High Impedance Differential Protection and Low Impedance Differential protection 1 HD

Free Electrical Calculator for android Best android app for Electrical Engineer and EEE student Download the app from play store: https://goo.gl/VPNp5h High Impedance Differential Protection and Low Impedance differential Protection: High impedance protection system is a simple technique which requires that all CTs, used in the protection scheme, have relatively high knee point voltage, similar magnetizing characteristic and the same ratio. These CT shall be installed in all ends of the protected object. In order to make a scheme all CTs belonging to one phase shall be connected in parallel. From the CT junction points a measuring branch is connected. The measuring branch is a series connection of one variable setting resistor (RS) with high ohmic value and overcurrent relay. Thus, the high impedance differential protection responds to a current flowing through the measuring brunch. However, this current is result of a differential voltage caused by this parallel CT connection across the measuring branch. This current and voltage are interrelated by Ohms Low. Low Impedance Differential Protection: Low-impedance bus differential relays are so named because the differential relay current inputs have a low impedance to the flow of CT secondary current. This means that the low-impedance bus differential relays can share the CTs with other relays, meters, transducers, etc. The lowimpedance bus differential scheme typically has one set of current inputs for each phase from every set of CTs in the scheme.