There are many kinds of electrical fault phenomena. For example, the same kind of fault may have different fault phenomena, and different kinds of faults may be the same fault phenomenon. The identity and diversity of this fault phenomenon bring complexity to finding faults.
However, the fault phenomenon is the basic basis and the starting point for finding electrical faults, so it is necessary to carefully observe and analyze the fault phenomenon, find out the most important and typical aspects of the fault phenomenon, and find out the time, place and environment of the fault.
1. Direct perception
Some electrical faults can be directly sensed by touching, seeing, smelling and listening through human hands, eyes, nose, ears and other organs, and the abnormal temperature rise, vibration, smell, noise and color change of the faulty equipment can be determined.
2, instrument testing
Many electrical faults can’t be located by people’s direct perception, but with the help of various instruments and meters, the voltage, current, power, frequency, impedance, insulation value, temperature, amplitude, speed and so on of the faulty equipment are measured to determine the fault location. For example, by measuring insulation resistance, absorption ratio and dielectric loss, it is determined whether the equipment insulation is affected with moisture; Through the measurement of DC resistance, the short-circuit point and grounding point of long-distance lines are determined. This paper introduces a complete set of formulas for electrical fault diagnosis.
I. Sensory diagnosis
1. Judgment of abnormal sound of power transformer
Normal transformer operation, clear and uniform buzzing. If the sound of distribution transformer is abnormal, judge the cause of the fault point. A loud hum, high pitch, overload or overvoltage.
Intermittent violent cackling, single-phase load increases sharply. The hammer clanged and the piercing screw was loose. Clapping applause, the core grounding wire is broken.
Intermittent bursts, poor grounding of iron core. The winding is slightly short-circuited and crackles. The winding is short-circuited seriously, making a huge roar.
There is a crack in the high-pressure casing, which makes a high-frequency hissing sound. High-voltage lead shell flashover, crackling and cracking. The low-voltage phase line is grounded, and the rumbling sound is heard far away.
Drop switch tap, poor contact and squeaking.
2. Use transistor radio to detect partial discharge of electrical equipment.
It is difficult to find partial discharge when patrolling power transformation and distribution equipment. Carry a pocket radio and tune to no radio station. Turn up the volume and listen to the sound, and the hum is normal.
If the sound is irregular, there is a loud firecrackers, or there is a loud squeak, there is a partial discharge nearby. Then turn down the volume and measure it one by one near the equipment.
After hearing firecrackers again, the equipment under test is faulty, which partially discharges and emits high-frequency electromagnetic waves.
3, using the listening stick to diagnose common faults of motor.
Use the listening stick to listen and determine the motor fault. The rotor and stator rub against each other when they hear a continuous creaking sound. Slow speed and hum, the coil touches the shell and touches the ground.
When the speed slows down, the coil is broken and one phase is missing. The bearing room hissed and the bearing lubricating oil dried up. The bearing rattles, and it is concluded that the bearing is damaged.
4, check the hollow wooden shaft with percussion method.
Patrol and check the wooden pole, and hammer around the pole body. Dangdang ringing sound is good, drumming sound is hollow.
5. Check the insulation condition of the bearing of the generator set with the insulated wire with the root peeled off.
When the generator set is running, the bearing insulation should be checked skillfully. Peel the insulated wire with a root. One end of the wire is grounded first, and the other end touches the rotating shaft. Touch it several times and look carefully.
Sparks are generated with poor insulation and good insulation without sparks.
6. Judgment of single-phase grounding fault in neutral ungrounded system
Who has the largest three-phase voltage, the next phase must be faulty.
7, patrol inspection power capacitor
Patrol and check the capacitor, and the temperature of oil leakage in the belly rises over. The cooing sound is abnormal, and there is a discharge fault inside.
8. Judge the quality of small capacitors by charging and discharging method.
The quality of small capacitors is roughly judged by charging and discharging method. Both ends of the capacitor are connected to the power supply and charged for about one minute. Use an insulated copper wire to short the two electrodes of the capacitor.
Spark shining is good, no spark has been damaged.
9. Identify the polarity of lead storage battery
Lead-acid batteries are bipolar, and the positive and negative signs are not clear. The color of the pole is distinguished, and the negative electrode is blue-gray and dark brown. The pole position is different, depending on the factory sign.
The poles are different in diameter, and the anode is thicker and thinner than the cathode. Break the pole column of the saw blade, and the hard pole is the positive pole. The pole lead is inserted into the sweet potato, and the green around the wire is the positive electrode.
Connect the two wires of the pole column and immerse them in dilute sulfuric acid solution to produce a bubble-end negative electrode and no bubble-end positive electrode.
10, scraping the fire method to check whether the battery cell short circuit.
The internal short circuit of the battery usually occurs in one or two grids. Whether the single battery is short-circuited, it is often checked by scraping fire. A thick cop wire is used to connect one pole of a single cell battery,
Hold the other end of the copper wire in hand and quickly wipe the other pole. Blue-and-white sparks appear, and the inspected sheet is in good condition. The red spark is short of electricity, and no spark has been short-circuited.
11. Check the wiring of two-element three-phase watt-hour meter by phase voltage method.
Three-phase three-wire watt-hour meter, check the phase voltage during pumping. Under the condition of constant load, disconnect the neutral voltage line.
Watch the watt-hour meter running, the disk is turning half slowly, the only correct wiring, otherwise the wiring is wrong.