Problems existing in operation of excitation carbon brush for generator and Countermeasures

The excitation system of Zhanjiang power plant as a static type three machine excitation system, main exciter motor generator with brush and '> D172 models, the constant pressure brush holder, main exciter brush 8, a total of 72 blocks' > generator brush motor. Brush motor generator is' > static contact and energy exchange device, brush operation is good or bad, is directly related to the safe operation of the motor generator, '> so brush operation problems can not be ignored.

Problems existing in operation of 1 excitation carbon brush

Since the 1 and 2 units of Zhanjiang power plant have been put into production, there has been a big fire accident. Many times, the incidents of brush cutting and frequent spark and carbon brush beating have brought great threat to the safety of our factory.

November 23, 1997, No. 2 unit active power 240MW, reactive power 70Mvar, duty officer found the motor generator excitation motor '>' > '> excitation brush spark, adjust immediately, but in any case the adjustment cannot eliminate the spark, and with the passage of time, the spark is more and more big, more and more hot brush,

Accompanied by heavy smoke, eventually forming a ring of fire. Make the No. 2 machine power down to 180MW, reactive power down to 6Mvar, replace the burnt carbon brush and constant pressure spring, the spark is controlled. After the examination, brush grip burned 17 blocks, slip ring burns, there are many small pits.

Unit 1 often brush braid burned, because the brush braid wrapped in the insulating sleeve, burnt, not easy to find, if not timely find and replace, will cause a lot of carbon burning due to overload, resulting in loss of magnetic motor generator '>.

1, unit 2, 1998, 1997 in 1999 to replace the carbon brush more than 1000, table 1 for 3 years for the brush brush was replaced in statistics, in part, carbon brushes are caused by wear too short replacement; mostly due to brush braid burnt out, beating by chipping and replacement.

2 Inspection and analysis

2.1 carbon brush quality is poor, and brush grip does not match

Many of the carbon brushes were found to be angular and loose with the brush. The reason for the collapse may be that the carbon brush is beating too much or the material is bad. The loosening of the brush braid and the carbon brush will cause the increase of contact resistance and the uneven distribution of the carbon brush current. The brush can still move up and down in the brush holder, but it can not move freely after the constant pressure spring on the card. This will cause the carbon brush to not touch the slip ring and make the actual sharing current be zero.

2.2 constant pressure spring pressure is not enough or uneven

When the self coiled constant pressure spring is heated, the spring will elongate and the elasticity becomes worse, and the pressure on both sides of the same spring may be different, resulting in a decrease in the actual contact area of the carbon brush. From the constant pressure spring instead of the inspection, part of spring fragments or crack, and spring pressure is different, resulting in different sharing is not the same as the current brush. In actual measurement, it is found that the current of a carbon brush is less than that before replacing the spring

10A after replacing the spring, the carbon brush can share the current up to 80A.

2.3 brush holder adjustment is wrong, the position of the brush can not be aligned with the normal direction of the circumference of the slip ring. By visual inspection, it is found that the part of the brush grip distance is different from the height of the slip ring, and some of them can not be parallel to the normal direction of the slip ring circumference.

The 2.4 motor generator slip ring brush '> eccentricity caused by beating

November 1, 1999 machine overhaul, the ring also had a car light treatment, because of the eccentric ring (measured 50, the unit after the start of multiwire) brush beating.

2.5, maintenance is not in place, causing carbon brush wear serious or stuck

Zhanjiang power plant is located in the coast, salt fog, after the outage of the unit, the slip ring is easy to rust, and if not promptly rust and polish, it will cause carbon brush beating, wear and tear increases, poor contact, and produce a large amount of carbon powder. Carbon powder gathered in the brush grip will cause carbon brush stuck.

2.6, operation adjustment is not timely, improper handling, resulting in a vicious circle

Carbon brush or spark brush should be adjusted and replaced in time. When adjusting and changing the carbon brush, it should be carried out strictly according to the rules and regulations. If the adjustment is not timely or improperly handled, it will spread to other carbon brushes, resulting in greater sparks.

3 measures to be taken in operation

3.1, strengthen operation and maintenance

The personnel on duty found motor excitation motor '>' > '> excitation carbon brush spark is large, should be carried out according to the methods provided in the operation rules.

3.2 to strengthen the monitoring of carbon brush current

(1) buy DC Clamp Meter to measure carbon brush current, set two times per shift, so as to fully grasp the current sharing of each carbon brush. If the carbon brush current in 12 ~ 80A, indicating the normal operation; if the carbon brush current zero and greater than 200A, indicating that the operation is not normal; more than 200A of carbon brushes will soon burn brush brush.

(2) according to the excitation current at that time, calculate the average current of each carbon brush, adjust and replace the current too much or too little carbon brush in time, so that each carbon brush current share little difference.

3.3, choose high-quality carbon brush

Replace the carbon brush, brush must check whether the appearance of good, check the carbon brush and the copper braid contact is necessary to brush the fastening surface of DC resistance measurement, to select qualified carbon brush, if not up to the requirements for the selection of good quality brush type.

3.4 replace the new constant pressure spring and brush holder

The original constant pressure spring is replaced by a middle pressure spring to overcome the defects that the original constant pressure spring does not have enough pressure or uneven pressure on both sides, so as to avoid the occurrence of the brush string burning event.

3.5, strengthen downtime maintenance

After the stop, rust prevention and rust removing of the slip ring, blowing and cleaning the slip ring groove and brush holder.