A
Adam Funk
- Jan 1, 1970
- 0
Recently there was a partial power failure on my street (including my
house), but our adjacent neighbours' electricity was still on. When I
phoned to report it, the power company said there was already someone
on the way to our substation to fix it.
AIUI, urban residential power supplies in the UK are provided from
three-phase underground cables. The cable running down our street has
four conductors: earth/neutral and three lives (red, yellow and blue)
each at 240 volts but 120 degrees apart. Each house is connected to a
phase in turn and to the earth/neutral, so for example houses 1, 7, 13
and so on are on the red phase; 3, 9, 15, ... on the yellow; and 5,
11, 17, ... on the blue. This provides load-balancing between the
phases.
I was surprised that one phase could trip while the other two on the
same transformer stayed on --- I would have expected the output of the
last transformer to go through a breaker that would disconnect all
three phases in the event of a fault. If only one phase trips,
doesn't that leave the load on the transformer unbalanced? And why
isn't that considered a problem?
house), but our adjacent neighbours' electricity was still on. When I
phoned to report it, the power company said there was already someone
on the way to our substation to fix it.
AIUI, urban residential power supplies in the UK are provided from
three-phase underground cables. The cable running down our street has
four conductors: earth/neutral and three lives (red, yellow and blue)
each at 240 volts but 120 degrees apart. Each house is connected to a
phase in turn and to the earth/neutral, so for example houses 1, 7, 13
and so on are on the red phase; 3, 9, 15, ... on the yellow; and 5,
11, 17, ... on the blue. This provides load-balancing between the
phases.
I was surprised that one phase could trip while the other two on the
same transformer stayed on --- I would have expected the output of the
last transformer to go through a breaker that would disconnect all
three phases in the event of a fault. If only one phase trips,
doesn't that leave the load on the transformer unbalanced? And why
isn't that considered a problem?