Electric Motor Components and Operation Explained
Electric Motor Components and Operation
The constitution of the electric motor comprises a casing, a fixed part or stator, and a rotating part or rotor:
Stator
The stator is a cylindrical ring composed of metal plates made and fitted under pressure into the motor housing. Its entire surface has available slots in which drivers are housed in the windings.
Rotor
The rotor rotates around the same axis as the stator. It consists of a cylinder formed by electrical sheets also pressed, with slots in its periphery. Drivers are housed in these slots.
In motors with windings, the rotor short-circuit is closed from the outside through some brushes and slip rings.
Rated Current
Rated current is the current that the motor takes from the network to produce the rated power on its axis.
Starting Current
Starting current is the current the motor draws from the network at boot time. This intensity is greater than the nominal motor current.
Power (kW)
Electric power.
Horsepower
Mechanical power.
Cosine φ
Cosine φ at full load usually takes values between 0.80 and 0.90, and in vacuum takes values close to 0.60.
Voltage Star
230/400V.
Voltage Triangle
400/690V.
Motor Starting
The starting of small motors for direct connection to the network does not cause significant disruption. According to manufacturers, for motors in excess of 1.5 kW power, a limiter device must be used. This type of boot is sewn for simply connecting the stator windings to the network, earlier in star or delta. Switches can be manual or electrically controlled.
Star-Delta Starter
The star-delta starter powers the motor to the network in a Y connection at startup, and during acceleration, passing the connection to the triangle when the rate has stabilized. This connection is only possible in cage motors whose final connection to the network is in a triangle.
Softstarter
Softstarters are static starters, semiconductor devices that are inserted between the network and the motor. They are used for phase motors, cages, small and medium power, and torque is increased from values of 0.2 Mn to 1.5 Mn -0.3.
Contactor
The contactor is a communication device that is actuated electromagnetically. An important fact is the contactor’s nominal employment. This is the maximum applicable to their contacts.
An important feature for choosing a contactor is the nature and way of being switched. The contactors of a contactor carry:
- At the time of closing (current setting).
- While closed (nominal use intensity).
- In the moment of opening under load (cutting intensity).
A contactor can connect and disconnect a particular receiver. The employment category defines the contactor.
Category AC1
When switching resistive loads.
Category AC3
When switching phase motors and these stabilize its rated speed.
Category AC4
When switching phase motors able to do special things.
On a contactor, is the tensile implementation of its coil, with subsequent closure of its contacts. The activated time is defined as the time between the start winding voltage and closing its contacts.
Thermal Relay
A thermal relay is an overload detection device based on its thermal effect. The detector element is a metal foil consisting of two soldiers, whose coefficients of thermal expansion are different. Being swept by the intensity control, there is a curling toward the side opposite the metal that expands more. The same effect occurs if the intensity is not the runs, but the heated indirectly.
Fuses
Fuses are devices for protection against overcurrents. Applied to the protection of electric motors, they supplement the protection provided by the thermal relay. An important feature of a fuse is its rated current. It is defined as the value of the stream which crosses, from which the merger will result in a longer or shorter time.
Circuit Breaker
The circuit breaker is a circuit breaker to disconnect the power of the network:
- Manually.
- When subjected to an overload.
- When a short circuit in the power line.
This device comprises, initially, the functions of the switch, thermal relay, and fuses in a single block.
Temperature Detectors
Temperature detectors do not adequately protect the engine if they are regulated at the rated current. In such circumstances, they are used to directly control the temperature of the windings by suitable detectors.
These detectors are small tablets that are inserted between the windings, whose resistance increases rapidly when the temperature exceeds certain limits.