400-Hertz Power Distribution

marking is shown in figure 3-17. Terminals for the high-voltage windings are marked H1, H2, H3, and so forth. The increasing numerical subscript designates an increasing voltage, denoting a higher voltage between H1 and H3 than the voltage between H1 and H2. The secondary terminals are marked X1, X2, X3, and so forth Two types of markings maybe employed on the secondaries. When the H1 and X1 leads are brought out on the same side of the transformer (fig. 3-17, view A), the polarity is called subtractive. The reason this arrangement is called subtractive is if & H1 and X1 leads are connected and a reduced voltage is applied across the H1 and H2 leads, the resultant voltage that appears across the H2 and X2 leads in the series circuit formed by this connection will equal the difference in the voltages of the two windings. The voltage of the low-voltage winding opposes the high-voltage winding and subtracts from it; hence the term, subtractive polarity. When the H 1 and X1 leads are brought out on opposite corners of the transformer (fig. 3-17, view B), the polarity is additive. If the H1 and X2 leads are connected and a reduced voltage is applied across the H1 and H2 leads, the resultant voltage across the H2 and X1 leads in the series circuit formed by this connection will equal the sum of the voltages of the two windings. The voltage of the low-voltage winding aids the voltage of the high-voltage winding and adds to it, hence the term, additive polarity. Polarity markings do not indicate the internal voltage stress in the windings. They are useful; only in making external connections between transformers. F’igure 3-17.-Polarity markings for large tramsformers: A. Subtractive polarity; B. Additive polarity. 400-HERTZ POWER DISTRIBUTION In addition to the 60-Hz power supplied by the ship’s service generators, ships also have 400-HZ systems. On some ships 400-Hz power is generated by motor-generator sets and distributed via special frequency switchboards (fig. 3-18) to the various 400-Hz equipment. These motor generators supply power to ship’s service special frequency switchboards. Figure 3-19 is a simplified line diagram of the 400-Hz ship’s service bus tie interconnections on an older ship. The circuits being fed from the 400-HZ ship’s service switchboards are deleted from the figure for simplicity. Newer ships get their supply of 400-Hz power through the use of 60/400-HZ static converters. The 400-Hz system consists of four MBT’s supplying 60-Hz power to four 60/400-Hz static frequency converters Figure 3-18.-400-Hz switchboard. 3-12