07/14/2020

GE OLTC replacement by VACUTAP® RMV-II in Mexican Cement Plant


Mission in the Mexican jungle: Sociedad Cooperativa Cruz Azul, a cement company with almost 90 years of history in México, needed to modernize two old GE transformers at its plant in Lagunas Oaxaca. The problem: the OLTCs in the transformers were defective and the original manufacturer no longer produces them. Furthermore, neither service nor spare parts are available on the market for such OLTCs. This was therefore a job for the service specialists of Reinhausen Mexico (RMX) and the VACUTAP® RMV-II.

Both transformers are from 1970 – as were the GE OLTCs – and were subject to heavy use.  As the plant is in the middle of the jungle and the transmission line is very long, the voltage has to be constantly regulated.  Added to this were the extreme weather conditions which led to the failure of the old OLTCs.  Since a repair was not an option due to the discontinuation of GE’s production, Cruz Azul was looking for an economical alternative solution.  The colleagues from RMX were able to offer such a solution with the VACUTAP® RMV-II reactor OLTC.

Since the existing transformers already had a reactor, the RMV-II was the best solution since it uses the same transition impedance, and the tank of the new OLTC can be welded in the same position as the existing one.  This meant that it was not necessary to make major adaptations or modifications to the transformer tank or to the customer’s existing facilities.

The proposed solution was evaluated by the technical departments at RMX as well as by Reinhausen Manufacturing (RM) in Humboldt, where the VACUTAP® RMV-II is manufactured.  The main problem which they found was that the transformer wall where the existing OLTC was installed had almost the same dimension as the new RMV-II welding flange.  In order to be able to mount the OLTC on the wall of the transformer, a special flange was designed.

In addition to the tap changer, the delivery from Humboldt included a TAPMOTION® MD-III motor drive and a voltage regulator, as well as high-quality accessories from Messko, such as pressure relief device, oil level indicator and maintenance-free dehydrating breather MTRAB®, which is very useful considering the humidity of the area.

Once the parts arrived, the RMX colleagues needed only 12 days to complete the service work.  Although various transformer tests had been evaluated in advance for planning purposes, the RMX colleagues performed various electrical tests and took oil samples before starting the replacement work.  Dry air was injected to avoid the ingress of humidity while draining the oil, and the existing leads were identified and disconnected.

One of the greatest challenges of the project was removing the existing OLTC and cutting through the wall of the transformer in order to remove internal barriers and fire retardants inside the transformer tank.  The OLTC was removed from the transformer using the arc-air method.  This is a critical activity as the transformer cannot remain in this condition for a long period.  As night work was not allowed, a special flange was mounted in order to prevent humidity ingress, after which the window was widened and the welding surface was prepared.  Once the new OLTC was welded in, the leads were connected.  Once the MD-II was installed by adding supports to the tank of the transformer and was synchronized to the transformer, electrical tests were performed.  The active part of the transformer was washed with oil and finally a vacuum process was carried out for 48 hours to remove residual moisture.  The transformer was then filled with oil and oil samples were taken.  Finally, the new voltage regular was commissioned and configured.

After the installation and the execution of final tests on the transformer, a training course was held for the technicians and engineers at Cruz Azul.

With this successfully completed retrofit, Cruz Azul can now once again guarantee a stable voltage level and safe processes, and continue to produce cement of excellent quality as they have been doing since 1942.

T.Santana@mx.reinhausen.com  
 
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