Power Flow in Transmission Line
Presented by
T.S.L.V.AyyaraoAssistant Professor
GMRIT
Power Flow in Transmission Line
E1 and E2 are the magnitude of the bus voltages,δ the angle between two and X the line reactance
The driving voltage drop EL is phasor difference E1-E2
The line current I = EL/X and lags EL by 900
The current flow in the line can be controlled by controlling EL or X or δ
Fig 1: A Simple two-machine System
Power Flow in Transmission Line
The rating of series controller would be a fraction of the rating of the line
If the angle δ is small, the current flow
largely represents the active power Increase or decrease of line
reactance X will greatly affect
the active power flow It is the cost effective means of controlling the power The active power at E1 end is P1 = E1E2 sin δ/X
Reactive power at E1 end is Q1 = E1(E1-E2 cos δ)/X
Fig 2. Phasor diagram
Power Flow in Transmission Line
The active power at E2 end is P2 = E1E2 sin δ/X Reactive power at E1 end is Q1 = E2(E2-E1 cos δ)/X Active power flow increases
up to δ = 900 and then falls to 0 Control is possible well below
δ = 900
Sufficient margin is required for transient and dynamicstability
Increase or decrease of X will raise or lower the curves Fig 3. power angle curves for
different X
Power Flow in Transmission Line
Power flow can be controlled by regulating the magnitude of E1 or E2
The driving voltage EL doesn’t
vary by much but its phase
angle does The change of magnitude
has much effect on
the reactive power than
the active power flow
Fig 4. regulating the magnitudes of voltages
Power Flow in Transmission Line
Current and hence power flow can be controlled by injecting a voltage in series of the line
By varying the magnitude and phase angle of the injected voltage, active and reactive power flow can be controlled.
Fig. 5 (a) quadrature (b) with phase angle
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