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 a three-phase asynchronous current motor.
Basic operating principles
The basis of the reversing starter is an electromagnetic three-pole AC contactor. This part is considered the most important, and it is also it that ensures the performance of all functions that relate to operation 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 working mode was called "long";
- second mode of operation is intermittent-continuous;
- third mode - intermittent;
- The last operating mode of the starter is short-term.
To find out the duration of switching on each individual model of the reversing starter, you must refer to its technicalspecification that comes with each product.
Starter connection
This switching device is connected in the same way as all the others, except for the reverse button, as well as the magnetic starter. For these reasons, the connection diagram of this type of starter does not differ too much from the usual, standard version.
The first thing to ensure in the circuit is the full performance 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 interlock system, which will prevent the second starter from turning on or off spontaneously. If two starters are allowed to turn on at the same time, 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 turned 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 connecting 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 in the event that two starters turn onat the same time.
Occurrence of a short circuit
In order to change the direction of rotation of an induction motor, you need to swap two phases. In other words, if they are in the order "A-B-C", then on the second they should be, for example, on "C-A-B". 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, there are permanently closed contacts in the network, which, when the starter is turned on, create a break in the control circuit of the second starter, and at the same time an electrical blockage occurs. However, there is also a mechanical type of blocking. The essence of this process is quite simple. At the moment when the second starter is connected to the network, the mechanical device turns off the first one.
Assembling the circuit
It's actually pretty easy to put together, and most people can do it themselves. The reversing starters are in the housing, all that is required for connection is the correct connection of the contacts. However, it is important to say here that a mechanical interlock cannot be made by yourself, 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 supplied to the machine, which are most often indicated as follows: yellow "A", green "B" and red "C". After that theyare fed to the power contacts of reversing starters, which are usually indicated in the diagrams as KM1 and KM2. On the other side of these phases, three jumpers are created between the central green phases.
After assembling this part, the wires are connected to the motor through a thermal relay. It is important to note here that the current will only be controlled in two phases. It makes no sense to control the current in the third phase, since they are all quite closely related to each other. 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 increasing this parameter to a critical level will cause both starter coils to turn off at once.
Reversing starters with mechanical interlock PML
The use of this type of reversing starter is also carried out where it is necessary to monitor the start, reverse and stop of an asynchronous three-phase motor.
The design of these devices is considered quite simple. The body is made of plastic, and inside there is an anchor and a core. A special pull-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 an anchor is installed. In addition, special bridges with springs are also mounted near this element, which are designed to block the product.
How this worksthe device is quite simple. When current is applied to the device, voltage accumulates in the coil, due to which the armature begins to be attracted to it. When these two parts close, the armature opens the closed contact and closes the open one. The PML reversing starter is switched off at the moment when the contacts open.
Starters "Schneider"
Quite a common technique in the market of electrical appliances. This company has the EasyPact TVS series. The advantages of reversing starters "Schneider" from this series will be the following:
- rated current ranges from 9 to 150 A;
- rated voltage reaches 690V;
- quite a wide operating temperature range - from -50 to +60 degrees Celsius;
- Snap-type auxiliary contacts built in;
- number of poles - 3 or 4;
- one of the most important advantages is a fairly wide control voltage range.
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 from a distance. This device allows you to turn on and off the engine. There are 4 parts in the reversing starter housing:
- Contactor.
- Thermal relay.
- Casing.
- Tools for management.
After the "Start" command arrives,the electrical circuit is closed. After that, the current begins to flow to the coil. At the same time, a mechanical blocking device is activated, which prevents unnecessary contacts from starting. It should be said here that the mechanical lock also closes the contacts of the button, which allows you not to keep it pressed all the time, but to release it calmly. 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.
