Method for fast three-phase reclosure of transmission lines with compensation by shunt reactor. RU patent 2518480.
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FIELD: electricity.
SUBSTANCE: invention relates to the field of electric engineering and suggests an adaptive switching method to control overload in result of three-phase reclosure of transmission lines with compensation by shunt reactor. Since an automatic circuit breaker (ACB) cuts the line off interaction between shunt admittance of the transmission lines and inductance of the reactive power compensator makes voltage between the ACB poles taking an oscillation form (beat). An optimal section for ACB reclosure corresponds to the section where voltage beat amplitude between the ACB contacts is minimum. It also allows a bigger time span for ACB operation after detection of the optimal section for reclosure, at that there are still several period of the main frequency ahead. The algorithm of the method is included into the control logic device for a digital relay of the three-phase reclosure of transmission lines thus creating a new digital relay for adaptive three-phase reclosure of transmission lines with compensation by shunt reactor.
EFFECT: high reliability at determining the first section of minimum voltage beat notwithstanding voltage zero crossing.
4 cl, 9 dwg
The technical field to which the invention relates
Physical phenomenon, which causes switching overvoltage in transmission lines (PL)is the propagation of electromagnetic waves along these lines. The negative impacts caused by these surges can be greatly reduced by controlling the opening and closing of contacts automatic switches (AB) so that this operation was carried out in a pre-set the best time using electrical signals voltage between contact breakers as a reference.
To illustrate the technical field to which the invention relates, in figure 1 as an example line diagram electrical power system, which includes the equivalent of the electricity system, presents an ideal source 1, line 2, with a compensation of reactive power of 3 and automatic switch 4.
In the above example uses a rated voltage of 500 kV and undamental 60 Hz. The transmission line provides the energy transfer by three phases, designated as phase a And phase In and phase C.
Simulated AB 4 receives three independent teams, each associated with one of the phases. Switch interrupts the electric current between 1 and line 2.
Shunt reactors 3 are designed to absorb part of the capacitive reactive power generated by transmission lines running without load or at low load.
Automatic switch 4 divides the electrical system 1 and line 2, when contacts (pole) three phases are open. After some time the contacts of the three phases re-closed. At the time of re-circuit sudden changes linear voltage that produce voltages in excess of the normal values that disappear after several periods of the fundamental frequency (transient overvoltages). These surges are distributed along the lines of the electric system. Three-phase re-enable transmission lines is an operation that is very often performed within the network and can cause extremely high transient overvoltages.
The traditional way to minimize the switching surges generated by three-phase re-enabling, involves the use predvkushenii resistors so that when you re-enable PL auxiliary contact initially connects produkujemy resistor in series with the PL. By connecting a resistor voltage that is applied to the line, is divided between a line and a resistor, while transient overvoltages, depending on the voltage applied to the line, are significantly reduced. After a short period of time the main contact AB transmission lines closed, samarajiva resistor, while voltage is applied to the line completely. Despite its effectiveness, this solution has the disadvantage is that it requires high cost of implementation and maintenance.
Negative effects caused by the switching overvoltage can be greatly reduced by controlling the contact closure AV so that this operation was carried out in a pre-set the best time using threshold voltage between the switch contacts.
At three-phase re-enable the contacts of the switch must be closed when the tension between them is minimal. This time is changed according to the configuration of the network and can be determined using the algorithm-dependent voltage signals measured between contacts AV. When implementing this solution uses the fact that wave voltage between terminals AB has vibrational form (beatings) due to interaction between cross-full conductivity line and inductance shunt reactor. Thus, there is a section of the waveform that is optimal for re-enable the automatic switch that corresponds to the area on which the amplitude of the oscillation in the minimum voltage.
The level of technology
At present to control the surge in three-phase switching on the transmission lines, as a rule, is applied predvkushenii resistor, but this method, although it is effective, in addition to the high total cost of production and the service switch is a low reliability.
In the publication of scientific papers IEEE (Institute of Electrical and Electronics Engineers, the Institute of electrical engineers and radio electronics) on transfer of electric energy, 1994 "Managed inclusion of transmission lines with compensation via shunt reactor. Part I. the Development of device activation control" describes the control device that determines the first section of the minimum amplitude beats and sends a command to enable the automatic switch to the next similar plot.
According to this method, first get the voltage signals from the side lines and from the supply power. These signals are controlled in a certain time interval (usually equal to the period of the fundamental frequency), providing the first set of data. These data store, then get a new set of data. Both sets are compared with each other. If these two sets of data are not equal, get the third set, and so on. When it turns out that the two data sets are identical, completes the reference periods signals and determines the minimum plot.
According to the above method of moments of time, considered as optimal for re-enable correspond to cross the zero during periods of low-amplitude beating voltage between terminals AV. Thus, this method first determines the preceding section minimal amplitude, and then send a command to turn on the AV on the next similar plot.
This method is unsuccessful, since the inclusion will only happen after the first phase of the minimum amplitude, which results in a longer, during which the line is removed from service. In addition, reducing over-voltage is lower when the activation is on the following areas minimum amplitude, making technical characteristics inherent in this same way predvkushenii resistor.
In the U.S. patent 5361184 revealed adaptive controller serial type to control circuit breaker or other switching device to avoid transient processes in distribution lines, called on and off AB. Adaptive device compensates for changes temporal characteristics AB due to the effects of aging and environmental influences. Voltage transformer provides the reference signal, related to the transition curve voltage crosses zero. The phase comparator compares the reference signal with the time of occurrence of the transition process the switch, generating a signal that indicates the need for adaptive adjustment. Similarly, when you turn off the automatic switch current transformer provides the reference signal, which is compared with the time for determining the transient process during off switch. Regulatory adaptive device performs temporary compensation that is appropriate modifications to reflect changes characteristic AB, including the effects of wear and weather conditions. Subsequent turning on or off the AV is activated at the time, adopted with appropriate compensation, so that he was enabled when the voltage passes through zero and off, when a current passes through zero, minimizing the transition process in line distribution. Phase angle can be used to control the off AV depending on the signal provided by a voltage transformer.
Similarly, the U.S. patent 5627415 also applies to the way of managing stress, which is considered the first signal voltage, over-the zero once detected, the off/on switch, and initiated a number of pre-defined and linked to certain moments of time steps to reduce or exclude the surge after turning off/on switch on the line of VSS.
Devoted to the same subject, i.e. managing the surge in transmission lines, U.S. patent 5629869 describes intellectual automatic switch or switching device, which includes three separate automated module, including the module status monitoring (ISS) 40, module control switch (MSY) 50 and the module synchronous control (LSG) 60. ISS 40 provides a thorough diagnosis, monitoring keys associated with the reliability of the automatic switch or the switching device. Online-Analytics by ISS, provides information to help you perform maintenance in accordance with the needs and identification of imminent failure. MSY 50 is a programmable system diagnostics and remote data transmission. This module replaces the Electromechanical controllers conventional type, traditionally used in the management of AB or switching devices. LSG 60 provides simultaneous control of switching devices with the aim of switching on and off the automatic circuit breakers. Ongoing management processes minimize the effect of transient processes in the system and wear on AV. Intellectual automatic switch or switching device to improve the work system and equipment maintenance.
Disclosure of the invention
The aim of the invention is to offer a way to manage a surge reenabling the transmission lines with compensation via shunt reactor. The basis of the invention lies the early determination of the optimum area of tension with the aim of switching automatic switch that enables the inclusion at the first minimum voltage between pins automatic switch later one after beating protection from exposure to dead time. This method allows to take into account the variation of parameters and dielectric characteristics of the circuit breaker during operation include, as a minimum plot beats more than a few periods of the fundamental frequency.
This method is used in digital relays for control fast three-phase switching of transmission lines with compensation via shunt reactor.
Brief description of drawings
Figure 1 shows the line diagram electrical system.
Figure 2 shows the voltage at the contacts of the circuit breaker (phase a, b, C) transmission line at 90% compensation with shunt reactor. Circle marks the site of the beating minimum amplitude.
Figure 3 shows a block diagram of the managed re-enable transmission lines with compensation via shunt reactor.
Figure 4 shows a graph curve voltage at the contacts of the circuit breaker for phase A.
Figure 5 shows a graph RMS voltage at the contacts of the circuit breaker.
Figure 6 shows a graph that identify the point in time when going off automatic switch.
7 shows a graph from the time of rise and fall of the filtered signal after tripping of the circuit breaker.
On FIG shows that identifies the first half.
Figure 9 shows the duration of the first half of the filtered signal.
The implementation of the invention
In method according to the invention is proposed to optimize the time the three-phase re-enable automatic switching to lower amplitude surge. Thus, the circuit breaker can be enabled faster, reducing the time of interruption of transmission.
In the present invention is determined in advance the optimal time for switching AV using the operation phase re-enable, which allows you to include AB at first beating stress after tripping of circuit protection with exposure to dead time. This model allows to take into account the variation of parameters and dielectric characteristics AB during the operation of inclusion, because lot of beating voltage with minimal amplitude more than one period of the fundamental frequency.
The procedure is performed using the described method provides more reliable determination of the previous period beating voltage regardless of transition curve voltage crosses zero. In addition, this procedure leaves more time to work AB after the discovery of the minimum plot, where there are still remains several periods fundamental frequency.
The main advantage of using the developed method is to substantially lower levels surge in performing transactions of re-inclusion in comparison with other methods due to the inclusion of the circuit breaker on the ground minimum of beating stress. The described method must be encoded in digital relay for three-phase re-enable the transmission lines with the introduction of new adaptive three-phase procedure of re-inclusion in the code digital relay, which previously played a re-enable the line on the basis of dead time, working in conjunction with predvkushenii resistor. The described method will lead to the creation of new digital relays.
After the occurrence of a fault in the transmission line protection circuitry disables three phases, isolating the failed plot line. Because most problems affecting the transmission lines are not permanent, after a predefined period of time, the protection circuit will re-include the disabled section of the line to ensure uninterrupted power supply.
When AV disables line running without load capacitive current is interrupted at transition through zero in each phase. When this occurs, the value of the line voltage is the maximum, leaving on a line captured charge, which will not be the same for all phases. At this first stage interrupt the voltage can reach up to 1.3 per unit, and, if captured, the charge will not be assigned a transformer or a reactor, the line will remain charged for a long time.
If the line is re-enabled drainage trapped charge, and pole circuit breaker are closed when the system voltage has opposite polarity line voltage, overvoltage transient process can be very high.
In the case of lines with reactive power compensation using the shunt reactor of the compensation degree has a significant effect on the voltage curve between the poles of AV. Due to the current generated cross-full conductivity line and inductance reactors, the tension between the poles of the circuit breaker when you re-enable characterized by oscillatory form (beatings). These beats occur because the voltage at each pole have different frequencies, in particular, the industrial frequency of the system on one side of the circuit breaker and the natural frequency equipment with compensated by power and transverse full conductivity line on the other side of the circuit breaker.
The period of beating depends on the degree of compensation of the line. The challenge captured by line-of-charge calls with time reducing the voltage amplitude. This challenge is a function of q compensating shunt reactor. The result is the maximum amplitude of beating stress tends to increase, while the minimum amplitude of beating stress tends to decline over time. Under these conditions, the optimal site re-enable AB will be the first minimum voltage at the site of the beating between the poles of the automatic switch, as shown in figure 2 red circle with the first section of the minimum beating.
In the way of fast three-phase re-enable transmission lines with compensation via shunt reactor pole AB close when the first minimum voltage at the site of the beating between the poles of the circuit breaker. To achieve this goal was realized described in detail below algorithm that determines in advance the optimal time to re-enable.
Implementation and evaluation of this method were carried out using a modeling tool PSCAD/EMTDC (Power Systems Computer Aided Design/ElectroMagnetic Transients including DC, computer modeling of power systems/electromagnetic transients, including persistent currents). Language CSMF (Continuous System Model Functions, functions simulation of continuous systems) tool PSCAD is used to implement synchronization sequence of operations switching, which allowed for dynamic interaction with the very PSCAD within the interval time sequence. It has made possible the modeling and control of switching devices, required for the development of way.
The sequence CSMF provides a more flexible modeling, due to which the state power system can be dynamically modified in the process of modeling using the software (or models)included in these sequences.
The developed algorithm of the method of managed inclusion of transmission lines at three-phase re-enabling detail using a flowchart depicted in FIGURE 3. Below are explanations for this scheme.
- Voltage electricity systems are continuously monitored voltage transformers (TN). For modelling purposes in this way is the manipulation of the actual voltage of the system, but implementation on the protective equipment (relay) will be used reduced value, converted with the help of TN. In addition, although the system is three-phase, the algorithm requires a voltage of only one phase, which sends a signal to the control of three-phase switching it on again.
- Using a voltmeter, part of the PSCAD is measured voltage from the system and the voltage from the side lines. Thus, you can define the shape of the curve voltage on open contacts AB (FIGURE 4).
- Using digital processing, you can get the RMS value of the voltage at the terminals of the circuit breaker (FIGURE 5)that runs in PSCAD using a pre-defined function. After that the signal is processed by the electronic filter.
- After this comes the countdown filtered signal when using the comparator, part of the tool PSCAD, which compares the levels of the two input signals, allowing you to determine the moment of switching off the automatic switch (6).
- Then defined moments of the rise and fall of the filtered signal after turning off the automatic switch (FIG.7).
- Generates a signal that has a single value during the first half period and a negative value after the first half-cycle (FIG).
- Having obtained these results, we can calculate the duration of the first half of the filtered signal (FIG.9).
- Finally, the value of the half period is doubled to obtain the length of time the beating.
After opening the contacts of the circuit breaker time re-enable you to adjust the largest value that can be 60C. In that moment of time, when the logical definition signal half period, send a command to replace the time you re-enable obtained period of the beating. Definition of optimum time of inclusion is achieved when ahead there are still some periods of industrial frequency, making possible further adjustment, if necessary in connection with the variation of parameters of the poles and the dielectric characteristics of the circuit breaker. The best site for three-phase re-enable consists of several periods fundamental frequency, therefore, the proposed method has a long period of time for execution of the amendments and adjustments, if necessary.
The invention is not limited to the embodiment, the experts understand that it can be made various changes on the form and detail without going beyond beings and scope of the invention, which is designed to promote understanding, and cannot be implemented without derogating from what is described inventive concept. The restrictive features of the invention described in the formula.
1. Method of adaptive three-phase quick re-enable applied to the transmission lines with compensation via shunt reactor, wherein includes the following steps; - gauge relay to adjust the time re-enable in accordance with typical maximum value after disconnection; - measure the voltage between pins of the circuit breaker with the help of voltage transformers; - receive RMS voltage between the poles of automatic breaker; - filter RMS to exclude high-frequency harmonics; - determine the moment of switching off the circuit breaker; - define the first half of the filtered signal; - define duration of the first half filtered signal; - define duration of the period of beating; and to regulate the time of re-enabled by setting it equal to the period of beating.
2. The method according to claim 1, characterized in that the typical largest value is 60 S.
3. The method according to claim 1 or 2, wherein get RMS voltage beating voltage between pins of the circuit breaker on this signal determine the first half of beating and calculates the optimal time re-enable.
4. The method according to claim 1 or 2, wherein the algorithm of its implementation preferably built-in digital relays.