into the adjacent network, especially if on one hand the compensated line is verylong with high degree of compensation, and the adjacent lines are, on the otherhand, relatively short.Extensive system studies are necessary before final decision is made onimplementation and location of series capacitors in network. It requires to correctlyestimate their influence on performances of (especially) existing distance IEDs. Itis possible that the costs for number of protective devices, which should bereplaced by more appropriate ones due to the effect of applied series compensation,influences the future position of series capacitors in power network.Possibilities for voltage inversion at remote buses should not be studied for shortcircuits with zero fault resistance only. It is necessary to consider cases with higherfault resistances, for which spark gaps or MOVs on series capacitors will notconduct at all. At the same time this kind of investigation must consider also themaximum sensitivity and possible resistive reach of distance protection devices,which on the other hand simplifies the problem.Application of MOVs as non-linear elements for capacitor overvoltage protectionmakes simple calculations often impossible. Different kinds of steady-statenetwork simulations are in such cases unavoidable.8.1.2.11 Distance protection SEMOD168320-338 v3Distance protection due to its basic characteristics, is the most used protectionprinciple on series compensated and adjacent lines worldwide. It has at the sametime caused a lot of challenges to protection society, especially when it comes todirectional measurement and transient overreach.Distance IED in fact does not measure impedance or quotient between line currentand voltage. Quantity 1= Operating quantity - Restraing quantity Quantity 2=Polarizing quantity. Typically Operating quantity is the replica impedance drop.Restraining quantity is the system voltage Polarizing quantity shapes thecharacteristics in different way and is not discussed here.Distance IEDs comprise in their replica impedance only the replicas of lineinductance and resistance, but they do not comprise any replica of series capacitoron the protected line and its protection circuits (spark gap and or MOV). This waythey form wrong picture of the protected line and all “solutions” related to distanceprotection of series compensated and adjacent lines are concentrated on findingsome parallel ways, which may help eliminating the basic reason for wrongmeasurement. The most known of them are decrease of the reach due to presenceof series capacitor, which apparently decreases the line reactance, and introductionof permanent memory voltage in directional measurement.Series compensated and adjacent lines are often the more important links in atransmission networks and delayed fault clearance is undesirable. This makes itnecessary to install distance protection in combination with telecommunication.The most common is distance protection in Permissive Overreaching Transfer Tripmode (POTT).Section 8 1MRK 506 369-UEN BImpedance protection182 Line distance protection REL670 2.2 IECApplication manual
