Answer / ravi

These terms appear in the calculation of fault currents.
Common sources of fault currents are rotating machines,
i.e., motors and generators. An important factor in
detrmining the magnitude of a fault current is a variable
reactance that changes rapidly after the initiation of the
fault until it reaches a steady state.

Subtransient Reactance:-usually denoted as X''d (X double
prime sub d), is the reactance used to determine the
current during the first cycle after the occurance of the
fault.
Transient Reactance:-In about 0.1 second this
reactance increases to the
level known as Transient Reactance usually denoted as X'd,
and after 0.5 to 2 seconds it increases to the leven known
as Synchronous Reactance and denoted as Xd, and this
determines the fault current after a steady condition is
reached.

Answer / chunkey pandey

These terms appear in the calculation of fault currents.
Common sources of fault currents are rotating machines,
i.e., motors and generators. An important factor in
detrmining the magnitude of a fault current is a variable
reactance that changes rapidly after the initiation of the
fault until it reaches a steady state.

Subtransient Reactance:-usually denoted as X''d (X double
prime sub d), is the reactance used to determine the
current during the first cycle after the occurance of the
fault.
Transient Reactance:-In about 0.1 second this
reactance increases to the
level known as Transient Reactance usually denoted as X'd,
and after 0.5 to 2 seconds it increases to the leven known
as Synchronous Reactance and denoted as Xd, and this
determines the fault current after a steady condition is
reached.

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