Zhejiang Zebo Electric Co. Ltd.

Preface

Low voltage harmonic filtering equipment development and production is 3 times, special in low-voltage power grid 5 times, 7 times, 11 times, 13 times and above harmonic passive filter. Suitable for intermediate frequency smelting, steel rolling, inverter, rectifier equipment environment. The device adopts inductance and capacitor compose a series resonant absorption circuit, harmonic effective load have to be absorbed, thus avoiding the harmonic current back to the power transformer, greatly reduce the harmonic content of the power grid, and helps the user of electric power transformer operation, lower power consumption, improve the reliability of equipment and other electrical components. Compensation of wattless power the device also provides certain capacity in addition, to improve the efficiency of user load. The device consists of integrated control cabinet and reactance cabinet, depending on the user requirements of different frequency, harmonic filter configuration are also different. Usually, a ZRTBBL system can filter 4 kinds of harmonic. The operation of the system can be divided into automatic and manual operation.

The basic definition and the basic knowledge of 1.2 harmonic

The basic concept of key words in the field of 1.2.1.

★harmonic ( harmonic ): Fu Liye series decomposition of periodic AC signal, get frequency is the fundamental frequency is greater than the integer times of 1 components. Power supply system of China"s frequency is 50Hz, so the 5 harmonic frequency of 250 Hz. The 7 harmonic frequency of 350 Hz. The 11 harmonic frequency of 550 Hz, 13 harmonic frequency of 650 Hz.

★public connection point: ( PCC ) connecting the user access network.

★ the total harmonic distortion ( THD ): the harmonic content completely flow to the root-mean-square and fundamental component of the root-mean-square value ratio (in percentage ). The total harmonic distortion of voltage THDU, current total harmonic distortion rate in THDI.

★harmonic source ( harmonic source ) : injection of electrical equipment of harmonic current and harmonic voltage in public supply network to the utility grid.

★perceptual wattless: motor, transformer in the energy conversion process of establishing variable magnetic field, equal power absorption in a cycle of power and release, this power is called perceptual wattless power.

★capacitive wattless power capacitors in AC power network connected in a cycle, the discharge power equal charging power half cycle and the lower half cycle, does not consume energy, the charge and discharge power called capacitive wattless power.

★power factor: active power and apparent power ratio is called power number.

★power-factor regulating tariff: the implementation of two part tariff system for electric power enterprises, power supply departments according to the average power factor and charged or reduction of tariffs, called the power-factor regulating tariff

Generation and harmfulness of harmonic of 1.2.2

●harmonic generation

Harmonic is mainly due to large capacity rectifier and converter equipment and other nonlinear loads, resulting in current waveform distortion caused by. These abnormal variable AC Fu Liye series decomposition, can be obtained by the harmonic component of 50Hz fundamental component and the frequency of the fundamental component of integer times.

●the harm of harmonic

Stable operation of power system. Effects: for power line and power transformer in distribution system, generally using electromagnetic relay, induction type relay or new microcomputer protection for detection and protection, in the system that belongs to the sensitive element, the relay is the influence of harmonics prone to malfunction, microcomputer protection due to the use of the rectifier circuit, and susceptible to the influence of harmonic cause misoperation or maloperation, stable and safe operation of such a serious threat to power system harmonics.

★influence the quality of electric power: harmonic can make the voltage and current waveforms and grid distortion, active power and harmonic voltage and harmonic current the same frequency to produce the same harmonic and idle power, thereby reducing the grid voltage, increasing circuit loss, waste of power capacity.

Wattless power compensation equipment . The effect of power supply system: power system substation has no power compensation equipment, when the harmonics may cause excessive current and load capacitor, the capacitance of abnormal heat: another harmonics will accelerate aging of capacitor dielectric, shorten service life of capacitor.

Using★influence power transformer: harmonic of the copper and iron losses of power transformer increase, directly influence the use efficiency of the transformer; can also cause transformer noise increases, shorten the service life of transformer.

Electrical equipment for★effect: harmonics cause the decline of efficiency of induction motor, motor noise increases; the low-voltage switch equipment malfunction; the normal communication of the industrial automation interference, affecting the accuracy of power electronic metering equipment.

The importance of 1.2.3 harmonics and reactive power compensation without

The filter can effectively filter out specific harmonics, while providing a capacitive wattless power to the grid, its importance is mainly manifested in the following aspects:

★filter the harmonic can be fixed electricity environment, reduce the apparent power, reduce the heating current harmonics in the electrical equipment and power transmission and distribution equipment, direct savings of active power; to eliminate the harmonic vibration, prolonging the service life of electrical appliance; effectively eliminate the influence to the sensitive element.

★because the filter circuit is formed by a reactor and a capacitor connected in series, so in the filtering process can be injected to the grid capacitive wattless power, improve power factor, so it can avoid the power-factor regulating tariff electricity sector high, because of the lack of reactive power current offset, as well as to improve the power distribution equipment capacity, reduced the loss. Wattless power compensation can improve the grid voltage terminal, is very important to optimize the electricity environment significance.

In the filter design, should first meet various load levels on the harmonic limit technical requirements, and then in the premise, to filter the most economically reasonable. In addition to the above economic analysis, design of the filter should also pay attention to the following two points:

1 ) the resonant frequency for monotone filter capacitance, inductance parameter deviation or change the change, the grid frequency will have a certain fluctuation, this will cause the filter detuning. The design shall ensure that in the normal case is harmonic filter device can still meet the requirements.

2 ) the grid impedance variation is especially has a great influence on filtering effect of single tuned filter which on the filtering device, the more serious is, the grid impedance and filtering device has a parallel resonance may, the design should be taken into account.

The owners of the 1.3 project

According to the power system data that provided by the user, the distribution system if the production line the existing power supply transformer 1 units, capacity of 1250KVA, low voltage bus in parallel operation, voltage ratio is 10/0.4, with 1 high-power intermediate frequency electric furnace. Because if machine is used in rectifier, thyristor, at work in different degrees of certain harmonic generation, according to data provided by the customer and our analysis shows similar projects for other harmonic test data, the work frequency of machine, the user distribution system, harmonic current content can reach 5 more than 20%, 7 harmonic current can reach more than 12%, the harmonic current and voltage harmonic distortion will far exceed the national standard " harmonic power quality utility " GB/T 14549-93 of the national standard limit. The upper end of harmonic current injected 10KV power system, will lead to higher harmonic content in the rapid growth of electric power system, the power supply voltage waveform distortion, increased the line loss and electric equipment loss, resulting in excess energy consumption, at the same time the influence of the network other electric equipment to normal operation, reduce the quality of electric energy, causing potential safety hazard to safe operation of equipment the. At the same time as the equipment run time changes along with the load power factor of transformer is larger, low load is only about 0.8, which will produce excess reactive loss caused to the user without power, large fines, users suffer larger electricity loss.

In order to ensure the normal operation of the equipment, the power supply system and reliable power supply and energy saving, need to take technical measures to restrain harmonic current to the device, while taking into account the fundamental wattless power compensation. According to China"s relevant provisions of grid voltage quality standards at home and abroad, as well as harmonic governance of research, using filtering and static compensation technology scheme, aiming at the characteristics of the rectifier to produce harmonic are respectively arranged filter circuit, absorbing the harmonic current, but also to compensate fundamental wattless power, energy saving effect.

The characteristic of harmonic treatment equipment company has changed the static following load, can effectively improve the power quality, power factor and energy saving of electric network, and improve the reliability and the operation efficiency of equipment of electric system operation, reduce the operation cost and maintenance cost, prolong the service life of the equipment, bring obvious economic benefits to the user.

1.4 if the load effects caused by the harmonic of power network and equipment

Intermediate frequency power supply can be divided into 6 pulse rectification according to the rectifier pulse number, pulse and 24 pulse 12, according to the work of the power factor can be divided into constant power if machine and ordinary if machine. The number of phase rectifier is higher, the lower the amount of generated harmonics, the smaller the impact on the grid, greatly reduce the risk.

Intermediate frequency power supply for electric drive adopts the thyristor rectifier technology, so in the work except for low power factor, but also produce high harmonic, if if a single winding of the power transformer side using the six-pulse rectifier technology, harmonic is produced mainly by 5, 7, 11, 13.

Main effects: harmonics on the grid caused by electrical equipment heating, vibration, increase the loss, shorten life, interfering with communication, the controllable silicon false triggering, protective relay misoperation, damaged electrical insulation aging.

The following made if machine unilateral ( one winding ) hardware simulation schematic diagram and the voltage and current waveforms six-pulse rectifier at work: