Skip to main content

Specification for procuring a generator

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.

Develop a typical specification while procuring a generator to be used in power plant design.

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

ItemTypical value
Type3-phase, salient-pole synchronous, vertical shaft
Rated output12.5 MVA at 0.85 pf lagging (10.625 MW)
Rated voltage / range11 kV ± 5%
Frequency50 Hz ± 2% (Nepal)
Rated speed / runaway speed600 rpm (10 poles) / withstand runaway for 15 min
ConnectionStar, neutral brought out
Sub-transient reactance Xd′′X''_d≤ 0.22 pu (unsaturated)
Short-circuit ratio≥ 1.0
Efficiency≥ 97.5% at rated load (guaranteed, with penalty)
Insulation class / temperature riseClass F insulation, Class B temperature rise
Inertia constant H / GD²As required by governor stability, e.g. H ≥ 2.5 s
CapabilityContinuous at rated MVA from 0.85 lag to 0.95 lead pf
Overload / unbalance10% for 1 h; I2I_2 continuous ≥ 10%, I22tI_2^2t ≥ 20 s
Harmonics, TIFTHD 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).

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Power Plant Design chapter 4 questions →