oilyneil
Member
- Messages
- 170
- Location
- Wiltshire uk
Regarding saftey on 3 phase supply, unless it is a balanced load (all 3 phases drawing the same current) the loss of the neutral star connection can have dangerous implications,as there is no longer a defined neutral connection. This leads to the phase which has the lowest current draw recieving a higher than normal voltage, up to full phase to phase voltage,with the phase with the highest load will be significantly down on voltage.
The problemof losing a phase in a 3 phase network will be motors not starting correctly and overheating as it tries to limp past the bad phase, all circuit breakers intended for 3 phase equipment are now "ganged" so a fault on 1 phase will disconnect all 3.
I work on the power distribution network and this is a real problem following cable faults, road accidents as it is still fused at substations with no ability to disconnect the healthy phases.
As an aside, in rural locations there is also split phase network still around, it is supplied by single phase HV and the low voltage is 230 volts phase to neutral and 460 phase to phase. This is not the same as 2 phases of a 3 phase system as it is basicly a 460v single phase transformer with a center tapp for a neutral.
The problemof losing a phase in a 3 phase network will be motors not starting correctly and overheating as it tries to limp past the bad phase, all circuit breakers intended for 3 phase equipment are now "ganged" so a fault on 1 phase will disconnect all 3.
I work on the power distribution network and this is a real problem following cable faults, road accidents as it is still fused at substations with no ability to disconnect the healthy phases.
As an aside, in rural locations there is also split phase network still around, it is supplied by single phase HV and the low voltage is 230 volts phase to neutral and 460 phase to phase. This is not the same as 2 phases of a 3 phase system as it is basicly a 460v single phase transformer with a center tapp for a neutral.