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    Estimating load with known diversity factors

    Good day all.

    I am going through old installation rules exam papers with no answers provided, and I attempmted to do one of the calculations as per topic title.

    Please could you have a look at this for me, and comment. I am a bit stumped by part two of the question as well, I cannot see another method of checking the result in the code.
    Also the max allowable loading of the supply transformer is 90% correct?

    Thanks in advance for your help.

    3.1 Calculate from the following information, the maximum amount of water heaters of 1kW each that may be installed according to the regulations:
    o 10kVa/220 v single phase transformer using a power factor of 0.95
    o Floor area 301m²
    o Two 0.75kW single phase motors
    o One electric oil heater of 500w
    o 20 lights

    3.2 Test your answer by making use of any other alternative method.



    3.1 answer:

    Total load :
    o Socket outlets -Floor area 301 m² = (5 kw for first 100 m²) + (1kw for second 100m²) +( 1kw for part of third 100m²) TOTAL = 7kw x diversity of .5 = 3.5kw
    o Motors = (.75kW x 2 ) = 1.5kW x diversity factor of 1 =1.5kW
    o Electric oil heater = 0.5kW x diversity of .5 = .25kW
    o 20 lights ( 20 x 60watts ) = 1200watts = 1.2kw x diversity of .5 = .6kW
    o
    o TOTAL LOAD ( 3.5kW+1.5kW+0.25kW+.6kW) = 5.85kW

    Therefore total current required = 5.85kW / 220v = 5850 /220 = 26.6A

    Max supply from transformer at full load (10000 *.95) /220 = 43.18 amps.

    43.18 max load x 90% = 38.86amps allowable.

    Therefore remaining amperage is 38.86-26.6 = 12.26Amps.

    Each heater requires: 1kw
    Therefore amps required per is 1kw/220 1000/220= 4.54 amps x diversity factor of 1 = 4.54 Amps.

    Therefore total amount of water heaters allowed is 12.26amps/4.54 amps = 2.7.


    To check total load with two connected : 26.6amps + (4.54 x 2) = 35.68
    To check total load with three connected 26.6amps + (4.53 x 3) = 40.19

    Therefore to enable the transformer to be loaded at 90% max only two may be added.

  2. Thanks given for this post:

    mikilianis (12-Oct-10)

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