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 protects the drive from the effects of overload. In addition, distinguish between non-reversible and reversible, closing and opening, open and closed starters.
PML magnetic starter is most often used for remote control of AC and DC motors. Fixed installations require direct connection to the electrical network. As such installations are used asynchronous AC motors with squirrel-cage rotor.
The installation of thermal relays having three poles on the PML starter protects 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 winding circuitry, breakage or loss of one of the phases of a three-phase system. This device is designed to operate in various control systems using microprocessors, which will allow the control coils to be shunted by a device to suppress interference.
In addition, the PML starter mounted on the electric motor may have additional functions, such as reversing the protected motor.
The PML starter has a fairly simple notation system, which includes an alphanumeric cipher. The PML lettering reflects the series designation. The first digit includes the designation of the magnitude 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 digit shows the degree of protection against climatic influences. It can be expressed in numbers from 0 to 6.
The fourth digital designation is responsible for the number and nature of the execution of the contacts present in the auxiliary control circuit. In addition, the purpose of the contact system is indicated: opening or closing. Fifth is the letter designation. The letter "D" is the PML starter with rated currents of 16 and 80 A for 1 and 4 values, respectively. And also this letter is used for 3 quantities with underestimated mass-dimensional indicators. The letter "M" following it means that it can be mounted on a standard rail or immediately on the desired plane.
The following are the designations of the category of premises in which this equipment will be installed. Last in the designation is a letter indicating the quality of wear resistance. It can be represented in the form of the letters “A”, “B” or “C”, this directly depends on the number of operations to which the PML starter is subject.
In addition to a starter of this type, other magnetic starters can be used to protect electrical circuits, for example, PMA, PME, KMI, KME and others. They have differences in the method of connection - to the stator or to the rotor of the motor. The KME type starter differs from the rest in that it is a complete system designed to protect circuits and control the motor, connected to a voltage of up to 400 V.