This paper describes the development of a mathematical model of three current transformers which are connected in a delta configuration as part of a differential protection scheme. The delta connected configuration is typically found in transformer differential protection schemes for star - delta transformers. This model can be used in real time algorithms for testing of relays and can also be used to study differential protection schemes off-line. The accuracy of the model is validated by comparing the simulations with waveforms recorded at a synthetic test plant.

This paper presents the simulation of multiple current transformers (CTs) operating in parallel into a common spill circuit. The voltage across the spill branch in the high impedance case can be quite high and a varistor (MOV) may be placed across the spill branch to keep this voltage within safe limits.

This paper describes the development of a mathematical model of an air gapped current transformer. Air gapped current transformers are widely used in generator protection since these have the capability to overcome some of the problems encountered when using conventional current transformers. The model developed here is validated by comparing simulation results with recorded waveforms from a manufacturers synthetic test plant.

Di¤erential protection schemes for busbars, generators or transformers connect multiple current transformers in parallel across a common burden. This paper describes the techniques used to simulate such an arrangement in real time.

The hysteresis loop of the core material in a test current transformer is simulated using the Jiles-Atherton theory. Comparisons are made between recorded and simulated waveforms and it is found necessary to replace the modified Langevin function used by Jiles and Atherton. Using an alternative function described in the paper, good agreement is achieved between test and simulated waveforms.

Differential protection schemes for busbars, generators or transformers connect multiple current transformers in parallel across a common burden. This paper describes the techniques used to simulate such an arrangement and concentrates particularly on the three current transformer case.

The Jiles/Atherton phenomenological model of a ferromagnetic material is used in the simulation of current transformers (CTs) in a differential current protection scheme. The results of simulation studies for a two CT scheme are compared to waveforms recorded during practical tests

This paper describes how an EMTP-based simulator can be used in conjunction with a relay test set to type-test a protection relay operating within a circulating current differential protection scheme. The combination of a simulator and a test-set is designed to replace a high power synthetic test plant that has been used for more than 30 years for type and approval testing of differential protection relays. The paper includes results that describe the operating performance of the new test system, on both internal and external faults, and these are compared with experimental results obtained from an identical set of tests on the synthetic test plant.