In June, NES where requested by a collaborating partner to assist them with startup of 3 synchronous machines in Congo. The line from Inga to Kolwezi has through the past 5 years been refurbished by installing a HVDC system. Also in Kolwezi the start equipment of three synchronous machines of over 70Mva has been refurbished. These machines have a rotating mass of over 90 tons. NES saw this as a great challenge, and Freddy Agledal, NES` highly skilled and experienced service coordinator, went to Congo end of August and started the work consisting of commissioning and startup of 3 3000A 690V air cooled frequency converters.
The machines where built in the 1970`s. At this time, they started the machines directly with 50% of the voltage. This consumed over 8000A on the 11,6KV side. This kind of starting method causes an enormous mechanical stress to the machine resulting in damage to machine and other electrical equipment. With the new starting method, a frequency converter is used to run the speed slowly up from 0-50Hz. The consumption now is less than 200A on the 11,6KV side. After the smooth start, the machine synchronizes to the grid and uses reactive load to stabilize the complete electrical grid in Congo.
Together with the rest of the commissioning team in Kolwezi Freddy Agledal completed the task within the time limits. The synchronous compensators are now starting and synchronizing to the grid within 10 minutes. If, for some reason, the synchronization fails, the frequency converter is able to catch the machine with a “flying start”. This is necessary since it takes 90 minutes before the machine have reached zero speed. It takes some time to stop 90 tons from rotating with 750 RPM.
The customer was very satisfied with the good results achieved. NES also provided necessary training to the parts involved.
The power plant in Congo