• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    System and method for locating ground faults in excitation windings of synchronous machines with indirect excitation based on grounding the neutral of the armature winding of the exciter machine by means of a high ohmic value impedance. The system and method determine the position of the fault by analyzing the voltage in the grounding impedance and the excitation current of the excitation machine, thanks to the calculation of the voltage components in the excitation winding of the synchronous machine. . (Machine-translation by Google Translate, not legally binding)
    公开号:ES2861530A1
    申请号:ES202130547
    申请日:2021-06-15
    公开日:2021-10-06
    发明作者:Gaona Carlos Antonio Platero；Vicente Miguel Angel Pardo；Fernández José Angel Sánchez；Mahtani Kumar Vijay Mahtani；Granados José Manuel Guerrero
    申请人:Universidad Politecnica de Madrid；
    IPC主号:
    专利说明:

    [0004] OBJECT OF THE INVENTION
    [0006] The present invention develops a new system and method for locating ground faults in the excitation windings of synchronous machines with indirect brushless excitation, capable of operating with the machine in operation.
    [0008] A clear application is in electrical power generation systems, in which synchronous generators are used. The system and method object of the present invention makes it possible to detect and locate the position of the ground fault produced in the excitation winding in machines with indirect brushless excitation, without the need to remove the rotor from the machine.
    [0010] BACKGROUND OF THE INVENTION
    [0012] All electrical installation must be equipped with protection systems that make it safe against possible short circuits and other defects that may cause damage to both the facilities themselves and people.
    [0014] In the case of electricity generating groups, said protections must also guarantee the supply of energy to the grid in the most reliable way possible, trying to discriminate the severity levels of the faults that occur.
    [0016] The excitation circuit of a generator is a direct current system isolated from ground. A single ground fault does not affect generator operation or cause immediate effect damage. However, the probability of a second earth fault occurring is higher after the first has occurred. When you have a second ground fault, a part of the excitation winding is short-circuited, producing unbalanced fluxes in the air gap of the ground. machine, which results in vibrations and heating.
    [0018] Contrary to what happens in synchronous machines with static excitation in which the excitation power comes from an alternating current network, by means of a transformer and a rectifier, possibly by self-excitation, in synchronous machines with indirect brushless excitation, given the regime rotary of the excitation circuit, it is not feasible to use protection relays, or protection by injection of alternating or direct current, nor the method known as resistive divider or potentiometric method of direct current. In any case, the methods mentioned are limited to signaling the existence of the fault and do not allow locating the position of the earth fault.
    [0020] Other extended experimental systems exist that allow the detection of earth faults in the field winding of synchronous machines with indirect brushless excitation by analyzing the available signals of voltages and currents. However, the execution of these methods is generally complex at the computational level, in addition to limiting itself to signaling the existence of the defect and not allowing its position to be located.
    [0022] Systems are also known for the detection of ground faults in field windings of synchronous machines with indirect brushless excitation based on the installation of rings and brushes, which are used only in certain time intervals and therefore do not represent a monitoring solution. .
    [0024] In addition, systems based on optical modules or infrared communication modules are known, as well as radio frequency communication modules, which despite operating continuously, only provide a binary trigger or non-trigger signal and have a limited reliability inherent to their own. comunication way.
    [0026] There are systems for detecting ground faults in field windings of synchronous machines with indirect brushless excitation of the telemetric type, consisting of the injection of direct current between the shaft and a point of the excitation circuit, in which the current is measured. leakage through said connection and a negative logic high frequency signal is emitted, which is not reliable since its activation depends arbitrarily on the severity of the fault with respect to the connection point to the excitation circuit. In addition, it does not allow locating the ground fault. Analogous systems by injection of alternating current are known that solve the previous drawbacks, although they do not stop requiring the installation of numerous elements typical of wireless communication, that is, mounted on the transmitter's own axis and in the environment the antenna and the receiver.
    [0028] However, the methods commonly used to locate the position of an earth fault in the excitation winding of synchronous machines involve disassembling the machine and measuring the winding insulation at different points until the damaged area is found. Obviously, these methods require the machine to be out of service to perform the diagnosis.
    [0030] A series of patents related to the invention should be taken into account:
    [0031] P200900403 System and method for detecting earth faults in direct current systems fed by rectifiers.
    [0033] This patent claims a method and system for the discrimination of defects between the AC and DC side for synchronous machines with static excitation, by using a grounding resistance between the neutral of the excitation transformer and ground. This system detects defects in the rotor in the event of a voltage in the grounding resistance, but this configuration is not applicable to the case in which the excitation is carried out indirectly without brushes.
    [0035] P200901881 System and process for locating ground faults in excitation windings of synchronous machines with static excitation .
    [0037] This patent claims a method and system for locating defects in field windings of synchronous machines with static excitation, in which a grounding resistance is also used between the neutral of the excitation transformer and ground, and cannot be applied in the case where the excitation is carried out indirectly without brushes.
    [0039] The invention is based on the use of a grounding resistor, but in this case and as the main novelty, it is connected to the neutral of the armature winding of the excitation machine in a way that allows detecting the existence of a fault and determining its location. by means of relationships between the direct and alternating components of the voltages in the grounding resistance and the excitation voltage.
    [0041] DESCRIPTION OF THE INVENTION
    [0043] The invention refers to a system and method for locating ground faults in the excitation winding of synchronous machines with indirect brushless excitation, that is, the supply of the excitation winding of the synchronous machine is carried out by means of a rotating rectifier bridge and an excitation machine, which is provided with an excitation winding and a rotating armature winding by means of a shaft that also includes the rectifier bridge and which is coupled to the rotating shaft of the synchronous machine.
    [0045] To locate the ground fault, a high ohmic grounding resistance is installed between the neutral of the armature winding of the exciter machine and a ground point (Figures 1 and 2). This ground connection is made accessible by a ring and brush to allow the armature winding of the exciter machine to rotate together with the diode bridge. In the case of a delta armature winding, an artificial neutral is used, as is known in the state of the art.
    [0047] The method of locating defects in the excitation winding of the synchronous machine is based on calculations from the measurements of the alternating and direct components of the current and the voltage in the grounding resistance, as well as the measurement of the current in the excitation winding of the exciter machine.
    [0049] Denominating:
    [0051] • Vdc, DC component of the voltage measured at the starting resistance to Earth.
    [0053] • Vac, AC component of the voltage measured at the grounding resistance.
    [0055] • Iexdc, measured excitation current of the exciter machine.
    [0057] • Vfdc, calculated DC component of the voltage in the excitation winding of the synchronous machine.
    [0059] • Vfac, estimated ac component of the voltage in the excitation winding of the synchronous machine.
    [0061] • Rpat, ohmic value of the grounding resistance.
    [0063] • Rdc, calculated ohmic value of the fault resistance.
    [0065] • Vdc 0 , DC component calculated in the earthing resistance in the event of an earth fault at the origin of the winding or end supplied with negative polarity.
    [0067] The method for calculating the position of an earth fault in the excitation winding of the synchronous machine is as follows (Figure 3):
    [0069] • From the measurement of the current flowing through the excitation winding of the excitation machine Iexdc, the direct component of the theoretical excitation voltage at the terminals of the excitation winding of the synchronous machine Vfdc is calculated. To carry out this calculation there are several possible models of the exciter machine and the rectifier bridge. Factory testing can also be performed to obtain this relationship. In turn, knowing the DC component and knowing that it is a diode-based rectifier bridge, it is possible to calculate the AC component at the terminals of the excitation winding of the synchronous machine Vfac.
    [0071] • From the measured Vac and the estimated Vfac, the fault resistance Rdc is calculated using the following expression, knowing the value of the Rpat parameter:
    [0074] • Once the value of the fault resistance Rdc is known, the next step is to obtain the relationship between Vdc and the fault position. Taking into account that this relationship is determined by a line (Figure 4), it is fully defined with only two of its points. One of them is determined by the midpoint of the excitation winding of the synchronous machine, since, when an earth fault occurs at this point, no DC component appears in the voltage of the earthing resistance, that is, Vdc = 0. Knowing this point, the value of the fault resistance Rdc determines the slope of the line and therefore the values that Vdc takes with respect to the position of the fault (Figure 5). If the origin of the field winding is called 0%, supplied with negative polarity, and 100% the other end of the same, supplied with positive polarity (Figure 6), in the particular case of a 0% defect, the value acquired by Vdc It is called Vdc 0 . The expression for the calculation of Vdc 0 is the following:
    [0075] Vfdc Rpat
    [0078] Note that the previously indicated line, hereinafter called the "Vdc - fault position" line, has central symmetry. The maximum value of Vdc in the event of a fault is reached when the fault occurs at one end of the excitation winding, and it becomes null if the fault occurs in the center of the fault At the opposite end of the winding the Vdc value is again maximum, but with opposite polarity (Figures 4 and 5).
    [0079] • Once the line "Vdc - fault position" is known, entering it with the measured Vdc, the point where the earth fault has occurred, if any, is obtained.
    [0081] For this, it is a system for locating ground faults in excitation windings of synchronous machines with indirect brushless excitation, by means of an excitation machine, and a rectifier bridge, where the synchronous machines are equipped with an excitation winding and an armature winding. , and the exciter machine is equipped with an excitation winding and an armature winding characterized by comprising:
    [0082] a grounding resistor connected to the neutral of the exciter machine armature winding, and connected to
    [0084] equipment for measuring the voltage in said grounding resistance by means of a ring-brush;
    [0086] equipment for measuring the current flowing through the excitation winding of the excitation machine;
    [0088] a block for calculating the alternating and direct components of the voltage at the terminals of the excitation winding of the synchronous machine, based on the signals from the equipment for measuring the current flowing through the excitation winding of the excitation machine.
    [0090] a block for calculating the direct and alternating components of the voltage in the earthing resistance from the signals coming from the equipment for measuring the voltage in the earthing resistance;
    [0092] a block for calculating a fault resistance, from the AC components of the voltage obtained in the grounding resistance and in the excitation winding of the synchronous machine;
    [0094] a block for calculating the relationship between the DC component of the voltage in the fault resistance obtained and the position of the ground fault within the excitation circuit of the synchronous machine, knowing that this component is zero if the fault occurs in the midpoint of the excitation winding of the machine;
    [0096] a block for calculating a straight line that relates the direct component of the voltage in the grounding resistance with the position of the fault within the excitation winding of the synchronous machine, knowing that the direct component of the voltage in the resistance of defect is null if the defect occurs at the midpoint of the excitation winding of the synchronous machine, and where said block for calculating a straight line is configured to calculate the position of the fault from the DC component of the voltage in the earthing resistance.
    [0098] The system and method described provide the following advantages over the state of the art:
    [0100] - Locate the fault of the ground fault without disassembling the machine.
    [0102] - It does not require the use of an auxiliary voltage or current source to inject any signal to the rotor.
    [0104] - It reduces maintenance costs and times, since it allows preventive and specific maintenance, compared to corrective maintenance with a lack of information.
    [0106] - Improved availability of generation groups.
    [0108] - Provides the possibility of anticipating possible failures and a possible fortuitous disconnection, avoiding the economic repercussions that may derive from these events (material damage, compensation, fines, etc.)
    [0110] - It is easy to implement.
    [0112] BRIEF DESCRIPTION OF THE FIGURES
    [0114] To complement the description and in order to help a better understanding of the characteristics of the invention, a series of figures is attached as an integral part of said description in which, with an illustrative and non-limiting nature, the following has been represented:
    [0116] Figure 1 shows a diagram of a system in which the present invention has application, being (1), the excitation winding of the exciter machine, (2), the armature winding of the exciter machine, (3), the bridge rectifier, (4) the excitation winding of the synchronous machine, (5) the armature winding of the synchronous machine, and (6) the grounding resistor, installed between the neutral of the armature winding of the machine exciter and ground, as well as the ring-brush device for measurement, represented by a black square. The elements (2), (3) and (4) are in a rotational regime in a common axis of the synchronous machine, represented in figure 6.
    [0117] Figure 2 shows a diagram similar to that of Figure 1 in which an earth fault produced in the excitation winding of the synchronous machine with its fault resistance (7) has also been represented. This defect will normally occur on the machine shaft, which in turn is grounded.
    [0119] Figure 3 shows the diagram of figure 1, in which the blocks required to carry out the fault location method have been included, indicating the expressions for the different necessary calculations, being from (1) to (6) the same elements indicated in Figure 1 and, in addition:
    [0120] (8), the equipment for measuring the voltage in the grounding resistance. (9), the equipment for measuring the current flowing through the excitation winding of the excitation machine.
    [0121] (10), the block that calculates the alternating and direct components of the voltage in the grounding resistance from the measurements of (8). (11), the block for calculating the alternating and direct components of the voltage at the terminals of the excitation winding of the synchronous machine from the measurement of (9).
    [0122] (12), the fault resistance calculation block.
    [0123] (13), the block for calculating a point on the line "Vdc - defect position".
    [0124] (14), the block for calculating the line "Vdc - defect position".
    [0125] (15), the output signal that indicates the position of the defect.
    [0126] (16), the ground fault locator analyzer.
    [0128] Figure 4 shows, in a generic way, the line "Vdc - fault position", which relates the values of the DC component of the voltage measured in the grounding resistance Vdc with the position of the ground fault within the winding. synchronous machine excitation at the 0-100% reference detailed in Figure 6 .
    [0130] Figure 5 shows, in a particular case of excitation of the synchronous machine, the lines "Vdc - fault position", for different values of the fault resistance Rdc. It is observed that in all cases the central symmetry is maintained
    [0133] With respect to the point (50%, Vdc = 0) and for each value of Vdco> 0 the lines pass through the points (0%, Vdc = Vdc 0 ) and (100%, Vdc = - Vdc 0 ) as appropriate.
    [0135] Figure 6 shows the 0% and 100% points of the excitation winding of the synchronous machine, which have been taken by convention as the negative and positive polarity extremes respectively. It is exemplified for a two-pole synchronous machine.
    [0137] PREFERRED EMBODIMENT OF THE INVENTION
    [0139] The present invention makes it possible to locate ground faults in field or excitation windings of synchronous machines with indirect brushless excitation. The system and the method have the advantage that the disassembly of the machine is not required to locate the defect, being able to operate at the operator's will continuously or for periods, in a non-invasive way. They highlight the need for an auxiliary voltage or current source to inject any signal to the rotor of the synchronous machine.
    [0141] Figure 1 shows the system used to provide an example of practical implementation of the invention, illustrative and non-limiting. This is the case of excitation of a synchronous machine that is fed by an exciter machine whose rotor is mechanically coupled to the rotor of the synchronous machine. While the lower power exciter machine has a configuration comprising an excitation winding (1) on the stator and an armature winding (2) on the rotor, the synchronous machine comprises an armature winding (5) on the stator and an excitation winding (4) on the rotor. The output of the exciter machine is rectified by means of the rectifier bridge (3), generally made of diodes, rotating on the common axis. Normally these are systems isolated from ground, so it must be referenced to ground through a grounding resistor (6) with a high ohmic value Rpat. According to Figure 3 , for the location of the ground fault, the voltage in said grounding resistance (6) is measured by means of a device (8), or, failing that, the direct component of the current is measured. From this measurement, the voltage of the direct component Vdc and the alternating component Vac is calculated by means of a block (10), and the current Iexdc flowing through the excitation winding (1) of the excitation machine is measured by means of a device (9), or, failing that, the voltage between its terminals is measured. In this way, as described, from of the lexdc current, the continuous component of the theoretical excitation voltage is calculated at the terminals of the excitation winding of the synchronous machine Vfdc, by means of a block (11), which, as mentioned, to carry out this calculation there are several possible models of the machine exciter and bridge rectifier, or factory tests can be performed to obtain this relationship. Once the DC component Vfdc is known and the rectifier bridge is of the type comprising diodes, it is possible to calculate the AC component at the terminals of the excitation winding of the synchronous machine Vfac, by means of said block (11). From the value of the resistance Rpat, Vfac and Vac, the fault resistance (7), Rdc, can be calculated according to the equation that was previously exposed in the description section of the invention.
    [0143] The next phase consists of obtaining the relationship between Vdc and the position of the defect that is determined by a straight line, such as the one represented in figure 4, which is calculated by means of block (14), and which is defined by two of its points, one of which is determined by the midpoint of the excitation winding (4) of the synchronous machine, in which when an earth fault occurs, no direct component appears in the voltage, so Vdc = 0. Knowing this point, the value of the defect resistance Rdc conditions the slope of the line, and consequently those of Vdc with respect to the position of the defect, as can be seen in figure 5.
    [0145] If the origin of the excitation winding (4), supplied with negative polarity, is called 0% and the other end of the same, supplied with positive polarity, 100%, as shown in figure 6, in the particular case of a fault in 0% the value that Vdc acquires is called Vdc 0 , whose value is calculated according to the equation that was indicated previously, by means of a block (13), so that it is possible to calculate the commented line, which has central symmetry and is called " Vdc - defect position ”, which is calculated by block (14).
    [0147] In the case of an earth fault, once this line is known, entering it with the value of Vdc, block (14) obtains the point where the earth fault has occurred, and generates an output signal (15 ) that indicates the position in which the defect has occurred.
    [0149] It is considered in the practical execution example that both synchronous machines They are three-phase and that the armature winding of the exciter machine (2) is connected in a star, a connection that allows the neutral to be earthed as shown in Figure 1 . In case said armature winding (2) has a delta connection, some grounding method based on an artificial neutral can be used.
    [0151] To connect the neutral of the armature (2) of the exciter machine to the earthing resistance (6), a ring and a brush must be used, since this resistance is located outside the machine.
    [0153] As has been described, the system and method make it possible to determine the point of the excitation winding of the synchronous machine where the earth fault is located, independently of the value of the resistance of said fault. The type of faults that the system locates are those represented generically in Figure 2 . Note that in the particular case of ground fault with zero fault resistance or free fault, the maximum value indicated as Vdc 0 corresponds to half the DC component of the supply voltage of the excitation winding of the synchronous machine (4 ), whose estimate has been called Vfdc. The Vdc value 0 decreases as the value of the fault resistance (7) increases until it is nullified for high values of fault resistances, similar to the values of the rotor insulation resistance.
    [0155] The analysis of the measured signals is exemplified in an illustrative and non-limiting manner in Figure 3 , which shows a block diagram, which allows to carry out the execution of the fault location method described. A ground fault in the excitation winding of the synchronous machine (4) will cause a fault current to flow through the grounding resistor.
    [0157] The output signal (15) represents information, alarm or trigger, adjusted according to need. The setting of the method should give it reliability, so it is not advisable to set an excessively low activation threshold given the normal flow of eddy currents to earth, nor is it advisable to set an excessively high one.
    1
    权利要求:
    Claims (4)
    [1]
    1. System for locating earth faults in excitation windings of synchronous machines with indirect brushless excitation, by means of an excitation machine, and a rectifier bridge (3), where the synchronous machines are equipped with an excitation winding (4) and of an armature winding (5), and the exciter machine is equipped with an excitation winding (1) and an armature winding (2) characterized in that it comprises:
    • an earthing resistor (6) connected to the neutral of the armature winding of the exciter machine (2), and connected to
    • an equipment for measuring the voltage in said earthing resistance (8) by means of a ring-brush;
    • a device for measuring the current flowing through the excitation winding of the excitation machine (9);
    • a block for calculating the alternating and direct components of the voltage at the terminals of the excitation winding of the synchronous machine (11), based on the signals from the equipment for measuring the current flowing through the excitation winding of the exciter machine (9).
    • a block for calculating the direct and alternating components of the voltage in the earthing resistance (10) from the signals from the equipment for measuring the voltage in the earthing resistance (8);
    • a block for calculating a fault resistance (12), from the AC components of the voltage obtained in the grounding resistance (6) and in the excitation winding (4) of the synchronous machine;
    • a calculation block (13) of the relationship between the DC component of the voltage in the fault resistance obtained and the position of the ground fault within the excitation circuit of the synchronous machine, knowing that this component is zero if the defect occurs at the midpoint the excitation winding of the machine;
    • a block for calculating a straight line (14) that relates the direct component of the voltage in the grounding resistance with the position of the fault within the excitation winding of the synchronous machine, knowing that the direct component of the voltage in the fault resistance is zero if the fault occurs at the midpoint of the excitation winding of the synchronous machine, and where said block for calculating a straight line (14) is configured to calculate the position of the fault from the component DC voltage on the grounding resistor.
    [2]
    2. System according to claim 1, wherein the block for calculating the straight line (14) is configured to generate a signal (15) indicative of the position of the defect and its existence.
    [3]
    3. Method for locating ground faults in excitation windings of synchronous machines equipped with an excitation winding (4) and an armature winding (5) with indirect brushless excitation,, by means of an exciter machine, and a rectifier bridge ( 3), where the excitation machine is equipped with an excitation winding (1) and an armature winding (2) characterized in that it comprises,
    • a voltage measurement stage in an earthing impedance (6) connected to the neutral of the armature winding of the exciter machine
    • a step for measuring the current flowing through the excitation winding of the excitation machine;
    • a stage for calculating the DC and AC components of the voltage at the terminals of the excitation winding of the synchronous machine from the signals from the stage of measurement of the current flowing through the excitation winding of the excitation machine .
    1
    • a step for calculating the direct and alternating components of the voltage in the grounding resistance from the signals coming from the step of measuring the voltage in the grounding impedance (6);
    • a step for calculating a fault resistance from the AC components of the voltage obtained in the earthing resistance (6) and in the excitation winding (4) of the synchronous machine;
    • a step for calculating the relationship between the DC component of the voltage in the fault resistance obtained and the position of the ground fault within the excitation circuit of the synchronous machine, knowing that this component is null if the fault occurs at the midpoint of the excitation winding of the synchronous machine;
    • a step for calculating a straight line that relates the direct component of the voltage in the grounding resistance with the position of the fault within the excitation winding of the synchronous machine, knowing that the direct component of the voltage in the resistance fault is zero if the fault occurs at the midpoint of the excitation winding of the synchronous machine,
    • a stage of calculating the position of the fault by accessing the straight line calculated with the value of the direct component of the voltage in the measured earthing resistance.
    [4]
    4. A method according to claim 1, comprising generating and emitting a signal (15) indicative of the position of the detected defect.
    1
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    ES2861530B2|2022-02-08|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    DE1938222A1|1969-07-24|1971-02-04|Licentia Gmbh|Arrangement for ground fault monitoring for a synchronous machine|
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