09-25-2009 09:40 PM
There is no "master" generator with a LSM setup. A LSM in droop will lower the speed command as the individual generator load increases, and will not react with the load sharing lines at all. A LSM in isochronous will adjust the speed command to drive the generator load percentage to the bus average without changing the system speed. In order for load sharing to work properly, all LSMs with generators connected to the bus need to be in the same mode. For isochronous operation, the droop connection should be tied into the paralleling circuit breaker auxillary contacts for that generator so that the LSM is in droop with the generator isolated, and isochronous with the generator on the bus (regardless of whether another generator is connected or not) -- at no time should the LSM be in isochronous with the generator paralleling breaker open, or it will cause the speed of the generators on the bus to decrease.
As for the CT sizing, I'm not sure if you'll be able to adjust the LSM load gain to get 6 volts across the test points with only 2 amps on the CT secondary, but you should be able to get the system to operate properly (although possibly with less accuracy) by setting the load gain to get a lower voltage across the test points that is the same on all generators at full load.
09-25-2009 10:43 AM
Working in saudi Arabia I am in charge of the power production for a wide site provided with 14 power plant equipped with new gensets CAT C18.
All C18 are mounted with load sharing module woodward 82686B to have a good sharing of the load between all gensets.
The dealer is unable to adjust correctly that installation so now I started to set myself the load sharing system.
First observation : for me with the LSM (load sharing module) there are 2 different types of regulation interconnected : isochronous mode concerns the genset which is the master (it keeps always same speed). Second mode is "droop mode", it means that LSM will modify the rpm of genset to modify the sharing.
But in all my C18 the "droop contact" is not mounted, all C18 are always in isochronous mode so for me in that configuration it's impossible to share the load.
I putted "droop contact" myself and now when I put one genset in isochronous mode (I call this genset MASTER) and others in droop mode (I call these gensets SLAVES) I obtain a good evolution of the speed but the sharing is wrong.
Second observation :
CT sends current to LSM which needs to know for each phase voltage and current to make load signal.
Normally at full load(about 1000 amperes for my 60Hz 681KVA/480KW C18) this current from CT to LSM must be 5 amperes but the CTs provide current in scale 2500/5 so of course with 1000 amperes of load my current is not 5 but 2 amperes ans LSM cannot made correct load signal.
Dealer has used CTs which are mounted by CAT to send current information to computer of the genset.
I think (but I would like to obtain confirmation) that I must modify connections of LSM to add "droop contact" for all my C18 (60 units ...) an I believe that I have to put in genset 3 new others CTs with range 2500/15 (to have 5 for 1000) and reconnect it to LSM.
What do you think about my problem, my analysis and my proposition ?
Sorry for my so bad english but I'm french (nobody is perfect ! lol)