Principle, Structure and Fault Analysis of Centrifugal Switch
Release time : 2023-09-28
The centrifugal switch is a switch that uses the principle of centrifugal force to control a circuit. It is mainly used to start and stop single-phase motors. It can automatically switch the starting winding and running winding according to the motor's speed, thereby achieving smooth starting and efficient operation of the motor. If you want to know what parts a centrifugal switch is made of, how it works, and what the consequences will be when it fails, then continue reading this article and I will break it down for you.
Catalog
Ⅰ.What is a centrifugal switch?
Ⅱ.Structural components of centrifugal switch
Ⅲ. The Principle of the centrifugal switch
Ⅳ.Advantages and Disadvantages of Centrifugal Switches
Ⅴ.Test methods for centrifugal switches
Ⅵ.What will be the impact if the centrifugal switch is not turned off after the motor is started?
Ⅶ.Do all single phase motors have centrifugal switches?
Ⅷ.Centrifugal switch in induction motor
Ⅸ.Why do most single-phase induction motors use centrifugal switches?
Ⅹ.Application of centrifugal switch
Ⅰ.What is a centrifugal switch?
Figure1:centrifugal switch
The centrifugal switch is a switch that uses the principle of centrifugal force to control a circuit. It is mainly used to start and stop single-phase motors. The function of the centrifugal switch is to automatically switch the starting winding and running winding according to the speed of the motor, thereby achieving smooth starting and efficient operation of the motor.
Figure2:centrifugal switch diagram
Ⅱ.Structural components of centrifugal switch
Magnet: The magnet is the core component of the centrifugal switch. It consists of two control magnets and a moving magnet, which are connected by a spring. The function of the magnet is to generate different magnetic fields according to changes in the power signal, thereby driving the movement of the swing rod.
Swing rod: The swing rod is the actuating part of the centrifugal switch. It consists of a weight and a pin, which are connected by a sliding mechanism. The function of the swing rod is to generate different centrifugal forces based on the driving of the magnet, thereby promoting the movement of the pin.
Contactor: The contactor is the control component of the centrifugal switch. It consists of a fixed contact and a moving contact, which are connected by a spring. The function of the contactor is to connect or disconnect the circuit based on the movement of the pin.
Special wiring body: The special wiring body is the connecting part of the centrifugal switch. It consists of a wire and a plug, and they are connected by welding. The function of the special wiring body is to introduce power signals from the outside to provide current to the magnets.
Ⅲ. The Principle of the centrifugal switch
Figure3:The Principle of the centrifugal switch
The centrifugal switch is a switch that uses the principle of centrifugal force to control a circuit. It is mainly used to start and stop single-phase motors. The working process of the centrifugal switch is as follows:
When the motor is stationary, the magnet attracts the swing rod, causing the contactor to close and the start winding and run winding to work in parallel. At this time, the motor's speed is low and requires larger starting current and starting torque.
When the motor reaches a certain speed, the swing rod is affected by centrifugal force, pushing the pin to move, causing the contactor to disconnect, the starting winding to exit, and only the running winding to work. At this time, the motor speed is higher and requires smaller operating current and operating torque.
When the motor stops, the swing rod returns to its original position under the action of spring force, causing the contactor to close and the start winding and running winding to be connected in parallel again.
The working principle of the centrifugal switch can be explained by the following physical formulas and diagrams:
Centrifugal force refers to the outward force generated due to inertia when an object moves in a circular motion. The size of the centrifugal force is related to the mass, angular velocity and radius of the object. The formula is:
Figure4:formula
The direction of centrifugal force is perpendicular to the direction of motion of the object and points toward the center of the circular motion. As shown below:
The swing rod in a centrifugal switch is a pendulum-like device that can make circular motions in a horizontal plane. When the swing rod is driven by a magnet, it rotates at a certain angular speed and generates centrifugal force. As shown below:
The pin in a centrifugal switch is a slider-like device that moves horizontally and has a contact point. When the swing rod is acted upon by centrifugal force, it pushes the pin to the right and opens the contactor.
As shown below:
Figure5:Perpendicular diagram of the direction of centrifugal force and the direction of motion of an object
Ⅳ.Advantages and Disadvantages of Centrifugal Switches
The advantages and disadvantages of centrifugal switches are as follows:
Advantage:
The centrifugal switch can automatically start and stop the motor without manual intervention and is easy to operate.
The centrifugal switch can automatically switch the starting winding and running winding according to the motor's speed, thereby achieving smooth starting and efficient operation of the motor.
The centrifugal switch can avoid overload or overheating of the starting winding and protect the safety of the motor and capacitor.
Centrifugal switches can save electrical energy and reduce motor losses and noise.
Disadvantages:
The centrifugal switch is a mechanical switch that is prone to mechanical wear and failure and requires regular inspection and maintenance.
The disconnection speed of the centrifugal switch is affected by many factors, such as power supply voltage, load, temperature, etc., which may lead to untimely or inaccurate disconnection and affect the performance of the motor.
The contacts of the centrifugal switch are prone to sparks or adhesion, which may cause dangers such as short circuit or fire.
Ⅴ.Test methods for centrifugal switches
Test method of electronic centrifugal switch: The electronic centrifugal switch is an intelligent electronic switch that can automatically determine the motor frequency and pole number through motor speed feedback. The test method is to connect the electronic centrifugal switch to the power supply, first read the power supply voltage and frequency, determine the frequency of the motor to be 50HZ or 60HZ, then test the number of poles of the motor, and finally control the motor according to the corresponding motor frequency and number of poles.
Test method of mechanical centrifugal switch: A mechanical centrifugal switch is a switch that uses a swing rod and a contactor to control a circuit. The test method is to connect the mechanical centrifugal switch to the power supply, observe whether the swing rod and contactor operate normally, check whether the contactor has sparks or adhesion, and measure whether the resistance of the starting winding and running winding meets the requirements.
Multimeter test method: A multimeter is an instrument that can measure physical quantities such as voltage, current, resistance, etc. The test method is to adjust the multimeter to the ohm range and measure the resistance values at both ends of the centrifugal switch. When the centrifugal switch is closed, a very small resistance value should be displayed; when the centrifugal switch is open, an infinite resistance value should be displayed.
Test lamp method: Test lamp is a simple tool that can detect whether the circuit is connected or not. The test method is to connect the test lamp to both ends of the centrifugal switch. When the centrifugal switch is closed, the test lamp should light up; when the centrifugal switch is disconnected, the test lamp should go out.
Ⅵ.What will be the impact if the centrifugal switch is not turned off after the motor is started
The starting winding and the running winding will always work in parallel, resulting in excessive current, increasing the loss and noise of the motor, and reducing the efficiency and life of the motor.
The starting winding and running winding will produce a mutual inductance effect, which will interfere with the normal operation of the motor, cause vibration and temperature rise of the motor, and even cause dangers such as sparks or short circuits.
The starting winding and running winding will affect the torque characteristics of the motor, making the motor unable to adapt to load changes, which may lead to overload or stalling of the motor.
Therefore, in order to ensure the safety and performance of the motor, the centrifugal switch should be checked and maintained in time to avoid the situation where the centrifugal switch does not turn off. If a fault is found that the centrifugal switch does not turn off, the motor should be stopped immediately, and the cause of the fault should be found, such as damage, looseness, jamming, etc. of the magnet, swing rod, contactor, etc., and repair or replacement should be carried out accordingly.
Ⅶ.Do all single phase motors have centrifugal switches?
The centrifugal switch is a switch that uses the principle of centrifugal force to control a circuit. It is mainly used to start and stop single-phase motors. The function of the centrifugal switch is to automatically switch the starting winding and running winding according to the speed of the motor, thereby achieving smooth starting and efficient operation of the motor.
Not all single-phase motors have centrifugal switches, only some special motors are equipped with centrifugal switches. These special motors are usually motors that require larger starting torque or higher operating efficiency, such as air conditioning compressors, water pumps, fans, etc.
If you want to determine whether a single-phase motor has a centrifugal switch, you can identify it through the following methods:
Appearance identification method: Observe whether there is a small cover on the end cover of the motor. If there is, then it is probably the location of the centrifugal switch; if not, then there is probably no centrifugal switch.
Touch identification method: touch the shell of the motor. If it feels hot, there is probably a centrifugal switch; if it feels cool, there is probably no centrifugal switch. This is because the centrifugal switch generates some heat when activated.
Circuit identification method: Open the end cover of the motor and check the internal circuit of the motor. If you see a centrifugal switch connected to the starting winding, it means there is a centrifugal switch; if you do not see it or it is not connected to the starting winding, it means there is not one. Centrifugal switch.
Sound identification method: Plug in the power supply and test run the motor, then disconnect the power supply. If you can hear the sound of the centrifugal switch disconnecting, it means there is a centrifugal switch; if you do not hear any sound, it means there is no centrifugal switch.
Ⅷ.Centrifugal switch in induction motor
An induction motor is a motor that uses alternating current to generate a magnetic field and induced current to drive the rotor to rotate. It is available in single-phase and three-phase. Since the single-phase induction motor has only one AC power supply and cannot generate a stable rotating magnetic field, it requires a starting winding and a running winding to work together to start and run the motor.
Figure6:Centrifugal switch in induction motor
Ⅸ.Why do most single-phase induction motors use centrifugal switches?
Figure7:Centrifugal switch in single phase induction motor
A single-phase induction motor is a motor that uses single-phase alternating current to generate a magnetic field and induced current to drive the rotor to rotate. It is divided into single-phase and three-phase. Since the single-phase induction motor has only one AC power supply and cannot generate a stable rotating magnetic field, it requires a starting winding and a running winding to work together to start and run the motor.
The centrifugal switch is a switch that uses the principle of centrifugal force to control a circuit. It is mainly used to start and stop single-phase induction motors. The function of the centrifugal switch is to automatically switch the starting winding and running winding according to the speed of the motor, thereby achieving smooth starting and efficient operation of the motor.
Most single-phase induction motors use centrifugal switches for the following reasons:
The centrifugal switch can automatically start and stop the motor without manual intervention and is easy to operate.
The centrifugal switch can automatically switch the starting winding and running winding according to the motor's speed, thereby achieving smooth starting and efficient operation of the motor.
The centrifugal switch can avoid overload or overheating of the starting winding and protect the safety of the motor and capacitor.
Centrifugal switches can save electrical energy and reduce motor losses and noise.
Ⅹ.Application of centrifugal switch
The application of centrifugal switch is very wide, it can be used in various types and specifications of single-phase motors, such as grinders, mixers, compressors, blowers, pumps, cranes, submersible motors and cleaners, etc. 23 The centrifugal switch not only protects the motor from overload or overheating damage, but also saves electricity, reduces noise, and improves efficiency and lifespan.
In addition to single-phase motors, centrifugal switches also have some special applications, such as electronic centrifugal switches and signal switches.
