July 5, 2011

Electrical Load Classification

Electrical Load Classification

Each Electrical Load may be classified into several different categories for example,
  1. Vital
  2. Essential
  3. Non-essential

Different companies often use their own terminology / terms such as emergency, normal, unmanned and manned operation. In general, there are three ways of considering a load or group of loads.

  1. Vital Loads - Safety of personnel or cause serious damage within the plant if loss of power.
  2. Essential Loads - Loss of the manufactured product (Production @ Economy) if loss of power.
  3. Non-Essential Loads - No effect on safety or production if loss of power.
A vital service is, by definition, a safety matter. Complete redundant of the energy source is required. Vital loads are normally fed from a switchboard /MCC that has one or more dedicated generators and one or more incoming feeders from an upstream switchboard/MCC. These back-up/emergency generators will provide power during the emergency when the main source of power fails. These generators are usually called driven by diesel engines or other generators like TEG, Solar and MTG.

The total power for vital loads is normally small compared to the normal load . The vital load is fed from uninterruptible power supplies (UPS), as AC or DC depending upon the functions needed.

Example of Vital AC Loads
  • Boiler feedwater supply system
  • Life support systems
  • UPS supplies
  • Emergency lighting  and escape lighting
  • Emergency generator auxiliaries
  • Helicopter pad lighting
  • Control room supplies
  • Vital LV pumps

Example of Vital DC loads
  • Public address system
  • Plant alarm systems
  • System shutdown system
  • Telemetry systems
  • Emergency radio supplies
  • Fire and gas detection system
  • Navigation aids

An essential supply is, by definition, an economic matter. Therefore the economics of partial or complete duplication of the energy source, of the lines of supply or of the equipment, or the introduction of automatic restarting or changeover facilities etc., shall be evaluated in relation to the consequences of service interruptions.

Example of Essential AC loads
  • Diesel fuel transfer pumps
  • Main generator auxiliaries
  • Main compressor auxiliaries
  • Main pump auxiliaries
  • Diesel fire pump auxiliaries
  • Electric fire pumps
  • Living quarters       
  • Air compressor
  • General service water pumps
  • Fresh water pumps
  • Equipment room HVAC supplies
  • Life boat davits
  • Anti-condensation heaters in
  • panels and switchboards
  • Security lighting supplies
  • Control room supplies
  • UPS supplies
  • Radio supplies
  • Computer supplies
  • Battery chargers for engine
  • starting systems
  • Instrumentation supplies

Example of Non-essential service
  • Power and lighting supplies to offices, warehouses, residential areas, etc.

All of the vital, essential and non-essential loads can be divided into typically three duty categories:
  1. Continuous duty.
  2. Intermittent duty.
  3. Standby duty (those that are not out of service).

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