Smart low side Rollover

CenterPoint Energy´s (CNP) system (5000 square-mile serving 2.26 million customers) has been experiencing rapid growth for many years. As a result, new infrastructure has been added actively to the system such as distribution circuits, substations and new transmission lines to alleviate the stress on the system. However, all of these projects require that departments have healthy budgets to achieve such projects. One major expensive component to alleviate stress on the distribution system is the power transformer itself. For example, if a typical low-profile system with two power transformers rated at 25 MVA max each had a load demand on both transformers greater than that, then there is a delicate situation where if one transformer was lost, the load that is rolled over could potentially cause the remaining energized transformer to trip due to over-current. Majority of time, this should not be a situation, because planning of the distribution system has determined that the load at a specific substation would not cause an additional transformer trip due to a loss of a transformer. But, when planning of distribution system does recognize that an upgrade on the transformer is needed due to rapid load growth, there are some occasions where the transformer might not get installed until a few years later due to budget constraints or vendor lead time. In this case, the Smart Rollover application would be implemented to safeguard the total load of the substation from being interrupted due to over-load of the remaining transformer. This paper will provide the details on how CNP´s Smart Low-Side Rollover is accomplished using distribution system remote control switches on feeders to transfer load to other nearby substations. A discussion on the configurations between the Remote Terminal Unit (RTU), ladder logic software, and micro-processor relay settings will be explained. In addition, this paper will explain the initial flaws with the application when attempted with elec- - tromechanical and microprocessor relays and discussed the solutions to these problems. This paper will also emphasize that this application can be considered a component of the Smart Grid concept by effectively using distribution system remote control switches to redistribute the loading of a substation to multiple substations. Also, this paper discusses the limitation of the ?Smart Low-Side Rollover? if incorporated in the Smart Grid concept.