Hi,
I have read every single thread related to generator neutral grounding and not grounding, third harmonics, circulating currents etc. I've read through Chapter 19 of Westinghouse T&D.
I'm not sure if it is my inability to understand, the different regulations or simply different site setups, but I can not get a grip on how I should go about the following.
The installation is as follows:
It is important to note that the generators are always connected to the grid so they are never operating in island mode. Each generator has only one circuit breaker connecting straight to the 415V LV bus. This LV bus is connected to the LV side of the star/delta 1500kVa transformer. On this same LV bus, 1200kVa worth of industrial equipment is also connected (mostly 3phase load), including some power factor correction gear with reactors blocking the 5th and 7th harmonics.
First only the 500kW generator were commissioned and worked fine with no excessive neutral currents. The neutral is directly connected to the neutral bus in the main switch room, which is directly earthed.
When installing the second generator (600kW) the problem started. This generator is connected exactly the same way as the first one. It's neutral is also connected to the neutral bus in the switch room. Both generators are set on PF control. On this I might also mention that the PF on the one 500 was set to 0.93 while the PF on the 600kW was set to 0.88. Can this have an affect on the problems I'm having?
The problem is the neutral current and third harmonics.
Since the installation of the second genset we've had capacitors blowing up, bus bars melting and fuses blowing out of the panels.
I have measured and am convinced that the neutral currents (same as phase currents in magnitude) are due to the third harmonics.
From reading all the threads I've seen heaps of different opinions but it could be due to slight variations on the specific sites.
Can I please get help on how to solve this one. I've seen solutions like zig zag transformers, disconnecting one of the generators' neutrals, NERs, neutral current eliminators, harmonic filters etc etc.
Help will be much appreciated.
I have read every single thread related to generator neutral grounding and not grounding, third harmonics, circulating currents etc. I've read through Chapter 19 of Westinghouse T&D.
I'm not sure if it is my inability to understand, the different regulations or simply different site setups, but I can not get a grip on how I should go about the following.
The installation is as follows:
It is important to note that the generators are always connected to the grid so they are never operating in island mode. Each generator has only one circuit breaker connecting straight to the 415V LV bus. This LV bus is connected to the LV side of the star/delta 1500kVa transformer. On this same LV bus, 1200kVa worth of industrial equipment is also connected (mostly 3phase load), including some power factor correction gear with reactors blocking the 5th and 7th harmonics.
First only the 500kW generator were commissioned and worked fine with no excessive neutral currents. The neutral is directly connected to the neutral bus in the main switch room, which is directly earthed.
When installing the second generator (600kW) the problem started. This generator is connected exactly the same way as the first one. It's neutral is also connected to the neutral bus in the switch room. Both generators are set on PF control. On this I might also mention that the PF on the one 500 was set to 0.93 while the PF on the 600kW was set to 0.88. Can this have an affect on the problems I'm having?
The problem is the neutral current and third harmonics.
Since the installation of the second genset we've had capacitors blowing up, bus bars melting and fuses blowing out of the panels.
I have measured and am convinced that the neutral currents (same as phase currents in magnitude) are due to the third harmonics.
From reading all the threads I've seen heaps of different opinions but it could be due to slight variations on the specific sites.
Can I please get help on how to solve this one. I've seen solutions like zig zag transformers, disconnecting one of the generators' neutrals, NERs, neutral current eliminators, harmonic filters etc etc.
Help will be much appreciated.
