LOAD LISTWIWIT PURWANTO

The Electrical LoadThe 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.

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.

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

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.

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.

Example Load List :

Bus A Bus B

Example

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

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

Step 3: Classify the loadsOnce 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.

Step 4: Calculate consumed loadThe 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).

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:

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 :

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:

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.

𝐷𝐿 = 1.2 ∗ 𝑃𝐿Where DL : The design load ( kW or kVAr )

PL : The peak load ( kW or kVAr )

The Load Summary of Load List :