--- title: "Temperature rise of machine field winding" subject: "Basic Electrical Engineering" chapter: 1 key: "semester_1/basic_electrical_engineering:field-winding-temperature-rise-160-185" source: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/field-winding-temperature-rise-160-185 site: BCT Engineering --- # Temperature rise of machine field winding Basic Electrical Engineering · Chapter 1: General Electric System - Asked in: 2068 Chaitra, 6 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/field-winding-temperature-rise-160-185 - Whole chapter: https://www.bctengineer.com/md/semester_1/basic_electrical_engineering/chapter-1 ## Question The temperature rise of the machine field winding was determined by the measurement of the winding resistance at 20°C the field winding resistance was 160 Ohm(Ω). After running the machine for some hours at full load the resistance is 185 Ω. If the temperature coefficient of resistance of the copper winding is 4.3 × 10⁻³/°C at 0°C. Determine the temperature rise of the machine. ## Short answer Find R0 = R20/(1+α0×20) = 147.33 Ω. Hot temperature t from R_hot = R0(1+α0 t) gives t = 59.46°C. Temperature rise = 59.46−20 = 39.46°C ≈ 39.5°C. ## Answer Copper resistance rises with temperature, so the rise can be found from the resistance values. #### Data R₂₀ = 160 Ω, R_hot = 185 Ω, α₀ = 4.3 × 10⁻³ per °C at 0°C #### Step 1: Resistance at 0°C R₂₀ = R₀ (1 + α₀ × 20) 160 = R₀ (1 + 0.086) = 1.086 R₀ R₀ = 147.33 Ω #### Step 2: Hot temperature R_t = R₀ (1 + α₀ t) 185 = 147.33 (1 + 0.0043 t) 1 + 0.0043 t = 1.2557 t = 59.46°C #### Step 3: Temperature rise Rise = 59.46 − 20 = 39.46°C **Answer: Temperature rise ≈ 39.5°C (final temperature ≈ 59.5°C)** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. alpha is given at 0 degC while 160 ohm is measured at 20 degC. What is done first? A. Use 160 ohm directly as R0 B. Find R0 from 160 = R0 (1 + 20 alpha0), giving 147.33 ohm C. Subtract 20 from 160 D. Divide 185 by 160 to get the temperature Answer: B. The formula Rt = R0 (1 + alpha0 t) needs the resistance at 0 degC. (Key point: Reference) 2. The hot temperature from 185 = 147.33 (1 + 0.0043 t) is: A. 20 degC B. 39.5 degC C. 59.5 degC D. 80 degC Answer: C. 1 + 0.0043 t = 1.2557, so t = 59.46 degC. (Key point: Hot temperature) 3. The temperature rise of the machine is: A. 59.5 degC B. 20 degC C. 25 degC D. 39.5 degC Answer: D. Rise = 59.46 - 20 = 39.46 degC, measured from the starting 20 degC. (Key point: Rise) ## Related in Basic Electrical Engineering - [Field winding final working temperature](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Adc-motor-field-winding-temperature) — Basic Electrical Engineering, chapter 1 - [Temperature rise from resistance change](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Acoil-resistance-temperature-rise-100-124) — Basic Electrical Engineering, chapter 1 - [Temperature coefficient of resistance](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Atemperature-coefficient-resistance-wire-4-6) — Basic Electrical Engineering, chapter 1 - [Temperature coefficient and effect on resistance](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Atemperature-coefficient-effect-on-resistance) — Basic Electrical Engineering, chapter 1 - [Transformer coil temperature and power rating](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Atransformer-coil-temperature-rise) — Basic Electrical Engineering, chapter 1 - [Copper and iron conductors current ratio](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_engineering%3Acopper-iron-parallel-current-division) — Basic Electrical Engineering, chapter 1 ## Related in other subjects - [Machine temperature after one hour of heating](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Amachine-temperature-after-hour) — Electric Machine Design, chapter 2 - [Temperature rise and tubes for 500 kVA transformer](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atank-tubes-500kva-single-phase) — Electric Machine Design, chapter 3, asked 2× - [Full-load heat run and 50% overload time](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Afull-load-overload-20-32) — Electric Machine Design, chapter 2 - [Shunt motor speed after load reduced by 20%](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Adcm-shunt-load-reduced-20) — Electrical Machines, chapter 4