) — Power Plant Design, chapter 4, asked 5× - [Design: 250 m head plant at Q25%](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2072-250m-q25) — Power Plant Design, chapter 4, asked 14× - [Design: 200 m head plant, bus MVA levels](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2070-200m-bus-mva) — Power Plant Design, chapter 4, asked 14× - [Design: 230 m head plant, 20 km line](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2070-230m-20km) — Power Plant Design, chapter 4, asked 14× - [Design: 250 m head plant, 66 kV double circuit](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adesign-2071-250m-0-92mh) — Power Plant Design, chapter 4, asked 13×