--- title: "Load scheduling and bus arrangement" subject: "Industrial Power Distribution and Illumination" chapter: 10 key: "semester_6/industrial_power_distribution_and_illumination:load-scheduling-bus-arrangement" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/load-scheduling-bus-arrangement site: BCT Engineering --- # Load scheduling and bus arrangement Industrial Power Distribution and Illumination · Chapter 10: Electrical Energy Audit in Industry - Asked in: 2068 Magh (old course), 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/load-scheduling-bus-arrangement - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-10 ## Question Explain the importance of load scheduling in an industry. Discuss the bus arrangement system in an industry and explain with reason which system is more reliable. ## Short answer Load scheduling flattens demand, reducing kVA charges, losses, and overloading. Bus arrangements: single bus (least reliable), sectionalised single bus, main-and-transfer, double bus. Double bus is most reliable because any bus can be isolated without interrupting supply. ## Answer #### Importance of load scheduling **Load scheduling** means planning when each major load or process runs so that the plant's maximum demand stays low and the load curve is flat. 1. **Lower demand (kVA) charges** – the monthly demand charge is based on the highest demand; staggering large motors, furnaces and compressors lowers it. 2. **Benefit from time-of-day tariff** – flexible loads (pumping, batch processes, charging) moved to off-peak night hours use cheaper energy. 3. **Higher load factor** – better use of transformer, cables and DG set capacity; postpones new investment. 4. **Avoids overloading and voltage dips** – motors are not started all at once. 5. **Lower losses** – a flat load has lower I²R loss than a peaky load for the same kWh. 6. **Helps the utility reduce system peak** and load shedding. #### Bus arrangements in industrial distribution 1. **Single bus system** – all incoming supplies and outgoing feeders on one bus. - Simple, cheap, easy to operate. - A bus fault or bus maintenance shuts down the whole plant. Least reliable. 2. **Single bus with bus sectionaliser** – bus split into two sections by a circuit breaker (bus coupler), each fed by its own transformer. - A fault on one section is isolated; the other continues. Loads can be shared between sections. 3. **Main and transfer bus** – a transfer bus with a transfer breaker allows any feeder breaker to be taken out for maintenance without interrupting that feeder. 4. **Double bus (double breaker or double bus single breaker)** – two main buses; each circuit can be connected to either bus through isolators/breakers. - Bus maintenance or bus fault: loads transferred to the other bus. - Most flexible and reliable, but costly. 5. **Ring main bus** – bus forms a closed ring with breakers between circuits; each circuit fed from two sides. ```text Single bus with sectionaliser T1 T2 | | =X===[CB]===X= (bus coupler) | | | | F1 F2 F3 F4 Double bus ==== Bus 1 =========== ==== Bus 2 =========== | | | | CB CB CB CB (each can select bus 1 or 2) F1 F2 F3 F4 ``` #### Which is more reliable and why The **double bus (especially double bus–double breaker) arrangement is the most reliable**, because: - any bus can be taken out for maintenance or isolated after a fault without loss of supply; - loads can be divided between buses so a fault affects only part of the plant; - every circuit has an alternate path. For most medium industries, a **sectionalised single bus fed from two transformers** is chosen as a good compromise: it gives continuity for essential loads at much lower cost than a double bus. The single bus without sectionalising is the least reliable. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does load scheduling aim to do? A. Run all large loads at the same time B. Plan when loads run so maximum demand stays low and the load curve is flat C. Increase connected load D. Reduce energy tariffs by law Answer: B. Staggering loads reduces the highest demand (lowering kVA charges), raises load factor and avoids overloads. (Key point: Meaning of load scheduling) 2. How does load scheduling use a time-of-day tariff? A. It shifts flexible loads to off-peak night hours with cheaper energy B. It shifts loads to the peak hours C. It removes the demand charge D. It increases power factor Answer: A. Flexible loads like pumping or batch processes moved to off-peak hours use cheaper energy. (Key point: Time-of-day tariff) 3. Why is a single bus system the least reliable? A. It is too costly B. It has two buses to maintain C. A bus fault or bus maintenance shuts down the whole plant D. It cannot supply feeders Answer: C. All feeders are on one bus, so any bus fault or maintenance outage interrupts every load. (Key point: Single bus weakness) 4. Why is the double bus arrangement most reliable? A. It uses fewer breakers B. It is the cheapest C. It has a single path to each load D. Either bus can be isolated and loads moved to the other, so each circuit has an alternate path Answer: D. A bus can be taken out for maintenance or after a fault without loss of supply, although cost is higher. 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