Electrical equipment maintenance inspection method and operation practice - Solutions - Huaqiang Electronic Network

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1. Intuitive method The intuitive method is a method of checking and judging faults by means of watching, smelling, and listening according to the external performance of electrical faults.
(1) Inspection steps:
Investigation situation: Inquire about the situation of the operator and the fault presence, including the external performance of the fault, the approximate location, and the environmental situation at the time of the fault. If there is no abnormal gas, open flame, whether the heat source is close to the electrical appliance, whether there is corrosive gas intrusion, whether there is water leakage, whether someone has repaired it, the repair content, and so on.
Preliminary inspection: According to the investigation, check whether there is any damage to the external electrical equipment, whether the connection is broken or loose, whether the insulation is burnt, whether the fuse indicator of the spiral fuse jumps out, whether the electrical appliance has water or grease, and the switch position. Is it correct? Commissioning: After preliminary inspection, it is confirmed that there will be further expansion of the fault and human and equipment accidents, and further test can be carried out. During the test, attention should be paid to whether there is serious flashover, abnormal smell, abnormal sound, etc., and should be stopped immediately after discovery. Cut off the power. Pay attention to check the temperature rise of the appliance and the operation procedure of the appliance to meet the requirements of the schematic diagram of the electrical equipment, so as to find the fault location.
(2) Inspection method:
Observe the spark: The electrical appliance's contacts will spark when they are closed, the breaking circuit or the wire head is loose. Therefore, it is possible to check the electrical fault according to the presence or absence of the spark. For example, when a spark is found between a normally fastened wire and a screw, the wire is loose or poorly contacted. When the contact of the electrical appliance is closed and the circuit is broken, the fire is extinguished to indicate that the circuit is open, and the flashing does not indicate that the circuit is unreachable. When the contactor of the main contact of the control motor has sparks in one phase and no spark in one phase, it indicates that the non-sparking one-phase contact is in poor contact or the phase circuit is open; the sparks of the two phases in the three phases are larger than normal, and the other phase is different. It is smaller than normal, and it can be judged that the motor is short-circuited or grounded. The three-phase sparks are larger than normal, and the motor may be overloaded or the mechanical part may be stuck. In the auxiliary circuit, after the contactor coil circuit is energized, the armature does not pick up, and it is necessary to distinguish whether the circuit is broken or the mechanical part of the contactor is stuck. Press the start button. If the button is normally open, the contact closure position is slightly sparked, indicating the circuit path, the fault is in the mechanical part of the contactor; if there is no spark between the contacts, the circuit is open.
Action procedure: The operating procedures of the appliance shall comply with the requirements of the electrical instructions and drawings. If the electrical device on a certain circuit moves too early, too late or does not move, it indicates that the circuit or electrical appliance is faulty.
In addition, it is also possible to analyze and judge the fault based on the sound, temperature, pressure, smell, etc. emitted by the appliance. Using the intuitive method, you can not only determine simple faults, but also narrow down more complex faults to a smaller range.
2. Measuring voltage method The measuring voltage method is based on the power supply mode of the electric appliance, and measures the voltage value and current value of each point and compares it with the normal value. Specifically, it can be divided into a step measurement method, a segment measurement method, and a point measurement method. The measuring voltage method measures the voltage value and current value of each point according to the power supply mode of the electric appliance and compares it with the normal value.
1 step measurement method (shown in Figure 1): When the travel switch SQ in the circuit and the normally open contact KA of the intermediate relay are closed, press the start button SB1, the contactor KMl does not pull in, indicating that the circuit is faulty. First measure the voltage at two points A and B. The normal value is 380V. Then press the start button and put the black test bar to point B. The red test bar is moved forward in sequence, and the voltages at points 2, 11, 9, 7, 5, 3, and 1 are measured.

figure 1
In the maintenance practice, depending on the fault situation, it is not necessary to measure point by point, but multiple test points, such as B and 11, B and 3, are used.
2-segment measurement method: the wire between the electrical appliances when the contacts are closed, the voltage drop is close to zero when energized. When the appliance, various types of resistors, and coils are energized, the voltage drop is equal to or close to the applied voltage. According to this feature, it is more convenient to check the circuit fault by using the segmentation measurement method. As shown in Fig. 2, if the contactor KM1 does not pull when the button SBl is pressed, the button SB1 is not pressed, and the first side A and B are two points. The voltage, the voltage is 380V, and the contactor does not attract the circuit to indicate that there is a break.
3-point measurement method: The circuit of the electrical auxiliary circuit voltage is 220V and the neutral line is grounded. The point measurement method can be used to check the circuit fault (as shown in Figure 3).
3. The resistance measurement method can be divided into a step measurement method and a segment measurement method. These two methods are suitable for electrical equipment with a large distribution distance of switches and electrical appliances.

1 step measurement method: When the trip switch SQ (Fig. 4) and the intermediate relay contact KA in the circuit are closed, press the start button SBl, the contactor KM1 does not pick up, indicating that the circuit is faulty. When checking, first disconnect the power supply and measure the two points of A and B (note that the button SB1 should always be pressed during measurement). If the resistance is infinite, the circuit is open.
2 segmentation measurement method: first cut off the power supply, press the start button SB1 (Fig. 5), the two test bars test the resistance of the adjacent two labels (except 2-11 points) step by step or focus, such as the resistance between the two points is very Large, indicating that the contact is poorly connected or the wire is open. For example, when it is measured that the resistance between two points is large, the contact of the travel switch contacts is poor.
These two methods are suitable for electrical equipment with a large distribution distance of switches and electrical appliances.

4. Contrast, replacement component, step-by-step open circuit (or access) method 1 Contrast method: Compare the test data with the drawing data and the normal parameters recorded in the usual time to judge the fault. For appliances that have no data and no usual records, they can be compared with the same type of intact appliances.
When the electrical components in the circuit belong to the same control property or multiple components jointly control the same device, the faults can be judged by using other similar or identical power supply components. For example, the asynchronous motor positive and negative control circuit, if the forward contactor KM1 does not pull, can be reversed to see if the contactor KM2 is sucked, such as suction, it proves that the KM1 circuit itself is faulty.
2 conversion component method: the cause of failure of some circuits is difficult to determine or when the inspection time is too long, but in order to ensure the utilization of electrical equipment, it is possible to replace the component experiments with good performance of the same phase to confirm whether the fault is caused by the appliance.
When using the replacement component method, it should be noted that when the original electrical appliance is removed, it is necessary to carefully check whether it has been damaged. Only when it is determined that the electrical appliance itself is damaged, the new electrical appliance can be replaced, so as to avoid damage to the newly replaced component.
3 Step-by-step open circuit (or access) method: When multiple branches are connected in parallel and the circuit is controlled to be short-circuited or grounded, there is generally obvious external performance, such as smoke and sparks. When the motor or the circuit with the shroud is short-circuited or grounded, it is not easy to find other external phenomena except for the fuse being blown. This situation can be checked by a step-by-step (or access) method.
a. Step-by-step open circuit method: When encountering a short circuit or ground fault that is difficult to check, the melt can be replaced again, and the multi-branch parallel circuit is disconnected gradually or critically from the circuit, and then the power is tested, if the fuse is no longer Fuse, the fault is on this circuit that has just been disconnected. Then divide this branch into several segments and access the circuit piece by piece. When a certain circuit is connected, the fuse is blown again, and the fault is on the circuit and an electrical component. This method is simple, but it is easy to completely burn out electrical components that are not seriously damaged.
b. Step-by-step access method: When the circuit is short-circuited or grounded, replace it with a new fuse. Step by step or focus on connecting each branch to the power supply and retest. When a fuse is connected, the fuse is blown again, and the fault is on the circuit that has just been connected and the electrical components it contains.
5. Forced closing method When the electrical fault is queued, after the visual inspection, the fault point is not found and there is no suitable instrument for measurement under the hand. The relay, contactor, electromagnet, etc. can be forcibly pressed by an external force with an insulating rod. The normally open contact is closed, and then observe various phenomena appearing in the electrical part or the mechanical part, such as the motor never turning to the rotation, the corresponding part of the device is never moved to normal operation.

When the electrical fault is eliminated, after the visual inspection, the fault point is not found and the appropriate instrument is not measured under the hand. The relay, the contactor, the electromagnet, etc. can be forcibly pressed with an insulating rod to make the normally open contact Close, and then observe the various phenomena appearing in the electrical or mechanical parts, such as the motor never turn to the rotation, the corresponding part of the equipment from the fixed to the normal operation.
1 Check the fault of one circuit: In the asynchronous motor control circuit (Fig. 3), if the start button SB1 is pressed, the contactor KM1 does not pick up, and a thin insulating rod or a well-insulated screwdriver can be used (note that the hand cannot touch the metal part) From the middle hole of the contactor arc chute (small contactor with two insulating rods aligned with the contact brackets on both sides), press quickly and then release quickly, the following may occur:
a, the motor starts, the contactor is no longer released, indicating that the start button SB1 is in poor contact.
b. When forced to close, the motor does not turn but has a squeaky sound. When it is loosened, it is seen that all three contacts have sparks and the brightness is uniform. The reason is that the motor is overloaded or the thermal relay FR in the auxiliary circuit is normally closed.
C. When the motor is forced to close, the motor runs normally. After the motor is released, the motor stops, and the contactor also trips. Generally, the fuse FU in the auxiliary circuit is blown or stopped, and the start button is in poor contact.
d. When the motor is forced to close, the motor does not turn and there is a click. When the main contact of the contactor is released, only the two contacts have sparks. Explain that the main circuit of the motor is disconnected. Poor contact of the main contact of the contactor.
2 Check the fault of the multi-branch automatic control circuit: In the multi-branch automatic control step-down starting circuit (Fig. 6), when starting, the series resistance R on the stator winding limits the starting current. When the motor rises to a certain value, the time relay KT operates, the normally open contact closes, the KM2 circuit is turned on, the starting resistor R is automatically short-circuited, and the motor operates normally. If the start button SB1 is pressed, the contactor does not pull in, the KM1 can be forcibly closed, and after the release, the KM1 is kept in the pull-in position, and the motor is started at the moment of forced closing. If KM1 is released with the insulation rod loosened, but the motor rotates, the fault is at stop button SB2 thermal relay FR contact or KM1 itself. If the motor does not turn, the fault is in the main circuit fuse, the power supply has no voltage, and so on. If the KMI is no longer released, the motor is running normally and the fault is at the self-locking contacts of the start buttons SB1 and KM1.

Figure 6
When the start button SB1 is pressed, KM1 is engaged, and the time relay KT is not engaged. The fault is in the time relay coil circuit or its mechanical part. If the time relay is closed, but the KM2 does not pull in, use a small screwdriver to press the micro switch on the KT. Pay attention to whether there is a sound of the switch action. If there is sound and the motor is running normally, the micro switch is not assembled correctly.
6. Short circuit method The fault of the equipment circuit or electrical appliance is roughly classified into six categories: short circuit, overload, open circuit, grounding, wiring error, electromagnetic and mechanical part failure of the electrical appliance. More of these types of faults are open circuit faults. It includes wire breakage, virtual connection, looseness, poor contact contact, virtual soldering, false soldering, fuse blowing, etc. In addition to the resistance method and the voltage method check for such faults, there is a simpler and more reliable method, which is the short circuit method. The method is to use a well insulated wire to short-circuit the suspected circuit breaker. If it is shorted to somewhere, the circuit works back to normal, indicating that the circuit is open. The specific operations can be divided into local short circuit method and long and short circuit method.

The faults of equipment circuits or electrical appliances are roughly classified into six categories: short circuit, overload, open circuit, grounding, wiring error, electromagnetic and mechanical part failure of electrical appliances. More of these types of faults are open circuit faults. It includes wire breakage, virtual connection, looseness, poor contact contact, virtual soldering, false soldering, fuse blowing, etc. In addition to the resistance method and voltage method inspection, there is a simpler and more reliable method for this type of fault, which is the short circuit method. The method is to use a well insulated wire to short-circuit the suspected circuit breaker. If it is shorted to somewhere, the circuit works back to normal, indicating that the circuit is open.
1 Local shorting method (Fig. 7): When it is determined that the stroke switch SQ and the intermediate relay normally open contact KA in the circuit are closed, the start button SB1 is pressed, and the contactor KM1 is not attracted, indicating that the circuit is faulty. When checking, you can first measure the voltages of A and B. If the voltage is normal, press and hold button SB1, shorting 1-3, 3-5, 7-9, 9-11 and B-2 respectively. When shorted to a point, the contactor pulls in, indicating that the fault is between these two points.
2 long and short connection method: long and short connection method refers to shorting two or more contacts or line segments at a time to check the fault. This saves time and compensates for some of the shortcomings of the local shorting method. For example, if the two contacts SQ and KA are in poor contact at the same time or the wire is broken (Fig. 8), the result of the short circuit method checking the circuit failure may be erroneous. The long and short connection method can be used to short-circuit 1-11. If the short contactor KM1 is connected, it means that there must be a disconnection on the circuit of 1-11, and then the local short circuit is used to check. There is no misjudgment.

Figure 7
The above several inspection methods should be used alive and in accordance with the safety regulations.
For components that are continuously burnt out, the cause should be identified and replaced; the voltage drop should take into account the voltage drop of the wire; do not violate the principle of electrical control of the equipment, the hand must not leave the power switch during the test, and the insurance should use the same amount or Slightly less than the rated current; pay attention to the choice of the gear of the measuring instrument.