GENERATING SITE INTERCONNECTION GUIDELINES
12/6/04
The following new generation interconnection guidelines were developed in 2004 The guidelines were developed with input from Duke Power’s Strategic & Business Planning, Generation, and Power Delivery areas.
The preferred option would be to have the switchyard located on the footprint of the generation site. However, the new sites being evaluated are frequently a significant distance from the nearest transmission circuit. The diagrams below show the typical options for generator interconnection. In cases where the generation is remote from the transmission circuit, the existing transmission lines are folded into the switchyard in a breaker and a half scheme for each line to prevent problems with the generator or its bus line(s) from tripping the transmission line. To minimize right of way costs, the switchyard is located close to the existing transmission circuit and bus lines are run to the generation site.
As a general rule, the standard transmission connection for baseload units up to 1200 MW should be as follows:
- Minimum of 2 independent paths connecting to different locations within the system. Configure with either 2 double-circuit 230 kv bus lines (Figure 1), 2 - 500 kV bus lines (Figure 2), or if at a tie station - 1 double circuit 230 kV line and 1 500 kV line.
- Once an exact location has been determined, this standard may be tweaked to account for the strength of the system in the area of interconnection, but the standard above should be sufficient for most locations.
- Add an independent path to a separate location on the system for each additional 500 MW to 600 MW
As a general rule, the standard transmission connection for intermediate and peaking units up to 700 MW should be as follows:
- Single transmission path connecting the generation switchyard to the transmission grid, either double-circuit 100 kV or 230 kV bus lines (Figure 3) or single circuit 500 kV bus line (Figure 4). Design changes such as BIL levels may be applied for enhanced reliability.
- Once an exact location has been determined, this standard may be tweaked to account for the strength of the system in the area of interconnection, but the standard above should be sufficient for most locations.
- Add an independent path to a separate location on the system for each additional 500 MW to 600 MW
Evaluating these design standards given the existing operational data:
- 230 kV lines trip about .02 times per year/mile and have a sustained outage (i.e. > 1 minute) about .004 times per year/per mile.
- 500 kV lines trip about .03 times per year/mile and have a sustained outage about .008 times per year/per mile.
- Double circuit 230 kV and higher - ~25 % of the time a line goes out, the parallel line also trips.
and assuming a 10 mile distance from the generating plant to the existing transmission circuit, shows that the baseload units up to 1200 MW would suffer a momentary complete loss of transmission event once every 12 to 20 years. The intermediate/peaking units up to 700 MW would suffer a complete loss of transmission event once every 3 to 20 years. Given the lower likelihood of intermediate/peaking unit operation and shorter restoration time this is acceptable. Sustained loss of transmission events would be lower by about a factor of 5.
230 kV
To GSU’s
(center breaker optional)
(two 100% capacity bus lines)
FIGURE 1
500 kV
To GSU’s
(center breaker optional)
(two 100 % capacity bus lines)
FIGURE 2
100 kV & 230 kV
To GSU
Tap lines on same tower
(two 100% capacity bus lines)
FIGURE 3
500 kV
To GSU
(May eliminate 2 breakers to form simple ring bus)
FIGURE 4