Electric motor! 6 and 12 end coil closure

 

A very common question among professionals in the Electrical Industry is about the connection scheme for electric motors. In this article we show how to close three-phase motors, explaining the detail of the coils and poles. So come on guys!

Electric motor connection
If you are an electrician you have certainly heard about star connection and triangle connection after all these two themes are all about the wiring diagram for three-phase motors.

To better understand the power of the electric motors, the first step is to understand that we are actually talking about the connection scheme for the motor coils. Therefore, it is essential to know how the three-phase motor stator works.

Electric motor stator
The stator is made of rolled steel, which is small sheets joined together. In the image below we can see all the overlapping plates of this stator, and also the bones that are these copper windings!

How to make a star connection and triangle connection?
Discover the stator of an electric motor, with details on the coil terminals!

In an electric motor, each coil creates two magnetic poles, a south pole and a north pole, and this happens in each of the phases. So a three-phase motor with 3 coils will have two poles per coil, being known as a two-pole motor. Therefore, three-phase motors can have 2, 4, 6, 8 or more poles, but always in even numbers and depending on the number of coils wound.

In case you don’t know, the number of poles in an engine and the electrical frequency of the network is what makes the motor speed vary, that is, the more poles you have, the slower the motor spins.

In the table below you can see and relate the frequency, a number of poles and the speed of the three-phase motors. Note that a 2-pole motor at 60Hz has a speed of 3,600 RPM, while a 4-pole motor at the same frequency of 60Hz has a speed of only 1,800 RPM.

How to start an electric motor?
Understand the relationship of frequency, number of poles and the speed of three-phase motors!

Three-phase sine cycle
Now you will be able to see the comparison of a 2-pole motor and a 4-pole motor, observing each instant of a three-phase sine cycle. See how the four-pole motor spins at half the speed of the two-pole motor.

At T1, the two-pole motor has the north pole at the top and the south at the bottom. The 4-pole motor has a north pole at the top and a north pole at the bottom, plus a south pole on the right and one on the left.

At time T2 it is possible to see that in the two-pole motor there is a 90-degree displacement, while in the four-pole motor the displacement was only 45 degrees. Note that in the following times this shift remains constant.

How to start an electric motor?
See the three-phase sine cycle of a 2 and 4 pole motor!

Following the changes in direction of the poles, we can see that the displacement of the two-pole motor at the end of the five times is 360 degrees, that is, a complete turn. In the 4-stroke engine, the turn is only 180 degrees.

Electric motor coils
The number of grooves in an engine is extremely relevant information for professionals in the electrical world who work with rewinding engines. The coil is attached to the stator inside these grooves, and the number of terminals on a motor indicates the connection possibilities of this motor.

The most common are 6-point motors and 12-point motors. The one we have here is a 12-motor, because it has 12 terminals to power the motor. Another important information is that the ends of the terminals are numbered according to the coils, as shown in the image below.

How to make a star connection and triangle connection?
See how the coil terminals of electric motors look!

Coil 1 has terminals 1 and 4, coil 2 has terminals 2 and 5, coil 3 has terminals 3 and 6, coil 4 has terminals 7 and 10, coil 5 has terminals 8 and 11 and coil 6 has terminals 9 and 12. The electrician who works with electric motors needs to know that any three-phase motor with 3 coils in the stator or six terminals, offers the option of being able to work with two different voltages. This happens through different connections between the coils, which are the famous triangle and star connections.

How to start an electric motor?
Three-phase motor with 3 coils in the stator or six terminals!

Electric motor: Star connection
The star connection is made by connecting terminals 4, 5 and 6 to each other. Each of the points 1, 2 and 3 is connected to the phases of a three-phase system forming a star, as shown in the image below. The point of connection between terminals 4, 5 and 6 forms a neutral point.

See how to make star connection and triangle connection
Example of a three-phase motor star connection

In the star connection each coil is connected between a phase and a neutral, and this type of connection accepts the phase voltage of a three-phase system. If you do not know what phase and line voltage are, there is a complete article here on the site explaining this, it is worth reading!

Electric motor: delta connection
The triangle connection is made by connecting terminals 1 with 6, 2 with 4 and 3 with 5, as shown in the image below! Each of these ends is connected in one of the phases of a three-phase system. In this type of connection, there is no neutral and each coil is connected to two phases. The delta connection accepts the line voltage of a three-phase system.