Test system for an intelligent electronic device in an electric sub-station

Examples of a test switch unit (100, 300, 600, 900, 1200, 1500) for testing an IED are described. Each of the test switch units may be utilized for opening of a trip circuit, the shorting of a CT circuit and subsequently the isolation of a VT circuit, respectively. Once the trip circuit has been opened, and the CT/VT circuits have been shorted and isolated, respectively, the IED may be tested by providing appropriate test signals. The opening, shorting and isolation function of the test switch units are triggered simultaneously by operating a lever (118, 324, 618) connected to a common shaft (116, 322, 616) which extends through all test switch units, wherein cams (114, 320, 614) located on the shaft open and close contacts of each test switch unit to achieve the respective function.