Short circuit fault between rotor windings is a common fault of generators. In the event of a slight short circuit between the turns, the unit can only continue to operate, but care should be taken to strengthen monitoring and testing. When the short circuit between the turns is serious, the current of the rotor will increase significantly and the temperature of the rotor will increase significantly. the rotor winding will increase, limiting the reactive power of the generator, or cause the unit to vibrate more, or even force it to shut down. Therefore, when an inter-turn short circuit fault occurs in the rotor winding, the inter-turn short circuit point must be found by testing and eliminated to restore normal operation of the generator. The generator rotor is grounded at one point and two points. Additionally, the rotor layer will also be grounded and cause a short circuit between the turns. The updatingRotor ground can be divided into instantaneous grounding, intermittent grounding and permanent grounding. It can also be divided into internal grounding and external grounding, metal grounding and resistive grounding. Personnel were working on the excitation circuit and the rotor was grounded due to accidental contact or other reasons.
Rotor slip ring insulation damage, rotor slot insulation damage, rotor slot insulation damage and end insulation, damage rotor wire insulation, etc. cause grounding. Insulation aging due to long-term operation, debris or vibration causing the insulation pads to move between certain revolutions of the rotor, partially blocking the rotor ventilation holes, causing local overheating and aging of the rotor. 'isolateion of the rotor winding, causing the rotor to ground. Rats and other small animals enter the excitation circuit, the insulated water pipe at the water inlet and outlet of the stator is broken and leaking, and the excitation circuit is dirty, causing the excitation to the rotor earth. When the rotor circuit is grounded at one point, no current loop is formed due to grounding at one point and no current passes through the fault point. The excitation system remains in a normal state and does not affect the normal operation of the unit. . Check if the rotor ground signal can be reset. If it can be reset, it is instantly grounded. If it cannot be reset, use a multimeter to measure the voltage from the positive and negative poles of the rotor to ground. As the voltage from one pole to ground drops to zero, the voltage from the other pole to ground rises to full voltage, indicating that a smallThe grounding has indeed occurred. How to handle rotor grounding: Check if anyone is working in excitation. If the problem is caused by a staff member, it must be corrected. Check if there is obvious damage to each part of the excitation circuit or if it is grounded due to dirt, it should be bled and the affected circuit should be inspected in detail if necessary, the rectifier. The cabinet should be shut down in turn to determine if this is caused by grounding of the DC circuit in the rectifier cabinet. Check whether the ground is in the excitation circuit or in the measurement protection circuit if the rotor is grounded to a stable metal. grounding at one point and the fault point cannot be identified, in addition to strengthening the monitoring of the unit operation, after obtaining shipment consent, apply two-way grounding protection pointts on rotor tripping and request shutdown treatment as soon as possible.
The following points can be excluded: 1. Check whether the brush length is too short and reaches the lifeline, making the pressure too weak and the brush cannot contact the slip ring; 2. Check whether the spring pressure is appropriate. If it is too low, it will cause the brush to trip and discharge. 3. Check the surface finish of the slip ring; too hairy, it will increase the contact resistance of the brush and cause large sparks; 4. Check the rotor electrical circuit to ensure that the resistance is normal and the revolutions are normal. 5. Check whether the oil space in the bearing. is too large, causing significant brush runout on the slip ring when the rotor rotates. Check whether the radial runout on the slip ring surface is veryop big. The brush bounces, causing sparks. 6. In addition, whether the brush conforms to the one used before and whether the brush is conductive;There are requirements for friction current and speed. Preventive measures
1. Carbon brushes and slip rings should be inspected daily. The main inspection items are:
(1) The wear length of carbon brushes does not exceed 2. /3. When the wear length of the carbon brush exceeds 2/3 (that is, the top of the carbon brush and the top of the brush holder are on the same plane), it should be replaced.
(2) There is no spark from the carbon brush. When the carbon brush just begins to spark, it is necessary to find the cause and eliminate it in time.
(3) The carbon brush has no gap from the outside of the slip ring and there are no cracks on thee edge of the carbon brush.
(4) The carbon brush braid is well connected to the brush holder and the carbon brush, and there is no heat or contact with the brush holder.
(5) The carbon brush does not jump, shake or get stuck in the brush holder.
(6) Regularly use a DC clamp meter to measure the current sharing of each carbon brush evenly, and use an infrared thermometer to measure whether the carbon brushes are overheated. If there are anomalies, they should be. replaced in time.
(7) The spring pressure is normal and there is no deformation or breakage. Normally, the pressure on each carbon brush should be uniform and stable. The unit pressure is generally between 1.1 kg and 2.5 kg. The unequal pressure difference between carbon brushes should be less than 5%.
(8) The distance between the brush holder and the slip ring cor matches the specified value. The distance between the generator brush holder and the slip ring: 2.5~3mm, the distance between the main excitation brush holder and the slip ring: 2~4mm.
(9) The surface of the slip ring should be free from discoloration, overheating and uneven wear, and the surface temperature of the slip ring should not exceed 120°C.
(10) Check if there is dirt on the brush holder and brush holder. If there is a lot of dirt, it should be swept away with a brush or blown out with compressed air.