Grand Isle Terminal Project
Vermont Electric Power Company (VELCO) is proposing to update an electric substation in Grand Isle, Vermont.
The Grand Isle terminal is the eastern terminus of six 115kV Self-Contained Fluid-Filled (SCFF) cables that cross underneath Lake Champlain to a western terminal on Cumberland Head, New York.
The Crossing consists of three parallel pairs, or phases, of high-voltage electric transmission cables, each pair consisting of one 500 thousand circular mills (mcm) cable and one 1000 mcm cable. Oil pressure in each cable is mainted by a pair of 20 gallon tanks in the Grand Isle Terminal substation.
Installation of the initial Grand Isle Terminal circa 1958 consisted of four 500 thousand circular mills (mcm) cable, three in service and one spare. Following a failure of one of the cables, three new 1000 mcm cables were installed and the failed cable was abandoned. To serve the new cables, two additional pairs of tanks were installed in 1970.
The oil level gauges on the four original pairs of oil tanks are inaccurate and result in false low-level alarms. The piping and valves have become obsolete and make it very difficult to maintain the oil system. Dut to the criticial status of the connection, technicians are immediately dispatched to investigate the alarms, which typically turn out to be the result of instrumentation error.
VELCO is proposing to replace the four original sets of gauges with new gauges of a type and accuracy of those installed in 1970. Other project components:
- installation of a control panel to transmit equipment signals back to VELCO's Control Center;
- installation of current flow monitoring capability at each cable and phase;
- replacing existing lead piping with copper pipes;
- adding oil sampling valves;
- installalation of new control wiring;
- installation of oil containment facilities;
- new control building