Transmission Systems

Transmission system is the connection links between the generation station and the distribution system and lead to other power systems over inter connection.

Under ground cables or over head transmission lines can be used for this purpose.

Types of Over Head Transmission Line (O.H.T.L):

1.   Short O.H.T.L
2.   Medium O.H.T.L
3.   Long O.H.T.L

1-Short O.H.T.L

The following figure shows short T.L 3-ph link between the power plant and the loads.

Parameter	Definition
VR	Receiving end voltage per phase = VR\√3
VS	Sending end voltage per phase    =   VR + ΔV
IL	Line current
R	Line resistance per phase
XL	Line reactance per phase
ΔV	Line voltage drop per phase
PR(w)	Active power at receiving end
SR(VA)	Apparent power at receiving end
QR(VAR)	Reactive power at receiving end
CosφR	power factor at receiving end
PS(w)	Active power at sending end
SS(VA)	Apparent power at sending end
QS(VAR)	Reactive power at receiving end
CosφS	power factor at sending end.
ΔV	=ZL * Il = ILR + jILXL

  

 The previous circuit can be represented as single line diagram as shown:

2-Medium O.H.T.L

In this type , the capacitance cannot be neglected due to its high value. As increasing the length of T.L and line voltage, as increasing the value of the capacitance so in long T.L Ferranti effect appears. 

The medium T.L can be represented using two models:

T- model :

   The previous circuit can be represented as single line diagram as shown:

Where:

Z = R_L  + J X_L  = R_{L +} J wL_L                                                    

Y = J wC_L    

π- model :  

  The previous circuit can be represented as single line diagram as shown:

Generalized Circuit Constants Of T.L:

Generally, any T.L can be represented by Is , Vs and IR,VR as following:

Vs=AVR+B*IR.

IS =CVR+D*IR

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Ahmad Atiia

Hi. I’m Designer of Engineering Topics Blog. I’m Electrical Engineer And Blogger Specializing In Electrical Engineering Topics. I’m Creative.I’m Working Now As Maintenance Head Section In An Industrial Company.

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