One of the standard connection schemes using a reversing starter allows you to change the direction of movement of the shaft. In addition, the purpose of the starter is to start, stop, and also protect the three-phase asynchronous current motor.
Basic principles of work
The basis of the reversing starter is an electromagnetic three-pole AC contactor. This part is considered the most important, and it is it that ensures the performance of all functions that relate to work with rated current and voltage, as well as with the switching capabilities of the starter and its resistance to mechanical wear.
The reversing starter can operate in several modes:
- the first operating mode was called "continuous";
- the second mode of operation is intermittently continuous;
- the third mode is intermittent;
- the last operating mode of the starter is short-term.
To find out the duration of the inclusion of each individual model of the reversing starter, you need to refer to its technical specification, which is attached to each product.
Starter connection
The connection of this switching device is carried out in the same way as all the others, with the exception of the reverse button, as well as the magnetic starter. For these reasons, the wiring diagram of this type of starter is not too different from the usual standard version.
The first thing that needs to be provided in the circuit is the full operability of the engine reverse, which should be carried out by changing the location of the two phases. At the same time, it is necessary to ensure the operation of the mechanical locking system, which will not allow the second starter to turn on or off spontaneously. If you allow the simultaneous inclusion of two starters at once, this will cause a short circuit.
Starter circuit operation
The circuit of a reversing starter with a mechanical interlock includes two identical starters. When the circuit is switched on, one of them starts the electric motor of the engine in one direction, and the second in the other. If we consider the essence of the connection, then the circuit is quite similar to the connection of two single starters, but there is still a difference. It consists in the presence of one common button "Stop", as well as two buttons "Forward" and "Back". In the same case, an electrical or mechanical interlock is used, which is designed to protect the device from a short circuit if two starters turn on at the same time.
Short circuit occurrence
In order to change the direction of rotation of the induction motor, two phases must be interchanged. In other words, if they are in the order "ABC", then on the second they should be, for example, on "ABC". It is this process of phase change that the reversing starter monitors. This suggests that the simultaneous shutdown of both models will lead to a short circuit in the circuit. In order to avoid this, the network has permanently closed contacts, which, when the starter is turned on, create a gap in the control circuit of the second starter, and at the same time, an electrical interlock occurs. However, there is also a mechanical type of lock. The essence of this process is quite simple. At the moment when the second starter is connected to the network, the mechanical device disconnects the first.
Circuit assembly
In fact, assembling such a scheme is quite simple, and most people can do it on their own. Reverse starters are located in the housing, all that is required to connect is the correct connection of the contacts. However, it is important to say here that mechanical locking does not lend itself to self-production, here you will have to buy a factory product.
It is recommended to start with the power part of the circuit. Three different phases are fed to the machine, which are most often indicated as follows: yellow "A", green "B" and red "C". After that, they are fed to the power contacts of the reversing starters, which are usually indicated in the schemes as KM1 and KM2. On the other hand, three bridges are created from these phases between the central green phases.
After assembling this part of the wire, they are connected to the electric motor through a thermal relay. It is important to note here that the current will be monitored in only two phases. It makes no sense to monitor the current in the third phase, since all of them are quite closely interconnected. In other words, if you increase the current strength in one phase, then the same thing will happen in the remaining two. This suggests that raising this parameter to a critical level will cause both starter coils to trip immediately.
PML mechanical interlock starters
The use of this type of reversible starters is also carried out where it is necessary to monitor the start, reverse and stop of the asynchronous three-phase motor.
The design of these devices is considered quite simple. The case is made of plastic, and inside there is an anchor and a core. A special pulling type coil is installed on the core. Due to the peculiarities of the circuit of this device, it turns out that the entire upper part of the body is occupied by traverse guides, over which the anchor is installed. In addition, special bridges with springs that are designed to lock the product are also mounted near this element.
The principle of operation of this device is quite simple. When current is applied to the device, the voltage accumulates in the coil, because of which the armature begins to attract to it. When these two parts are closed, the anchor opens a closed contact and closes an open. The PML reversing starter is disconnected at the moment when the contacts open.
Schneider starters
A fairly common technique in the market of electrical appliances. This company has the EasyPact TVS series. The benefits of Schneider reversing starters in this series are as follows:
- rated current is in the region from 9 to 150 A;
- rated voltage reaches 690 V;
- a fairly wide range of operating temperature - from -50 to +60 degrees Celsius;
- there are built-in additional contacts of instant type;
- number of poles - 3 or 4;
- one of the most important advantages is a rather wide range of control voltage.
Design and operation of a reversing magnetic starter
The distribution of these models is becoming wider every year, as they provide an exceptional opportunity to control an asynchronous motor at a distance. This device allows you to turn on and off the engine. The reverse starter housing has 4 components:
- Contactor.
- Thermal relay.
- Cover.
- Management Tools.
After the Start command is received, the electric circuit is closed. After that, the current begins to be supplied to the coil. At the same time, a mechanical locking device is triggered, which prevents unnecessary contacts from starting. It is worth saying that the mechanical lock also closes the contacts of the button, which allows you not to keep it pressed constantly, but to calmly release it. Another important detail is that the second button of this device, along with the launch of the entire device, will open the circuit. Because of this, it turns out that even pressing it does not give any result, creating additional security.