J&T

What are the cause of the unbalanced three-phase 380 v motor?

by:J&T     2020-07-01
In the chemical industry, electric equipment often use three-phase 380 v power supply, the three-phase imbalance is an important index of power quality, although there are many factors that can affect power system, but most of the sex imbalance situation because of asymmetric three-phase components, circuit parameters or load. Because of three-phase load factor is not certain, so the three-phase voltage and current of the power supply points easy to appear the phenomenon of imbalance, loss line. Not only that, but its motor to power point will be adversely affected, the normal operation of the damage motor. Therefore, if the unbalanced three-phase beyond the scope of distribution network can bear, so the safety of the whole power system operation will be affected. The cause of the unbalanced three-phase distribution network are: a, bolt break but not grounding fault if a photograph, or circuit breaker, isolating switch is not connected to a phase, voltage transformer blown fuse are asymmetrical three-phase parameters. On a break when a phase line voltage level, a voltage level of performance for three phase voltage is lower, compared to one of the low, but both high voltage value is close to than the other two. Line break at the corresponding level, disconnect phase voltage is zero, no break line phase voltage is still the phase voltage. Second, ground fault when the single-phase grounding line a phase of bolt and is caused by three-phase voltage imbalance, but after the grounding voltage values are not changed. Single-phase grounding into metallicity and non-metal earthing two kinds. Grounding metallicity, the fault phase voltage to zero or near zero, the fault phase voltage increases 1. 732 times, and the constant; Non-metallic grounding, grounding phase voltage is not zero but is reduced to a certain value, the other two phase rise less than 1. 732 times. Resonance with the rapid development of industry, plenty of non-linear power load increases, the certain load harmonic generation, not only has caused the power supply voltage fluctuation and flicker, and even cause unbalanced three-phase voltage. Three, to match varying load monitoring efforts to weaken in the management of the distribution network, often ignore the management problems in three-phase load distribution. On the detection of the distribution network, the distribution transformer three-phase load and no regular testing and adjusting. In addition, there are many factors cause the three-phase unbalanced phenomenon, for example, the influence of the circuit and three-phase load torque does not, and so on. Four, electricity load changing the cause of unstable electricity load including the II often appear demolition, move the table or the increase of the electricity users; The instability of temporary electricity utilization and seasonal. So on the amount and time of uncertainty and is not concentrated on making electricity load has to follow the actual situation and change. Five, the improper operation and maintenance operator can't regularly for electrical equipment inspection and maintenance work, is a man-made motor leakage, lack of phase operation, a major factor in the production of unbalance current. Improper operation and maintenance is mainly manifested in: 1, the installation personnel group operation, the zero line. Into the line into the junction box, leakage current. 2, each connection switch, loose contact, the oxidation phenomenon of lack of phase or causes such as frequent starting, the starting time is too long or too short, cause the fuse is broken. 3, use for a long time, lack of maintenance, make the motor aging, local insulation degradation. Six, three phase load of unreasonable allocation of many staff of table, there is no professional knowledge of three-phase load balancing concept, therefore when I answer the electricity and didn't notice to control the three-phase load balancing, is blind and random loading forms to take charge of the circuit, this is largely caused by the unbalanced three-phase load. Second, our country most of the circuit are power and lighting for the integration of mixed, so when using single phase electric equipment, will reduce the efficiency of electricity, such differences further exacerbated the imbalance in distribution transformer three-phase load. Seven, resonance caused by unbalanced three-phase voltage resonance: 1, the fundamental frequency characteristic is similar to the single phase grounding, namely the phase voltage is reduced, the other two phase voltage rise, to find the cause of the problem is not easy to find fault point, users can now special inspection, if not for grounding, is likely to be caused by resonance. 2, the resonance frequency division: the other is a frequency or high frequency resonant, characterized by three-phase voltage rise at the same time. In addition, also note that the bus drop removal of part of single-phase earth fault lines or disappears, such as a ground signal, and a phase and two phase or three phase voltage more than line voltage, voltage meter pointer to an end, and at the same time, to move slowly, or three-phase voltage rises in turn over line voltage, encounter this kind of situation, usually caused by resonance. Eight, the overload operation of the motor load, especially when starting, motor, the rotor current increase fever. Slightly long, winding current unbalance phenomenon appear easily. Under the heavy load is mainly manifested in: 1, the coupling part skew, a foreign body actuator stuck. Belt and gear transmission mechanism too tight or too loose. 2, dry lubricant, bearing block, mechanical rust ( Including motor mechanical failure itself) 。 3, voltage too high or too low, make the loss increased, the load collocation is improper, the motor rated power is less than the actual load.
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