《current_transformer_paper》.pdf

Selecting Current Transformers Part 1 By Darrell G. Broussard, P.E. Introduction: • A secondary winding around the As engineers, we are aware that electrical power core systems have grown. How much have they • Insulating material grown? When was the last time you specified a When current travels through a current 2400-volt system, a 4160-volt 250 MVA system, caring device, such as a cable or bus duct it a 15 kV 500 MVA system or specified a 2000- develops a magnetic field at right angles to amp 480-volt system? An industrial plant now the flow of current. The strength of the requires a larger and more complex system than magnetic field varies as the current magitude was required just a few years ago. The 2400-volt changes during all operating conditions. As systems have all but disappeared; 4160-volt learned in transformer theory, when a systems have expanded from 350 MVA to 63 kA magnetic field strikes a wire, it will cause a (equivalent to 500 MVA). The 15 kV systems current to flow in the wire. By using the also have expanded to 63 kA (equivalent to 1500 strength of the magnetic field and knowing MVA). Has all of the electrical system the turns ratio, we can obtain a value of expanded? current that is useable for meters, relays and other current sensing device. In order to monitor and to protect the power system we must measure the energy flow. To In order to scale a value of high current connect a meter, relay or other current sensing flowing in a conductor, the engineer needs device in series with a lar