Load list calculation
- 1. LOAD LIST WIWIT PURWANTO
- 2. The Electrical Load The part or component in a circuit that converts electricity into light, heat, or mechanical motion. Examples of loads are a light bulb, resistor, or motor.
- 3. Load Schedule/List An estimate of the instantaneous electrical loads operating in a facility, in terms of active, reactive and apparent power (measured in kW, kVAr and kVA respectively). The load schedule is usually categorized by switchboard or occasionally by sub-facility / area.
- 4. Why do the calculation ? Preparing the load list is one of the earliest tasks that needs to be done as it is essentially a pre-requisite for some of the key electrical design activities (such as equipment sizing and power system studies). Equipment sizing : generator, transformer, cable, switchgear, bus duct, feeder, protection device ,etc. Power system studies : power flow, short circuit, transient stability, harmonic, coordination of protection device, etc. Balancing Load
- 5. When to do the calculation? The electrical load schedule can typically be started with a preliminary key single line diagram (or at least an idea of the main voltage levels in the system) and any preliminary details of process / building / facility loads. It is recommended that the load list is started as soon as practically possible.
- 6. Calculation Methodology The basic steps for creating a load list are: Step 1: Collect a list of the expected electrical loads in the facility Step 2: For each load, collect the electrical parameters, e.g. nominal / absorbed ratings, load factor, power factor, efficiency, etc. Step 3: Classify each of the loads in terms of switchboard location, load duty and load criticality Step 4: For each load, calculate the expected consumed load Step 5: For each switchboard and the overall system, calculate operating, peak and design load.
- 7. Example Load List :
- 8. Bus A Bus B Example
- 9. Step 1: Collect list of loads The first step is to gather a list of all the electrical loads that will be supplied by the power system affected by the load schedule. Electrical Loads : List of rotating equipment such as motor List of static equipment List of instrument and telecommunication loads Lighting and small power distribution boards. List of HVAC
- 10. Step 2: Collect electrical load parameters A number of electrical load parameters are necessary to construct the load schedule: Rated power Absorbed power Power factor Efficiency
- 11. Step 3: Classify the loads Once the loads have been identified, they need to be classified accordingly: Voltage Level What voltage level and which switchboard should the load be located? Large loads may need to be on MV or HV switchboards depending on the size of the load and how many voltage levels are available. Load duty Loads are classified according to their duty as either continuous, intermittent and standby loads: Continuous loads are those that normally operate continuously over a 24 hour period, e.g. process loads, control systems, lighting and small power distribution boards, UPS systems, etc. Intermittent loads that only operate a fraction of a 24 hour period, e.g. intermittent pumps and process loads, automatic doors and gates, etc. Standby loads are those that are on standby or rarely operate under normal conditions, e.g. standby loads, emergency systems, etc.
- 12. Step 4: Calculate consumed load The consumed load is the quantity of electrical power that the load is expected to consume. For each load, calculate the consumed active and reactive loading, derived as follows: Note : The loads have been categorized into three columns depending on their load duty (continuous, intermittent or standby).
- 13. Step 5: Calculate operating, peak and design loads Many organizations / clients have their own distinct method for calculating operating, peak and design loads, but a generic method is presented as follows: Operating load The operating load is the expected load during normal operation. The operating load is calculated as follows:
- 14. Peak load The peak load is the expected maximum load during normal operation. Peak loading is typically infrequent and of short duration, occurring when standby loads are operated (e.g. for changeover of redundant machines, testing of safety equipment, etc). The peak load is calculated as :
- 15. Design load The design load is the load to be used for the design for equipment sizing, electrical studies, etc. The design load is generically calculated as the larger of either: 퐷퐿 = 1.2 ∗ 푃퐿 Where DL : The design load ( kW or kVAr ) PL : The peak load ( kW or kVAr ) The design load includes a margin for any errors in load estimation, load growth or the addition of unforeseen loads that may appear after the design phase.
- 16. The Load Summary of Load List :