Change three-phase 3 kW motor into generator
The method of generating electricity by three-phase motor can use diesel engine as power to drive three-phase motor to generate electricity in remote areas or special occasions. In the three-phase winding of three-phase asynchronous motor (hereinafter referred to as motor), after each phase is equipped with appropriate excitation capacitor, it is changed into self-excited generator. The specific methods are introduced as follows for reference.
1、 Make preparations before making changes
First of all, the capacity of the motor should be correctly selected to meet the power needs of users. The maximum power consumption can be estimated as 0.7 times the nominal power of the motor used for power generation.
Before modification, the three-phase winding of the motor shall be simply tested, focusing on the phase to phase and ground insulation strength of the motor. The motor with qualified insulation withstand voltage test and winding DC resistance test can be changed to generator.
In addition, the mechanical part of the motor shall be intact. If the rotor rotates flexibly, the bearing shall not be loose or broken The end cover is complete and the installation foundation is stable.
2、 Connection method of motor used for power generation
The motor converted to power generation generally adopts star connection method, and the three-phase load imbalance is found in time, so as to reduce the possibility of accidents caused by star point displacement.
The following figure is the distribution wiring diagram of changing a 10kW asynchronous motor into a generator.
Capacitor configuration and connection method of changing three-phase asynchronous motor into generator
When the induction motor is operated as an induction generator, there is no need to make any changes to the inside of the motor, just add a capacitor to the outside of the motor, and the reform is very simple. To make the induction generator produce alternating current with frequency of 50Hz, the rotor should be dragged to synchronous speed. Different from synchronous generator, the load current of induction generator increases and its terminal voltage decreases greatly. When three-phase short circuit occurs in the output, the terminal voltage disappears rapidly and the short-circuit current drops rapidly to zero. Therefore, induction generator does not need short-circuit protection. It is recommended to change the motor three corner connection to star connection, so that the neutral line (zero line) can be led out from the neutral point. In order to save capacitance, the capacitor should adopt triangular connection as far as possible, Connected in parallel to the three-phase wiring of the motor, the capacitor can adopt 450V AC non-polar capacitor
Capacitance per phase required for no-load excitation C
C = motor no-load current x 1000000 / 2x 1.73x3 Rated voltage of motor (UX phase / line)
When the load is loaded to full load with pure resistance, the capacitance of each phase needs to be increased by about 25% of C. when there is inductive load in the load, the capacitance at full load needs to be increased on this basis
Empirical capacitance value of 5.5kW motor to generator (delta connection of capacitor bank): capacitance of each phase is 25-35uf, and total capacitance is 75-105uf
At most, each phase can be equipped with 220V bulb, about 1.8kw. The output voltage of induction generator varies greatly with the load. It is recommended not to use expensive electrical appliances to prevent damage
When the load changes greatly, the voltage needs to be adjusted: first, change the value of generator excitation capacitance, that is, divide the capacitance into several groups and switch with the change of load. Second, adjust the prime mover speed properly- Generally, the voltage is roughly adjusted by changing the capacitance and finely adjusted by changing the speed.
Change three-phase 3 kW motor into generator
1. Main circuit elements of power generation
The power of diesel engine or water turbine for prime mover for power generation shall be 10 ~ 15% greater than the power of the motor, and the generator shall reach the nominal speed after passing through the transmission device. Co refers to a group of main excitation capacitors, and the switch DKO (380V, 60a) is used to control the power transmission and power off of the line; C2 refers to several groups of auxiliary capacitors, which are connected in a star mode, and then adjust the electric capacity value according to the change of load. The switch DK2 (380V, 60a) is used to control the power transmission and power failure of the line. Rd refers to the breakdown fuse, which is used to prevent the prime mover from flying or the voltage rise caused by suddenly shaking off the load from breaking down the generator insulation; V is the voltmeter (1t1-v-450) and a is the ammeter (1t1-a-30). They are used to monitor the three-phase load voltage and current. If the three-phase voltage and current can be balanced with an error of less than 5%, only one voltmeter and ammeter can be used.
If the speed of prime mover is unstable, install a frequency meter (1d1-h2-45 ~ 55) to monitor whether the frequency is normal.
The distribution board is made of 30mm thick wood. Holes shall be dug on the surface of the board and wrapped with 0.5mm thick galvanized iron sheet to prevent accidents caused by loose wiring and ignition. Install the instrument at the upper part of the power distribution panel Install switch and screw fuse (RL1-60) in the middle. The capacitor is placed in the lower part of the distribution board.
There are three methods to change three-phase asynchronous motor into single-phase asynchronous motor:
Rated current: the line current and rated voltage of stator winding under rated working state of motor and rated power output: the line voltage of stator winding under rated working state of motor.
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Change three-phase 3 kW motor into generator
Large cross-section conductor shall be used for power generation and transmission, with remarkable power saving effect, and the increased investment can be recovered soon. As the line is in light load operation for a long time, the service life of the line will be greatly prolonged. China stipulates that the current density of the line with "annual operation hours" of 5000 hours / year shall be I = 0 95A / mm2。
2. Main electrical components composed of electric parts
In the figure, lamp L represents resistive lighting load and M represents inductive load of motor. C2m is the reactive capacitor that separately compensates the motor.
3. Selection and connection method of excitation capacitor
When the motor is changed into a generator, it is very important to correctly select, connect and use the excitation capacitors CO and C2.
The nominal withstand voltage of the capacitor shall be greater than 5 ~ I0% of the output voltage of the motor. The capacitor with star connection shall be 250V withstand voltage; the capacitor with triangle connection shall be 400V withstand voltage.
The excitation capacitor of the generator must be non-polar AC capacitor (such as oil immersed capacitor), and any electrolytic capacitor must not be used. There are two types of commercially available oil immersed capacitors: YY type and YL type. YL type capacitor has small volume and long service life. When in use, three capacitors are used as the main excitation capacitance of each phase, while several capacitors with small capacity are connected in parallel as auxiliary capacitors, which are increased step by step and switched. To meet the load requirements of different sizes.
The capacitance value of the motor is mainly related to the motor power. The greater the power consumption, the greater the motor power and capacitor capacity. In practice, in order to avoid complex calculation When the requirements are not high and the load is not large, it can be determined by referring to the following table.
The reactive power compensation capacitor is represented by c2m and is star connected. The bulb and motor of the power consumption part represent resistive load and inductive load respectively. When the power grid supplies power to inductive loads, it consumes not only active power, but also reactive power. The solution is to shunt capacitors at both ends of the load and use capacitive reactive power to offset inductive reactive power. This will not only reduce the reactive power loss, increase the active output by 20 ~ 24%, but also increase the network supply voltage by 3 ~ 5%. The capacitance value c2m is selected as 7.5% for each IKW of motor capacity according to the use experience 8UF is reasonable.
Change three-phase 3 kW motor into generator
3、 Generator operation
To generate electricity by motor, start the machine according to the following steps:
1. Turn on the switch dk0 and input the main excitation capacitor Co.
2. Turn on the switch DK2, input part of the auxiliary capacitor C2, and then close the switch DK to turn on the power supply line.
3. Start the prime mover and the corresponding no-load voltage can be established after 15 seconds.
4. When driving the load, the principle of large load first, then small load, power first and lighting power later shall be mastered The motor below 4kw in the electric circuit can be started directly, 5 5kW~7. 5kW motor can only be started by step-down. Starting on a blind day will lead to major accidents and regret.
The following principles shall be followed when the generator is shut down:
1. First disconnect the power switch DK2 of the auxiliary capacitor C2 to prevent overvoltage from damaging the insulation of the generator. Then disconnect the load switch (such as DK2 and DKI) and interrupt the power supply of motor and lighting.
2. Stop the machine after all auxiliary capacitors and loads on the line are disconnected.
3. After the prime mover stops running, finally disconnect the switch dk0 of the main excitation capacitor Co.
Change three-phase 3 kW motor into generator
During the operation of the generator, pay attention to the following matters:
1. Pay special attention to monitor the three-phase voltage and current of the generator, and keep the balance basically, and the error shall not exceed 5%. The three-phase current output value must not exceed the rated current value of the generator for a long time, otherwise the temperature rise of the generator is too high, which will affect the service life of the winding.
2. Generally, the working temperature of capacitor shall not exceed 60 ℃; The working current and working voltage shall not exceed 1.1 times of the rated value for a long time to prevent premature aging and breakdown of insulating oil.
Preventing the generator from generating excessive voltage is a necessary condition for safe operation. To do this:
1. The speed of prime mover shall gradually reach the rated speed of generator from slow to fast within 15 seconds. The speed of prime mover shall be constant and the adjustment shall be flexible. Avoid suddenly increasing the speed after deceleration to make the voltage rise too fast.
2. After disconnecting the load switch, the corresponding auxiliary capacitor switch must be disconnected in time.
3. When the load of the electric circuit is changed from motor to lighting, do not forget to disconnect the reactive power compensation capacitor of the motor, otherwise it will increase the excitation current, increase the voltage and produce overvoltage.
4. The capacitor shall be free from abnormal phenomena such as oil leakage, oil shortage, ignition and arcing. When the capacitor is disconnected from the power supply, a certain residual voltage is still maintained on its electrode plate. In the three-phase AC circuit, it may reach about twice the network voltage. If the human body touches it, the consequences are very serious. Therefore, when replacing or repairing the capacitor, reliable grounding should be used to discharge the capacitor for many times.
5. For generators operating in areas with more lightning strikes, when the overhead transmission line is long (about 500m), two groups of fsi-0.5 low-voltage valve type arresters shall be installed on the first and end towers at the outlet of the generator and reliably grounded, and the grounding resistance value shall be less than 10N.
6. To sum up, the switches, capacitors and motors in the machine room should be clearly marked
Note the purpose and number to prevent misoperation. Formulate corresponding generator operation procedures,
The purpose is to ensure the safe operation of the generator.
