Through long-term investigation and research, it is found that the low-voltage reactive power compensation device has many problems in the process of switching, and the reasons for the problems and corresponding countermeasures are described in the paper.
Key words: compensation device, component, failure, cause analysis, corresponding countermeasure
The reactive power compensation device is one of the main equipments in the power distribution system. Its function is to improve the power factor, reduce the power loss and power loss, improve the voltage quality and reduce the user's electricity cost, so the power supply department and the power unit need the reactive power compensation device. Both are very high. However, the reactive power compensation device often has many problems during operation, mainly related to whether the compensation device selects the electrical component configuration reasonably, whether the electrical component is used correctly, whether there is harmonic interference in the power grid, and the installation process.
1 controller problem
A common problem with the electrical components (controllers) of the compensation device is that the cosφ display on the compensation controller is not accurate.
There are two possibilities for this to happen:
(1) The compensation controller generates misoperation and error, mainly due to harmonics generated in the power grid or from the load source. The corresponding method is to replace the anti-harmonic controller or install anti-harmonic components in the power distribution system.
(2) The compensation controller is related to the sampling current or voltage. When the capacitor is put into normal under load, the power factor should be gradually increased from the hysteresis value to 1.00. If the capacitor is re-input, the power factor should be advanced, and the input value should be reduced to normal;
1) Always show only 1.00.
2) The grid load is in a hysteresis state, and the compensator always shows the lead.
3) The grid load is hysteresis, and the compensator shows hysteresis. However, after the capacitor is input, the hysteresis value does not change (increase) in the normal direction. On the contrary, the more the input capacitor, the smaller the hysteresis value.
4) The grid load is a hysteresis state. Although the compensator shows the hysteresis value, the hysteresis value does not change after the capacitor is input, and the hysteresis value only changes with the load.
The above situation: 1) is often because the sampling current is not sent to the compensator.
2, 3) The general situation is because the sampling current and sampling voltage phase is incorrect
4) In general, the current generated by the switching capacitor does not pass through the sampling transformer.
The compensation controller can operate normally, the sampling current must be correct, and the current generated by the load current and the capacitor switching must be reflected from the sampling transformer.
2 fuse problem
In the reactive power compensation device, the fuse is often blown during the compensation switching process.
(1) Cause analysis
1) The fuse fuse is related to the rationality of the configuration.
2) Fuse blow is related to calculating the corresponding multiple of the actual switching current.
3) The fuse blow is related to the switching time of the compensation controller.
4) Fuse blow is related to harmonics generated by the grid system or load equipment.
5) Fuse blow is related to phase current imbalance.
6) The fuse is blown and related to the installation process and working environment.
(2) Corresponding countermeasures
1) To fully consider the characteristics of the reactive power compensation device, it is very important to select the fuse core when the inrush current is large during the switching process (generally around 15~30In). Generally, the É‘m type (strong overload capability) or the same type is selected. The fuse core, not the JL type (low overload capacity) or the same type of melting core.
2) The fuse protects the capacitor. It is very important to calculate the actual switching current. However, for the characteristics of the reactive power compensation device, the fuse current should be considered. Normally, the actual switching current should be 1.35 to 2 times.
Example: The voltage is 400V. In the circuit with a frequency of 50Hz and a three-phase common-capacitance capacitor capacity of 20kvar, the actual switching current and the fuse current of each channel are obtained.
The actual switching current should be I1=■×20kvar
I1≈28.87A
Take 1.4 times the fuse factor current should be
I2=■×20kvar×1.4
I2≈40.41A
3) The fuse of the fuse has a certain relationship with the switching time set by the compensation controller. After the capacitor is cut off from the network, the voltage in the capacitor gradually decays with time. When the interval time is short and input, the residual voltage and the applied voltage form a superimposed voltage, causing overvoltage and overcurrent. The long-term operation will cause the capacitor to break down or short-circuit, and the strong current will blow the fuse. Therefore, it should not be too short when setting the switching time. Generally, it is suitable to set 20~30s.
4) The harmonics generated by the power grid or the load device will change the original 50-60 Hz voltage property of the power supply. When the harmonic content is high, the amplified fundamental current caused by the harmonic will blow the fuse. .
5) The three-phase current in the operation of the compensation device is unbalanced for a long time, which will also cause the fuse to be partially blown. If the three-phase current imbalance is found, it is necessary to find the cause in time. When replacing the fuse with a non-three-phase current imbalance, it is best to replace the three-phase fuse at the same time. If only one phase of the fuse has been blown, then the other two phases of the damaged fuse are put into operation, and the fuse will be blown if the time is not long.
6) The fuse of the fuse has a certain relationship with the installation process and the use environment, especially the use environment. In some cases, the temperature is very high, and the time is up to 70C°. In this case, the temperature reduction measures must be taken.
3 capacitor contactor problem
In the process of switching the reactive power compensation device, the damage of the capacitive contactor is particularly prominent. From a subjective point of view, the capacitive contactor is a consumable item, but objectively speaking, there are other aspects that cause damage to the capacitive contactor.
(1) The switching time set by the compensation controller is too short, and the superimposed voltage caused by the secondary suction causes the inrush current to be too large to damage the contactor.
(2) The damage of the contactor has a certain relationship with the correct installation of the contactor. In particular, the wire connection part of the contactor must be tightly connected and not covered with an insulating sleeve.
(3) When the harmonic content in the circuit is high, the voltage and current waveforms are severely distorted. The expansion of the fundamental current will cause the contactor to burn the contacts, and the phases are short-circuited with the phase or relative, causing damage to the contactor.
(4) When the range of the current imbalance is increased, long-term operation will also cause damage to the contactor.
(5) The quality of the contactor itself also has a great relationship. At present, there are many manufacturers of capacitive contactors in China, and there are many models, but the quality of the materials and products produced are not the same. The current compensation requirements are very high. It is best to use capacitive contactors that resist surge, anti-harmonics or withstand harmonics when selecting.
4 capacitor problem
Capacitor damage during operation is more prominent, such as breakdown can not heal, short circuit, belly and running time is not long capacity decline, serious or even explosive. The current capacitors are basically self-healing. Under normal circumstances, once the breakdown occurs, it will heal automatically. If the breakdown is repeated and healed, the capacitor will be completely damaged.
(1) Capacitor damage
1) The mis-projection mis-cut caused by the compensation controller quality problem causes the capacitor to be damaged.
2) The current that is instantaneously cut during compensation is very large, causing damage to the capacitor.
3) The three-phase current and voltage are unbalanced for a long time, causing damage to the capacitor.
4) Superimposed voltage (formed due to the short switching time set by the controller).
Example: The capacity of each capacitor is 30kvar, which is compensated by 8 channels. The total compensation capacity is 240kvar. If the switching time is set to 5s, the interval of 8 channels is less than 1 minute (5s × 8 channels = 40s). Under normal circumstances, the capacitor drops to 50V within 1 minute of power failure, and if it is frequently switched, it will cause superposition. The actual voltage for switching the number of capacitors per channel should be
380V+(≤50V)+(≤50V)+(≤50V)+(≤50V)+...N times
5) Harmonic interference to the capacitor.
(2) Corresponding countermeasures
1) Use a controller of better quality.
2) When the instantaneous surge current is very large during compensation, it is recommended to connect more than 30In to the electrical components such as reactors.
3) If the phase loss or three-phase current and voltage imbalance is found, it is necessary to find the cause in time and solve it in time.
4) The setting of the controller is not too short to prevent the formation of a superimposed voltage. If the actual compensation capacity is insufficient or does require frequent switching, the compensation capacity should be increased or a combination of local compensation and centralized compensation should be performed.
5) If there is harmonic interference in the power grid, measures should be taken in time to install a filtering device or install anti-harmonic components.
5 Conclusion
In order to improve and improve the compensation requirements achieved by the reactive power compensation device, it is necessary to understand whether the power grid or the load source has harmonics, the rationality of the electrical component configuration of the reactive power compensation device, and the correct use of the compensation device to make the reactive power compensation device non-faulty. It reaches normal operation.
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