Automatic Maximum Demand Calculations

Easily calculate the lowest possible maximum demand with optimal phase balancing

Introduction

The new maximum demand module provides fast and accurate calculations for loads in accordance with rules from the Standards and for custom loads.  An ingenious automatic phase balancing algorithm ensures maximum demand and phase imbalance are both minimised.

With the press of a button and in accordance with the Standard the lowest maximum demand will be calculated, and the phases will be automatically balanced.

Top Benefits

  1. Amazingly fast and accurate maximum demand calculations.
  2. Automatically applies all the rules from the Standards.
  3. Automatically balances the loads across the phases.
  4. Lowest possible maximum demand reducing cable costs.
  5. Custom loads and diversity factors.
  6. User defined rules beyond the scope of the Standard.
  7. Manually allocate loads to phases specified by the user.

How It Works

  1. Loads from Installation types and Load Groups are added by the user.
  2. Loads are automatically grouped, and their ratings are calculated according to the rules.
  3. Three phase load ratings are added to the maximum demand.
  4. Single phase load ratings are automatically assigned to the lowest loaded phase.
  5. The phase imbalance is minimised.
  6. The phase with the maximum load is the maximum loaded phase.

Worked examples of calculating maximum demand

To perform the calculation of maximum demand by hand you need to use the tables from the Standard and to apply the rules, then you need to allocate the loads quantities to the phases.

Refer to our article which contains the maximum demand tables from the Standard.

https://elek.com.au/articles/maximum-demand-tables/

It is complicated to apply the rules for calculating maximum demand and time consuming to balance all the loads across the phases.

In these examples the maximum demand is calculated by hand and compared with the software.

Using software to calculate maximum demand saves a lot of time and the automatic algorithm achieves better phase balancing resulting in lower maximum demand.

Example 1 – Single domestic installation

This example is based on Example 2 from Appendix C in AS/NZS 3000.

The installation consists of the following loads:

  1. 26 lighting points
  2. 24 x 10 A single phase single socket outlets
  3. 15 A single phase socket
  4. 16,600 W three phase electric range consisting of two 5000 W hotplates and one 6600 W oven.
  5. 4000 W air conditioner
  6. 12960 W three phase instantaneous water heater
  7. 3600 W single phase clothes dryer

The first step is to choose the appropriate Load Group and Subgroup for each of the loads.

Load Groups and Subgroups – Single domestic installation

Results - Manual Calculation

Each Load Group and Subgroup has a set of rules.  Loads should be grouped according to the rules.  Next the rating of the loads are calculated.  Finally, the load quantities are assigned to the phases, keeping in mind the order in which loads are assigned affects the balance between the phases.

Maximum loaded phase – Blue

Phase loading – R – 40.19 A

                                W – 34.97 A

                                B – 35.65 A

Phase Imbalance – 8.8 %

 

Time taken: 28 minutes

Results - Software Calculation

The software calculation results in a lower maximum demand and better phase balancing.

Maximum loaded phase – Blue

Phase loading – R – 35.65 A

                                W – 37.11 A

                                B – 38.05 A

Phase Imbalance – 3.48 %

Example 2 – Non-domestic installation

Calculating maximum demand is more complicated when there are more loads and where there are certain load types such as motors and lifts, where the rating of the load depends on the availability of a similar load on the phase.  Also, the allocation order plays an important role in obtaining a good phase balance.

This example is based on Example 4 from Appendix C in AS/NZS 3000.

The installation consists of the following loads:

  1. 200 x 60W lighting points
  2. 30 x 50 W single phase exhaust fans
  3. 10 x 10 A single phase single socket outlets (non-permanently heated or cooled area)
  4. 90 x 10 A single phase single socket outlets (permanently heated or cooled area)
  5. 4 x 15 A single phase socket outlets
  6. 2 x 5500 W hotplates
  7. 6600 W oven
  8. 750 W three phase pump motor (2 A per phase name plate rating)
  9. 6000 W single phase sauna heater.

Load Group and Subgroups – Residential Institutions, hotels, boarding houses, hospitals etc. 

Results – Manual Calculation

Maximum loaded phase – Blue

Phase loading – R – 89.29 A

                                W – 89.83 A

                                B – 95.16 A

Phase Imbalance – 4.08 %

 

Time taken: 34 minutes

Results – Software Calculation

The software calculation results in a lower maximum demand and better phase balancing.

Maximum loaded phase – Blue

Phase loading – R – 89.72 A

                                W – 89.66 A

                                B – 89.98 A

Phase Imbalance – 0.21 %

Cable Pro Web

Cable sizing and maximum demand software in the cloud. No installation, use on any device.

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