ALLInterview.com :: Home Page
 Advertise your Business Here     
Browse  |   Placement Papers  |   Company  |   Code Snippets  |   Certifications  |   Visa Questions
Post Question  |   Post Answer  |   My Panel  |   Search  |   Articles  |   Topics  |   Errors
   Testimonials Refer this Site  Refer This Site to Your Friends  Site Map  Contact Us      
   
 
Categories >> Engineering >> Electrical Engineering
 


 

 
Question what is surge impedance loading and it's significant in
power system?
 Question Asked In Companies ::     < I also faced this Question! >
 Question Submitted By :: praveen420
  Answer Posted By  
 
Answer
SURGE IMPEDANCE LOADING (SIL)



The surge impedance loading or SIL of a transmission line is
the MW loading of a transmission line at which a natural
reactive power balance occurs. The following brief article
will explain the concept of SIL.



Transmission lines produce reactive power (Mvar) due to
their natural capacitance. The amount of Mvar produced is
dependent on the transmission line's capacitive reactance
(XC) and the voltage (kV) at which the line is energized.
In equation form the Mvar produced is:





Transmission lines also utilize reactive power to support
their magnetic fields. The magnetic field strength is
dependent on the magnitude of the current flow in the line
and the line's natural inductive reactance (XL). It follows
then that the amount of Mvar used by a transmission line is
a function of the current flow and inductive reactance. In
equation form the Mvar used by a transmission line is:





A transmission line's surge impedance loading or SIL is
simply the MW loading (at a unity power factor) at which the
line's Mvar usage is equal to the line's Mvar production.
In equation form we can state that the SIL occurs when:









If we take the square root of both sides of the above
equation and then substitute in the formulas for XL (=2pfL)
and XC (=1/2pfC) we arrive at:









The term in the above equation is by definition the "surge
impedance. The theoretical significance of the surge
impedance is that if a purely resistive load that is equal
to the surge impedance were connected to the end of a



transmission line with no resistance, a voltage surge
introduced to the sending end of the line would be absorbed
completely at the receiving end. The voltage at the
receiving end would have the same magnitude as the sending
end voltage and would have a phase angle that is lagging
with respect to the sending end by an amount equal to the
time required to travel across the line from sending to
receiving end.



The concept of a surge impedance is more readily applied to
telecommunication systems than to power systems. However,
we can extend the concept to the power transferred across a
transmission line. The surge impedance loading or SIL (in
MW) is equal to the voltage squared (in kV) divided by the
surge impedance (in ohms). In equation form:





Note in this formula that the SIL is dependent only on the
kV the line is energized at and the line's surge impedance.
The line length is not a factor in the SIL or surge
impedance calculations. Therefore the SIL is not a measure
of a transmission line's power transfer capability as it
does not take into account the line's length nor does it
consider the strength of the local power system.



The value of the SIL to a system operator is realizing that
when a line is loaded above its SIL it acts like a shunt
reactor - absorbing Mvar from the system - and when a line
is loaded below its SIL it acts like a shunt capacitor -
supplying Mvar to the system.



Figure 1 is a graphic illustration of the concept of SIL.
This particular line has a SIL of 450 MW. Therefore is the
line is loaded to 450 MW (with no Mvar) flow, the Mvar
produced by the line will exactly balance the Mvar used by
the line.

Is This Answer Correct ?    39 Yes 0 No


 
  gautam kumar
 
View All Answers
 
 
Please Help Members By Posting Answers For Below Questions
 
 Question Views   Select
 
why the India electrical supply transmission loss is high when compare to us 328
What is d main advantage of using double circuit 3 phase transmission ? 242
how electricity is generated an supplied till consumer 310
What is true sine wave or pure sine wave inverter?? Is it sine wave or step wave?? If it is step wave, waves with how much step is considered as pure sine wave? Is it possible to produce pure sinewave using power electronics? 234
What is the use of mc( moving coil) in dc voltmeter and dc ammter and what is the use of ( moving iron)in ac voltmeter nd ac ammeter 1018
what are the dimensions for 200 kva transformer plinth (plateform),in which pcc m20 is used.. 4304
what is the procedure for erection of a transformer 1238
What happen Grid EARTH plat got cut. 512
what is the meaning of impedance protected in instrument cooling fan 577
Leakage current,un balance current which relay using for high voltage transmission? 383
What will happened if the neutral of secondary of Xformer ( Star point) Note it's above KVA rated Xformer 269
Give details on how you intend to handle a challenging position you are posted to manage unexpectedly as a company staff? 1376
control & auxilary circuits used for circuir breakers 340
what is the role and fuction of automatic transfer switch in rotary ups 292
What is the minimum insulation value required for a cable between phase to phase and phase to earth of 380 Vac 50Hz circuit, having load arround 800 amps. 298
E-Mail New Answers        Answer Selected Questions