JNTU B.Tech IV ELECTRICAL DISTRIBUTION SYSTEMS Previous Question Paper (September - 2022 - R16)

The secondary distribution system is designed to provide reliable, safe, and efficient power to end-users at utilization voltages, typically 400V/230V. The design practice involves the following key considerations:

• Voltage Regulation: The system is designed to maintain voltage within specified limits (usually ±5% of nominal) at the consumer terminals. This is achieved by selecting appropriate conductor sizes to minimize voltage drop and optimizing the location of distribution transformers.
• Transformer Sizing and Placement: Distribution transformers are placed at the load center of a group of consumers to minimize the length of low-voltage secondaries. Sizing is based on the connected load, diversity factor, and expected load growth.
• Circuit Configuration: Common configurations include radial systems, which are simple and economical, or banked secondary systems, which provide better voltage regulation and reliability by interconnecting transformer secondaries.
• Conductor Selection: Conductors are chosen based on current-carrying capacity (ampacity) and mechanical strength. Aerial bundled cables (ABC) are widely used in modern practice to improve safety and reduce faults.
• Protection: Each secondary circuit is protected by fuses or circuit breakers at the transformer secondary terminals to isolate faults and prevent damage to the distribution infrastructure.

Electrical loads are classified based on their nature, usage patterns, and impact on the distribution system. The primary categories and their characteristics are:

• Domestic Load: Includes lights, fans, appliances, and small motors. It is characterized by low power factor, high diversity factor, and peak demand occurring typically in the morning and evening hours.
• Commercial Load: Includes shops, offices, and business establishments. It has a higher power factor compared to domestic loads and follows business hours, contributing to the daytime peak load.
• Industrial Load: Includes motors, furnaces, and manufacturing equipment. These are typically three-phase loads, characterized by high power consumption, relatively constant demand, and a significant inductive component, often necessitating power factor correction.
• Agricultural Load: Primarily consists of irrigation pump sets. This load is highly seasonal and often characterized by a low load factor and long operating hours, usually during off-peak times.
• Municipal Load: Includes street lighting, water supply, and sewage pumping. Street lighting is a predictable, fixed-time load, while water pumping is often controlled to manage system demand.

Key characteristics defining these loads include the Load Factor (average load/peak load), Diversity Factor (sum of individual peaks/coincident peak), and Power Factor, all of which are critical for sizing distribution equipment and determining system efficiency.