Abstract: A method of automatically plotting the loci curves of multi-stage distance relays. The comparison impedances, required for the measurement, are automatically provided for given impedance angle by adjustable currents and voltages. During the determination of the loci curves there is started with a defined, predetermined impedance value which is either greater or smaller than that which is sought to be found. By taking the half of this impedance value or by doubling with subsequent halving, when starting with smaller impedance values, it is possible to incrementally approach the sought of impedance value as a function of whether or not, for the corresponding timing stage of the distance relay, its measuring element responds or does not respond.

Abstract: A method, and apparatus for, protecting an object, and specifically detecting ground shorts in the rotor circuit of a generator, wherein for essentially completely detecting a ground short the phase of an alternating signal is modulated to produce an alternating injection or test signal which is delivered to the object to be protected, i.e. the rotor circuit. A response signal corresponding to the injection signal and indicative of the ground short is derived from the rotor circuit. The modulated alternating signal may be at the network frequency and modulation of the phase thereon preferably encompasses continuously switching the phase of the alternating signal between two phase positions in the sense of a phase oscillation. The alternating signal is preferably in the form of an alternating voltage.

Abstract: The intermediate current transformer is replaced by a shunt resistor which bridges the secondary winding of the main current transformer and is of such magnitude that the secondary winding of the main current transformer is virtually short-circuited, but the voltage at the shunt resistor is still sufficient for evaluation in the electronic relay. The shunt resistor consumes only very little power and can therefore be located in the base of a plug-in device. This base, being a permanent part of the assembly, remains in circuit even when the relay is changed or removed for inspection or testing purposes.

Abstract: A test apparatus for checking test objects, such as protective relays, especially voltage, current and/or frequency relays for the protection of a generator of a power supply network, comprising a first circuit for generating and converting test signals or magnitudes to be delivered to the test objects and a second circuit for pre-programming the test signals or magnitudes to be delivered to the test objects. The first circuit comprises a first test signal generating circuit for supplying the voltage relay and the current relay with voltage and current test signals, respectively, and contains a first secondary winding of a test transformer. A static potentiometer is connected in parallel with this first secondary winding. The potentiometer supplies test signals in finely stepped or graduated values to the test objects. The first circuit further comprises a second test signal generating circuit for supplying the frequency relay with frequency test magnitudes.

Abstract: A method of, and apparatus for, protecting electrical devices, such as generators connected in parallel against ground faults or shorts, wherein when there arises a ground short at one of the parallely connected generators a ground or earth current (response signal) flows between the fault location and a ground location. The network is grounded at the ground location by means of a ground transformer and a ground resistance. In order to essentially completely detect the ground short the phase of an alternating signal is modulated to produce an alternating injection or test signal which is delivered to the network containing the parallely connected generators. A response signal corresponding to the injection signal and indicative of the ground short is derived from the electrical network.