With the rapid development of China's economy, elevators are becoming more and more widely used in large public buildings and residential buildings. However, their power quality problems are becoming more and more prominent. So what points should we pay attention to?
According to the relevant national standards, the elevator industry belongs to the special equipment industry. At the same time, the power quality problems of elevators are also prominent. Among them, imbalance, harmonics, inrush current, transient and energy efficiency are the key points. Nowadays, elevator accidents occur frequently and quality problems On the one hand, the issue of power quality cannot be ignored. Therefore, the analysis and protection of power quality problems is a necessary way to deal with the safety hazards of the elevator industry.
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In summary, the problem of power quality disturbance in the elevator industry is mainly divided into steady state disturbance and transient disturbance. Steady-state disturbances include overvoltage, undervoltage, voltage imbalance, harmonics, etc. Transient disturbances include voltage swell, voltage sag, voltage fluctuations, and voltage interruptions. Relevant information shows that more than 90% of complaints about power quality problems are caused by voltage sag. It can be seen that the primary problem of power quality is the voltage sag problem.
Voltage sag refers to a temporary decrease in the effective value of the supply voltage, and then resumes normal power supply. According to the European standard EN 50160 and the American Institute of Electrical and Electronics Engineers recommended standard IEEE Std.519-1992, the voltage sag is defined as: The effective value of the supply voltage suddenly drops to 90% to 10% of the rated voltage (0.9 pu ~ 0.1 Pu ) and then return to normal voltage, the duration of this process is 10 ms to 1 m in. With the development of the economy, high-tech equipment has been widely used. These devices are sensitive to voltage changes. Short-term power interruptions or voltage rms drops often cause equipment to malfunction and cause downtime. The voltage sag is proposed for this problem. The main cause of voltage sag is lightning strikes or external short-circuit faults in power grids or electrical equipment. Some electrical equipment (such as electric motors) start or suddenly load will also cause the grid voltage to drop instantaneously. Compared with the long-term power interruption accident, the voltage sag has the characteristics of high frequency and difficulty in detecting the cause of the accident, which is difficult to handle. The voltage sag can cause unnecessary action of the sensitive controller (causing tripping), causing the computer system to malfunction, the automatic device to pause or malfunction, the inverter to stall, etc.; causing the contactor to trip or the low-voltage protection to start, causing the motor, The elevator waits for a pause.
This shows that the analysis of power quality problems is imperative. Guangzhou Zhiyuan E6500 Power Quality Analyzer's original recording analysis function supports 10s-10min timing/manual/background recording function, which can effectively help customers find and analyze power quality problems. Recording files can be temporarily used by the host computer software. Sub-analysis of important indicators such as rise, voltage sag, harmonics, unbalance, etc., and can generate custom or national standard reports, restore field waveforms, capture subtle waveform changes, and widely used in motors and microelectronics industries.
Figure 2 Recording settings interface
The E6500 uses a 16-bit high-precision analog-to-digital converter with a sampling rate of 25.6 kHz per channel. It provides 512 samples per cycle, ensuring voltage and current measurement accuracy of over 0.1%. The high sampling rate is very important for event waveform sampling. As the number of weekly wave samples increases, the sampled waveform is closer to the actual waveform, making it easier to find abnormal waveforms. For voltage dips/sag/swell events, the high sampling rate clearly shows transients caused by surges. Figure 4 shows the waveform acquired at 128 points/cycle, and Figure 5 shows the waveform acquired at 512 points/cycle.
Figure 3 Waveforms acquired at 128 points/cycle
Figure 4 waveform acquired at 512 points/cycle
As you can see, the number of weekly wave samples in Figure 4 is 128 points, and the recorded waveform is relatively smooth. As shown in Fig. 5, the waveform of 512 points is sampled by the weekly wave, which is closer to the actual waveform, and it is easy to find the waveform abnormal signal. This is the advantage of high sampling rates.
actual caseOn December 9, 2016, Guangzhou Zhiyuan Electronic Engineer went to an agency in Guangzhou to capture the current waveform and voltage sag curve of the elevator.
Figure 5 A field measured current waveform
Figure 6: A scene capture voltage sag
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