Electrical Encyclopedia: Three-phase motor changed to single-phase motor method
Introduce several simple and easy methods to change the three-phase motor to single-phase operation without changing the internal winding of the motor.
First, the addition of capacitance method
At this time, the output power of the motor is 55% to 90% of the nominal power. C1 is the running capacitor and C2 is the starting capacitor. All power capacitors are required, and the withstand voltage must be no less than 450V. The capacity of C1 and C2 can be estimated as follows:
C1=1950I/U×cosθ
C2=(1~4)C1
In the formula, the unit of C is (uF); I is the rated current of the motor (A); U is the rated voltage of the motor (V); cos θ is the power factor, generally 0.5 to 0.7.
In particular, for a three-phase asynchronous motor with a power of 1 KW or less, C2 may not be used, but the value of C1 is appropriately increased. It can be estimated by C1=13I, where the unit of C1 is (uF) and I is the rated current (A) of the original motor. The capacity of the capacitor should be selected properly, otherwise the motor will not operate normally and the temperature rise will be too high.
For small-power three-phase asynchronous motors with only a few hundred watts, the capacitance can be selected according to C=0.06P (Y-connected) and C=0.1P (Δ-connected). The unit of C is (uF), P is Motor power (W). The capacity of C1 and C2 can be the same. If the speed is too fast, the load can be increased or the capacity can be reduced. If the speed is too slow, the load can be reduced or the capacity can be increased.
Second, the improved addition capacitance method
In order to improve the output power of the motor, the selection of C1 is the same as C1, C2, C3, and R in "Method 1": C2 = (2 ~ 4) C1
C3=2C1
R=0.25U/I
Third, capacitance, inductance phase shift method
Using an inductor (note the current carrying capacity of the inductor L) and a capacitor to obtain a three-phase symmetrical voltage from a single-phase power supply, this method is more adaptable, but to configure the core inductor, it is also possible to use single-phase auto-coupling. Regulator to replace. This method should be used for larger motors. For example, when the motor is 2.2 KW with "â–³ connection", the capacitance C is 254uF, and the inductance L is 78mH. Capacitor C, inductor L can be selected as follows:
C=(Ssin(60+φ)×10^6)/(1.5WU^2)
L=(1.5U^2)/(WSsin(60-φ))
Where the working capacitance of C is (uF); L: inductance (H); S: rated power of motor (VA); φ: power factor angle (degrees) when rated load of motor; W: angular frequency (W = 2πF=314)
Fourth, with the resistance method
The choice of resistor R should be appropriate. The value of R can be selected to be 5 to 10 times the resistance of the two-phase winding.
Five, plus switching method
With the start switch K, you can access single-phase operation.
Sixth, electronic control law
For a three-phase asynchronous motor with a power of 2 to 3 kW, the capacity of the phase shifting capacitor needs to be 200 to 300 uF or more. Due to the high withstand voltage, the volume is large and the price is high. However, this method does not require a phase shifting capacitor. It has been proved that when the motor adopts "â–³ connection", the rotation speed does not exceed 1500 rpm, and the starting device can work effectively with it.
Note: For three-phase asynchronous motors, the rated current per kW is generally about 2A, that is, the rated current of a 2.2kW three-phase asynchronous motor is about 4.4A.
Electrical Encyclopedia: Use of Residual Current Action Protector
The residual current action protector is generally referred to as a protector, and is now widely used and popularized in rural areas as a measure to effectively prevent personal electric shock and casualties. Correct understanding of the role of the protector in the power distribution system is of great significance for strengthening the management of the low-voltage power grid and improving the reliability and safety of the power supply.
These requirements should be noted in the actual work:
(1) The grounding device of the equipment should be treated with anti-corrosion treatment.
(2) The installation of the grounding wire shall be strictly in accordance with the design and construction and meet the requirements of the regulations.
(3) During the management of the Taiwan area, the grounding device of the equipment shall be inspected regularly, and problems shall be discovered in a timely manner.
1 Use of residual current action protector in rural power grid
The rural distribution network has small capacity and distributed load distribution. However, the overall low-voltage power grid can be roughly divided into three layers: distribution station area, branch distribution box, and user side.
Tertiary protection is a form of direct contact protection and indirect contact protection. According to the situation of the rural low-voltage power grid, different types of protectors are installed in the first, middle and end layers of the power supply line.
A direct-type (no delay) protector with an operating current of 30 mA is required for direct contact protection at the end of the line. The first end and the middle part shall be protected by indirect contact, and a protector with coordinated action characteristics shall be installed. As the first-stage protection of the system, the rated residual current value of the protector should be adjusted. The maximum value is specified by the regulation: the grid with small leakage current is 75mA/200mA, and the grid with large leakage current is 100mA/300mA. The system with perfect protection can be increased to 500mA. The middle section is used as the shunt protection. The rated residual current value of the protector is selected between the rated residual operating current values ​​of the upper and lower protectors.
For the selection of the breaking action time, the upper-stage protector should use the delay action type protector, and the breaking time should be increased by at least 0.2 s compared with the breaking time of the next-stage protector.
In this way, the three-level protection of the network cooperates with each other in the action current and the action time. When the terminal power receiving device fails, the third-level protector operates; when the network end fails, the intermediate-level protection action; when the network middle segment fails, Total protection action to reduce the scope of accident blackouts.
In short, in the rural low-voltage power grid, the residual current action protector is a "firewall" in the network to prevent personal electric shock and casualties caused by leakage of equipment. In addition, because the protector can isolate faulty equipment in time, it becomes a technical measure in the network to prevent electrical fire and equipment damage caused by leakage. Whether the protector operates normally or not is safe to the person and equipment. In the daily management of the low-voltage power grid, the maintenance of the three-level protector is a very important task. The protector operation rate and operational reliability can directly reflect the safety status and management level of the low-voltage power grid.
The residual current action protector is generally referred to as a protector, and is now widely used and popularized in rural areas as a measure to effectively prevent personal electric shock and casualties. Correct understanding of the role of the protector in the power distribution system is of great significance for strengthening the management of the low-voltage power grid and improving the reliability and safety of the power supply.
2 Residual current action protector use requirements
The low-voltage grid with the residual current operated protector must be a direct neutral grounding system for the power supply. The rural low-voltage power network basically adopts the TT system, that is, the neutral point of the low-voltage side of the distribution transformer is directly grounded, and the exposed conductive part of all the power-receiving equipment in the network is connected to the electrical system by the protective grounding wire (PE line). The location is not directly connected to the grounding pole.
In actual work, you should pay attention to:
(1) The N-line in the power grid must not have repeated grounding and should maintain the same good insulation as the phase conductor.
(2) Lighting and other single-phase loads should be evenly distributed to the three-phase as much as possible, and can be adjusted in time with the load change. When the low-voltage line is buried, the three-phase length should be as close as possible.
(3) For overhead lines, tree clearing work should be done regularly.
(4) Rural living lighting has poor indoor line conditions and belongs to the self-raised area of ​​rural power grid reconstruction. Measures to reduce leakage of lines should be taken actively.
3 Residual current action protector protection
3.1 Direct contact protection
Prevent electric shock and death caused by direct contact with human body and live conductors of electrical equipment.
This type of protector should be selected with a higher sensitivity general action type (no delay) protector, rated residual operating current value I △ n ≤ 30 mA.
This configuration is chosen because, in physiology, when a large external current hits the human body after an electric shock, the normal pulsation of the heart is inevitably affected. If the electric shock current and the energization time exceed a certain limit, the normal beat of the heart will be disturbed, and the pumping function will be lost, leading to death. According to experimental studies, there is an interval of about 0.1 s between the two beating cycles of a healthy heart. In terms of normal human body weight, 50 mA will cause destructive ventricular fibrillation, and 30 mA has certain safety and does not cause dangerous ventricular fibrillation.
3.2 Indirect contact protection
In the electrical equipment equipped with anti-indirect contact protector, in the actual operation, the rated residual operating current of the protector is selected to be greater than 30 mA, and the rated operating time is selected to be greater than 0.1 s. Thus, the protector can be accurately and timely operated in the event of a leakage fault. A very important prerequisite for exiting the system to ensure personal safety is the selection and installation of the grounding wire and the requirements for grounding resistance.
Electrical Encyclopedia: Operating Procedures for High Voltage Power Distribution Rooms
First, the purpose
Ensure the safety and correctness of the operation of the equipment in the high-voltage power distribution room and ensure that the equipment is in good condition.
Second, the scope of application
Operation of power distribution equipment in high voltage power distribution rooms. Each management office may prepare detailed operational procedures based on the actual conditions of this jurisdiction.
Third, the manual operation mode:
The running technician sends power to each busbar as required. At this time, the bus coupler switch must be opened. If one of the incoming lines loses voltage or lacks power, that is, delays the trip, the operating technician can choose to exit the line-in switch where the voltage is lost, and then close the bus-coupled switch, and send power to the busbar to resume power supply.
Fourth, automatic operation mode:
When the incoming line power is normal, automatic operation can be selected. If there is voltage loss or power shortage, the delay will be tripped first, then the high voltage bus coupling switch will be automatically closed to restore the power supply; but when the incoming line returns to normal power supply, the bus switch It is necessary to select the manual operation by the on-duty personnel, and first divide the bus-coupled switch, and then put in the line switch to restore the normal power supply.
V. Accident handling:
1. Overcurrent fault: If the line over-current (including over-current and quick-break), the line switch car will automatically trip, and the fault indication will light on the instrument panel. The duty officer must understand the cause of the fault, clear the fault, and then manually reset the button.
2. Ground fault: The indication and processing procedures are the same as the overcurrent fault.
3. Transformer temperature rise fault: The indication and processing procedures are the same as the overcurrent fault.
4. Loss of voltage trip fault: The indication and processing procedures are the same as the overcurrent fault.
Electrical Encyclopedia: The main reason for the rejection of leakage circuit breakers
The main reasons for the rejection of the leakage circuit breaker are as follows:
1. In the TN-CS system, if the detection circuit is between the PEN line and the L line of the TN-C section, the leakage circuit on the PE line of the TN-S section will refuse to operate;
2. In the TN-S system, since the circuit installer puts the N line into the switch, if the N line is broken and there is leakage on the L line, the leakage circuit breaker will appear to be rejected because the detection circuit will not detect the leakage signal. ;
3. In the TN-CS system, since the circuit installer connects the N line and the PE line together, if leakage occurs, the leakage circuit breaker will appear to reject the action;
4. When installing and using, the sensitivity of the leakage circuit breaker is too low, and the actual leakage value does not reach the specified value, it will also refuse to operate.
The main causes of malfunction of the leakage circuit breaker are as follows:
1. In the TN-CS system, the circuit installer reverses the PE line and the N line, causing malfunctions;
2. In the three-phase four-wire system of lighting and power, the three-pole leakage circuit breaker is selected incorrectly, and the zero line of the load directly causes the malfunction on the power supply side of the protector;
3. There is a high-power electric appliance near the leakage protector. When the electrical appliance is opened or closed, electromagnetic interference may cause malfunction.
4. The insulation resistance of the phase line and the neutral line is too low, and some of the current leaks to the earth through the leakage, so that the current vector and the zero current of the zero-sequence current transformer cause the circuit to malfunction.
Electrical Encyclopedia: What are the characteristics of transformer magnetizing inrush current?
The magnetizing inrush current has the following characteristics:
1 The change of the initial phase angle of the closing has different effects on the three-phase excitation inrush current, and some phases are large, and some phases are small.
2 A non-periodic component containing a large component tends to bias the inrush current to one side of the time axis.
3 Contains a large number of high-order submarine wave components and is dominated by secondary submerged waves.
4 The excitation inrush current waveform has a discontinuity (the waveform is divided into zero currents in one cycle).
The purpose of full voltage charging is to check the internal insulation weak point of the operating transformer and to check the mechanical strength of the transformer and whether the relay protection device can avoid the magnetizing inrush current without malfunction.
Electrical Encyclopedia: Principles of AC Contactor Structure
The contactor can be divided into an AC contactor and a DC contactor according to the type of the controlled current.
AC contactors are widely used as breaking and control circuits for electric power. It uses the main contact to open and close the circuit, and the auxiliary contact to execute the control command. The main contacts generally have only normally open contacts, while the auxiliary contacts often have two pairs of contacts with normally open and normally closed functions. Small contactors are often used as intermediate relays in conjunction with the main circuit.
The contact of the AC contactor is made of silver-tungsten alloy and has good electrical conductivity and high temperature ablation resistance.
The AC contactor is mainly composed of four parts:
(1) Electromagnetic system, including attracting coil, moving iron core and static iron core;
(2) The contact system comprises three main contacts and two normally open and two normally closed auxiliary contacts, which are connected with the moving iron cores;
(3) Arc extinguishing device, the AC contactor with large capacity is generally equipped with arc extinguishing device to cut off the arc quickly and avoid burning the main contact;
(4) Insulating housing and accessories, various springs, transmission mechanisms, short-circuit rings, binding posts, etc.
H-K9L (N-BK7) is crystal clear and has excellent transmittance from visible to near infrared (350-2000nm). It is the most commonly used optical glass for the preparation of high-quality optical components. When the additional advantages of UV fused silica are not required (in When the ultraviolet band has good transmittance and low thermal expansion coefficient), H-K9L is generally selected for optical coating and other fields.
The ball lens is a very useful optical element used to improve the signal coupling between the fiber, the transmitter and the detector. In addition, it is also suitable for applications such as endoscopes, barcode scanning, pre-processed materials for Aspheric Lenses and sensors. The ball lens is made of a single glass substrate and can focus or output parallel light, depending on the geometry of the input source. Hemispherical lenses are also very common, and are used interchangeably with (full) spherical lenses when the physical constraints of the application require a more compact design.
H-K9L Ball Lens,N-Bk7 Ball Lens,H-K9L Optical Ball Lens,High Precision Ball Lens
Bohr Optics Co.,Ltd , https://www.bohr-optics.com