27 November 2010



Concepts of tie line with reference to MiPower

The Tie line refers to those lines connecting one utility to other or those lines, which island the system, when kept open. In inter connected operation of power system, it is the responsibility of individual utility to operate the system such that tie line exchange remains constant, Consider two systems A& B connected by a tie line as shown in figure.

Following an increase in load in area B, say by 25 Mw, after the primary control (governor action), a case may arise wherein A will be exporting 10MW extra to B. Hence the representation becomes.
If the flat tie line control were to be there, then A to B should be brought back to 50 MW I.e. the tie line scheduled power. In order to do that, rise signal should be given to generator in area B to increase the generation. The control is called secondary control or AGC (Automatic generation control). In MiPower, it is possible to schedule the tie line flow, by changing the generator set points of all generators trying to participate in the secondary control.
A simple system with two generators and 4 loads all connected at same voltage through bus couplers. The total load is 4x7.5MW. One generator is scheduled for 20 MW and other is slack with generation capacity of 10 MW, the program is not saying converged but it shows generation output of slack generator as 29.54 MW with 0 MVAR and other generator with 0 MW and 12 MVAR while MVAR load total is 13 MVAR. What is the reason ?
  • In Elements - Generator Data there is one Heading called as "Real power optimization Data under which Give Real Power Min = 0.0, And Real Power Maximum = ( your specified power or scheduled power )
  • If in the system, generation is more and load is less, slack bus takes / absorbs additional power
  • Observe the following in the LFA report
    • Total Real Power Generation
    • Total Reactive Power Generation
    • Total Real Power Load
    • Total Reactive power Load
The above values should almost match to get converged result
Which are the primary parameters considered in a load flow study?
  • P Active power into the network.
  • Q Reactive power into the network.
  • |V| Magnitude of bus voltage
  • & Angle of bus voltage referred to a common reference.


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