Dual Slope Transformer Differential Relay

http://files.engineering.com/download.aspx?folder=c68ca315-4790-4fc9-9ef1-60fb78e28833&file=Low_Z_Differential_Relay_Protection_Settings.pdf

Differential relay slope transformer can be tested by first determining the starting point of the slope which is mentioned in the relay setting in the form of restraining current value.

When dealing with transformer differential protection, before diving into what the relay can offer, the protection engineer must 1st know the following: 1. Vector group 2. Transformer connection (standard or non standard) 3. CT connection also take account of the polarity (differential and non differential) These information will be helpful in properly setting the relay more importantly the winding compensation that will be offered by the relay itself. 1. Pickup current, you can convert analog quantities (test points) to per unit values (Iop and Irt) that the relay itself is using in determining if the sum of the HV and LV currents are within a tolerance value as to not issue a differential tripping signal. That is why vector group is important in properly setting the relay. Since a +30 degrees increment or a -30 degrees in the phasor angle of the test points will have an impact in the Iop and Irt quantities measured by the relay. 2.Initial slope, final slope and crossover point plus the minimum pickup (idiff>) determines the characteristic of the operate and restraint region of the relay. One good application when setting up the relays is that set a value of the SLP1 that will be enough to cover inrush currents and magnetizing currents as to not issue false tripping. Also for the SLP2 one must considered the effects of CT saturation as to not also issue false tripping. A good differential relay offers not only differential protection but also Harmonic blocking and harmonic restraint.

Yeah! It's really seams to be good.