The document outlines the concept of electrical loads and the importance of a load schedule, which estimates the active, reactive, and apparent power in a facility. It details the methodology for creating a load list, including collecting load parameters, classifying loads, and calculating operating, peak, and design loads. The load schedule is crucial for equipment sizing and power system studies, thus serving as a foundational task in electrical design activities.

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 :