Why is it not recommended to connect a neutral wire to a three-phase resistive furnace powered by a thyristor voltage regulator?
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Why is it not recommended to connect a neutral wire to a three-phase resistive furnace powered by a thyristor voltage regulator?
The GB50056-93 Code for Design of Electric Heating Equipment and Power Installations stipulates that for resistance furnaces powered by a three-phase supply using thyristor voltage regulators or power controllers, it is not advisable to use a star connection with a neutral wire; instead, a star or delta connection can be employed. This is because thyristors may trigger accidentally, or one phase may fail to trigger, or half-wave triggering may occur, resulting in three-phase imbalance and high current in the neutral wire. When the cross-sectional area of the neutral wire is insufficient, this can often lead to damage to the wire.
Phase control technology is now highly mature, so the probability of the aforementioned situation occurring is extremely low.
Prevent three-phase imbalance, as a large current flows through the neutral wire!
I have no experience in this area, but I’m offering some ideas for the original poster’s reference. Is it to prevent excessive harmonics (mainly the 3rd harmonic) from causing a series of problems due to their accumulation on the neutral line?
I don’t think it’s likely that an unbalanced current will burn out the neutral wire; if its cross-sectional area is too small, it can be increased to match that of the phase wires. The view supporting the 5th floor is valid; there is no need to use a neutral wire, probably due to considerations related to third harmonics and harmonics that are multiples of 3.