Slack bus

In electrical power systems a slack bus (or swing bus), defined as a Vδ bus, is used to balance the active power |P| and reactive power |Q| in a system while performing load flow studies. The slack bus is used to provide for system losses by emitting or absorbing active and/or reactive power to and from the system.

For power systems engineers, a load flow study explains the power system conditions at various intervals during operation. It aims to minimize the difference between the calculated and actual quantities. Here, the slack bus can contribute to the minimization by having an unconstrained real and reactive power input.

${\displaystyle P_{i}=P_{Gi}-P_{Li}}$

${\displaystyle \Delta P_{i}=P_{i}-P_{i,calc}}$

${\displaystyle \Delta Q_{i}=Q_{i}-Q_{i,calc}}$

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