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Page 111

| may exist between corresponding secondary windings before such units can be connected in parallel or in banks. |

| The typical three-phase transformer has a nameplate which includes a diagram (called a voltage-vector diagram) showing the relations between the voltages of the three phases in accordance with one of the groups shown in Table 7-1. The angular displacement between the H and X voltages (the high-voltage and low-voltage winding) is the angle between lines passing from the neutral point of the voltage-vector diagram through H1 and X1 respectively. |

| Leads are marked so that the sequence of the H and X voltages (usually referred to as the phase rotation) in the order H1, H2, H3 and X1, X2, X3 will be the same. That is, if a three-phase motor could be connected across the terminals H1, H2, and H3 (let the imagination forget the difference in voltage magnitudes for time being) it would rotate in the same direction as when connected across the terminals X1, X2, and X3. |

| To check for phase displacement, one of the H leads is connected to one of the X leads, as shown in Table 7-1. The primary of the transformer is connected to a low-voltage, three-phase source (preferably much lower than |

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