Reduce the generator excitation current, reduce the generator potential, the power factor angle becomes advanced, the generator load current generates the magnetically assisted armature reaction, the generator delivers the active power to the system, but absorbs the reactive power, this operation Phase-in operation
When the generator is in normal operation, it provides active power to the system and also provides reactive power. The stator current lags behind the terminal voltage by an angle. This state is the late phase operation. When the excitation current is gradually reduced, the generator is changed from providing reactive power to the system to absorbing reactive power from the system, and the stator current changes from hysteresis to an angle of the leading generator terminal voltage. This state is the phase-in operation. When the synchronous generator enters phase, the excitation current is greatly reduced in the later phase operation state, and the generator potential Eq is also reduced accordingly. From the P-power angle relationship, in the case of constant work, the power angle must increase correspondingly, the ratio of the whole step work is also reduced, and the static stability of the generator is reduced. Its stability limit is related to the generator short circuit ratio, external reactance, automatic excitation regulator performance and whether it is put into operation.
During the phase-in operation, the magnetic flux leakage at the stator end of the generator increases as the phase is delayed. In particular, the load of the large generator line is high, and the leakage current at the end of the large-scale generator is relatively large. The temperature of the connecting piece at the end of the iron core is increased, and the temperature rise is intensified due to the increase of the leakage flux during the phase-in operation. During the phase-in operation, the voltage at the end of the generator is reduced, and the power consumption voltage of the plant is also reduced accordingly. If it exceeds 10%, it will affect the operation of the plant.
Therefore, the phase advance operation of the synchronous generator is determined by experiment. That is to say, in the state of supply of certain active power, how much reactive power can be absorbed to maintain the system's static stability and transient stability, the temperature rise of each component is not exceeded, and can meet the voltage requirements.
What factors are limited by the phase in operation of the generator.
When the system supplies more inductive reactive power than needed, it will cause the system voltage to rise, requiring the generator to have less reactive power or even reactive power. At this time, the generator can be converted from the late phase operation to the phase inversion operation.
What is the phase-in operation of the generator? Under normal circumstances, due to the inductive load, the general generator is emitted; when the generator enters phase, the outlet voltage is lower, and the plant power voltage is also low; what is the phase-in operation of the generator, under-excitation, loss magnetic? What is the relationship between the three; because the power grid below 500KV generally requires a large amount of inductive reactive power; but when the grid voltage is high and the transmission distance is long, the transmission line itself; what is the power factor of the generator; Electromagnetic conversion power generation, in which part of the reactive power is used;
Inductive reactive power is also emitted to meet the requirements. At this time, the generator increases the excitation voltage and current, and the power factor of the generator lags. However, in the high-voltage and ultra-high-voltage transmission lines, since the capacitance effect of the line is greater than the inductive effect of the load, the generator is required to emit capacitive reactive power to satisfy Claim. At this point, the generator will reduce the excitation voltage and current, and the generator power factor will run ahead of time, also called phase-in operation.
When the generator is in phase operation, the outlet voltage is low and the plant power supply voltage is also low. Not all generators can do it, and special requirements are required when ordering.
What is the phase-in operation of the generator, under-excitation, and loss of magnetism? What is the relationship between the three?
Since the grid below 500KV generally requires a large amount of inductive reactive power, the generator operating under this voltage is expected to output inductive reactive power, while the generator output is inductive and reactive, and the excitation current needs to be increased. At this time, the power factor of the generator is positive.
However, when the grid voltage is high and the transmission distance is long, the capacitive effect generated by the transmission line itself can compensate for the above-mentioned inductive reactive power, and there is excess, so the generator output capacitive reactive power is needed to compensate. It is necessary to reduce the excitation current of the generator to output capacitive reactive power. Since the field current is reduced, the generator is in an under-excited state. At this time, the power factor of the generator is a negative value. The generator running state is the phase-in operation state. When the generator excitation system fails, the generator will be in a state where there is no excitation current. At this time, the generator is out of flux operation and needs to stop immediately.
What is the power factor of the generator?
The generator is powered by electromagnetic conversion, in which part of the reactive power is used to generate the magnetic field, and the electromagnetic conversion is performed. The other part of the active power is delivered to the user, and the proportion of the output to the user in the total power is the power factor.
The cosine of the phase difference (Φ) between the generator voltage and current is called the power factor and is represented by the symbol cosΦ. In terms of value, the power factor is the ratio of active power to apparent power, ie cosΦ=P/S
The stator and rotor of the generator are completely independent and do not interfere with each other except for a motive drag.
The stator of the generator is an active source, which generates an induced electromotive force and current, and outputs alternating current under the driving of the motive force.
The rotor of the generator is a reactive power source, and the winding introduces a direct current from the outside to establish a magnetic field, and under the driving of the motive force, the reactive power is transmitted outward.
What should you pay attention to when adjusting the power factor of the generator?
Try to adjust to close to 1 is it.
First, according to the power rate assessment requirements of the power supply department, the second is not to exceed the allowable rotor current, and the third is that the stator current does not exceed. If the fan is trying to reduce the excitation current, the generator should not be in phase and not oscillate. For a single-machine generator, there is no problem of adjusting the power factor, provided that the generator is properly stabilized.
The power factor of a typical generator is between 0.8 (hysteresis) and 1, and you can adjust it within this range. Generally, the generator will not enter the phase. In addition, the power factor is set according to the requirements of your scheduling.
What is the meaning of the generator's active power, reactive power and power factor? a little more popular
The power is divided into three types of power, active power P, reactive power Q and apparent power S.
The cosine of the phase difference (Φ) between voltage and current is called power factor and is represented by the symbol cosΦ. In terms of value, the power factor is the ratio of active power to apparent power, ie cosΦ=P/S. Three power and power factors. CosΦ is a right-angle power triangle relationship: two right-angled sides are active power and reactive power, and the oblique side is apparent power.
Active Power Square + Reactive Power Square = Apparent Power Squared. In the three-phase load, these three kinds of power always exist at the same time, and the power generated by the engine should include these three kinds of power:
Apparent power S=1.732UI
Active power P=1.732UIcosΦ (power for work heating)
Reactive power Q=1.732UIsinΦ (establishing the power of the magnetic field to transmit energy) Power factor cosΦ=P/S (active power/apparent power) sinΦ=Q/S (reactive power/apparent power)
What is the difference between transformer zero-sequence overcurrent protection and single-phase grounding protection?
Question added:
However, single-phase grounding will result in zero-sequence current, and both protections are simultaneously protected in the same transformer.
When the inter-turn short circuit occurs inside the transformer, or the three-phase load imbalance exceeds a certain allowable range, the zero-sequence current will appear. At this time, the transformer does not have any grounding. This is the zero-sequence overcurrent protection and single-phase grounding protection of the transformer. The difference.
What is the main protection circuit of the transformer?
Mainly refers to the two main protection of the transformer! One is the protection of the electrical quantity, that is, the differential protection as the main protection of the short-circuit fault of the winding cable lead-out of the transformer / there is also a gas, which is divided into light gas and heavy gas. Mainly as the internal fault of the transformer is the decomposition of the transformer oil to generate a large amount of gas, gas is a protection to monitor these gases! The main protection circuit is the secondary wiring of two protections!
The working principle of the differential protection of the power transformer and the working principle of the differential protection of the transmission line?
First, understand the principle of differential protection. Differential protection works by using the Kirchhoff current theorem, that is, considering the protected electrical equipment as a contact, then the current flowing into the protected device is equal to the current flowing out, and the differential current is equal to zero. When a device fails, the current flowing into the protected device is not equal to the current flowing out, and the differential current is greater than zero. When the differential current is greater than the setting value of the differential protection device, the protection action will jump off the circuit breakers on each side of the protected device to disconnect the power supply from the faulty device. The equipment is protected between the current transformers at both ends of the input (can be electrical equipment such as lines, generators, motors, transformers, etc.). The differential protection of the power transformer, the current is the transformer current transformer taken from the high and low voltage sides of the transformer.
For the differential protection of the transmission line, the current is the current transformer used in the line in the substation at both ends of the line.
What is the basic principle of power system primary frequency modulation?
One frequency modulation means that when the grid frequency exceeds the specified normal range, the change of the grid frequency will cause the speed control system of each unit participating in the primary frequency modulation in the grid to automatically increase or decrease the power of the unit according to the change of the grid frequency, thereby achieving new The balance and the function of limiting the variation of the grid frequency within a certain range. A frequency modulation function is an important means to maintain grid stability.
The load fluctuation causes the frequency change, and the system frequency can be within the specified change by the primary and secondary frequency modulation. For the frequency change caused by the small change of the load and the short change period, it is generally adjusted by the governor of the generator. This is called primary frequency modulation. For the frequency shift caused by the large load change and the long change period, the governor cannot limit it to the specified range. It is necessary to use the frequency modulator to adjust the frequency. This is called quadratic frequency modulation.
In order to ensure the frequency stability of the power grid, the power link is generally frequency-modulated, that is, primary and secondary frequency modulation. The secondary adjustment of the frequency refers to the frequency converter of the generator set, which has a large variation range (0.5~1.5%), and the change period Adjustments made by longer (10s~30min) frequency deviations. There are generally FM plants to carry out this work.
The grid cycle is a random variable that changes dynamically with time and contains different frequency components. The primary frequency modulation of the grid is a random process. Because the system load can be regarded as composed of the following three kinds of varying loads with different variation laws [1]: 1 The variation range is small, the change period is short, (generally within 10s), the random load component; The load component with a long change cycle (generally 10s to 3min) is mainly composed of electric furnaces, rolling mills, etc.; 3 slowly changing continuous load, the main cause of load change is the factory's work schedule, the people The law of life and so on. The one frequency modulation adjusts the random component superimposed on the long-period variation component, which determines the random nature of the primary frequency modulation of the power grid.
When the scale of the system is small, the research on the peaking and frequency modulation of the power system is mainly carried out from a static perspective. For example, before the mid-1980s, research focused on static economic allocation of power plant loads, static scheduling of safety and economy, static optimal power flow, etc., and many dynamic information about the system, especially in many time directions. Constraint information is not enough, which is relatively limited in system size and load development.
The early days are acceptable. However, with the rapid development of system scale and load, many new problems and characteristics have appeared in the peak shaving and frequency modulation of the power grid. At this time, it is difficult to achieve the effect of multi-party coordination from the static point of view.
The concept of the primary frequency modulation characteristic based on the static category is simply to attribute the load distribution law of each unit in the power grid to the inverse relationship with the unequal rate, but the actual situation is not so simple. When investigating the primary frequency response of a steam turbine generator set to the change of the cycle, it is necessary not only to look at the amplitude of the cycle change, but also to see the speed of the cycle change. Therefore, it is necessary to involve the difference in the ability of different units to adapt to the load disturbance of different frequencies, such as Thermal and non-reheating units. This concept cannot be described by the concept of static characteristics, so it is necessary to rethink the problem from a dynamic perspective.
In addition, the turbine governing system has different responsiveness to each frequency component of the cycle change. For example, for a reheat unit designed with a high-pressure regulating valve dynamic over-opening capability and without such a capability, even if the static characteristics of the two are exactly the same, their power output responses to the frequency-variation signals of different frequencies may be inconsistent. Therefore, it is also necessary to reconsider this issue from the dynamic category.
The difference between primary frequency modulation and secondary frequency modulation of power systems. ?
One frequency adjustment is to participate in the grid cycle adjustment with a certain limit and dead zone. The second frequency modulation is to accept the middle command or manual command.
The primary frequency modulation is performed by the governor device, and the small frequency modulation range is a fine adjustment. The secondary frequency modulation is done by the frequency modulator! The large frequency range is a coarse one-time frequency modulation:
When the units are connected to the grid, the frequency of the grid changes due to changes in external load. At this time, the regulation system of each unit participates in the regulation, changing the load of each unit to balance it with the external load. At the same time, it also tries to reduce the frequency change of the grid, which is a frequency modulation.
Secondary frequency modulation:
One frequency adjustment is a difference adjustment, and there is no change in the frequency of the grid, which can only moderate the degree of change of the grid frequency. Therefore, it is also necessary to use the synchronizer to increase or decrease the load of some units to restore the grid frequency. This process is called secondary frequency modulation.
Only after the second frequency modulation can the grid frequency be accurately maintained at a constant value. There are currently two methods for secondary frequency modulation:
1. The adjustments were ordered by the factories to adjust the load. 2. The unit adopts the AGC method to realize the automatic dispatching of the unit load. Simply speaking, the primary frequency modulation is the turbine speed control system. According to the change of the grid frequency, the unit load is adjusted spontaneously to restore the grid frequency. The secondary frequency modulation is artificially based on the grid frequency. To adjust the unit load
The main difference is:
One frequency modulation is done by the governor, and no differential frequency can be achieved.
The secondary frequency modulation is completed by the frequency modulator, and the frequency difference can be adjusted.
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