Power module PFSK160A

 Power module PFSK160A

 Power module PFSK160A

Distance protection due to its basic characteristics, is the most used protection principle on series compensated and adjacent lines worldwide. It has at the same time caused a lot of challenges to protection society, especially when it comes to directional measurement and transient overreach.

Distance IED in fact does not measure impedance or quotient between line current and 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 the characteristics in different way and is not discussed here.

Distance IEDs comprise in their replica impedance only the replicas of line inductance and resistance, but they do not comprise any replica of series capacitor on the protected line and its protection circuits (spark gap and or MOV). This way they form wrong picture of the protected line and all “solutions” related to distance protection of series compensated and adjacent lines are concentrated on finding some parallel ways, which may help eliminating the basic reason for wrong measurement.

The most known of them are decrease of the reach due to presence of series capacitor, which apparently decreases the line reactance, and introduction of permanent memory voltage in directional measurement. Series compensated and adjacent lines are often the more important links in a transmission networks and delayed fault clearance is undesirable.

This makes it necessary to install distance protection in combination with telecommunication. The most common is distance protection in Permissive Overreaching Transfer Trip mode (POTT)