DSP MKII is a ground fault relay. It comes with a grounding resistor. It's the vintage model of the I-gard.
If you have feeder modules, it will tell you which phase is grounded and on which feeder. It leaves you live with one occurring ground fault (Alarm). If you get a second ground fault on a different phase, it will trip that feeder. All feeders have a zero-sequence CT, to detect this additional short-circuit.
Since OP has an delta system, an artificial ground is needed and this is done with a zigzag transformer. The neutral of this zz transformer is grounded via a grounding resistor.
These GF systems may come with the option of ''pulsating'' the resistor, that let you track this pulsating signal with a flexible zero-sequence CT between the switchboards of the faulty branch and hopefully find the problem.
