Interconnected power system and advantages

An interconnected power system is one in which several generating stations, possibly of different types and owners, are connected together through a transmission network (grid) so that they jointly supply all the loads connected to it.

Typical diagram

 Hydro G1         Thermal/Solar G2      Hydro G3
   |11kV             |11kV                |11kV
 [GT]              [GT]                 [GT]
   |                 |                    |
 ==+=====220/132 kV==+=========132 kV=====+==
   |                 |                    |
 [S/S]            [S/S]---tie line--->Neighbour grid
   |33 kV            |33 kV
 [33/11]          [33/11]
   |11 kV            |11 kV
 [11/0.4]--loads  [11/0.4]--loads

Advantages over an isolated system

1. Higher reliability: If a plant fails, others supply the load.
2. Less reserve capacity: Spinning reserve is shared, so installed capacity per area falls.
3. Economic operation: Cheapest plants (e.g. run-of-river hydro) are loaded first; base and peak load plants are used optimally.
4. Use of diverse sources: Wet-season hydro surplus can be exported and dry-season deficit imported (Nepal–India exchange).
5. Load diversity: Peaks of different areas occur at different times, reducing total required capacity.
6. Better voltage and frequency stability.
7. Larger, more efficient units can be installed.
8. Exchange of energy between utilities and countries.

Disadvantage: fault level increases and a disturbance can spread unless protection is well coordinated.