Phase connection with delta

When you connect the phase windings of a three-phase generator with a triangle (Fig. 1), the beginning of H 'of one phase is connected to the end of K «the other, the beginning of the other H» — to the end of the third K '»and the beginning of the third phase H '» is connected to the end of the first H '.

The phase windings of the generator form a closed loop with low internal resistance. But with symmetrical e. etc. v. (equal in magnitude and equally displaced relative to each other) in phase and with the external circuit disconnected, the current in this circuit is zero, since the sum of three symmetrical e. etc. c. is equal to zero at any given moment. In this connection, the voltages between the line conductors are equal to the voltages of the phase windings:

If all three phases of the generator are loaded exactly the same, then equal currents flow in the line wires. Each of these line currents is equal to the geometric difference between the currents in two adjacent phases. So, the linear current vector Azc is equal to the geometric sum of vectors in phases Azsa and Azsb (Fig. 2, a). The vectors of the phase currents are shifted relative to each other at an angle of 120 ° (Fig. 2, b).

Rice. 1. Delta connection of generator windings.

From figure 2, b it follows that the absolute value of the line current

Like generator windings, a three-phase load can be turn on the star and a triangle.

Rice. 2. Vector diagram of currents.

So, three-phase electric motors are designed to connect the windings, depending on the voltage in the network, in star Y or in delta Δ.

If there is no neutral wire in the network and therefore the user has three line voltages available, he can artificially create phase voltages. For this purpose, three identical resistances (loads) are connected to the network according to the star scheme. Each of these loads will be connected to a phase voltage (Fig. 3):

The connection of the windings of the generator according to the triangular scheme is mainly used in mobile power plants of small power with a network of limited length (power plants of electric shear units, etc.).

In a four-wire, three-phase system, the neutral wire is reliably grounded at the power plant, at network branches, and at certain distances along the line. This wire is used to ground the metal boxes of pantographs at the consumer.

Rice. 3. Connection of three current collectors with equal resistance according to the star scheme in three linear wires.

Rice. 4. Connection diagram to a three-phase four-wire network of lighting (220 V) and power (380 V) loads.

Figure 4 shows a diagram for connecting lighting and loads to a three-phase four-wire network. The lighting load is connected to a phase voltage of 220 V. They strive to evenly load all three phases with a single-phase load.For this purpose, one phase with a neutral wire for lighting is carried out on one street of the settlement, on the other - the second phase and the neutral wire, on the third - the third and neutral wire, etc. motors, welding transformers), as well as powerful three-phase heating devices are connected to mains voltage.