Surge Arrestor - 3 Wire Medium Voltage System
Surge Arrestor - 3 Wire Medium Voltage System
(OP)
How should a surge arrestor be rated on an overhead 12kV, 4 wire grounded neutral system that drops the neutral halfway along the circuit and becomes 3 wire. Would it still be considered solidly grounded system at the end of the 3 wire line, or sized like it's ungrounded?






RE: Surge Arrestor - 3 Wire Medium Voltage System
RE: Surge Arrestor - 3 Wire Medium Voltage System
If soil resistance is guaranteed to always be low and ground rods always good, you can calculate the voltage rise of a fault using the ground resistance and select a lower level suppressor based on the maximum voltage rise that can occur. If low enough you can get away with standard insulation.
RE: Surge Arrestor - 3 Wire Medium Voltage System
Regards
Marmite
RE: Surge Arrestor - 3 Wire Medium Voltage System
On a line with all loads being Delta connected there is a good chance line devices would trip, since ground pickup can be set at a very low value. (few amps) However,In a system where the the equipment grounding conductor is also used as a load neutral (multi-grounded neutral system) (which may be the case with the OP), the breaker/reclosers are set often with a very high ground pick up value. In the USA usually 1/3 to 2/3 of the phase pickup value. That combined with high soil resistance may result in over voltage values for an extended period of time without load showing it (ie, voltage drop, flickering)or line equipment clearing.
RE: Surge Arrestor - 3 Wire Medium Voltage System
RE: Surge Arrestor - 3 Wire Medium Voltage System
voltage values of the insulation are rather high in relation to the system voltage.
Regards
Marmite
RE: Surge Arrestor - 3 Wire Medium Voltage System
And a line to neutral fault far out on a distribution circuit may exhibit some of the characteristics of a line to ground fault due to the impedance of the neutral system. (Neutral system; the combined impedance of the neutral conductor and parallel paths through the multiple grounding points that are common on distribution circuit neutral conductors.)
Bill
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