Answer Posted / jeffrey tay
U0 is the cable conductor and shield design with metal
cover layer or between the rated power frequency voltage; U
is a cable designed for use between conductors rated
frequency voltage (three-phase line voltage); Um is the
maximum operating voltage of the system; Up is cable
designed for use in each line of core and shield or metal
sleeve Lightning impulse withstand voltage between the
peak.
U0 value is based on cable systems where the single-phase
ground fault occurs when the duration of the permit
determined. In the GB 12706. 1 -91 stipulated in the two
types of cables: Category 1 cables, U0 for 21 kV, for each
single-phase ground fault time is not greater than 1 min of
the system can be used for single-phase ground fault time
of the most length of no more than 8 h, an annual total of
no more than 125 h of the system; Class 2 cable, U0 for 26
kV, for a longer ground fault systems, and cable insulation
performance requirements for high occasions.
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