Harm and Prevention of Generator Rotor Grounding
1 Rotor point grounding causes and color ring In the generator excitation circuit, the most vulnerable to insulation is the part of the excitation winding. When the generator set is running, the rotor is constantly running, so that the coil is subjected to a large centrifugal force. After a long period of operation, the rotor winding will run for a long time. This proves that this kind of power supply works well when it is tripped. In the event of an electric accident, only 1 person can easily switch off the 4 units in a matter of seconds.
3 advantages and attention should be paid to the author to understand, use. 8 It is also the first time in the country to use the power supply for accident shutdown of hydropower stations. Practice has proved that this method has the following advantages: very small footprint, only needs to correspond to the size of one open magazine; it is particularly cheap, and the investment is only about one thousand yuan; it is particularly simple to transform, and the effect is particularly remarkable. It is particularly suitable for small hydropower plants that have opted for Type 01 and Type 1 governors with an emergency shutdown solenoid valve and no independent incident DC power supply. It should be noted that slight loosening results in damage to the winding insulation. At the same time, the excitation current passing through the coil will accelerate the deterioration of the insulation of the rotor winding due to the thermal effect. In addition, long-term operation, dust and other dirt in the air will accumulate on the winding. During inspection and repair, the maintenance personnel carelessly dropped foreign objects from the mesh of the large rotor cover and damaged the windings. The insulation was damaged and a ground fault occurred.
When the rotor of the generator is grounded, because the current does not form a current path to the ground, no current flows through the fault port 1 instead of the port 3, so the electric pool is connected and cannot be operated for a long time. When the generator sets are all turned off, the governor opens. Degree means the black needle is closed to zero and after turning off the governor oil supply main valve, the water guide vane is reopened after the transfer switch is reset. 5 switch switch back to avoid 08 long-term work.
The point is that the voltage applied to the insulation of the excitation winding to the ground will increase, and it will not directly harm the unit itself. The field winding will remain in the normal state and the generator will continue to operate.
2 Hazard of two-point grounding of the rotor When the rotor is earthed at the point where it is not grounded, it can continue to operate without timely and effective processing. Once the insulation level of the other parts of the rotor field winding is reduced, another starting point ground fault may occur. The rotor is grounded at two points. This is a very serious short circuit accident.
It usually produces the following kinds of hazards. After the generator excitation winding is grounded at two points, the winding part is short-circuited, so that the DC resistance of the winding becomes smaller and the excitation current increases; if the number of short-circuit turns is large, the generator magnetic circuit will be made. The reduction of the main magnetic flux reduces the inductive reactive power output from the unit to the outside, causing the outlet voltage of the machine to drop, and the stator current may increase rapidly.
Because of the distortion of the magnetic field of the rotor, the symmetry of the magnetic potential in the air gap is destroyed, which causes the torque to be unbalanced, which will cause the rotor to vibrate violently and even cause resonance, which endangers the safety of the unit and the structure of the building.
When the rotor is grounded at two points, a large short-circuit current will flow between the two ground points. The current-generated arc may burn out the excitation coil and the rotor body, and even cause fire.
The two points of the rotor are grounded on the control screen. The exciting current and the stator current increase, the excitation voltage and the outlet voltage of the machine drop, the power factor rises and even enters the phase, accompanied by violent vibration. At this time, emergency shutdown should be performed and the water-moving part should be closed immediately. At the same time, the excitation switch should be opened.
3 Prevention of Rotor Earthing From the above, it can be seen that the two points of the rotor grounding are caused by the timely and effective treatment after the rotor is grounded.
The rotor point grounding is the prelude of the two-point grounding of the rotor. To completely prevent the two points of the rotor from being grounded, it is necessary to immediately and effectively handle the point when the rotor is grounded. Therefore, it is necessary to understand the status of rotor winding insulation at any time, and do a good job in insulation monitoring and protection of rotor windings, and take corresponding preventive measures.
Check under stop state In the stop state, the winding insulation resistance can be measured by the shake measurement method. If the value is above zero, it is usually considered as normal. The insulation resistance between the shafts will be 0. The insulation resistance between the rings is 5, but if the resistance of the insulation resistance is measured to be less than 0.00, it can be considered that a point ground fault has occurred. At this time, it is necessary to inspect the insulation of each part of the rotor circuit. The carbon brush should be removed from the carbon brush holder and handled accordingly. It is generally to use insulation tape to bind or coat the insulation paint at the insulation damage.
Inspection and monitoring during operation The small capacity of the small hydropower station is small, almost no rotor point grounding protection device is set, and the yaw method can only be checked during shutdown, which leaves hidden dangers for the safe operation of the unit. The power station shall, based on specific conditions, seek to install additional monitoring devices for rotor point earthing protection. The following types of protection monitoring devices for rotor point earthing are well suited for the use of small hydropower plants. Now we will introduce the principle of operation and wiring as follows 3.2.1 and use voltage with the voltage method. Connected in the excitation circuit to create a wide-point grounding monitoring device, the principle of wiring in accordance with the excitation voltage level, select a suitable DC voltage, and the other with a 12 Comment 2.2 type conversion open position point number in the off position When the front of the handle and the contacts on the back of the contact box turn the switch left-handed and right-handed. If the unit is operating normally, the voltage is displayed with the excitation voltage. When the rotor insulation level is lowered or the point is grounded, the reading on the voltage will change. . Take the switch left rotation as an example to describe the working principle of this method. When the switch is rotated to the left, the contact point is 24 to 68. At this time, the voltage measures the voltage of the excitation winding. If the rotor is grounded, the ground point and the grounding point of the switch When the voltage is measured by the partial winding voltage, not the voltage of all the windings, the reading will change.
3.2.2 Superimposed DC principle method The principle of this protection device is wiring 2. Superimposed DC current is obtained from the rectifier bridge 82. To protect the actuator, 1 is the insulation resistance of the generator excitation winding to ground. Normally, a small current flows through the relay 2 = not enough to make the actuator act. When the insulation of the rotor circuit is reduced or directly grounded, the current flowing through the relay is z = +122 this time, because d is average, obviously 212, when, When the operating current of relay 1 is greater than the value, the protection operates and signals.
The advantage of this type of protection is that it protects against dead zones and is not affected by the capacitance to the earth, but this kind of protective device cannot be used for generators whose rotor insulation resistance is inherently low, such as a double-water internal-cooled generator. Should pay attention to it.
3.2.3 Current relay method The current relay is directly connected between the negative pole of the excitation loop and earth to constitute a rotor point ground protection. This kind of protection wiring is simple, the principle wiring 3, when the rotor circuit is normal, the relay flows a small current, when the insulation level of the rotor circuit is reduced or the point of the ground, the current flowing through the relay increases, but when the relay is more than the setting current The relay will act and signal. However, in this kind of protection, when the grounding point is close to the negative pole, the current flowing in the relay is difficult to reach the setting value, so the relay will refuse to move and the protection has a dead zone.
In short, when determining the choice of rotor point grounding protection, the most appropriate protection method should be selected according to the actual conditions of the power station to ensure the safe operation of the unit.
Rotary right rotation input position
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