I had an email from the IET to say that the DPC for AMD 1 was published yesterday for 60 days for public comment. I can't post a link but you can find it via the IET and BSI websites. It's all about electric vehicle charging.
if one phase goes open circuit at the substation then if all the loads are single phase, every third light or house goes out.
However, more industrial loads with things connected t 3 phases are more fun. Spinning 3 phase motors, if they keep spinning, will try and generate the missing phase. If this does not happen then 400v loads connected phase to phase now see 230 instead of 400, and with the wrong phase relationship.
In practice, I agree 130V sounds like phase off, but it could have been almost any voltage less than 230.
It is nastier if the neutral falls off, as then the 400V between phases is retained, delta wired loads do not really notice, but it is bad for single phase and star wired loads, which see the neutral move from the centre and being equally 230v from each phase to almost anywhere in the triangle. In principle if the single phase loads are a very much out of balance then you could have one phase of near zero volts to ground/ local neutral , and the other two at more or less 400V - as the fuses tend to disconnect loads on the over-volted side this is an unstable condition, and can do a lot of damage.
There is also a similar problem with faults from phase to true terra-firma earth with too low an electrode impedance, if the fault earth is less resistive than the electrode resistances at the transformer end of things - not impossible if perhaps the fault is to the frame of a steel piled building, and the transformer feeding it is a small pole-pig with 10-20 ohms of rod electrode resistance.
In that case the phase gets grounded, the bulk of the fault voltage is dropped at the transformer electrode, so the transformer star point and everything that uses that as an earth gets pulled off ground. If for example the L to ground fault is 3 ohms, and the transformer earth is 10 ohms then this neutral voltage lift is 10/13 of 230v, or about 180V relative to any electrode or other earthed metal outside the near field of the transformer earth electrodes. The faulted phase however ends up about 60V off true ground. Unless there is an RCD, or the supply is lightly fused, this condition is likely to persist for some time before it is noticed, as nothing will trip - in this example 230V /13ohms , or about 16 amps, will flow from the faulted phase to ground so the electricity bill will be high, but that is about all that will happen.
There are more fault modes than the obvious shorts to the CPC or occasional broken phase or PEN to consider.
if one phase goes open circuit at the substation then if all the loads are single phase, every third light or house goes out.
However, more industrial loads with things connected t 3 phases are more fun. Spinning 3 phase motors, if they keep spinning, will try and generate the missing phase. If this does not happen then 400v loads connected phase to phase now see 230 instead of 400, and with the wrong phase relationship.
In practice, I agree 130V sounds like phase off, but it could have been almost any voltage less than 230.
It is nastier if the neutral falls off, as then the 400V between phases is retained, delta wired loads do not really notice, but it is bad for single phase and star wired loads, which see the neutral move from the centre and being equally 230v from each phase to almost anywhere in the triangle. In principle if the single phase loads are a very much out of balance then you could have one phase of near zero volts to ground/ local neutral , and the other two at more or less 400V - as the fuses tend to disconnect loads on the over-volted side this is an unstable condition, and can do a lot of damage.
There is also a similar problem with faults from phase to true terra-firma earth with too low an electrode impedance, if the fault earth is less resistive than the electrode resistances at the transformer end of things - not impossible if perhaps the fault is to the frame of a steel piled building, and the transformer feeding it is a small pole-pig with 10-20 ohms of rod electrode resistance.
In that case the phase gets grounded, the bulk of the fault voltage is dropped at the transformer electrode, so the transformer star point and everything that uses that as an earth gets pulled off ground. If for example the L to ground fault is 3 ohms, and the transformer earth is 10 ohms then this neutral voltage lift is 10/13 of 230v, or about 180V relative to any electrode or other earthed metal outside the near field of the transformer earth electrodes. The faulted phase however ends up about 60V off true ground. Unless there is an RCD, or the supply is lightly fused, this condition is likely to persist for some time before it is noticed, as nothing will trip - in this example 230V /13ohms , or about 16 amps, will flow from the faulted phase to ground so the electricity bill will be high, but that is about all that will happen.
There are more fault modes than the obvious shorts to the CPC or occasional broken phase or PEN to consider.
