CN116231589A - Current quick-break protection method without matching with motor starting current - Google Patents
Current quick-break protection method without matching with motor starting current Download PDFInfo
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- CN116231589A CN116231589A CN202211502483.6A CN202211502483A CN116231589A CN 116231589 A CN116231589 A CN 116231589A CN 202211502483 A CN202211502483 A CN 202211502483A CN 116231589 A CN116231589 A CN 116231589A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
- H02H7/085—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load
- H02H7/0854—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load responsive to rate of change of current, couple or speed, e.g. anti-kickback protection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0092—Details of emergency protective circuit arrangements concerning the data processing means, e.g. expert systems, neural networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
- H02H7/085—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load
- H02H7/0856—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load characterised by the protection measure taken
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Abstract
The invention discloses a current quick-break protection method without matching with a motor starting current, which comprises the steps of setting a motor current quick-break protection fixed value; setting and calculating a fixed value of a motor protection device; measuring and storing the effective value of the electric quantity in the starting process of the motor; determining the change rate of the starting current of the motor relative to time in the starting process; calculating a current quick-break protection fixed value and checking sensitivity; and storing the generated current quick-break protection fixed value in a read-only memory EEPROM for the program call of the relay protection module of the device. By utilizing the difference of the motor starting current and the short-circuit fault current in terms of the change rate, the current quick-break protection of the relay protection device does not need to be matched with the motor starting current any more, and the sensitivity and the quick-action performance of the current quick-break protection are improved essentially.
Description
Technical Field
The invention relates to the technical field of current quick-break protection, in particular to a current quick-break protection method without matching with starting current of a motor.
Background
The motor is applied to the modern society, the equipment such as washing machines, air conditioners, smoke exhaust fans, elevators and the like in daily life are not separated from the motor, the systems such as machine tools, cranes, fans, water pumps, fire protection and the like in factories and mines are also not separated from the motor, a large number of motors are used on various equipment such as transformer air cooling, ventilation of a GIS room, energy storage of a breaker mechanism, operation of a disconnecting switch and the like in a power system, the motor which is generally applied to all industries in all regions according to statistics occupies 70% of the generated energy, and about 95% of the motor in electric dragging machinery is provided with kinetic energy by a three-phase asynchronous motor. Due to various reasons, the motor often causes accidents such as electric shock and fire disaster due to faults such as overload, short circuit, phase failure and poor grounding, thereby not only affecting the normal operation of production, but also often causing personal casualties and huge loss of property. According to the data of the motor protection and control special commission, the serious accident caused by the fault is hundreds of times, the direct economic loss is hundreds of yuan, and the safe operation of various motors is related to national folk life.
The motor protection system widely adopted today is subjected to multiple technical improvements, which comprise JR 0-16 series thermal relay protection developed by the Soviet Union technology introduced in the beginning of fifty years, LR1 series protection introduced from French TE company introduced in the beginning of eighty years, T series protection introduced from ABB company, 3UA5, 3UA6 series and other bimetallic strip type thermal overload relay protection introduced from Siemens, and intelligent motor protectors formed by micro-processing chips have been developed, wherein a single chip microcomputer is mainly used as a controller, so that the intelligent comprehensive protection of motors can be realized, the remote communication function is realized, and the online comprehensive monitoring and control of a plurality of networked motors can be realized on a PC. The method has a qualitative leap in the aspects of sampling and setting precision, can carry out software nonlinear correction on the sampling signal, and can realize true effective value calculation, thereby greatly reducing the influence of waveform distortion of the measured signal and truly realizing high-precision sampling. In the setting aspect, the numerical setting is adopted, the user can set the numerical setting on site by himself through a keyboard, and a plurality of more scientific inverse time limit curves can be set for overload protection. Because the singlechip is adopted, the appearance of the comprehensive protector integrating multiple functions and a whole body under the same hardware condition is possible. The method is characterized in that:
1. the change of the current of the detection line (including the adoption of positive sequence, negative sequence, zero sequence and overcurrent) can be used as a principle, and the phase failure or overload signal can be detected, so that the detection line has the functions of phase failure protection, overload protection, locked rotor protection and the like.
2. The intelligent protection device has the intelligent protection functions of remote measurement, remote control, remote regulation, communication and integration, and can realize protection when faults such as open-phase, overload, short circuit, undervoltage, overvoltage, electric leakage and the like occur to the motor; the system has the advantages of current and voltage display, time control, software self-diagnosis, incoming call self-recovery, self-starting sequence, fault memory, self-lock and remote transmission alarm, current and voltage fault display during fault and the like, and is provided with an RS485 communication interface to realize computer networking. Meanwhile, the work of a plurality of motors can be monitored.
3. The alternating current sampling technology, the multipoint linear correction technology and the automatic range switching technology are adopted, so that the high sampling precision can be maintained in the current measuring range.
The intelligent motor protector is widely applied in actual work and has good operation effect.
In the protection of motors of various generations from the history, the current quick-break protection of the motor is required to be matched with the starting current of the protected motor when the fixed value of the protection device is set, and on the basis of the technical principle, the current quick-break protection fixed value of the motor is caused to generate the contradiction which is difficult to overcome in the action current and the action time.
The current leading relay protection device manufacturer designs and produces a current quick-break protection with a fixed value capable of being automatically adjusted, and the action principle is that a high fixed value is used to avoid the starting current of a motor when the motor is started, and the device automatically reduces the high fixed value to a low fixed value to operate after the motor is detected to finish the starting, so that the sensitivity of the current quick-break protection in the operation process is ensured.
However, since a high constant value is required to be greater than the maximum starting current of the motor, this results in losing sensitive and rapid protection of the motor for a period of time after power-up to completion of starting. Because the motor quick-break protection is mainly used as protection from a power point to a motor winding outgoing line, and the motor winding outgoing line is constrained by a physical structure, faults occur in the place, and because the fault current in the place is the area with the largest fault current in all faults of the motor, if the quick-break protection cannot be realized, the motor is often damaged.
The sensitivity and the speed of the motor current quick-break protection still need to be improved by finding a method.
Disclosure of Invention
The invention aims to solve the problems of the existing motor current quick-break protection, and provides the current quick-break protection which does not need to be matched with the starting current of a motor. Some simplifications or omissions may be made in this section as well as in the description summary and in the title of the application, to avoid obscuring the purpose of this section, the description summary and the title of the invention, which should not be used to limit the scope of the invention.
The present invention has been made in view of the above and the problems existing in the current quick-break protection method that does not have to be matched with the motor starting current.
The problem to be solved by the present invention is therefore how to provide a method of current quick break protection that does not have to be matched to the motor starting current.
In order to solve the technical problems, the invention provides the following technical scheme: the current quick-break protection method without matching with the starting current of the motor comprises the following steps:
setting a motor current quick-break protection fixed value;
setting and calculating a fixed value of a motor protection device;
measuring and storing the effective value of the electric quantity in the starting process of the motor;
determining the change rate of the starting current of the motor relative to time in the starting process;
calculating a current quick-break protection fixed value and checking sensitivity;
and storing the generated current quick-break protection fixed value in a read-only memory EEPROM for the program call of the relay protection module of the device.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: the protection method comprises a motor current quick-break protection fixed value setting technology;
the calculation, analysis and measurement of stored data of the electric quantity of the motor in operation;
determining the change rate of current with respect to time in the starting process;
the relay protection device automatically completes calculation and sensitivity verification of the current quick-break protection fixed value;
the current quick-break protection fixed value is saved by the EEPROM for the device program to call.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: the starting power supply measures and stores the effective value of the electric quantity through the voltage converter and the current transformer, and the effective value is filtered and transmitted to the multichannel A/D conversion module which can convert the current when the motor is started into time and transmit the time to the relay protection module program, and then the judging value of the fixed value and the sensitivity is determined according to the fixed value setting calculation mode of the motor protection device, and whether the power-off protection is carried out or not is screened and transmitted to the liquid crystal display and finally transmitted to the relay protection module.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: the power-off protection technique comprises the following steps:
performing device operation when the current quick-break protection method judges that the current quick-break protection fixed value is not met;
when the current quick-break protection method judges that the current quick-break protection fixed value can be met, the optimized fixed value is obtained, and the transmission protection device calculates and judges whether the tripping requirement is met;
when the operation of the protection transmission device judges that the tripping requirement is met, immediately executing protection tripping;
and when the operation judgment of the protection transmission device does not meet the tripping requirement, entering a power continuous system to judge and circulate.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: setting a fixed value of the protection method device and a calculation mode;
I dz ＝6I e (A)
t dz ＝1.2t qd
setting protection device I e Rated current of motor in normal operation, P is rated power of motor, U e For the motor to operate at a nominal voltage,
for motor power factor, η is mechanical efficiency, I dz Current quick break protection current setting value, t dz And setting the current quick-break protection time.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: a current change rate algorithm relative to time in the starting process;
t n-1 -t n ＝2ms
wherein I represents the parameter of the current in the starting process; t represents a time node in the power-on process. I 1 I 2 For the first and second current data size, t 1 t 2 Data is recorded for the first and second times, ms being expressed in milliseconds.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: the power-off protection technology adopts a sensitivity algorithm
The sensitivity coefficient of protection is:
requirement K m And if the current rapid-break protection fixed value is more than or equal to 1.2, the original rapid-break protection fixed value can be maintained.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: constant value calculation mode for current quick-break protection
I dz ＝K m ×I e
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: the action equation of the relay protection device is designed as follows
Wherein: k (k) dz.ROC The current change rate action is fixed for the current quick break protection, k k.ROC For the current change rate reliability coefficient (taking 5-10), k sc.ROC The method is characterized in that the normal starting current change rate of the motor is actually measured; k (k) dl.ROC To minimize the rate of change when a short circuit occurs, I dz Setting action value, k for current quick break protection k For protecting the reliable coefficient (1.2) of current quick break, I e Rated for the motor current.
As a preferred embodiment of the current quick-break protection method without matching with the starting current of the motor, the invention comprises the following steps: the time-specific conversion of the electric quantity effective value in the starting process of the motor can be carried out through the calculation of the current quick-break protection fixed value and the sensitivity verification, and the electric quantity effective value is stored in a read-only memory EEPROM for the program calling of a relay protection module of the device, so that whether the power-off protection is carried out or not can be accurately judged through various limits.
The invention has the beneficial effects that
1. The difference of the motor starting current and the short-circuit fault current in terms of the change rate is utilized, so that the current quick-break protection of the relay protection device does not need to be matched with the motor starting current, and the sensitivity and the quick-action performance of the current quick-break protection are improved essentially;
2. the novel technical principle is eliminated from the traditional setting calculation method, so that the setting difficulty of the current quick-break protection setting value of the relay protection device is greatly reduced;
3. the relay protection device automatically measures the electric quantity of the protected motor, automatically completes calculation, automatically sets the fixed value of the device, and reduces setting errors caused by human factors.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. Wherein:
fig. 1 is a block diagram of an apparatus according to an embodiment 1, which does not need a current quick-break protection method in cooperation with a motor starting current.
Fig. 2 is a hardware block diagram of a motor protection device according to embodiment 1, which does not need a current quick-break protection method in cooperation with a motor starting current.
Fig. 3 is a process flow of a motor protection device according to the embodiment 1, which does not need a current quick-break protection method in cooperation with a motor starting current.
Fig. 4 shows a motor protection device setting calculation personnel for a current quick-break protection method without matching with the motor starting current in embodiment 1, which completes setting calculation according to the motor factory parameters.
FIG. 5 is a schematic diagram showing the change rate of the motor starting current without the need of the current quick-break protection method according to embodiment 2
FIG. 6 is a schematic diagram of a short circuit current during a short circuit fault in example 2 of a current quick-break protection method without matching with the motor starting current
FIG. 7 is a graph showing the effect of the actual test on the change rate of the starting current of the microcomputer motor protection device without the current quick-break protection method matched with the starting current of the motor in embodiment 2
FIG. 8 is a schematic diagram of setting calculation of a current quick-break protection method without matching with the starting current of the motor in embodiment 2
Detailed Description
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present invention is not limited to the specific embodiments disclosed below.
Further, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic can be included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
Example 1
Referring to fig. 1 and 2, a first embodiment of the present invention provides a current quick-break protection method without matching with a motor starting current, including:
a current quick break protection without coordination with motor starting current, comprising the steps of:
1. the integral wiring of the motor and the protection device is shown in figure 1, the hardware block diagram of the motor protection device is shown in figure 2, and the program flow of the motor protection device is shown in figures 3 and 4. And a motor protection device fixed value setting calculator completes fixed value setting calculation according to the factory parameters of the motor, and then a field worker manually sets the fixed value of the motor protection device according to a fixed value setting notification sheet and rechecks the fixed value.
2. The motor is put into the power system to operate by the power switch of the motor on by the personnel of the motor using department, the electric quantity is automatically measured by the protection device, the effective value of the electric quantity in the starting process of the motor is measured and stored in data, and then the stored electric quantity is analyzed and calculated by the protection device to obtain the change rate of the starting current of the motor relative to time in the starting process.
3. The principle that the motor starting current transformation change rate is different from the fault current change rate to a certain extent is utilized, the relay protection device automatically completes the calculation and the sensitivity verification of the current quick-break protection fixed value, and the newly generated current quick-break protection fixed value is stored in a read-only memory EEPROM for the relay protection module program of the device to call.
And (3) finishing the setting calculation of the setting value according to the factory parameters of the motor by a setting calculator of the setting value of the motor protector according to the step (1), and then manually setting the setting value of the motor protector and rechecking the setting value by on-site personnel according to a setting notification sheet.
The rated power of the fixed-value motor of the setting protection device is set as rated voltage, the rated voltage is set as power factor, the mechanical efficiency is set as minimum breaking current in a current quick breaking protection zone, and the overall wiring mode of the system is shown in figure 1.
The general settings were as follows:
I dz ＝6Ie(A) (1)
t dz ＝1.2t qd (2)
the sensitivity coefficient of protection is:
requirement K m ≥1.2
For ease of understanding, the following description of the current snap-off protection settings will be given in terms of an example motor:
and (3) closing a motor power switch according to the step (2) to put the motor into a power system to operate, automatically measuring the electric quantity by a protection device, measuring and storing data of an effective value of the electric quantity in the starting process of the motor, analyzing and calculating the stored electric quantity by the protection device, and solving the change rate of the starting current of the motor relative to time in the starting process.
| I(A) | I 1 | I 2 | …… | I n |
| T(s) | t 1 | t 2 | …… | t n |
Wherein t is n-1 -t n ＝2ms
And (3) automatically completing calculation and sensitivity verification of the current quick-break protection fixed value by the relay protection device according to the step (3), and storing the newly generated current quick-break protection fixed value in a read-only memory EEPROM for the program call of a relay protection module of the device.
The key point of the invention is that the change rate of the starting current of the motor is obviously different from the change rate of the short-circuit fault current. Since the motor is an inductive device, the current cannot be suddenly changed, and when the switching-in system voltage starts, the current is a relatively gentle process, as shown in fig. 5.
Actual measurement of the starting current change rate according to (8)
And the current quick-break protection areas are all resistive conductors, and when a short-circuit fault occurs in the areas, the short-circuit current can rise sharply, and the fault current waveform is shown in figure 6.
From fig. 6, it can be seen that the short-circuit current period component increases sharply to 2 times the rated current within 0.01 seconds.
The comparison of the formula (9) and the formula (10) shows that the short-circuit current change rate reaches 66.7 times of the motor starting current change rate, and the recognition degree is extremely high.
The action equation of the relay protection device is designed by utilizing the characteristic as follows:
wherein: the current change rate action constant value is the current change rate reliable coefficient (5-10) for the current quick break protection, and the current change rate is the normal starting current change rate of the actually measured motor; the minimum change rate when short circuit occurs is set as a current quick-break protection set action value, a current quick-break protection reliability coefficient (1.2) is set as a rated current of the motor.
Example 2
Referring to fig. 4 to 8, in order to verify the beneficial effects of the present invention, a current quick-break protection method without matching with the starting current of the motor is scientifically demonstrated through economic benefit calculation and simulation experiments;
let us assume a rated power p=30kw, rated voltage U e =380V, power factor
Three-phase asynchronous motor with mechanical efficiency eta=85%, and minimum breaking current I in current quick breaking protection area d.min =460 (a), and the overall system connection is shown in fig. 1.
The current quick-break protection fixed value is set.
First, the rated current of its motor is calculated
Wherein I is e Rated current of motor in normal operation, P is rated power of motor, U e For the motor to operate at a nominal voltage,
The prior setting method is as follows (4-12) I e Selecting a current quick break protection setpoint here 6I is selected e The current quick-break protection current setting value is as follows:
I dz ＝6I e ＝6×60.94＝365.64(A) (5)
the current quick-break protection time setting is estimated by running experience:
t dz ＝1.2t qd ＝1.2×4＝4.8(s) (6)
the sensitivity coefficient of protection is:
according to the rule K m And the temperature is more than or equal to 1.2, which meets the requirements and can be put into use.
According to the power switch of the motor, the motor is put into the power system to operate, the protection device automatically measures the electric quantity, the effective value of the electric quantity in the starting process of the motor is measured and stored in data, and then the protection device analyzes and calculates the stored electric quantity to obtain the change rate of the starting current of the motor relative to time in the starting process.
| I(A) | I 1 | I 2 | ...... | I n |
| T(s) | t 1 | t 2 | ...... | t n |
Wherein t is n-1 -t n ＝2ms
And automatically completing the calculation and the sensitivity verification of the current quick-break protection fixed value according to the relay protection device, and storing the newly generated current quick-break protection fixed value in a read-only memory EEPROM for the program call of a relay protection module of the device.
The key point of the invention is that the change rate of the starting current of the motor is obviously different from the change rate of the short-circuit fault current. Since the motor is an inductive device, the current cannot be suddenly changed, and when the switching-in system voltage starts, the current is a relatively gentle process, as shown in fig. 5.
Actual measurement of the starting current change rate according to (8)
And the current quick-break protection areas are all resistive conductors, and when a short-circuit fault occurs in the areas, the short-circuit current can rise sharply, and the fault current waveform is shown in figure 6.
From FIG. 6, it can be seen that the short-circuit current period component i is within 0.01 seconds P And proliferate to 2 times the rated current.
Comparing equation (9) and equation (10) shows the short-circuit current change rate k dl.ROC Reaches the starting current k of the motor qd.ROC The change rate is 66.7 times, and the identification degree is extremely high.
The action equation of the relay protection device is designed by utilizing the characteristic as follows:
wherein: k (k) dz.ROC The current change rate action is fixed for the current quick break protection, k k.ROC For the current change rate reliability coefficient (taking 5-10), k sc.ROC The method is characterized in that the normal starting current change rate of the motor is actually measured; k (k) dl.ROC To minimize the rate of change when a short circuit occurs, I dz Setting action value, k for current quick break protection k Reliable protection for current quick breakCoefficient (1.2) I e Rated for the motor current.
The invention will now be described in detail with reference to the drawings and specific examples.
Assuming that a motor rated power P=30kw and rated voltage U are provided e =380V, power factor
Three-phase asynchronous motor with mechanical efficiency eta=85%, and minimum breaking current I in current quick breaking protection area d.min =460 (a), and the overall system connection is shown in fig. 1.
The current quick-break protection fixed value is set according to the method of the invention.
First, the rated current of its motor is calculated
Wherein I is e Rated current of motor in normal operation, P is rated power of motor, U e For the motor to operate at a nominal voltage,
The starting current change rate is actually tested by a microcomputer motor protection device (engineering application is that the cycle acquisition is 3 points, see figure 7)
Constant current change rate: k (k) dz.ROC ＝k k.ROC ×k sc.ROC
k dz.ROC ＝10×34＝340(A/s) (15)
K in the above k.ROC 10 is taken to ensure that measurement errors do not affect reliable blocking current snap-off protection.
According to formula (10), the theoretical change rate of the short-circuit current is
According to (15) k dz.ROC ＝10×34＝340(A/s)
Reliably satisfies (10) k dl.ROC ＞k dz.ROC Therefore, the motor current quick-break protection does not need to be matched with the effective value and the starting time of the starting current of the motor, and is directly matched with the rated current of the motor, and the following formula is adopted in consideration of avoiding the overcurrent of the motor.
The current quick-break protection fixed value can be calculated according to the requirement of the novel method:
I dz ＝K m ×I e ＝3×60.94＝182.82(A) (16)
t dz ＝0.1s
the sensitivity coefficient of the setting protection is as follows:
far more than 1.2, and meets the requirements. Setting calculation opinion figure 8
Accounting for current change rate blocking sensitivity conditions:
compared with the original empirical algorithm, the protection action sensitivity reaches 2.52 (see formula 17) which is 2 times of the protection sensitivity of 1.26 (see formula 7) of the original empirical algorithm, the action time of the protection device is 0.1 second, 4.7 seconds is improved compared with the original setting method, and the rejection rate caused by motor damage is greatly reduced.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
Claims (10)
1. A current quick-break protection method without matching with a motor starting current is characterized by comprising the following steps:
setting a motor current quick-break protection fixed value;
setting and calculating a fixed value of a motor protection device;
measuring and storing the effective value of the electric quantity in the starting process of the motor;
determining the change rate of the starting current of the motor relative to time in the starting process;
calculating a current quick-break protection fixed value and checking sensitivity;
and storing the generated current quick-break protection fixed value in a read-only memory EEPROM for the program call of the relay protection module of the device.
2. The method of protecting against rapid current interruption without coordination with motor starting current of claim 1, wherein: the protection method comprises a motor current quick-break protection fixed value setting technology;
the calculation, analysis and measurement of stored data of the electric quantity of the motor in operation;
determining the change rate of current with respect to time in the starting process;
the relay protection device automatically completes calculation and sensitivity verification of the current quick-break protection fixed value;
the current quick-break protection fixed value is saved by the EEPROM for the device program to call.
3. A method of protecting against rapid current interruption without coordination with motor starting current as recited in claim 2, wherein: the starting power supply measures and stores the effective value of the electric quantity through the voltage converter and the current transformer, and the effective value is filtered and transmitted to the multichannel A/D conversion module which can convert the current when the motor is started into time and transmit the time to the relay protection module program, and then the judging value of the fixed value and the sensitivity is determined according to the fixed value setting calculation mode of the motor protection device, and whether the power-off protection is carried out or not is screened and transmitted to the liquid crystal display and finally transmitted to the relay protection module.
4. The method of protecting against rapid current interruption without coordination with motor starting current of claim 1, wherein: the power-off protection technique comprises the following steps:
performing device operation when the current quick-break protection method judges that the current quick-break protection fixed value is not met;
when the current quick-break protection method judges that the current quick-break protection fixed value can be met, the optimized fixed value is obtained, and the transmission protection device calculates and judges whether the tripping requirement is met;
when the operation of the protection transmission device judges that the tripping requirement is met, immediately executing protection tripping;
and when the operation judgment of the protection transmission device does not meet the tripping requirement, entering a power continuous system to judge and circulate.
5. The method of protecting against rapid current interruption without coordination with motor starting current of claim 1, wherein: setting a fixed value of the protection method device and a calculation mode;
I dz ＝6I e (A)
t dz ＝1.2t qd
setting protection device I e Rated current of motor in normal operation, P is rated power of motor, U e For the motor to operate at a nominal voltage,
for motor power factor, η is mechanical efficiency, I dz Current quick-break protection current settingConstant value, t dz And setting the current quick-break protection time.
6. A method of protecting against rapid current interruption without coordination with motor starting current as recited in claim 2, wherein: a current change rate algorithm relative to time in the starting process;
t n-1 -t n ＝2ms
wherein I represents the parameter of the current in the starting process; t represents a time node in the power-on process. I 1 I 2 For the first and second current data size, t 1 t 2 Data is recorded for the first and second times, ms being expressed in milliseconds.
7. A method of protecting against rapid current interruption without coordination with motor starting current as recited in claims 1, 2 and 4, wherein: the power-off protection technology adopts a sensitivity algorithm
The sensitivity coefficient of protection is:
requirement K m And if the current rapid-break protection fixed value is more than or equal to 1.2, the original rapid-break protection fixed value can be maintained.
8. The method for protecting against rapid current interruption without coordination with motor starting current of claim 4, wherein said method for calculating a constant value for current interruption protection
I dz ＝K m ×I e
9. A method of protecting against rapid current interruption without coordination with motor starting current as recited in claims 5 and 6, wherein: the action equation of the relay protection device is designed as follows
Wherein: k (k) dz.ROC The current change rate action is fixed for the current quick break protection, k k.ROC For the current change rate reliability coefficient (taking 5-10), k sc.ROC The method is characterized in that the normal starting current change rate of the motor is actually measured; k (k) dl.ROC To minimize the rate of change when a short circuit occurs, I dz Setting action value, k for current quick break protection k For protecting the reliable coefficient (1.2) of current quick break, I e Rated for the motor current.
10. A method of protecting against rapid current interruption without coordination with motor starting current as recited in any one of claims 1, 2, 3, 4, 5, 6, 7 and 9, wherein: the time-specific conversion of the electric quantity effective value in the starting process of the motor can be carried out through the calculation of the current quick-break protection fixed value and the sensitivity verification, and the electric quantity effective value is stored in a read-only memory EEPROM for the program calling of a relay protection module of the device, so that whether the power-off protection is carried out or not can be accurately judged through various limits.
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