DC MCB

wfl6wfl6 Registered Users Posts: 5
I has question need to ask regarding of the MCB.

If i want to design DC MCB for the solar panel. which voltage i need to look in on the solar panel .

Is it the maximum voltage or the open short circuit voltage,

Example:

power output is 270W
voltage at Pmax: 34.9
open circuit voltage: 43.7
current at Pmax: 7.44
short circuit current: 8.18


i will connect the 21 panel in a string .
the total voltage is 732.9v.

The MCB that 1 chose is s800 PV ABB.
will it suitable on it .

or

I need to take the open circuit voltage for finding suitable MCB .

the total voltage is 917.7v
so that i need to find MCB voltage around 1000v .

thanks

Comments

  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: DC MCB

    You need to look at Voc. But do you really need an MCB? Grid tied solar inverters usually come with a DC disconnect switch built in. Can your inverter really handle 1000V input? Most have a limit lower than this, around 600V.
  • wfl6wfl6 Registered Users Posts: 5
    Re: DC MCB

    Hi stephendv,

    Thanks for your advise.
    i am using the SMA inverter, the model is STP17000W . they can handle thw voltage up to 1000v.
    inverter inside is build it disconnected switch but for the design requirement on the government we need a DC MCB.
    Do any brand has 1000v DC MCB with 2 pole. if not can i series the MCB?
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: DC MCB

    like these ?

    http://www.gepowercontrols.com/eu/product_portfolio/residential/minature_circuit_breaker/mcb_ep100uc.html

    What does the Government requirement actually say?
     
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  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: DC MCB
    westbranch wrote: »

    Looking at the 104, it lists Maximum DC Operating voltage as 1000 all right, but whatever "Maximum DC Un...." is, it is only 880, and they describe the maximum load rating as 880 volt, 63 amp.

    The more detailed information in the PDF clarifies that 1000 as the maximum open circuit withstanding voltage with all four poles of the 4 pole unit in series. It cannot open against a voltage that high.
    Rated voltage DC Un (V) 500 880
    SMA SB 3000, old BP panels.
  • wfl6wfl6 Registered Users Posts: 5
    Re: DC MCB

    actually i know that the MCB is not really on it ..
    due to the design require b4 the inverter need a MCB .
    So that i need to design it with MCB.
    the time i design i face a problem that the MCB voltage rating for 2 pole is around 800 v.
    but the VOC of my design is around 920++ .i need to find a mcb with voltage range 1000vdc.
    it is 4 pole will be wasted if i using it solar panel??
    between that why i cant design the DC voltage with Voltage maximum (in Pm). rather than i using voltage open circuit
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: DC MCB
    wfl6 wrote: »
    actually i know that the MCB is not really on it ..
    due to the design require b4 the inverter need a MCB .
    So that i need to design it with MCB.
    the time i design i face a problem that the MCB voltage rating for 2 pole is around 800 v.
    but the VOC of my design is around 920++ .i need to find a mcb with voltage range 1000vdc.
    it is 4 pole will be wasted if i using it solar panel??
    between that why i cant design the DC voltage with Voltage maximum (in Pm). rather than i using voltage open circuit

    1. You cannot design for the Vmp rather than the Voc because when the relay is open the voltage across it will be Voc!
    2. What kind of inverter are you using which can take 1000 volt input?
    3. The four poles are not wasted because you have to wire all 4 poles in series to get enough contact spacing and interrupting capacity to withstand 800-1000 volts. It will only be switching one circuit, with no "spare" poles.
    4. When you list a design Voc of 920 volts, have you calculated the highest possible Voc when the panels are cold? That can be as much as 25% higher than the voltage at standard temperature.
    (For a cell with a temperature coefficient of -.5% per degree C, the voltage at -25 C will be about 25% greater than it is at 25 C. ) If you have not done this, you will have failures in cold weather! (And they will be catastrophic.)
    SMA SB 3000, old BP panels.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: DC MCB

    As things are going, I smell a coming disaster - - - -
  • wfl6wfl6 Registered Users Posts: 5
    Re: DC MCB
    inetdog wrote: »
    1. You cannot design for the Vmp rather than the Voc because when the relay is open the voltage across it will be Voc!
    2. What kind of inverter are you using which can take 1000 volt input?
    3. The four poles are not wasted because you have to wire all 4 poles in series to get enough contact spacing and interrupting capacity to withstand 800-1000 volts. It will only be switching one circuit, with no "spare" poles.
    4. When you list a design Voc of 920 volts, have you calculated the highest possible Voc when the panels are cold? That can be as much as 25% higher than the voltage at standard temperature.
    (For a cell with a temperature coefficient of -.5% per degree C, the voltage at -25 C will be about 25% greater than it is at 25 C. ) If you have not done this, you will have failures in cold weather! (And they will be catastrophic.)


    i am using sunny trio power 17000w. the DC voltage that can be handle is 1000v. Due to the installation place in Malaysia so that i think the temperature will not be going too low. after connect panel together max voltage will be around 700v and the Voc will around 900-932v. In this case i need to take Voc as a references for choosing the right MCB?
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: DC MCB
    wfl6 wrote: »
    i am using sunny trio power 17000w. the DC voltage that can be handle is 1000v. Due to the installation place in Malaysia so that i think the temperature will not be going too low. after connect panel together max voltage will be around 700v and the Voc will around 900-932v. In this case i need to take Voc as a references for choosing the right MCB?

    Just because the Sunny Tripower 17000 can handle a maximum input voltage of 1000V does not mean that you should design all the way up to that voltage!

    The specs I am looking at indicate that its "nominal" input is 600V and the range over which it can actually do MPP tracking is 400 V – 800 V. I am not convinced that the operating efficiency of the Tripower will be significantly greater with an array with Vmp of 700 volts than with an array with Vmp of 600 volts. I do n
    I guess if you are worried about theft of the panels, there is a certain attractiveness to using a voltage which will produce an ArcFlash when someone tries to cut or disconnect a wire. But unlike the situation with theft of conventional power infrastructure, with PV all you have to do is wait till nightfall.
    SMA SB 3000, old BP panels.
  • wfl6wfl6 Registered Users Posts: 5
    Re: DC MCB

    thanks for the reply .
    from ur opinion is it i connect the panel Vmp around 600v.
    But from the panel to the inverter my length is a bit far. i think the length will around 125m.
    so that i connect the 20 panel in a string.

    For this design do you has a suggest for me ??
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: DC MCB

    SMA has a software design package (array/inverter configuration software) that can be downloaded and run on a Microsoft PC of some sort:

    http://www.sma-america.com/en_US/products/software/sunny-design.html

    Can download and run this application on one of your computers?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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