66kv Transformer Fault Analysis For a 66kV transformer secondary winding deformation fault case, we elaborated
This article explains all the issues related to electric transformer. If you have any questions about using the electric transformer you will find the answers to any questions you may have in this article.
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The most important components of an the electric transformer include: core the windings, an oil tank breather, oil pillow heat sink that is explosion-proof and insulating bushing, as well as a gas relay, tap changer thermometer, net-oil and more.
Semi-insulation forms the primary insulation in the neutral portion of the windings of the electric transformer, whose insulation is less than the tail winding. contrary to the general electric transformer’s first and tail windings’ insulation level is similar to that described as fully insulated.
The purpose that the transformer plays within the power supply system serves to change the voltage to facilitate the transfer of energy. After the voltage is increased through the step-up transformer, it is able to reduce loss in the line, enhance the efficiency of power delivery, and fulfill the objective of power delivery over long distances. And the step-down electric transformer is able to transform the voltage that is high into the required voltage of the user to be used at any level to meet the requirements of the user.
Fragments in the cabling may decrease the strength of the insulation. They can also cause more damages to insulation up until is destroyed. The water that is trapped in the crack can also fracture the casing if it freezes. It is apparent that cracks in the casing pose a serious dangerous to the safety of the transformer.
High-voltage circuit breakers will not just cut off the current of no-load and load currents in the circuit that is high-voltage under the normal circumstances, it can can also collaborate along with the device of protection as well as the automatic device when there is a fault within the system to swiftly end the fault current in order to stop the spreading of the problem and ensure the safety of operation of the system.
Blocker is the main carrier communication with high frequency security vital components of high-frequency communication It stops the flow of high frequency current to other branches, and helps minimize the impact of energy loss at high frequencies.
A current-voltage electric transformer converts the huge current into a smaller current according to a particular ratio, and provides various relay and instrument protection using current, and also isolates it from the primary system’s high-voltage. It is not only a way to ensure the safety of individuals and equipment, but helps in making the manufacturing of relays and instruments simple and standard, which improves the efficiency of economics.
The wiring of the current electric transformer is comprised of two electric transformers with two-phase V-shaped wiring as well as 2-phase current-differential wiring. There are three current electric transformers that use three-phase Y-shaped wiring as well as three-phase D-shaped wiring. zero-sequence wiring.
The power sources that are reactive within the power system include:
ZnO arrester is installed to avoid the risk of operation overvoltage that can be experienced after the power capacitor has been shut or pulled to ensure safe use of electronic equipment.
The power meter shows the instantaneous production of power, consumption and supply of power generators that are generated, transmitted and consumed by the quantity of electric power. the amount of power measured by the meters is cumulative for the time period that it is generated, transmitted, and consumed using the quantity of electrical power.
The potential for electric power of the two batteries in parallel must be equal or the battery with a large electric potential could discharge to the battery that has a lower electric potential, and create an internal ring current within the pack of batteries. Furthermore both batteries’ internal resistance must also be identical in order to avoid any discharge voltage of the batteries that has low internal resistance could be too high. Batteries with different levels of both old and new batteries are not recommended to be utilized in parallel.
Central Signal is device used to monitor the performance of electrical equipment within the substation. It is based on the characteristics of faults in electrical equipment, to send light and audio signals that alert the staff operating the equipment to swiftly identify, and take the appropriate decision and provide the security of the operation of equipment.
A cable line is similar to a capacitor. Even after an outage it still retains its charge. There is the possibility of a gap between ground. If the power goes out immediately tests the pen with a test indicate that the line contains electricity. So, it should be completely discharged and there should be not generating electricity following the test, prior to the installation of the grounding wire.
Internal overvoltage can be caused by incidents, accidents, or other causes that result from abrupt changes in the condition of the system. It can occur from a stable condition to an unstable state during the process of transition, and in this case, it can be hazardous to the system’s overvoltage. Overvoltages can be caused by the fluctuation and accumulation of energy within the system, which is known as internal overvoltage.
After the addition of an equal pressure ring, it will ensure that the voltage distribution of the arrester is equally.
Zero protection is the system that under normal circumstances does not charge metal components, but only the wire and method for direct connection. Use the safety of zero to protect your personal safety, to avoid electric shock accidents.
winding is is joined at a common point of connection that is referred to as the neutral point of power. If you connect the neutral points of your grounding device and the power supply are in good contact to each other, this point is known as the zero point. And from the zero point it leads to the wire and is known as”the zero line.
DC substation system for control signals protection for relays, control devices, accident lighting and more. to supply DC power. It also provides *operation power for operation. It is the DC system plays an essential function in the functioning of the substation. It provides a guarantee for the an uninterrupted operating of the station.
To keep the battery charged to its full state, every battery connected to DC bus needs to be kept at 2.15V during float charging.
It is not permissible to operate for an extended duration in the DC substation’s substation as if grounding occurs in a different spot on the same pole it can cause problems for the relay protection, signal device as well as the control circuit. Furthermore, if there is a pole grounded and another pole is grounded, it could result in an DC shorter circuit.
Floating charge is contained within two charge units; one of which is the primary charging unit, while the second is a floating charge unit. Floating charging helps compensate for the loss of self-discharge in the battery, ensuring your battery is usually fully charged.
Busbars in outdoor areas are frequently susceptible to weather conditions such as rain, wind snow, sun and freezing. These elements can increase the rate of corrosion and oxidation of the busbar joints, causing the resistance to contact of the joints rise, and the temperature rises.
If the system oscillates, the following events occur
(1)substation voltagemeter, current and power meter pointer are constantly swinging, as in contact lines. The main reason for this is that the meter’s swing is obvious.
The closer the central point of oscillation of the system more intense the voltage swing. Incandescent lights are dim and bright and very evident.
The light signal cannot be reversed to the sign is intended to alert the duty officer, in the recording of the step, so as to prevent mistakes caused by mistake, must be aware of the prompt reversion of the signal in order to avoid repeat action, in order that before and after the two signals can not be distinct.
Common cables can decrease the insulation that is part of it. DC system.
If the DC insulation has been damaged (3) If the insulation is damaged, damage to the DC mixed line can result in a short circuit, or relay protection malfunction or other false operation.
The value of the insulation resistance in the circuit that is used for secondary purposes.. It’s recommended to use a megohmmeter with a voltage of 1000V in the event that there is no 1000V megohmmeter , it can be utilized with 500V.
The insulation standard is not less than 1 megawatt operating with a new input at least 20 megohm indoors and not less than 10 megohm outside.
Circuit breaker oil itself, with normally closed and normally open contacts to alter the closing and opening positions and connect the circuit closing and tripping circuit as well as sound signal circuits, to fulfill the function for the circuit breaker, which is to stop or shut off the circuit. It can accurately send out the sound signal to start the automatic device, and protect for the security of an interlocking circuit and so on.. If the circuit breaker’s is used as an auxiliary contact in the circuit to close and tripping must be connected to an interval of time.
SF6 gas is insoluble the water as well as in electric transformer oil and does not form a bond with aluminum, oxygen, argon and a myriad of other compounds when heated to incandescent temperature. However, under the influence of corona and arc, the gas will break down and create low fluorine compounds.
The reaction to decomposition of SF6 is a lot to have to do with moisture, which is why it is necessary to take measures to eliminate the moisture.
If an issue with a phase short circuit occurs in the power grid the current will surge and the voltage may suddenly fall, the overcurrent protection function is to alter the current action that the relay is operating to meet the requirements of line selection. When the fault current on the line is greater than the limit for the current relay the current relay will act conforms to the specific requirements of the device protecting it cutting out the line of fault.
When the electric transformer’s is able to change the volume of oil in response to changes of temperature and shrinkage or expansion, the oil pillow serves the role of storing oil and oil replenishment. It is able to make sure that the tank is filled with oil at the same time, due to the placement on the pillow to ensure it is that electric transformer as well as the surface that contacts air are diminished, thereby reducing the speed of oil degradation. The oil pillow is also fitted with an oil level gauge, that can be used to monitor changes of the level of oil.
The electric transformer’s core and the other components are in the electric field surrounding the winding. For instance, if not grounded. The core and the accessories will generate an a specific voltage, depending on the applied voltage. When the voltage induced is greater than the voltage at which the discharge occurs that is applied to the ground it can cause a discharge phenomena. To avoid an internal charge of the transformer it is recommended that the core be grounded.
The electrical transformer that is in operation is able to circulate the oil through the purifier due to the difference in temperature between the upper oil temperature and lower temperature. The harmful elements within the oil, such as water, carbon free oxides, and water. are taken up by silica gels in the purifier of oil, along with the flow of the oil. This ensures that oil gets cleaned and has good chemical and electrical properties. It also is involved in regenerating the transformer’s oil.
The majority of the oil flow of the electric transformer that is equipped with an air-cooling unguided device is redirected back to the space between the wall of the box and the winding. only a tiny portion of the flow goes through the core and the winding and the cooling effect of the device isn’t significant.
and the cooling oil flowing into the tank for oil inside the electrical transformer that is the guidance of strong oil air cooling is pumped through the oil-flowing controlled partition, which effectively flows through the core as well as inside the winding, which enhances the cooling effect as well as reducing the temperature increase of the winding.
Thermometer is utilized to measure the temperature of the oil in the upper layer of the tank. It is used to check the operation of the electric power transformer. Thermometer based on the power transformer’s capacity can be classified in mercury thermometers, signal thermometers resistance thermometer with three temperatures measurement techniques.
The purpose of the break buffer is to avoid damage to circuit breakers’ components due to the enormous force generated by the release of energy from the spring.
The function of the buffer for closing is to stop the force from the closing force from closing too deeply and cause damage to the casing.
Circuit breaker is in closing at anytime, but if there is a protection action is activated on the circuit that is tripping occurs, the circuit breaker may be * disconnected, this is known as free release. When you release Circuit breaker you can ensure that the circuit breaker has been was closed during the event of a short circuit is quickly disconnected to limit the extent of the incident.
The gas SF6 has the following performance.
Conductivity of the column in the arc is extremely high, the voltage in the arc column is extremely low, the energy of the column is low.
If the AC current reaches zero the dielectric insulation power of SF6 gas is quickly recovered approximately 100 times more quickly than air. That is, its arc-silencing capability is 100 times greater than air’s.
Its insulation capacity that is present in SF6 gas is greater.
Vacuum circuit breaker features an opening distance of a tiny contact and a short time for arc-burning and a slight contact burn when breaking the fault current and so on. This is why it needs minimal energy for operation and quick operation. Additionally, it has the benefits of being small in dimensions, lightweight as well as low maintenance as well as fireproof, explosion-proof and has a low noise level.
While the camera is in operation the magnetic fields of the stator and the rotor both rotate along the same direction at the same rate this is known as the synchronization.
Consider a 10kV voltage electric transformer for an example. The maximum rated current for the primary second fuse on the side is 0.5A. The fuse that is filled with quartz sand is superior in interrupting capability and greater current breaking capacity. It additionally, it serves the purpose of restricting any short circuits. The standard fuse is unable to be able to meet requirement for breaking current.
Current electrical transformer secondary side grounding is part of the grounding for protection. Because one or two sides insulation gets damaged, which is that is the first side connected by the high-voltage string will be grounded to the secondary side could endanger the safety of the people on the equipment, hence the secondary side has to be grounded.
FKL-10-2×750-6 is a nameplate for an aluminum cable split reactors that has a rated reactance of 6percent with a voltage of 10kV as the rated voltage and the rated current of 750A for two branches.
The line shunt generator will compensate for the capacitive charging line’s current reduce the voltage of the system increase, and also the production of overvoltage in operation and ensure the safe functioning that the line is operating.
Busbar series reactors may reduce the short-circuit voltage and keep a high residual current at the busbar. The capacitor bank series of reactors can reduce the harmonics and decrease the reactance.
A single bus section wiring could lessen the effects of bus faults as well as increase the availability of power sources.
If a portion that is part of the bar exhibits an issue and the circuit breaker for the section is triggered, in conjunction and the safety relay will be triggered to take out the damaged section, allowing the bus bar that is not damaged can keep the normal power supply. For users who are important the power source can be sourced from various segments to guarantee continuous power supply.
Double busbar wiring comes with the following drawbacks.
(1) The wiring and operation is more complicated, and the reverse operation is more prone to failure.
(2) Busbar Disconnect Switches are more complex, and the design of distribution devices is more complex, resulting in the economics are poor.
Fault recorders are utilized by the power systems to automate and precisely record the fluctuations of electrical quantities in various ways before or after a fault has occurred within the system. by analyzing and comparing of the electrical parameters they play a significant part in the analysis and handling of the incident, determining if the safety system is operating correctly and also enhancing the safety in the system.
Objects exhibit the characteristics of Thermal expansion as well as contraction busbars in operation can cause changes in length as a result of heat.
To prevent the possibility of a change in temperature as well as contraction in the busbar, it is important to ensure that the bar as well as the insulator that supports it are subject to excessive stress and wear and therefore the expansion joint must be placed on the hard busbar.
The variation between the inductance current and the capacitance current of the coil that extinguishes the arc in addition to the percentage of capacitance currents of the grid is referred to as”the degree of compensation..
After the inductance of the coil that extinguishes the arc compensates for the capacitance current the current remaining in the junction is referred to as residual current.
Normal operation of the system, because of the line between the three pair of ground capacitance imbalance the neutral point of the network and the ground, between the existence of a particular voltage, the voltage is directly linked to the capacitance imbalance. Under normal conditions, voltage at the neutral spot cannot exceed 1.5 percent of the nominal phase voltage.
electric transformer oil is used not only in electric transformers but also in other oil-filled electrical equipment. These include insulating bushings, circuit breakers, disconnect switches, tap changeover switches, as well as electric transformers and reactors.
In electrical equipment, electric transformer oil can isolate the charged parts with different potentials (potentials) so that they do not form short circuits. Because the dielectric constant of air is 1.0, and the dielectric constant of electric transformer oil is 2.25, the insulation strength of oil is much greater than that of air.
Suppose, the electric transformer coils are exposed to air, they will soon be broken down when the equipment is running, while filled with electric transformer oil between the electric transformer coils, it increases the dielectric strength, it will not be broken down, and as the quality of electric transformer oil improves, the safety factor of the equipment will be greater.
So the reliable insulation performance of electric transformer oil is one of its main functions.
electric transformer in the process of running with electricity, because the coil has resistance, core has magnetic corrosion and eddy current loss, when the current passes, it is bound to heat up like other electrical appliances.
If this heat inside the coil is not emitted, it will certainly make the coil and core inside the accumulated heat more and more, so that the core and coil internal temperature rises sharply, damaging the solid fiber insulation wrapped around the outside of the coil, so that the coil is burned.
If electric transformer oil is used as the cooling medium, the heat generated inside the coil is first absorbed by the oil and then circulated through the oil so that the heat is dissipated and does not accumulate inside the coil, thus ensuring the safe operation of the equipment.
The cooling method of electric transformer oil which absorbs heat is natural circulation cooling, natural air cooling, forced oil circulation water cooling and so on. Generally, most of the large-capacity power electric transformers use the cooling method of forced oil circulation.
So heat dissipation and cooling is the second major function of electric transformer oil.
In switchgear, electric transformer oil mainly plays the role of interrupting the arc. When an oil-immersed switch cuts off the electrical load, an arc is generated between its fixed and sliding contacts.
If the heat of the arc column is not taken away and the contacts are cooled, there will be continuous arcing after the initial arc, which will easily burn up the equipment and cause overvoltage and damage to the equipment.
When the oil-immersed switch is initially opened and closed by the arc, the high temperature of the arc causes the oil to undergo a violent thermal cracking, in which about 70% of the cracking products are hydrogen.
Since the thermal conductivity of hydrogen is large, hydrogen can absorb a large amount of heat and conduct this heat to the oil, which directly cools the switch contacts, thus achieving the purpose of arc extinguishing.
Therefore, the arc extinguishing function of electric transformer oil is the third major function.
As the viscosity of electric transformer oil is relatively low, so the fluctuation is good, it can be easily filled into the gap of insulation, so it can play a role in protecting the core and coil components.
As the oil fills the voids of the insulation, it reduces the content in these voids to a minimum. In other words, the oil causes the oxygen mixed into the equipment to oxidize first, thus delaying the erosion of the insulation material by oxygen.
In summary, electric transformer oil mainly plays the role of insulation and heat dissipation cooling in electric transformers, reactors, electric transformers and bushings, but if there is an arc in the above equipment, it can also play the role of arc extinguishing, in the oil switch mainly plays the role of arc extinguishing and insulation.
Several overvoltage generated in the grid, the real impact on the electric transformer insulation and protection devices, mainly depending on the overvoltage waveform. Magnitude and duration.
There are three types of voltage waveforms that assess the level of equipment insulation: lightning waves before short waves, operating waves before long waves, and low-frequency voltage waves. The ability of equipment insulation to withstand lightning, operating or industrial frequency voltage should be tested by the corresponding waveform voltage.
Among the accidents where overvoltage causes damage to electric transformers, lightning overvoltage causes the most chance of insulation breakdown damage.
When the power grid suffered a lightning strike, in the line wire will produce a large amplitude, the effect of a very short time non-periodic pulse voltage wave, it is transmitted at the speed of light along the line, first in the line arrester discharge, the residual wave by the electric transformer into the ground, when the residual wave by the electric transformer protection arrester, will produce a voltage drop (residual voltage) and the effect on the electric transformer.
If there is a certain electrical distance between the electric transformer and the arrester, the residual voltage will oscillate in this distance before entering the wire and lead to an increase in voltage, resulting in the voltage added to the electric transformer is higher than the residual voltage, thus causing a threat to electric transformer insulation safety. So in the installation of electric transformer protection arrester, should try to achieve the arrester and electric transformer to maintain a zero distance.
The resonant overvoltage or operating overvoltage that occurs in the power grid also has a high overvoltage amplitude and a long duration. The same will also threaten the safety of electric transformer operation, and even lead to insulation breakdown and destruction of the electric transformer.
In addition, the danger of inverting overvoltage on the electric transformer should not be ignored. When the electric transformer lightning arrester for lightning protection, the arrester grounding line, electric transformer neutral line and electric transformer shell using the “trinity” of the way grounding.
electric transformer operation if the high-voltage side of the lightning strike, will cause the arrester discharge, the residual voltage generated in the high-voltage winding.
As the high-voltage winding impedance is very large, capacitive resistance is very small, lightning current only in the high-voltage winding and capacitance to ground flow through the circuit by the grounding point discharge, will produce a large impact voltage drop on the grounding resistor, this voltage after the neutral line will also be applied to the low-voltage winding, and low-voltage winding flow through the lightning current will also produce magnetic flux.
According to the principle of electromagnetic induction, this flux will produce a high induced voltage on the high-voltage winding according to the electric transformer changes, this voltage is called “inverted overvoltage”. The voltage amplitude is several times to dozens of times larger than the residual voltage, the same will also cause electric transformer insulation breakdown and damage.
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