Capacitor compensation cabinet debugging and maintenance - Database & Sql Blog Articles

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1. Influence of system supply voltage on capacitors and capacitors The capacitor reactive power of a capacitor cabinet is proportional to the square of the system supply voltage. If the supply voltage is lower than the rated value of the capacitor, it will increase the loss of the capacitor and will shorten its service life. Therefore, the national standard stipulates that the capacitor must not exceed 1.1 times its rated voltage for a long time. If it exceeds 1.1 times, the capacitor should be out of operation. At present, the ABB power factor regulator installed on the capacitor cabinet has such overvoltage protection function, and the overvoltage protection action value should be monitored frequently during operation. If it is not suitable, appropriate adjustment should be given in time. Capacitor cabinet, compensation cabinet, capacitor compensation cabinet, Shenzhen capacitor cabinet.
2. Monitor the operating current of the capacitor bank. Each capacitor is marked with the rated voltage on its nameplate. When the system supply voltage value is rated, the operating current of the capacitor should also be the rated value; if there is more deviation from the rated value and the three-phase is unbalanced, it should be checked and analyzed:
1) If the current value is too small, the power supply voltage is low, or some capacitors in the capacitor bank are faulty;
2) If the current value is too large, the supply voltage is too high, or the influence of higher harmonics in the system;
3) Three-phase current imbalance is mostly caused by faults in some capacitors in the capacitor bank, which can be checked by clamp-type ammeter;
4) The current value greatly exceeds the rated value, and the current meter pointer swings up and down abruptly, and most of the capacitors and the higher harmonics in the system generate parallel resonance, so that the capacitor is seriously overloaded in the harmonic state.
In response to the abnormal situation of the above ammeter, corresponding measures should be taken to prevent further expansion of abnormal events.
3. Reduce the probability of switching oscillations. Switching oscillation refers to an unstable operation state in which the capacitor group is repeatedly input and cut off continuously. The components are frequently turned on and off, which will accelerate aging and shorten the service life. Therefore, the operation should be exhausted. It is possible to reduce the chance of its switching. Its formation mainly has the following two reasons:
1) When the system is running in a certain state, after a set of capacitors is put into operation, the system will overcompensate. Repeated switching is performed so that the switching power factor is stopped after the load power factor in the system changes and the working conditions are met. There are two ways to mitigate this:
1 Select the appropriate reactive power automatic compensator. At present, there are two commonly used methods: one is the value of cosφ, regardless of the load value in the system, as long as the value of cosφ is higher or lower than the set value, the automatic compensator will issue an instruction of “input” or “cut”; According to the magnitude of the inductive load value in the system, if the inductive load in the system is less than the set value of the compensator, the compensator will not issue an “input” command if the cosφ is low in the system. Reduced the chance of switching.
2 Change the capacitor equal volume group to the inequality grouping. At present, most capacitive screens are isometric groups, that is, the capacity of each group of capacitors is equal. If the capacity of one of the capacitors is reduced, or the capacitor with the rated capacity of 400V is equal to the capacitor with the rated capacity of 500V, the capacitor with the rated voltage of 500V is derated. (The capacity after the step-down is the original rated capacity. 64%), can also reduce the chance of switching.
2) Switching oscillation caused by overvoltage. When the power supply voltage rises to the over-voltage action value of the compensator, the original input capacitor is cut off one by one; when the power supply voltage is lower than the set value, the over-voltage protection is taken out again. The overvoltage protection action value of the compensator is generally set at 436~438V, and the return value cannot be too high. The difference between the two is called the hysteresis, and the hysteresis voltage is generally about 6V. If the hysteresis voltage is too small, it is easy to cause switching oscillation. During operation, it is possible to check whether the overvoltage protection setting value and the hysteresis voltage value are appropriate according to the system operating voltage.
4. Should have a reliable discharge circuit No matter which form of capacitor cabinet, there must be a reliable discharge circuit. If there is no reliable discharge circuit after the capacitor bank is disconnected from the system power supply, when the capacitor bank is put back again, the capacitor may be subjected to a higher superimposed voltage, thereby being damaged; at the same time, a large closing surge current is easily damaged. About electrical equipment. When the operator uses manual switching, the residual charge cannot be reliably played back to a safe range; at the same time, the internal resistance is intact and difficult to check. Therefore, the author believes that three signal lights should be connected in parallel with each capacitor, indicating both the discharge circuit and the switching indication.
5. Master the correct operation method 1) When manual operation is used, the cutting speed should not be too fast, and it is necessary to ensure sufficient discharge time.
2) The sub-cabinet also has a switch that selects both automatic and manual modes of operation. The sub-cabinet is required to be automatically switched with the main cabinet. Before the main cabinet is put into operation (or in the majority of the main cabinet capacitor group), the sub-container switch is pre-operated in the automatic working position, but it is exhausted. It is possible to avoid the main cabinet switchgear being switched from manual or stop to avoid the impact of large current on the system and damage the equipment.
6. Sampling and load phase arrangement The phase connected by such load should be reflected on the sampling transformer. Otherwise, the phase connected by the load should be adjusted to make the controller work normally according to the sampling position.
7. Prevent high-order harmonics from harming capacitors The high-order harmonic sources in the power grid mainly come from non-linear loads, such as thyristor rectifiers in the power grid, nonlinear saturation of transformer cores, and electric arc furnace inverters. High-order harmonics are very harmful to capacitors. First, capacitors are over-current, heat-generating, and loss-increasing, resulting in dielectric insulation degradation, which ultimately causes internal breakdown. At the same time, current resonance may be formed. Once current resonance occurs, large capacitors will be over-current. The fuse blows or causes an explosion. To prevent the damage of high harmonics to capacitors, measures can be taken from the following two aspects:
1) Capacitor series reactor. According to the measurement and analysis, the higher harmonic components appearing in the system vary with the nature and state of the load. According to the relevant data analysis, usually 5th harmonic, can be in the capacitor bank series reactor, the fundamental wave reactance value is 5% to 6% of the capacitor's fundamental wave capacitance value;
2) Increase the rated working voltage of the capacitor bank to increase the dielectric strength of the capacitor. For example, a capacitor having a rated voltage of 500V is used for a 400V power supply.
8. Monitor the temperature rise of the capacitor. The temperature rise of the capacitor during normal operation will not be very high, generally not exceeding 20K. If the hand touches its outer casing and feels lukewarm, it is normal; otherwise, if the outer casing is very hot, then there must be a fault inside, and the power should be turned off to run out.
9. Strengthen daily maintenance 1) Regularly clean the equipment and tighten the first and second circuit screws.
2) Regularly check whether the instrument indication is normal? Is the circuit connection part and the main components overheated? Is there any abnormal noise? Is the discharge circuit intact? If problems are found, they should be dealt with in time.