Summary of control technology knowledge for wind turbine motors in Shandong, with one copy for each electrical control personnel
Shandong wind turbine motor star connection method: Three windings, each end connected to one phase of the three-phase voltage, and the other end connected together.
Triangle connection method: Three windings are connected end-to-end, and three-phase voltage is connected at each of the three connection ends.
Reduced voltage starting: When the motor capacity is large, the power supply voltage is reduced and connected to the stator winding of the motor to start the motor.
Main circuit: The main circuit is a circuit from the power source to the motor or the end of the line, which is a circuit through which strong current passes,
Auxiliary circuit: The auxiliary circuit is a small current passing through the circuit
Shandong wind turbine motor speed relay: a non electrical signal detection electrical device that takes speed as input. It can output a switch signal when the measured speed rises or falls to a predetermined set value.
Relay: A relay is a control component that converts electrical or non electrical signals into electromagnetic force (with contacts) or causes a step change in output state (contactless) by utilizing changes in various physical quantities
Thermal relay: It is a protective electrical device that operates based on the principle of the thermal effect of current.
Communication relay: a relay that attracts coil current for alternating current.
Temperature relay: A protective electrical device that operates by indirectly reflecting the winding temperature using an overheated element is called a temperature relay.
Jogging circuit: Press the inching button, the coil is energized and attracted, the main contact is closed, and the motor is connected to the three-phase AC power supply
Start rotation: Release the button, the coil is powered off and released, the main contact is disconnected, and the motor is powered off and stopped.
Variable pole speed regulation: a speed regulation method for asynchronous motors that changes the number of stator poles.
Variable frequency speed regulation: a speed regulation method for asynchronous motors that changes the power frequency.
The principle of energy consumption braking for three-phase asynchronous motors: Energy consumption braking is the process of cutting off the three-phase power supply to the stator winding when the motor stops, and connecting the stator winding to a DC power supply to generate a static magnetic field. By utilizing the interaction between the rotor induced current and the static magnetic field, a braking torque is generated for braking.
What is the difference between short-circuit protection and overload protection: When a short circuit occurs, the circuit will generate a large short-circuit current and electric force, causing damage to electrical equipment. Need to quickly cut off the power supply. Common short-circuit protection components include fuses and automatic switches.
The motor allows for short-term overload, but long-term overload operation can cause the winding temperature to rise beyond the allowable value, and the motor must also be powered off for protection. The commonly used overload protection component is a thermal relay
When the motor starts, the current is very high. Why does the thermal relay not operate? Due to the thermal inertia of the thermal element of the thermal relay, it will not deform quickly. When the motor starts, the current is very high, but the starting time is short, and the high current is not enough to deform the thermal element and cause contact action.
What types of relays are commonly used according to their operating principles: electromagnetic, magneto electric, inductive, electric, photoelectric, piezoelectric, time and temperature (thermal) relays, etc. In the main circuit of an electric motor, why install thermal relays when fuses are installed? What's the difference between them?
Fuses can only be used for short-circuit protection and cannot be used for overload protection; Thermal relays can only be used for overload protection and cannot be used for short circuit protection. So it is necessary to install both in the main circuit.
What are the applicable situations for reverse braking and energy consumption braking of three-phase AC motors?
Reverse braking is suitable for small capacity motors below 10KW that do not frequently brake. Energy consumption braking is suitable for large capacity electric motors that require smooth, accurate braking, and frequent starting.
What is the difference between intermediate relays and contactors? Under what conditions can intermediate relays be used instead of contactors?
The main contact capacity of the contactor is large, mainly used for the main circuit; The intermediate relay has a large number of contacts and is mainly used for control circuits. When the circuit current is low (less than 5A), intermediate relays can be used instead of contactors.
What are the characteristics of reverse connection braking and energy consumption braking for three-phase AC motors?
When the power supply is reversed for braking, the relative speed of the rotating magnetic field between the rotor and stator is close to twice the synchronous speed of the motor. Therefore, the reverse braking current flowing through the rotor winding at this time is equivalent to twice the starting current of the motor at full voltage starting. Therefore, the reverse braking torque is large and the braking is rapid.
In energy consumption braking, there are two control methods based on the connection of DC power: time principle control and speed principle control. Both methods require the addition of a DC power supply and transformer, resulting in slow braking.
In the "forward reverse stop" control circuit of the electric motor, the composite button has already played an interlocking role. Why use the normally closed contacts of the contactor for interlocking? Because when the main contacts of the contactor are "welded" together by a strong arc or when the contactor mechanism fails and the armature is stuck in the suction state, if the other contactor moves, it will cause a power short circuit. When the normally closed contacts of the contactor interlock with each other, it can avoid the occurrence of short circuit accidents in this situation.
What is self-locking control? Why is it said that the self-locking control circuit of the contactor has undervoltage and undervoltage protection? A self-locking circuit is a device that uses the interlocking of the output signal itself to maintain the output action. When the power supply voltage is too low, the contactor coil loses power, and the self-locking contact returns to disconnect the coil circuit. When the voltage rises again, the coil cannot be powered on, forming undervoltage and undervoltage protection.
