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