What is a primary action taken when congestion occurs in PJM?

When congestion occurs in the PJM (Pennsylvania-New Jersey-Maryland Interconnection) transmission system, a primary action taken is to re-dispatch generation. This involves adjusting the output of electricity-generating units to manage the flow of power more efficiently across the transmission network. By redispatching generation, PJM can alleviate the congestion by either increasing the output from generators that are not constrained by transmission limits or reducing output from those that are causing the congestion.

Re-dispatching is essential because it helps maintain system reliability and ensures that electricity can be delivered where it is needed most. This action can optimize the use of available resources while adhering to the operational limits of the transmission system, thus minimizing the overall costs associated with congestion and maintaining a balanced load across the network.

In contrast, load shedding, which involves intentionally disconnecting consumers from the grid, is a more drastic measure used in emergencies to prevent system failure. Incrementing load does not address congestion; it might actually exacerbate it by increasing demand on the system without increasing supply. Increasing reactive power, while important for voltage stability, does not directly resolve the congestion issue. Thus, re-dispatching generation is the most effective and straightforward way to manage congestion in the PJM system.