Harmonic suppression measures in the electrical de

Harmonic suppression measures in theater electrical design Abstract: This paper discusses the necessity and specific measures of harmonic suppression in theater electrical design through the analysis of the generation, characteristics and harm of theater electrical harmonics

key words: harmonic theater stage thyristor dimmer harmonic suppression measures in theater electrical design Tanghai normal Tanghai 25 t05:31:00z t05:31:00z 2391 2232 QH 1842741 9.3821 5.25 pounds 7.8 pounds 0 the process of deformation increasing with time 2 due to the use of nonlinear electrical equipment, periodic non sinusoidal electricity is generated. Fourier series decomposition of these periodic non sinusoidal electric quantities can obtain not only the same components as the frequency of the electric fundamental wave, but also a series of components larger than the frequency of the electric fundamental wave, which is called harmonics. There are many nonlinear load harmonic sources in the electrical equipment of civil buildings, such as fluorescent lamps, gas discharge lamps, computers, UPS devices, electronic speed regulation equipment, soft start equipment, etc. In the electrical equipment of the theater, there are also a large number of harmonic sources, especially the current waveform distortion caused by the silicon controlled dimming device of stage lighting, which makes the harmonic problem particularly serious. 1. The generation and characteristic analysis of electrical harmonics in the theater silicon controlled dimmer is the mainstream dimmer on the stage at present. All kinds of dimmers used in stage lighting are essentially a single-phase phase controlled AC voltage regulator. At a certain time T1 (or a certain phase angle WT1) after the zero crossing of the sinusoidal AC voltage, a trigger pulse is added to the gate of the thyristor to make the thyristor turn on, which will be maintained until the end of the positive half cycle of the sine wave. Therefore, in the positive half cycle of the sine wave (i.e. 0 ~ p interval), the thyristor in the range of 0 ~ WT1 is not conductive. This range is called the control angle, which is usually represented by a; The range of thyristor conduction between WT1 and P is called conduction angle, which is commonly used as "conduction angle"? express. Similarly, in the negative half cycle of the sinusoidal AC voltage, a trigger pulse is applied to another thyristor (for two unidirectional thyristors in reverse connection with low cycle load cycle, deformation cycle and displacement cycle) at time T2 (i.e. phase angle WT2) to make it turn on. In this way, the conduction of sine wave is controlled for each half cycle to obtain the same conduction angle. If the application time (or phase) of the trigger pulse is changed, the conduction angle is changed? (or control angle a). The larger the conduction angle, the higher the voltage output by the dimmer, and the brighter the lamp. From the above silicon controlled dimming principle, the voltage waveform output by the dimmer is no longer a sine wave. The Fourier series decomposition of the periodic non sinusoidal electric quantity shows that the load voltage output in the thyristor dimming process contains not only the fundamental component with the same frequency as the power supply, but also a series of high-order harmonics with the frequency of odd times the power supply frequency. These high-order harmonics radiate a lot into the air and will also be transmitted to other loads through wires, causing the waveform distortion of the power supply voltage. 2. The harm of harmonics, the distortion of power supply voltage waveform causes electric harmonic pollution, and many abnormal phenomena and faults appear in the power generation, supply and consumption equipment of the power system. The harm of harmonics is multifaceted. As far as the theater electrical system is concerned, there are mainly the following aspects: 2.1 Harm to power supply and distribution lines in three-phase distribution lines, integral multiple harmonics of 3 on the phase line will be superimposed on the neutral line, so that the current value of the neutral line may exceed the current on the phase line. Harmonic voltage and harmonic current of the same frequency should produce active power and reactive power of the same harmonic, so as to reduce electric voltage and waste electric capacity. Under the influence of harmonics, the relay can not play a comprehensive and effective role in protection, resulting in maloperation or refusal to operate, which will seriously threaten the stability and safe operation of the power supply and distribution system. With the increase of harmonic number and high frequency, the skin effect of cable conductor becomes more and more obvious, which leads to the increase of AC resistance of conductor and the decrease of allowable passing current of cable. In addition, the resistance of the cable, the bus side of the system and the line reactance are connected in series with the system. The capacitor used to improve the power factor and the capacitive reactance of the line are connected in parallel with the system, and resonance may occur under a certain value of inductance and capacitance. 2.2. Harm to power equipment when there are harmonics in the electricity, the terminal voltage of the power capacitor increases after it is put into operation, and the current through the capacitor increases more, which increases the loss power of the capacitor and accelerates the aging of the insulation medium. In the case of serious harmonic, it will also make the capacitor bulge, breakdown or explosion. Especially when the capacitor is put into the electricity whose voltage has been distorted, it may also aggravate the harmonic of the electricity, that is, produce the phenomenon of harmonic expansion. Harmonics increase the copper consumption of power transformer, including resistance loss, eddy current loss in conductor and stray loss caused by magnetic flux leakage outside conductor. Harmonics also increase the iron loss of the transformer, which is mainly reflected in the increase of hysteresis loss in the core. At the same time, due to the increase of losses in the above two aspects, the actual use capacity of the transformer should be reduced, or the harmonic content in the electricity should be considered when selecting the rated capacity of the transformer. For the circuit breaker used in power distribution, due to the influence of harmonic current, the skin effect of conductor and the increase of iron loss will cause heating, which will reduce the rated current and tripping current, and may cause malfunction due to harmonic. 2.3. The interference to the weak current system equipment is too heavy for the computer, and windows, which focuses on graphics, entertainment and networking, is too heavy. Weak current equipment such as networking, communication, cable television, automatic fire alarm and building automation, harmonics in the power system are coupled to these systems through electromagnetic induction, electrostatic induction and conduction, resulting in interference. Among them, the coupling strength of electromagnetic induction and electrostatic induction is directly proportional to the interference frequency, while the conduction is coupled through the common ground, and a large amount of unbalanced current flows into the grounding electrode, thus interfering with the weak current system. 3. Theater electrical harmonic suppression measures in order to suppress the above interference, certain measures should be taken. In the electrical design of new technologies and new products in theater development, the following measures can be taken: