The set of differential test modules is used to test the operation of protective devices that implement the IEEE function 87 and includes the following modules to test the operation values and also the trip blocking by the harmonic restrain:

Classic Differential 87C: Module used to check the operation of conventional differential relays (usually electromechanical or static).
Transformer Differential 87T: Designed for testing numerical relays for differential protection of transformers.
Generator/Motor Differential 87GM: Designed for testing rotating machines differential relays.
Busbar Differential 87B: Designed for testing busbar differential relays.

Classic Differential 87C: The module's functionality is distributed in the following sections:

• Technical Data: section to set up the general parameters associated with the data of the protected object, the characteristics of the protective device and the applied settings: number of windings, tap settings, restraint current calculation, current and time tolerances.
• Differential Operating Characteristic: section for configuration of the characteristic and the operating times of the relay, as well as defining the parameters for the harmonics restrain. ROOTS allows to edit in a very simple way the relay characteristic, either by implementing various types of predefined characteristics,  or by custom design. In tests designed for harmonic restrain in differential relays, ROOTS allows to add a certain component of a harmonic to the fundamental frequency value. Although the common practice is to work with the 2nd harmonic (Inrush Blocking) and 3 ° or 5 ° (Blocking by over excitation), harmonics from the second to the eighth can be manipulated.
• Harmonics Restraint Test: The harmonic restraint test evaluates the response of the relay to the harmonic content variation in measured current signals. Current is injected through one or more phases in a previously selected winding, where it is possible to indicate the phases which contain harmonics or not. The reaction of the relay is evaluated according to the adjusted set parameters. The test points are defined in the harmonic restraint characteristic with the zones of tolerance, where the differential current is drawn over the harmonic content of the test current. For simulating different inrush conditions, the initial phase shift between fundamental and harmonics can be specified. An automatically generated relay connection scheme is shown before the test is executed.

• Test List: Multiple tests can be attached to the module from the test types: click sequence, search, and harmonic restraint.
• Click Sequence Test: in Test Values window the user can define the test points for each phase, to be inserted in several ways, by coordinates values, clicking on the graph or by Smart Sweep insertion of multiple test points evenly distributed at the limits of the tolerance zone, in the selected fault loops. In the graph the operating characteristic of the relay is shown with the zones of tolerance in the Idiff/Ibias plane. The evaluation of the test points, either trip or no trip, will be done according to its position above or below the characteristic of the relay, or within the tolerance zone, and the different relay behavior in each case.
• Search Test: This test allows finding the boundary trip values which corresponds with the characteristic of the relay. It's actually a confirmation of the accuracy of the relay. The test is done by injecting consecutive faults by means of pulse ramps that are coming into the searched zone. The search for a point stops when the protection trips and then starts the search of the next point. There is a window to display the wiring of the analog current channels. In the text setting window the user can establish common parameters for all selected test points, such as the search type, search resolution and interval, and the windings to test.