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-   -   How to calculate the additional load can be add to existing system? (https://www.askmehelpdesk.com/showthread.php?t=723346)

  • Dec 18, 2012, 08:57 PM
    weirdwired
    How to calculate the additional load can be add to existing system?
    Hi all, I am not in the electrical field but I am curious about this matter so that is why I am going to ask. I have a 3-phase switchboard using 2500A TP 50kA 3 sec ACB as a main breaker to cater a design load of 1052kW of maximum demand. The system already run for 2 years, and now I am going to add 2 nos of 90kW pump into the system. Here the normal run reading for the system: IL1=1137A, IL2=1222A, IL3=1180A, VL1=411.3V, VL2=410.7V, VL3=411.6V. The question, can the existing system able to cater the additional 180kW loads? Please help me.
  • Dec 18, 2012, 08:59 PM
    smoothy
    THis is homework... did you read the homework rules?

    If its not homework, you aren't qualified to do this work and would void your insurance.
  • Dec 18, 2012, 09:05 PM
    weirdwired
    Quote:

    Originally Posted by smoothy View Post
    THis is homework...did you read the homework rules?

    If its not homework, you aren't qualified to do this work and would void your insurance.

    FYI, this is not a homework. I just measure the line-to-line current and voltage and stuck from there. What should I do next? What to calculate? What is the formula? This is my problem because I just know the idea/concept but don't know the technical. I need to present the idea of cost saving. Please help. TQ
  • Dec 19, 2012, 06:31 AM
    tkrussell
    Assuming the nominal voltage is 400 volts 3 phase, the amp load per phase for the 180kW load is:

    180kW / (400 V x 1.73) = 260 amps

    Existing load per phase is approx 1200, round numbers. 1200 + 260 = 1460 amps per phase.

    This will leave approx 1000 amps capacity available on the 2500 A switchboard, before any applicable derating factors.

    I get from your verbage your not locatied in North America.

    Here standard Code is to derate by80%. If you have the same standards, the 2500 A switchboard can only be loaded 2000 Amps continuous, thus leaving 540 amps available capacity for future loads, unless your system is rated 100%.

    You need to determine what Codes or Standards are applicable in your location.

    I do have to ask, if your "not in the electrical field:", how did you manage to get these amps and volts readings safely ?
  • Dec 19, 2012, 10:36 AM
    hfcarson
    Your location would be helpful...
    If you are in a location that uses the IEC codes, then the Electrical Code does offer two methods to substantiate the service capacity for additional loading.
    The code section in NFPA 70 (The Electrical Code) is 220.87 which directs you to use the maximum recorded demand load from the most recent twelve months or record the demand load for at least 30 days and add the largest of the heating or HVAC loads.
    Please review this code section for the specific language.


    Edited**** Changed ICC to IEC, for International Electric Commission***

    IEC is a popular standard away from North America.

    The UK uses British Standard BS 7671

    Good answer HR

    Tk
  • Dec 23, 2012, 08:57 PM
    weirdwired
    1 Attachment(s)
    Quote:

    Originally Posted by tkrussell View Post
    Assuming the nominal voltage is 400 volts 3 phase, the amp load per phase for the 180kW load is:

    180kW / (400 V x 1.73) = 260 amps

    Existing load per phase is approx 1200, round numbers. 1200 + 260 = 1460 amps per phase.

    This will leave approx 1000 amps capacity available on the 2500 A switchboard, before any applicable derating factors.

    I get from your verbage your not locatied in North America.

    Here standard Code is to derate by80%. If you have the same standards, the 2500 A switchboard can only be loaded 2000 Amps continuous, thus leaving 540 amps available capacity for future loads, unless your system is rated 100%.

    You need to determine what Codes or Standards are applicable in your location.

    I do have to ask, if your "not in the electrical field:", how did you manage to get these amps and volts readings safely ?

    Many thanks for all the reply. I am located in Kuala Lumpur, Malaysia which is our practices here is more similar to British and International Standard.

    For the question on how I get those readings is from the LCD of Janitza Power Quality Meter in front of the Main Switch Board (MSB) panel.

    I just got new info regarding this panel; the incomer supply for this MSB is from 1600kVA, 33kV/433v transformer. And I just read an article on how to sizing the breaker that requires me to consider the volt-drop at MSB and at new motors (2 x 90kW, star-delta starter) during starting and continuous run. I have no idea about this.

    *notes: sorry if my English is bad. I will share the single-line diagram and MSB layout as attached.

    Thanks again and wishes all of you guys, Merry X-Mas and Happy New Year 2013!
  • Dec 23, 2012, 09:03 PM
    smoothy
    Likewise... Your English is pretty good (very good actually) for someone living where its not the main language and by someone for whom its not their first language. Technical terminology in a second language is VERY difficult to master. I know.
  • Dec 23, 2012, 10:04 PM
    weirdwired
    1 Attachment(s)
    Quote:

    Originally Posted by smoothy View Post
    Likewise....Your English is pretty good (very good actually) for someone living where its not the main language and by someone for whom its not their first language. Technical terminology in a second language is VERY difficult to master. I know.

    Thanks smoothy..

    I have put the new pump as cloud in the pdf attached. If I am using Terasaki brand breaker (MCCB/VCB) what size of the breaker will be? I choose Terasaki here because it's cheaper in Malaysia (to include in my budget presentation later).

    Thanks.
  • Dec 24, 2012, 03:19 AM
    tkrussell
    Assuming that the CB needs to be a minimum of 25% higher than the load, a 300 Amp Cb would be enough for you to get a budget cost from the supplier of the switchboard.

    You should check with the designer of the one line to be sure of the size CB if this actually is installed.
  • Dec 30, 2012, 08:04 PM
    weirdwired
    Quote:

    Originally Posted by tkrussell View Post
    Assuming that the CB needs to be a minimum of 25% higher than the load, a 300 Amp Cb would be enough for you to get a budget cost from the supplier of the switchboard.

    You should check with the designer of the one line to be sure of the size CB if this actually is installed.

    Thanks a lot, =tkrussell;3352789 for the answer. I will check this with the single-line designer sooner.

    What if the new loads is 110kW x 2 nos. instead of 90kW x 2 nos as per discussed? Will the main breaker able to cater this size of loads?

    Thanks again.

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