Star-Delta motor connection

The obvious superiority of asynchronous motors lies in the simplicity of their design (there are no brushes and a collector), unpretentiousness in operation and unprecedented durability in case of compliance with the maintenance regulations. The need for a three-phase power supply – the main disadvantage of machines of this type – does not at all cancel the possibility of their power supply from a single-phase 220 V household network

Just about complex theory

In essence, a three-phase network is a combination of three single-phase power lines, but with a strictly defined phase shift equal to 120^O Therefore, the motor windings are physically located relative to each other with the same angular distance. This design assumes that the current flows in series through the first, second and third windings. This, in fact, creates a torque, causing the rotor to rotate

When connecting an asynchronous machine to one phase, it is enough to simulate the presence of two more on its base. For this, various tricks were used, for example, a capacitor delay, which is widely used to this day. of these methods are characterized by a significant (sometimes significantly exceeding 30%) loss of engine power relative to the nominal value and, accordingly, a decrease in its efficiency. Therefore, more civilized methods have recently been used more often, connecting the machine through a frequency converter (FC), as the best option

About the stars and more

Any asynchronous motor operates in one of the – a star or a triangle, so called because of the way the windings of the machine are connected. In the first case, it resembles a three-beam star, and in the second – triangle

When connecting the windings with a star, despite the interphase 380, only 220 V of one phase is applied to each winding. This dictates modest starting currents. The disadvantage of the circuit lies in limiting the power of the machines, which leads to its use for relatively low-power motors

In the delta-connected windings, the end of each of them is connected to the beginning of the other, which explains the current 380 V between them. This causes large currents and, of course, the ability to connect powerful motors over 7.5 kW

There is no star/delta mode at allThis combined mode serves to reduce starting currents and increase torque when starting the machine (star) After a set of revolutions, a triangle is turned on, which is optimal for powerful engines Switching between modes is most often performed automatically, using, for example, by means of a time relay

Why do you need an inverter

IF – a device that converts a sinusoid of 50 Hz, which is far from perfect in our energy industry, into a series of pulses with a frequency of up to 1 kHz with inverters are not limited Modern devices of this type, ESQ-A500-021, for example, automatically create three full-fledged phases of 220 V / 50 Hz from one, which makes it extremely easy to connect three-phase loads to a household network. Most inverter models also provide the following preferences:

• implements protection against short circuits, overloads and power surges, providing emergency shutdown of the load;
• indicates the main parameters of the engine operation (depending on the model, it is possible to save them);
• optimizes power consumption according to machine load and allows high torque start

In addition, connecting through the inverter significantly reduces the noise and temperature of the motor windings, extending its life

The only disadvantage of using an inverter to power asynchronous motors is to limit their power to 4 kW But for most needs that require connecting a three-phase machine to 220 V, half this value is enough Circular saw, d / o machine and / or similar equipment most often equipped with power units of not more than 1.5 kW