Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 17 replies
  • Subscribers 32 subscribers
  • Views 2514 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Cross sectional area of a protective conductors

MS01
Can someone give me a some advice on if we have a earth electrode system made up of the structural rebar when using the adiabatic equation to size of the bonding conductor comes out at 300mm. MY questions is does each bond need to be this size or can it be made up via a series of smaller bonds that are equal or exceed the 300mm requirement? My opinion is each bond needs to be this size to deal with the fault current as the direction it will flow is unknown. What are peoples thoughts? I cannot see anything in the regs on this.

Parents
  • 0
    Still feels a bit odd - if the 1.7kA is the HV side to earth fault current, we are looking at  6.4kV to ground (for 11kV phase to phase) so perhaps the HV electrode impedance is  something like 3.8 ohms

    Well perhaps not really, that is HV electrode plus the HV phase loop impedance, but  at  5MW  you are looking at perhaps 150 amps per line  on the primary at full load I'd assume the HV feed is not drooping by 10%  at that point -or there will be horrible problems of secondary side voltage drop)

    Presumably then most of the HV fault loop is indeed electrode related and it is at least a couple of ohms. and may be more like 3. Part of me is then a bit surprised that HV and LV earths are combined - it does not sound a very 'cold' site (due to LV side bounce during HV faults).


    In any case, you will not get thousands of amps flowing into your rebar, which is as well, as the rebar would probably need to be beefed up to take it, so the cable to the rebar can be reduced accordingly.
Reply
  • 0
    Still feels a bit odd - if the 1.7kA is the HV side to earth fault current, we are looking at  6.4kV to ground (for 11kV phase to phase) so perhaps the HV electrode impedance is  something like 3.8 ohms

    Well perhaps not really, that is HV electrode plus the HV phase loop impedance, but  at  5MW  you are looking at perhaps 150 amps per line  on the primary at full load I'd assume the HV feed is not drooping by 10%  at that point -or there will be horrible problems of secondary side voltage drop)

    Presumably then most of the HV fault loop is indeed electrode related and it is at least a couple of ohms. and may be more like 3. Part of me is then a bit surprised that HV and LV earths are combined - it does not sound a very 'cold' site (due to LV side bounce during HV faults).


    In any case, you will not get thousands of amps flowing into your rebar, which is as well, as the rebar would probably need to be beefed up to take it, so the cable to the rebar can be reduced accordingly.
Children
No Data

Community Rules & Guidelines