1 The cause and color of the rotor point grounding In the generator excitation circuit, the most vulnerable part of the insulation is the field winding part. When the generator set is running, the rotor is running continuously, so that the coil is subjected to a large centrifugal force. After a long period of operation, the rotor winding time will be run, which proves that the power supply works well and encounters a line trip. In the case of an electric accident, it is only necessary for one person to easily close the four units in a few seconds.
3 advantages and should pay attention to the question I understand, use. 8 As the power source for accident shutdown of hydropower stations, it is also the first time in the country. Practice has proved that this method has the following advantages: the floor space is extremely small, and it only needs to be equivalent to the size of a magazine opening size; the price is extremely cheap, and the investment is only about 1,000 yuan; the transformation is particularly simple and the effect is particularly remarkable. It is especially suitable for small hydropower plants that have used the Type 01 and Type 1 governors with emergency stop solenoid valves and no independent accident DC power supply. It should be noted that slight looseness is caused and the insulation of the winding is damaged. At the same time, the excitation current passing through the coil accelerates the deterioration of the insulation of the rotor winding due to the thermal effect. In addition, dust and other dirt in the air will accumulate on the windings for a long time. During the overhaul, the maintenance personnel accidentally dropped the foreign matter from the mesh of the large cover of the rotor and damaged the winding in the insulation and caused a ground fault.
When the generator rotor is grounded, because the ground does not constitute a current path, no current flows through the fault 1 port 3 instead, so the electric pool wiring, the aging can not work for a long time, when the unit is completely closed, the governor is open The degree is that the black needle is turned to zero and the main valve of the governor is turned off to prevent the guide vane from reopening after the changeover switch is reset. 5 switch switch cut back to avoid 08 long-term work.
Point, only the voltage applied to the insulating material of the field winding to the ground will increase, there is no direct harm to the unit itself, the field winding remains in the normal state, and the generator can continue to operate.
2 Harm of two-point grounding of the rotor When the rotor is grounded, if it fails to get timely and effective treatment and continues to operate, if the insulation level of other parts of the rotor excitation winding is reduced, another grounding fault may occur. It forms the grounding of the rotor at two points, which is a very serious short circuit accident.
It usually produces the following kinds of damages. 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 magnetic circuit of the generator will be generated. The reduction of the main magnetic flux reduces the inductive reactive power of the unit's outward output, causing the terminal outlet voltage to drop and the stator current to rise sharply.
Because the rotor magnetic field is distorted, the symmetry of the magnetic potential in the air gap is destroyed, causing the torque imbalance, which will cause the rotor to vibrate violently and even cause resonance, which jeopardizes the safety of the unit and the plant structure.
When the rotor is grounded at two points, a large short-circuit current will flow between the two grounding points, and the arc generated by the current may burn the exciting coil and the rotor body, and even cause a fire.
When the two points of the rotor are grounded on the control panel, the excitation current and the stator current increase, the excitation voltage and the outlet voltage of the machine are decreased, the power factor is increased or even phased, and the vibration is accompanied by severe vibration. At this time, it should be handled as an emergency stop, immediately turn off the water moving part, and jump off the excitation switch.
3 Prevention of Rotor Grounding As can be seen from the above, the two-point grounding of the rotor is caused by the fact that the rotor is grounded and not processed in time.
The grounding of the rotor point is a prelude to the two-point grounding of the rotor. To completely prevent the two-point grounding of the rotor, it is necessary to immediately and effectively handle the grounding of the rotor when it is grounded. Therefore, it is necessary to understand the insulation condition of the rotor winding at any time, conscientiously do the insulation monitoring and protection work of the rotor winding, and take corresponding preventive measures.
The inspection under the stop state can measure the insulation resistance of the winding by the shaking measurement method in the stop state. If the value is above 0, it is usually regarded as normal. The Shuangmiao Lake Power Station within the jurisdiction of the ship uses the shake to measure the rotor and the large The insulation resistance between the shafts will be 0. The insulation resistance between the collector rings is 5, but if the insulation resistance is 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 treated accordingly. Generally, the insulating tape is used to tie or coat the insulating paint at the insulation damage.
In-service inspection and monitoring The small hydropower station has a small single-unit capacity, and almost no rotor point grounding protection device is provided. The shaking method can only be checked at the time of shutdown, which leaves hidden dangers for the safe operation of the unit. The power station should try to add a rotor point grounding protection monitoring device according to the specific conditions. The following types of rotor point grounding protection monitoring devices are suitable for small hydropower stations. The operating principle and wiring are respectively introduced as follows: 3.2.1 Connected voltage method voltage and Connected to the excitation circuit to make a wide-area grounding monitoring device. The principle wiring is based on the excitation voltage level, and the appropriate DC voltage is selected. The other one is equipped with a 12-level 2.2-type conversion switch-off position point in the disconnected position. When the front of the handle and the contact on the back of the contact box rotate the switch to the left and right, if the unit is running normally, the voltage is the excitation voltage. When the rotor insulation level is lowered or the point is grounded, the reading on the voltage will change. . Now take the switch left-handed as an example to describe the working principle of the method. When the switch is left-handed, the contact 24 68 is connected. At this time, the voltage is measured by the voltage of the field winding. If the rotor is grounded, the ground point and the grounding point of the transfer switch Forming the path, when the voltage is measured by the voltage of part of the winding, 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 2, the superimposed DC current is obtained from the rectifier bridge 82, to protect the actuator, and 1 is the insulation resistance of the generator excitation winding to the ground. Normally, a small current flowing through the relay 2 = is insufficient for the actuator to operate. When the rotor circuit insulation is lowered or directly grounded, the current flowing through the relay z = now +122, because d is all, obviously 212, when When it is larger than the operating current of the relay 1, the protection operates and a signal is emitted.
The advantage of this kind of protection is that it protects the dead zone from the ground capacitance, but this type of protection device cannot be applied to generators with low rotor insulation resistance, such as dual water internal cooling generators. Should pay attention to.
3.2.3 Current relay method The current relay is directly connected between the negative pole of the excitation circuit and the earth to form the rotor point grounding protection. This kind of protection wiring is simple, the principle is wiring 3. When the rotor circuit is normal, a small current flows in the relay. When the insulation level of the rotor circuit is lowered or the point is grounded, the current flowing through the relay increases, and when it is greater than the setting current of the relay. The relay will act and signal. However, when the grounding point is close to the negative pole, the current flowing through the relay is difficult to reach the setting value, so the relay will refuse to protect the dead zone.
In short, when determining the choice of rotor point grounding protection, the most suitable protection method should be selected according to the actual situation of the power station to ensure the safe operation of the unit.
Rotate left and right to position
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