In electrical systems, loads are categorized based on their criticality and potential impact on human life and production. Here are the four main classifications of electrical loads:
1. Normal Loads:
Normal loads refer to those where a single contingency failure would not pose a risk to human life or cause significant production losses. These loads can withstand prolonged power failures without resulting in a plant shutdown. Examples include secondary office buildings, warehouses, and workshops. Supplying such loads can be achieved through a radial or primary-selective system.
2. Critical Loads:
Critical loads are characterized by the potential consequences of a single contingency failure, which could be hazardous to human life or cause substantial production losses, leading to a major shutdown. Examples of critical loads include major office buildings, computer or IT centers, and process units. To ensure uninterrupted power supply to these loads, a secondary-selective system is employed.
3. Emergency Loads:
Emergency loads are essential for safeguarding equipment or maintaining certain operations. These loads can tolerate short interruptions in service but require automatic restart and re-feeding through an emergency generator. Emergency loads are supplied through an emergency switchgear connected to a secondary-selective system and emergency generator.
4. Vital Loads:
Vital loads directly or indirectly impact personnel safety and must not experience power supply interruptions. These loads are critical and typically powered by an uninterruptible power supply (UPS) system. Examples of vital loads include distributed control systems (DCS), fire alarms, gas detection systems, and substation control systems.
Understanding the classification of electrical loads helps in determining the appropriate supply systems and backup requirements for different types of loads. It ensures the safety of personnel and the continuity of essential operations in various electrical applications.