Sizing a transformer for lighting loads involves determining the appropriate transformer capacity based on the connected lighting load requirements. The process generally includes the following steps:
Identify the lighting load: Determine the total connected lighting load in kilowatts (kW) or kilovolt-amperes (kVA). This involves calculating the sum of the power ratings of all the lighting fixtures or equipment that will be connected to the transformer.
Consider the diversity factor: Lighting loads often have diversity, meaning not all fixtures are operating at their full rated power simultaneously. Some fixtures may be turned off or operated at reduced power during certain periods. The diversity factor accounts for this and helps in sizing the transformer appropriately. It is typically expressed as a percentage (e.g., 80%, 100%, etc.).
Calculate the transformer capacity: To size the transformer, divide the total connected lighting load by the diversity factor to get the required capacity in kVA. The formula is:
Transformer kVA = Total Connected Lighting Load (kVA) / Diversity Factor
Select a suitable transformer: Based on the calculated kVA value, choose a transformer with a capacity equal to or higher than the calculated value. Transformers are available in standard sizes, so choose the nearest higher capacity that meets or exceeds your requirement.
Check the voltage rating: Ensure the selected transformer's primary and secondary voltage ratings match the system voltage of your installation. Transformers are available in different voltage ratios, and it's essential to choose one compatible with your power distribution system.
Consider additional loads: If there are other loads connected to the transformer apart from lighting, such as motors, receptacles, or other equipment, make sure to consider their requirements in the transformer sizing process.
Verify with local codes and standards: Always check with local electrical codes and standards to ensure compliance and safety.
Keep in mind that the sizing process may differ depending on the specific requirements of your installation. If you are not experienced in electrical system design, it's advisable to consult a qualified electrical engineer to ensure the proper sizing of the transformer and the overall electrical system.