The transformer winding on which alternating voltage from the outside moves is called primary. Other windings from which tension moves on consumers are called secondary. To define what of windings is intended for use as primary, it is possible experimentally.
1. If it is precisely known that the transformer is lowering and it is calculated on food from network, measure by an ohmmeter of resistance of all its windings. At one of them it much more, than at the others - it also is primary. At measurement do not concern conclusions of the transformer and probes - in spite of the fact that it is not included in network, and measuring tension is not enough, amplitude of splashes in a self-induction can be rather high for painful electric shocks.
2. The anode and also combined anode and filament transformers can have both lowering secondary windings, and raising therefore to use the criterion described above it will not turn out. It is possible to find primary winding in this case on indirect signs. For example, its conclusions can be located separately from conclusions of the others. If it is visible where exactly the conductors going from conclusions to windings quite often are directed to find among them primary it is possible, knowing that most often it is reeled up in the beginning (that is, it is located most closer to the middle of a framework).
3. Modern transformers quite often have the partitioned frameworks. In this case primary winding usually is located in separate section. This section can be wound with a red insulating tape, and existence under a thickening insulation layer (for the thermosafety lock) is a sure sign of the fact that the winding is primary.
4. At the majority of the transformers calculated for work with a frequency of 50 Hz, the number of rounds on volt is close to 10. Reel up on it a temporary additional winding and give on it alternating voltage with the same frequency and with the operating value to 1 V. Being careful, measure tension on other windings - primary it will be possible to consider that on which tension is close to 220 V. Zatem remove an additional winding.
5. If primary winding has branch, it can work from two tension: 127 and 220 V. In the second case it is necessary to include in network it completely. If is there are two separate windings (on 127 and 93 V), it is possible to include them consistently (for tension in 220 V) only inphase. For this purpose in the previous experiment try to include them in consistently two ways (before reswitching remove stress from an additional winding). That option at which the resulting tension will be much more and corresponds to inphase inclusion.