Good or Bad practices

[vennivivi]

Hi,

I have seen many installations where the star point of MV alternators are high impedance grounded. There are nothing uncommon with these practices and they are done almost all the times. What is uncommon is that when the alternator is not in service, the network works ungrounded. I just came across one of these installations. I am of opinion that when an alternator or alternators are connected to a common bus, the best practice is to earth the network through a neutral earthing compensator fitted to a service transformer on the network to avoid the ungrounding issue.
Any comment ?

Grundig

 

[dpc]

It depends on the situation and the percentage of time the system would be operating ungrounded. Modern practice is to provide some type of ground reference for medium-voltage systems. Short periods of ungrounded operation would not concern me if proper ground fault detection was functioning. On the other hand, there are many 4160 V systems that have been operating ungrounded for 40 or 50 years.

 

[Sungate]

It’s very common for MV utility networks to be operated ungrounded. In neutral grounded grid, any phase to ground fault should trip the system due the high current through ground loop. Therefore, it is depend on maintenance troubleshooting practice how to minimize system interruptions and provide good power supply performance.
If you have MV star connection so you will get neutral floating that can affect single phase load and your alternators start. In case, you decide to put neutral earthing compensator / resistor the value of that to be coordinated with inductance/capacity of the network, especially on non-loaded condition.