PML starter: designation and characteristics

Magnetic starters (PML, PMA, PME, etc.) are designed to start, reverse and stop asynchronous motors. In the event that this unit is equipped with a thermal relay, this makes it possible to protect the electric drive from the effect of overload. In addition, there are non-reversing and reversing, closing and opening, open and closed starters.

The magnetic starter PML is most often used for remote control of DC and AC motors. Stationary installations require direct connection to the electrical network. In the role of such installations, asynchronous AC motors with a squirrel-cage rotor are used.

The installation of thermal relays having three poles to the PML starter allows to protect the control circuits and motors from possible short circuits and overloads, which entail unacceptable currents in duration and magnitude. Overloading can occur under various conditions, for example, when changing the circuits of winding, breaking or falling out of one of the phases of a three-phase system. This device is designed to work in various control systems with the help of microprocessors, which will allow the control coils to be shunted by a device for suppressing interference.

In addition, the PML starter mounted on the drive can have additional functions, such as reversing the protected motor.

The PML starter has a fairly simple notation system, which includes an alphanumeric cipher. The letter designation PML reflects the symbol of the series. The first digit includes the designation of the value of the starter, which directly depends on the rated current. This parameter can take a value from 1 to 6 at a current of 10-160 A. The second digit indicates the presence and purpose of the thermal relay. The third figure shows the degree of protection from climatic influences. It can be expressed in digits from 0 to 6.

The fourth digital designation is responsible for the number and nature of the contacts present in the auxiliary control circuit. In addition, the purpose of the contact system is indicated: disconnecting or closing. The fifth is the letter designation. Letter "D" - starter PML with rated currents 16 and 80 A for 1 and 4 values respectively. And also this letter is used for 3 values with understated mass-dimensional indicators. The letter "M", following it, means the possibility of attaching to a standard rail or directly to the desired plane.

Next follows the designation of the category of premises in which this equipment will be installed. The last in the designation is a letter indicating the quality of wear resistance. Can be represented in the form of letters "A", "B" or "B", this directly depends on the number of trips to which the PML starter is susceptible.

In addition to the starter of this type, other magnetic starters can also be used to protect electric circuits, for example, PMA, PME, KMI, CME and others. They differ in the way they are connected - to the stator or to the motor rotor. The starter type CME differs from the others in that it is a complete system designed to protect the circuits and control the motor that is connected to a voltage of up to 400 V.