1. Understand the wiring of single-phase distribution transformers
Since transformers are basically AC devices, they do not have fixed polarity like DC power supplies. However, they have relative polarity markings that must be observed when connecting them together in different arrangements. Polarity is the instantaneous voltage obtained by the primary winding relative to the secondary winding.
Single-phase distribution transformer connecting leads are usually led out of the transformer's steel bushing through insulating bushings. In all transformers, the H terminal is always the high voltage terminal and the X terminal is always the low voltage terminal. Can be designated as primary or secondary, depending on which is the source and which is the load. By convention, terminals Hi and X1 have the same polarity, which means that when H1 is temporarily positive, X1 is also temporarily positive. These markings are used to establish correct terminal connections when connecting single-phase transformers in parallel, series, or three-phase configurations.
2. Single-phase distribution transformer wiring: add and subtract variable capacitor terminal markings
In fact, the terminals on the transformer are installed in a standard way, giving the transformer negative and positive polarity. The transformer is considered to have added value when terminal H1 is diagonally opposite terminal X. Likewise, when terminal Hi is adjacent to terminal X1, the transformer has reducing polarity.
3. Single-phase distribution transformer connection: double voltage transformer and its secondary winding in parallel
With this in mind, the H1 and H2 leads are labeled. Next, connect a jumper between the H1 lead and its adjacent low voltage lead, and connect a voltmeter between H2 and the other low voltage lead. Then apply a low voltage to the H1 and H2 leads and record the voltmeter reading. If the voltmeter reading is greater than the applied voltage, the transformers are additive and XI will be the right lead. If the voltmeter reading is less than the applied voltage, then the transformer subtracts, Xi on the left. In this polarity test, the jumper effectively connects the secondary voltage ES in series with the primary voltage E. Therefore, Es can be added to or subtracted from E. From this you can see how the terms "plus" and "minus" are derived. Two single-phase distribution transformers connected in parallel, another form of polarity marking is the point of use. Dot symbols are used in schematic diagrams to indicate which terminals are positive at the same time.
Single-phase distribution transformer
