--- title: "Electrical energy; classes of consumers and demand" subject: "Utilization of Electrical Energy" chapter: 1 key: "semester_7/utilization_of_electrical_energy:electrical-energy-consumer-classes" source: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/electrical-energy-consumer-classes site: BCT Engineering --- # Electrical energy; classes of consumers and demand Utilization of Electrical Energy · Chapter 1: Introduction - Asked in: 2079 Baisakh, 8 marks; 2073 Shrawan (asked 2 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/electrical-energy-consumer-classes - Whole chapter: https://www.bctengineer.com/md/semester_7/utilization_of_electrical_energy/chapter-1 ## Question What do you mean by electrical energy? Explain the different class of electrical consumers and their demand. ## Short answer Electrical energy is the work done by electric power over time, measured in kWh. Main consumer classes: domestic (low load factor, evening peak, 230/400 V), commercial (medium load, daytime peak), industrial (high load factor, 400 V to 132 kV), agricultural (seasonal), and public services like street lighting. Their distinct demand patterns guide system planning and tariff design. ## Answer **Electrical energy** is the energy carried by the flow of electric charge, i.e. the work done by electric power over time: $E = P \times t$, measured commercially in kilowatt-hours (kWh, a "unit"). It is produced by converting other forms (hydro, thermal, solar, wind, nuclear), transmitted over lines, and converted back at the consumer into mechanical work (motors), heat, light, sound or chemical energy. #### Classes of electrical consumers and their demand Utilities group consumers by the nature of their use, load pattern and supply voltage. The main classes (also the basis of NEA tariff categories) are: **1. Domestic (residential) consumers** - Loads: lighting, fans, TV, refrigerator, water heater, induction cooker, iron, pumps. - Demand: small connected load (typically 0.5 to 10 kW), single-phase 230 V (three-phase 400 V for large houses). - Peak in the evening (about 5 to 10 pm); low load factor (about 10 to 20 %), high diversity. **2. Commercial consumers** - Shops, offices, hotels, hospitals, banks, malls, cinemas. - Loads: lighting, air-conditioning, lifts, computers. - Demand: medium; peak during working hours; load factor about 25 to 40 %; supplied at 400 V or 11 kV. **3. Industrial consumers** - **Small industries** (up to about 50 kW): 400 V three-phase. - **Medium industries** (about 50 kW to 1 MW or more): 11 kV. - **Large industries** (MW range: cement, steel, paper): 33 kV, 66 kV or 132 kV. - Loads: motors (largest share), furnaces, welding, electrolysis. - Demand: large; high load factor (60 to 80 % for continuous-process plants); reactive power demand due to induction motors. **4. Agricultural (irrigation) consumers** - Pumps for irrigation, agro-processing. - Demand: seasonal (dry season), low load factor. **5. Public services** - **Street lighting**: night only, fixed hours; predictable load. - **Water supply and sewage pumping**: fairly continuous. - **Traction** (trolley bus, electric railway, EV charging stations): fluctuating load. **6. Others**: temples and religious places, community consumers, government institutions, bulk supply to other utilities. | Class | Typical voltage | Load factor | Peak time | |---|---|---|---| | Domestic | 230/400 V | Low | Evening | | Commercial | 400 V / 11 kV | Medium | Day | | Industrial | 400 V to 132 kV | High | Day/continuous | | Agricultural | 400 V / 11 kV | Low, seasonal | Dry season | | Street light | 230/400 V | About 45-50 % | Night | ```text Load (MW) | industrial ______________ | ____/~~~~~~~~~~~~~\ /\ <- domestic |__/ \______/ \_ evening peak +---------------------------------------> hour 0 6 12 18 24 ``` Knowing each class's demand helps the utility forecast load, size generation and network, set tariffs, and apply demand side management to flatten the evening peak. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Electrical energy used commercially is measured as: A. E = P x t in kWh (unit) B. E = V / I in ohm C. E = P / t in kW D. E = I x t in coulomb Answer: A. Energy is power multiplied by time and is billed in kilowatt-hours. (Key point: Definition of electrical energy) 2. Which describes domestic consumer demand? A. High load factor of 60-80 %, supplied at 33 kV B. Seasonal, dry-season demand C. Small connected load, evening peak and low load factor D. Night-only fixed-hour load Answer: C. Domestic loads are small, peak about 5-10 pm and have a low load factor (about 10-20 %). (Key point: Domestic demand pattern) 3. Which statement about industrial consumers is correct? A. They are all supplied at 230 V single-phase B. Large industries are supplied at 33, 66 or 132 kV and have high load factors, with reactive demand from induction motors C. They have the lowest load factor of all classes D. Their load is only lighting Answer: B. Industry has large demand, high load factor for continuous plants, and motor reactive power demand. (Key point: Industrial consumers) 4. Why does a utility study each class's demand? A. To forecast load, size generation and network, set tariffs and flatten the evening peak by DSM B. To increase the evening peak C. To remove all industrial loads D. To avoid metering Answer: A. Knowing class demand supports forecasting, planning, tariffs and demand side management. 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