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Change phase sequence

It is absolutely impossible for a utility to change the phase sequence. Why? Because the utility is connected to the local grid, the local grid to the regional grid, the regional grid to the national grid, and the national grid to the international grid. So, unless you don't change the phase sequence in the entire network you cannot change it locally. What will happen if one will change the phase sequence and phase A will come in phase B's place? If everything is operational nothing will happen. And that's because the breaker will not close since it will be never possible to synchronize the two networks. If someone will be smart enough to close the breaker without synchronization, than the breaker will become a piece of junk and some other breakers will open on the network to isolate the fault here.

OK. Now suppose that our factory is the only one connected to a substation through a line. If some works are to be done in the substation on this cell, your factory probably has another energy supply and will energize the affected busbar through the meaning of the second power supply (spare). This is done by first connecting the second power supply to this busbar (with synchronization check) and then disconnect the main breaker of the line that needs work. When the work is done and you have to connect back the main line, the operations are the same, you close the main breaker with synchronization check and if somebody have mess the things up and changed 2 phases, the breaker will not close.

Now, the only way to change 2 phases:
The utility needs some work on the line thus de-energize the line. All equipment that are connected to that line is not energized from another source! This is sometime possible but first of all, the utility have to check the phase sequence after every work that can lead to a phase sequence change. And I can assure you that this check is done every time just because the effects of a such mistake can be disastrous. More than this, the client connected to the utility has to check by himself the phase sequence that is available in the incoming lines. Remember that all the power was out for this client so, when the power is back available, the busbar that will be energized from the incoming line will be free of any load (all the breakers on the busbar in open position, except the breaker for the measuring cell if applicable).

In power generation, distribution and transport, the rules are very clear and are obeyed by every professional. If the basic rules of the energize- deenergize operations are not followed, the company must fire the one in charge with the management of this department.
In addition, there are some automation and interlock systems that prevent the operators to do some mistakes.

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