Nghiên cứu xử lý số sóng hài bậc 3, chế tạo relay bảo vệ chạm đất máy phát điện trong vùng công suất thấp

This article shows distribution model of the third harmonic of voltage in the winding of three phase salient pole rotor alternating-current synchronous  generator (DMHW).The base on that to put forward a mathematical formula for formalize to process for physically, which occurs on winding of  the generator by the third harmonic of voltage  and called  be Winding Characteristic Equation and it is abbreviated to WCE. These  many different methods are based on WCE to protect the stator winding in the case of ground faults in high resistance grounded synchronous generator above. Using third harmonic of voltage to protect winding with standard ANSI 27/59NT 3rd harm by filter harmonic wave voltage measured at terminal or  neutral. In the method, function of third harmonic of voltage  has variable to be real power. But WCE could reject the variable by to algebraic subtract the third harmonic of  voltage of the neutral transformer from the third harmonic of voltage of the third harmonic terminal transformer. It is possible to infer the third harmonic electromotive force(e3rd) from per unit length of the winding is equal, because the flux magnet of third harmonic wave swept them is similar in the magnetic field intensity. On the other hand, according to our calculations, sum of e3rd on the stator winding equal zero. Base of  that, quotient of the third harmonic voltage at terminal and neutral  exactly reflects the ratio of the area on the  stator  winding  and the  stator winding  length , where occurs ground fault  position. For this reason, we have proposed a protection formula, which it is non-dimensional. Reality, with above principle, we have made a new equipment which is aimed to obtain a 100% protection of the stator winding in the case of ground faults on every power range [-40MVA; 110MVA] of the generator operation. The components of the equipment have origin of Siemens and Russian. And it has fitted up at the our Company, in October , 2012

EFFECT OF GENERATOR GROUNDING METHOD ON TRIPLEN HARMONICS PRODUCED BY SYNCHRONOUS GENERATOR

Salient pole synchronous generator is one of harmonic sources that cause various power system harmonic problems especially related to neutral. This paper is aim to study the characteristic of third harmonic voltage and current from generator when connected to balanced load, generator load connection with different generator neutral grounding resistor and generator load connection shunted by zig-zag transformer. Lab scale experiments have been conducted to vary all parameters related generator neutral grounding resistor and reactance earthing under various combined resistive and inductive load. The value for NER and reactance earthing is varied for each combined resistive and inductive load. Zig-zag transformer is connected to various combined resistive and inductive load. Generator neutral grounding resistor can effectively reduce the third harmonic in the phase and neutral. However care should be taken not to use very high generator neutral grounding resistor that can also restrict earth fault current that may pose problem to the sensitivity of earth fault protection system. Zig-zag transformer efficiently divert third harmonic current from generator to enter the load but high circulating third harmonic current between generator and zig-zag transformer may pose heating problem to the equipments. Reactance earthing can greatly reduce the third harmonic in the phase and neutral compared to both NER and zig-zag transformer

The Study of Third Harmonic Current Contribution During Three phase-to-ground Fault

Harmonic is defined as the voltage and current distortion in the waveform. It exists from the source such as synchronous generator and non-linear load. Third harmonic is the presence of voltage and current distortion expressed in terms of harmonics frequencies 150 Hz. During three phase-to-ground fault, the fundamental fault current share the same return path as third harmonic. Thus, the synchronous generator is used as the source of third harmonic in the lab experiment to investigate the characteristic of third harmonic and the amount of its contribution to the system during three phase-to-ground fault. In the experiment, the variables that are varied including the fault impedance (Zf), filter mode (by zig-zag transformer) and Neutral Earthing Resistor (NER). The load impedance sets are also changed to study how the load can affect the contribution of third harmonic current

EFFECT OF GENERATOR GROUNDING METHOD ON TRIPLEN HARMONICS PRODUCED BY SYNCHRONOUS GENERATOR

Salient pole synchronous generator is one of harmonic sources that cause various power system harmonic problems especially related to neutral. This paper is aim to study the characteristic of third harmonic voltage and current from generator when connected to balanced load, generator load connection with different generator neutral grounding resistor and generator load connection shunted by zig-zag transformer. Lab scale experiments have been conducted to vary all parameters related generator neutral grounding resistor and reactance earthing under various combined resistive and inductive load. The value for NER and reactance earthing is varied for each combined resistive and inductive load. Zig-zag transformer is connected to various combined resistive and inductive load. Generator neutral grounding resistor can effectively reduce the third harmonic in the phase and neutral. However care should be taken not to use very high generator neutral grounding resistor that can also restrict earth fault current that may pose problem to the sensitivity of earth fault protection system. Zig-zag transformer efficiently divert third harmonic current from generator to enter the load but high circulating third harmonic current between generator and zig-zag transformer may pose heating problem to the equipments. Reactance earthing can greatly reduce the third harmonic in the phase and neutral compared to both NER and zig-zag transformer

Third Harmonic Filter Design in Mitigating High Current At the Generator Neutral

Harmonic is commonly known power quality problem which caused by non-linear load. Nevertheless, harmonic was also found at the synchronous generator instead of at the load. The effect of the triplen harmonic to the generator neutral is high current which lead to high temperature of the component at the generator neutral. Recent researches had identified the major component of the triplen harmonic is third harmonic which initiated by the synchronous generator itself. There are numerous techniques to reduce the effect of harmonic in power system network. By installing harmonic filter is one of the techniques to mitigate the harmonic current. A study about installing harmonic filter at the generator neutral had been introduced to counter this arising issue. The objectives of this study are to study the various harmonic filters used in mitigating the third harmonic current and to design harmonic filter that can reduced the third harmonic current at generator neutral and validate the modelling with experimental value

The Study of Third Harmonic Current Contribution During Three phase-to-ground Fault

Harmonic is defined as the voltage and current distortion in the waveform. It exists from the source such as synchronous generator and non-linear load. Third harmonic is the presence of voltage and current distortion expressed in terms of harmonics frequencies 150 Hz. During three phase-to-ground fault, the fundamental fault current share the same return path as third harmonic. Thus, the synchronous generator is used as the source of third harmonic in the lab experiment to investigate the characteristic of third harmonic and the amount of its contribution to the system during three phase-to-ground fault. In the experiment, the variables that are varied including the fault impedance (Zf), filter mode (by zig-zag transformer) and Neutral Earthing Resistor (NER). The load impedance sets are also changed to study how the load can affect the contribution of third harmonic current

INTERACTION OF TRIPLEN HARMONICS PRODUCED BY SYNCHRONOUS GENERATOR WHEN CONNECTED WITH RECTIFIER

The third harmonic has caused much power quality problem in the neutral of distribution system. Salient pole synchronous generator and non-linear load have been known and recognized as the source of triplen harmonics. Main purpose of this project is to study the characteristics of triplen harmonics current produced by synchronous generator when connected with rectifier and various types of loads. This research is done by shunt connecting full bridge rectifier between synchronous generator and load. The measurement of third harmonics is taken at generator, rectifier and load to see the characteristics of the third harmonics. In this research, the phase angle of the third harmonics is also taken into account. When full bridge rectifier is shunt connected between synchronous generator and load, the third harmonic current at rectifier and load are actually coming from the generator that depend on the load impedance and phase angle. The third harmonic current of the generator is the vector sum of both load and rectifier third harmonic current for generator load with rectifier connection. In parallel operation of synchronous generator with rectifier and load, the third harmonic current at generator does not affected by rectifier due to the delta of transformer blocking the third harmonic from flowing to the load and rectifier. However, the third harmonic current recorded at rectifier is due to the rectifier drawing the current in non-sinusoidal form from the star side of transformer. From overall findings of the project, the rectifier affects the third harmonic current level at generator when operated in island mode with and without the existence of transformer. However, it does not affect the third harmonic currents level at generator in parallel operation

Third Harmonic Filter Design in Mitigating High Current At the Generator Neutral

Harmonic is commonly known power quality problem which caused by non-linear load. Nevertheless, harmonic was also found at the synchronous generator instead of at the load. The effect of the triplen harmonic to the generator neutral is high current which lead to high temperature of the component at the generator neutral. Recent researches had identified the major component of the triplen harmonic is third harmonic which initiated by the synchronous generator itself. There are numerous techniques to reduce the effect of harmonic in power system network. By installing harmonic filter is one of the techniques to mitigate the harmonic current. A study about installing harmonic filter at the generator neutral had been introduced to counter this arising issue. The objectives of this study are to study the various harmonic filters used in mitigating the third harmonic current and to design harmonic filter that can reduced the third harmonic current at generator neutral and validate the modelling with experimental value

The Study of Third Harmonic Current Contribution during Ground Fault

Third harmonic current exist in the electrical power system due to non-linear loads and from the salient pole synchronous generator. In Universiti Teknologi PETRONAS (UTP), the campus has its own power plant which is the Gas District Cooling (GDC) plant and studies show the plant produces third harmonic current. Third harmonic current magnitude tripled at the neutral, when it flows back, has caused damages to the Neutral Earth Resistor (NER) at the GDC generator. Studies need to be conducted to see whether the third harmonic current will have the same characteristic when it is in steady-state conditions and also during ground fault. The objective of this project is to study the characteristic of third harmonic current and voltage during steady-state and ground fault. Data and information about third harmonic current will firstly be gathered and studied to have a strong basic about harmonics current and voltages. A lab-scale experiment with two types of connection which is generator-load and generator-transformer-load connection will be conducted. A fault is intentionally occurred at Phase A in each experiment to simulate a single-phase-to-ground fault. During each experiment, measurement for third harmonic current and voltage will be taken at the generator and load terminal for generator-load connection and generator, load and transformer terminal for generator-transformer-load connection. During steady-state condition, third harmonic current will tripled of phase magnitude at the neutral at the generator and load terminal for generator-load connection. When Delta-Wye transformer is added, third harmonic current will only circulate at the Delta transformer and will not flow through the load and travel back to generator through the neutral. When single-phase-to-ground fault occurred at Phase A, all the current carrying third harmonic current will flow through the fault back to the neutral of the generator for both of the experiment connection. When ground fault occur, third harmonic current flowing back to generator is higher than third harmonic current during steady-state

The Study of Third Harmonic Characteristics from Salient Pole Synchronous Generator under Unbalanced Load

A non-linear load draws non-sinusoidal current that consists of frequencies that are multiples of the fundamental frequency. This is the basis of harmonics and it creates distortions when interacting with power systems. In medium voltage systems, loads are always balanced due to the presence of power transformers of delta-wye winding configuration, by which the triplen harmonics currents only circulate at the delta winding of transformer, unable to reach the load. However, in low voltage systems, loads remain unbalanced. Generators are found to be a source of third harmonics and factors influencing the production include slot skew, distribution factor and pitch factor