A protective relay system and method

Abstract

The application provides a kind of relay protection system and method, comprising: the real-time current data of the inflow in the equipment to be protected is collected, and the real-time current data is converted into digital signal after A / D conversion;According to the current data after A / D conversion, the heat capacity is calculated, and according to the relay protection time under the setting of different multiple rated current, the integral value operation of current thermal effect is carried out, and the overcurrent inverse time limit action time is determined.The application realizes the relay protection of multiple systems based on microprocessor and other hardware circuits, the real-time current data of the protected equipment is collected by hardware device, and is converted into digital quantity after AD conversion, the calculation is carried out through microprocessor, according to the relay protection time set, integral operation is carried out, overcurrent inverse time limit action time is calculated, instantaneous operation of relay protection is realized, calculation precision is high, action is reliable, application is flexible, inverse time limit action time of different rated current multiple can be set according to needs, and the application range is wide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of relay protection, in particular to a relay protection system and method. BACKGROUND

[0002] At present, the power system is developing rapidly, and the demand for electric energy in various industries is increasing, and high-voltage transmission is also increasing. Therefore, the safety management of the power system is very important. In order to reduce the electric power accident, the relay protection is indispensable, and at present, the high-performance circuit breaker, the inverse-time action of the contactor or the relay protection for large current instantaneous action is mainly used.

[0003] The high-performance relay or contactor used in the existing relay protection has high cost, and the protection action is not flexible, so it is difficult to achieve coordination of different levels. When the relay is used as the relay protection, the relay itself is limited by the voltage level, and the versatility is poor, and various voltage levels cannot be used universally. SUMMARY

[0004] In view of this, the present application provides a relay protection system and method, which aims to solve the problem that the high-performance relay or contactor used in the existing relay protection has high cost, and the protection action is not flexible, so it is difficult to achieve coordination of different levels.

[0005] In one aspect, the present application provides a relay protection method, comprising:

[0006] Step 1, collecting real-time current data flowing into the device to be protected, and converting the real-time current data into a digital signal after A / D conversion;

[0007] Step 2, calculating the heat capacity according to the A / D converted current data, and performing current heat effect integral value operation according to the set relay protection time under different multiple rated currents to determine the overcurrent inverse-time action time.

[0008] Further, in the above-mentioned relay protection method, the A / D converted digital signal is filtered in step 1.

[0009] Further, in the above-mentioned relay protection method, the calculation value C of the heat capacity is calculated according to the following formula:

[0010] C=N1*[(1.1I e ) 2 -I e 2 ]

[0011]

[0012] Wherein, T1 is 1.1 times the rated overcurrent time; t is the current data collection period; m is a constant, which is a positive integer; I eIs the rated current; U1 is the A / D conversion interface voltage, and U0 is the reference voltage.

[0013] Further, in the above-mentioned relay protection method, the integral coefficient k is calculated according to the following formula:

[0014]

[0015] Wherein, i is the overcurrent multiple, which is a positive integer greater than 1.1 and less than or equal to 7; Ti is the i times rated overcurrent time; C is the thermal capacity; m is a constant, which is a positive integer; I e Is the rated current; t is the current data collection period.

[0016] Further, in the above-mentioned relay protection method, the integral coefficient k is calculated according to the following formula:

[0017] k=k i1 +(k i1+1 -k i )*(i-i1)

[0018] Wherein, i1 is the maximum integer less than i, and k i is the i th integral coefficient, k i1 is the i1 th integral coefficient, and k i1+1 is the i1+1 th integral coefficient.

[0019] Further, in the above-mentioned relay protection method, if the actual current I collected is less than the rated current I e , k=1; if I e ≤I<1.1I e , k=0; if I is greater than 1.1 times the rated current I e , the overcurrent multiple i is calculated, and if i is greater than 7, the circuit breaker is instantaneous, otherwise the coefficient k is taken according to the following formula:

[0020] i is an integer, and k=k i .

[0021] Further, in the above-mentioned relay protection method, the overcurrent inverse time action time is determined according to the following formula:

[0022]

[0023] k=k i , C1 is the current thermal effect integral value, and C1 is initialized to 0; when C1 is less than 0, C1 is equal to 0; when C1 is greater than or equal to C, the action time of the overcurrent inverse time is the corresponding overcurrent time, and the relay is tripped.

[0024] The relay protection method in the application, by collecting real-time current data of the protected equipment, collecting current value through AD conversion, comparing the current value with the rated value, calculating thermal effect, realizing inverse time limit operation of thermal effect, calculating protection action time, realizing inverse time limit relay protection of the power system, and according to the comparison of collected current and instantaneous current, performing instantaneous protection, when the circuit breaker fault appears, the upper level circuit breaker can be cut off in time to realize cascade protection of different levels, increase the reliability of relay protection, and greatly improve the power safety.

[0025] In another aspect, the application further provides a relay protection system, comprising: a current data collection module, configured to collect real-time current data flowing into a device to be protected, and convert the real-time current data into digital signals after A / D conversion;

[0026] A calculation module, configured to calculate thermal capacity according to the A / D converted current data, and perform current thermal effect integral value operation according to the set relay protection time under different multiple rated currents, to determine overcurrent inverse time limit action time.

[0027] Further, the relay protection system further comprises: a relay tripping module, configured to realize circuit breaker tripping operation according to the overcurrent inverse time limit action time output by the calculation module.

[0028] Further, the relay protection system further comprises: a sampling circuit; wherein,

[0029] One side of the sampling circuit is connected with the secondary side of the current transformer, and the other side of the sampling circuit is connected with the level conversion circuit, and the level conversion circuit is connected with the processor.

[0030] The relay protection system provided by the application realizes overload inverse time limit action and short-circuit current instantaneous relay protection effectively and accurately by collecting current through a microprocessor, performing integral operation according to the set relay protection time, calculating overcurrent inverse time action time, and judging instantaneous current to realize instantaneous operation of relay protection. BRIEF DESCRIPTION OF DRAWINGS

[0031] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the application. Moreover, the same reference numerals are intended to denote the same components throughout the accompanying drawings. In the drawings:

[0032] Figure 1 A flowchart of the relay protection method provided by the embodiments of the application;

[0033] Figure 2The flow chart of the calculation method of the inverse time action time in the relay protection method provided by the embodiment of the present application is shown in the figure.

[0034] Figure 3 The circuit diagram of the current data collection in the relay protection system provided by the embodiment of the present application is shown in the figure.

[0035] Figure 4 The A / D conversion circuit diagram in the relay protection system provided by the embodiment of the present application is shown in the figure.

[0036] Figure 5 The circuit diagram of the breaker tripping control output in the relay protection system provided by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0037] Exemplary embodiments of the present disclosure will be described in greater detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure can be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure can be more thoroughly understood, and so that the scope of the present disclosure can be completely conveyed to those skilled in the art. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0038] Referring to Figure 1 , the relay protection method of the embodiment of the present application comprises:

[0039] In step S1, real-time current data flowing into the device to be protected is collected, and the real-time current data is converted into a digital signal after A / D conversion.

[0040] Specifically, the real-time current data flowing into the device to be protected is collected by the current data collection circuit, and the real-time current data is converted into a corresponding voltage signal, and then the voltage signal is converted into a suitable level for the microprocessor A / D conversion through a circuit, so as to meet the calculation accuracy and be input to the A / D pin of the microprocessor.

[0041] During the collection of the current data, the current transformer of the three-phase circuit of the neutral point grounding system is configured in three phases, and the current transformer of the neutral point non-grounding system can be configured in two phases. A protection type current transformer with a secondary side rated current of 1A is selected, and the current sampling circuit is as shown in the figure. Figure 2 The data collection circuit of the current is shown in the figure, and the current value is converted into a corresponding voltage signal through two parallel resistors, and then the voltage signal is converted into a suitable level for the microprocessor A / D conversion through a circuit, so as to meet the calculation accuracy and be input to the A / D pin of the microprocessor.

[0042] The microprocessor completes the filtering of the digital signal at the bottom layer data A / D conversion link, and the data of the same interface of N times of AD conversion is added and averaged as shown in the following formula (1). The average filtering method is used to eliminate the interference signal of the current data. The switching value device is also deburred to obtain the device running state. When the device state changes, the switching value 0→1 or 1→0, and after a delay of 10-20 ms, the state is unchanged and then confirmed.

[0043]

[0044] In step S2, the heat capacity is calculated according to the A / D converted current data, and the current heat effect integral value operation is performed according to the set relay protection time under different multiple rated currents, to determine the overcurrent inverse time limit action time.

[0045] Specifically, the current data includes a filtering collection period t, and the inverse time limit protection time of the relay protection, such as 1.1 times the rated overcurrent time T1, 2.0 times the rated current T2, 3.0 times the rated current T3, and up to 8 times the rated current instantaneous action. When the line current is less than 1.1 times the rated current, it can be continuously operated for a long time. According to the current heat effect related to the current square, the current heat effect is calculated, and the inverse time limit action time is further calculated. In order to meet the requirement that the inverse time limit action time of 1.1 times the rated current is T1, N1 is determined N1 is an integer, and m is an integer, which can be 1. When the calculated N1 is too large, m can be 1, 2, 3, …, and the calculated value C of the heat capacity is calculated according to the following formula.

[0046]

[0047] Wherein, T1 is 1.1 times the rated overcurrent time; t is the current data collection period; m is a constant, which is a positive integer; I e is the rated current; U1 is the A / D conversion interface voltage, and U0 is the reference voltage.

[0048] According to the A / D conversion, when the secondary current of the mutual inductor is 1A, the primary side current is the rated current, the voltage of the resistance divider shown in Figure 2 is 0.25V, the reference voltage is 2.5V, and the AD conversion digital quantity of the microprocessor is 12 bits. Thus, the digital quantity Ie at the rated current can be calculated as shown in the following formula (5):

[0049]

[0050] In order to meet the requirement that the action time is Ti when the current is 2 times the rated current or more, the integral coefficient k is calculated:

[0051]

[0052] Wherein, i is the overcurrent multiple, taking positive integer greater than 1.1 and less than or equal to 7; Ti is the i times rated overcurrent time; C is the heat capacity; m is a constant, taking positive integer; I e is the rated current; t is the current data collection period.

[0053] For example, i can take 2, 3, 4, 5, 6, 7, and the corresponding 2 times rated current calculation coefficient k2, and 3 times, 4 times, 5 times, 6 times, 7 times current integral coefficient k3, k4, k5, k6, k7 can be calculated. Let k1 = 1.

[0054] Further, in order to further improve the calculation accuracy, the integral coefficient can be accurately calculated by interpolation method

[0055] The integral coefficient k is calculated according to the following formula:

[0056] k = k i1 +(k i1+1 -k i )*(i-i1) (8)

[0057] Wherein, i1 is the maximum integer less than i, k i is the i integral coefficient, k i1 is the i1 integral coefficient, and k i1+1 is the i1+1 integral coefficient.

[0058] The integral coefficient k calculated by the interpolation method further improves the accuracy of the overcurrent inverse time limit, and more k values can be set by the 3-2 formula to improve the accuracy. The rated current multiple of the instantaneous overcurrent action can be set according to actual needs, and the 8 times rated current used in the present application can also be set to other values.

[0059] Continuing to refer to Figure 2 , in this embodiment, if the actual current I collected is less than the rated current I e , take k = 1; if I e ≤I<1.1I e , k = 0; if I is greater than 1.1 times the rated current I e , calculate the overcurrent multiple i, if i is greater than 7, the circuit breaker is instantaneous, otherwise take the coefficient k according to the following formula:

[0060] i is an integer, k = k i .

[0061] In the embodiment, the rated current value of each loop is acquired, the inverse-time action time under different overcurrent multiples and the instantaneous action overcurrent multiple are set by the user. According to the collected current signal, the thermal effect is calculated, the thermal effect of the rated current is compared, the action time of the inverse-time is calculated according to the overcurrent multiple, the relay protection is realized, when the circuit breaker fails and cannot port the large current, the back protection is started, the current of the previous stage or the current of the associated other loop is cut off.

[0062] In the specific implementation, the inverse-time action time is calculated by using the algorithm of current thermal effect integral accumulation, the program flow is as shown in Figure 2 The actual current is compared with the rated current, the calculation coefficient is selected according to the overcurrent multiple, and the inverse-time action time of the overcurrent is determined according to the following formula:

[0063]

[0064] k=k i C1 is the integral value of current thermal effect, C1 is initialized to 0, when C1 is less than 0, C1 is equal to 0; when C1 is greater than or equal to C, the action time of the overcurrent inverse-time is the corresponding overcurrent time, at this time, the relay is tripped.

[0065] In practice, each device has a unique device code in the computer management platform, according to the flow chart shown in Figure 3 The relay protection overcurrent calculation is performed according to the calculation result, the relay tripping action is performed, and the time control of the relay protection is realized.

[0066] The above is the calculation method according to the current of one phase, the currents of the other two phases are the same as the calculation method, the same inverse-time action time and instantaneous current multiple are set in the same loop. The inverse-time action time and the instantaneous current action multiple are different in loops of different voltage levels. In the center point grounding system, the three-phase currents can be calculated at the same time. In the neutral point ungrounded system, only two-phase currents can be calculated. Because the three-phase current vector sum of the neutral point ungrounded system is 0. The present application realizes the action control of the relay protection of multiple systems by using the simple circuit of the microprocessor, has low cost, reliable action, and convenient application. It can be applied to different circuits and flexibly set the action time.

[0067] The relay protection method provided by the application collects current values through AD conversion of a microprocessor, compares the current values with rated values, calculates thermal effects, realizes inverse-time operation of the thermal effects, and calculates protection action time.

[0068] In combination Figures 3-5 The application further provides a relay protection system, which comprises:

[0069] A current data collection module is configured to collect real-time current data flowing into a device to be protected, and convert the real-time current data into digital signals after A / D conversion.

[0070] A calculation module is configured to calculate thermal capacity according to the A / D converted current data, and perform current thermal effect integral value operation according to relay protection time under different multiple rated currents to determine overcurrent inverse-time action time.

[0071] Referring to Figure 3 In the above embodiments, the sampling circuit further comprises: a sampling circuit, one side of which is connected with the secondary side of the current transformer, and the other side of which is connected with the level conversion circuit, and the level conversion circuit is connected with the processor.

[0072] Specifically, the sampling circuit comprises two parallel resistors. The current cable passes through the current transformer, and the secondary side of the transformer is connected with two 2Ω resistors in parallel. The parallel resistors are used to prevent the resistors from being disconnected or damaged to form an open circuit at the secondary side of the current transformer. When the current is the rated current, the voltage across the sampling resistors is 1V.

[0073] In this embodiment, the data collection of the operating current is converted into a voltage signal through the secondary side of the current transformer, and the voltage value is converted into a voltage range for the microprocessor to collect. The current value is collected through AD conversion. The operating current is converted into a digital signal for the single-chip microcomputer to calculate and process.

[0074] Figure 4 The level conversion circuit is divided by resistors R29 and R24. When the rated current is 1V, the voltage is changed to 0.25V after division, and is connected to the A / D conversion interface of the microprocessor after being filtered by a resistor-capacitor filter. The reference voltage of the AD conversion is 2.5V, and the maximum current value collected is 10 times the rated current, which meets the protection overcurrent requirement.

[0075] Referring toFigure 5 In the above embodiments, it further includes: a relay tripping module, used to realize the circuit breaker tripping operation according to the overcurrent inverse time limit action time output by the calculation module.

[0076] Based on the calculation results, an output signal is used to trip the circuit breaker and disconnect the fault current. The relay trip output circuit is as follows: Figure 5 As shown, this is the passive node output of the relay. PB12 is a passive pulse signal output by the microprocessor, ensuring reliable relay tripping time and preventing damage to the circuit breaker tripping coil due to prolonged current. Ports 13 and 14 are connected to the relay tripping coil. If tripping of the circuit breaker at this level is not possible, it can be checked whether the upstream circuit breaker is within the system. If it is within the system, the upstream circuit breaker is directly disconnected; otherwise, a circuit breaker fault alarm signal is issued.

[0077] The relevant parts of the device embodiment and the above method embodiment can be referred to each other, and will not be repeated here.

[0078] This invention can obtain the rated current value of each circuit, and the user can set the inverse time limit action time and instantaneous action overcurrent multiple under different overcurrent multiples.

[0079] This invention utilizes a microprocessor or single-chip microcomputer to collect current data via A / D conversion and current transformers, calculates the thermal effect of the current, and controls the circuit breaker operation based on the set inverse time protection time or instantaneous current value, achieving multi-circuit breaker protection. It can also combine temperature detection to automatically determine overload and overheating operating states, achieving real-time protection. It is easy to use, low-cost, and highly functional. It solves the problem of multi-level relay protection in power systems, improves electrical safety, reduces relay protection costs, and saves on operation and maintenance costs.

[0080] In summary, the relay protection system of this invention implements multi-system relay protection based on hardware circuits such as microprocessors. It collects real-time current data of the protected equipment through hardware devices, converts it to digital values ​​via an analog-to-digital converter (A / D converter), and calculates the inverse-time overcurrent action time through microprocessor calculations based on the set relay protection time. It then determines the instantaneous current to achieve instantaneous relay protection operation. When the relay trips, it assesses the circuit breaker's status; if an electrical fault is detected, it trips the upstream relay to cut off the fault current. It can protect different voltage levels, offers flexible inverse-time action times, and provides unified data management and access to a control platform. This relay protection system can simultaneously provide multi-system relay protection. It is simple, practical, safe, reliable, facilitates unified data management, is low-cost, has high calculation accuracy, reliable operation, and flexible application. Different inverse-time action times based on rated current multiples can be set as needed, making it widely applicable.

[0081] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A method of relaying protection, characterized by, The method comprises the following steps: Step 1, collecting real-time current data flowing into a device to be protected, and converting the real-time current data into digital signals after A / D conversion; Step 2, calculating thermal capacity according to the A / D converted current data, and calculating current thermal effect integral value according to relay protection time under different multiple rated currents to determine overcurrent inverse time limit action time; The calculation value C of the thermal capacity is calculated according to the following formula: C = N1*[(1.1I e ) 2 -I e 2 ] Wherein, T1 is 1.1 times rated over-current time; t is current data collection period; m is a constant, taking positive integer; I e Is the rated current; U1 is A / D conversion interface voltage, U0 is reference voltage; The integral coefficient k is calculated according to the following formula: wherein i is the overcurrent multiple; Ti is the i times rated overcurrent time; C is the heat capacity; m is a constant, taking a positive integer; I e is the rated current; t is the current data collection period; If the actual current I collected is less than the rated current I e , take k = 1; if I e ≤ I < 1.1 I e , k = 0; if I is greater than 1.1 times the rated current I e , calculate the overcurrent multiple i, if i is greater than 7, the circuit breaker is instantaneous, otherwise take the coefficient k according to the following formula: i integer, k = k i ; The overcurrent inverse time limit action time is determined according to the following formula: k = k i C1 is the current thermal effect integral value, C1 is initialized to 0, when C1 is less than 0, let C1 equal to 0; when C1 is greater than or equal to C, the action time of the overcurrent inverse time is the corresponding overcurrent time, and the relay is tripped.

2. The method of claim 1, wherein, In the step 1, the A / D converted digital signals are filtered.

3. The method of claim 1, wherein, The integral coefficient k is calculated according to the following formula: k = k i1 + (k i1+1 - k i1 ) * (i - i1) where i1 is the largest integer less than i, k i is the ith integration coefficient, k i1 is the ith integration coefficient, k i1+1 is the ith integration coefficient, k 4. A relay protection system using the relay protection method according to any one of claims 1 to 3, characterized by, The method comprises the following steps: A current data collection module is configured to collect real-time current data flowing into a device to be protected, and convert the real-time current data into digital signals after A / D conversion; A calculation module is configured to calculate thermal capacity according to the A / D converted current data, and calculate current thermal effect integral value according to relay protection time under different multiple rated currents to determine overcurrent inverse time limit action time.

5. The protection system according to claim 4, characterized in that Further comprising: A relay tripping module is configured to realize circuit breaker tripping operation according to the overcurrent inverse time limit action time output by the calculation module.

6. The protection system of claim 4, wherein, Further comprising: a sampling circuit; wherein, One side of the sampling circuit is connected with the secondary side of the current transformer, the other side of the sampling circuit is connected with the level conversion circuit, and the level conversion circuit is connected with the processor.

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