IEC phasing standards cannot use the method described above to communicate the phasing to a digital transformer relay. The European designation uses a clock system, with each hour set at a 30บ increment of a lagging phase angle from the X1 bushing to the H1 bushing.
The clock is divided into 12 segments.
Each segment number indicates the number of 30บ increments by which the phase angle is shifted (e.g., 1 = 30องศา and 11 = 11 x 30องศา = 330องศา). The letter “D” is used to designate a delta winding and the letter “Y” is used to designate a wye winding. The letter that is capitalized is the primary or “H” winding of the transformer.
Figure 7 illustrates the clock concept and the standard IEC-phasing
examples.