In one of our recent project. There are multiple generators and individually feeding to each MDBs. Consultant instructed to loop all the Generator Neutral between each generators. Our proposal to provide individual neutral earthing for each generators.
Is it advisable to loop Generator Neutral Earthing (These generators are not synchronizing)
The answer to all this is that we don't know Mike. Usually there is an assumption that protection of the generator output cables themselves is not required (it is not there in packages either) because winding faults are much more likely and these cables can be safely looked after (sheathed and in trunking for example). Generator shorts to earth are power limited by the engine anyway, and fusing which blows on short at this point is difficult to arrange (10X current is simply not available for any useful period), and the current may be very large at 230/400V say 1500A per phase a 1MW set. The current may also be monitored by the excitation circuits via a CT, and then electronic load limiting may be arranged.
The MCCB or RCD for small sets on the ones you have seen is there for load protection just like any installation, We need a low enough Ze value to operate CPDs on an Earth fault outside the generator, it cannot protect the innards. As a large excess current is not available we use other methods of Earth fault detection, but this is not Additional Protection at 30 mA, except possibly on the smallest generators, say 60 kVA, because there will be significant Earth current if the installation is of any size, we may use 30mA on the final circuits, but leakage on a 1MW set driving a hospital could be several amps, because there are hundreds of appliances. The distribution circuits are protected against faults by being TN-S, with suitable CPDs to suit the expected current.
When generators are operated in parallel there may be significant currents between them caused by slight differences in engine phase and exact load, and throttle response times. However this does not appear to be relevant here.
The answer to all this is that we don't know Mike. Usually there is an assumption that protection of the generator output cables themselves is not required (it is not there in packages either) because winding faults are much more likely and these cables can be safely looked after (sheathed and in trunking for example). Generator shorts to earth are power limited by the engine anyway, and fusing which blows on short at this point is difficult to arrange (10X current is simply not available for any useful period), and the current may be very large at 230/400V say 1500A per phase a 1MW set. The current may also be monitored by the excitation circuits via a CT, and then electronic load limiting may be arranged.
The MCCB or RCD for small sets on the ones you have seen is there for load protection just like any installation, We need a low enough Ze value to operate CPDs on an Earth fault outside the generator, it cannot protect the innards. As a large excess current is not available we use other methods of Earth fault detection, but this is not Additional Protection at 30 mA, except possibly on the smallest generators, say 60 kVA, because there will be significant Earth current if the installation is of any size, we may use 30mA on the final circuits, but leakage on a 1MW set driving a hospital could be several amps, because there are hundreds of appliances. The distribution circuits are protected against faults by being TN-S, with suitable CPDs to suit the expected current.
When generators are operated in parallel there may be significant currents between them caused by slight differences in engine phase and exact load, and throttle response times. However this does not appear to be relevant here.
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