CN106786385A - A kind of differential protecting method for being suitable for adjustable frequency motor - Google Patents
A kind of differential protecting method for being suitable for adjustable frequency motor Download PDFInfo
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- CN106786385A CN106786385A CN201611143355.1A CN201611143355A CN106786385A CN 106786385 A CN106786385 A CN 106786385A CN 201611143355 A CN201611143355 A CN 201611143355A CN 106786385 A CN106786385 A CN 106786385A
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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
Abstract
The invention discloses a kind of differential protecting method for being suitable for adjustable frequency motor, it is combined with sampling value difference using the phasor based on frequency-tracking is differential, decides whether to send tripping operation outlet after both phase "AND".Sampled point is respectively provided with the generator terminal and neutral point of adjustable frequency motor, gather the instantaneous value of both sides electric current, the running frequency and real-time adjustment sample frequency of motor are detected by current tracking Frequency Patterns, keep constant per cycle sampling number, then the electric current phasor of both sides is calculated using difference half-wave fourier, obtain corresponding difference current and stalling current, differentiated according to certain acting characteristic, increase the sampling value difference not influenceed by frequency change simultaneously, so as to avoid, phasor during frequency discontinuity is differential to produce difference conductance to cause malfunction, improve the antijamming capability of differential protection.
Description
Technical field
Differential protection action logic the present invention relates to how to realize adjustable frequency motor in high voltage frequency conversion system, belongs to electricity
Force system relay protection field.
Background technology
The progressively implementation of policy such as break up the family with factory's net, surf the Net at a competitive price, reduction station service power consumption rate in power plant is imperative.Frequency conversion
Motor widely should be obtained with its excellent speed governing, starting and braking ability in the fan-type and load of the pumps in power plant
With.High Pressure Frequency Conversion Technical is carried out to Auxiliary Machinery of Power Plant, motor soft-starting can be realized, reduce motor starting current,
Reduce the impact to motor stator winding insulation layer and mechanical wear.Meanwhile, traditional mechanical flow restriction control mode economy
It is poor, frequency control is changed to, station service power consumption rate can be effectively reduced, improve system motors efficiency.
Relative to the economic benefit that Frequency Conversion Modification brings, it is ensured that the safe and reliable operation of subsidiary engine equipment is also power plant emphasis
The problem of concern.No matter the frequency converter of which kind of form, different degrees of harmonic voltage and electric current is produced in operation, make electronic
Machine runs under non-sinusoidal voltage, electric current.The problems such as frequency converter brings harmonic wave and heating to motor, to the long-term of equipment
Operation produces certain influence.Traditional motor differential protection is designed based on power frequency, power frequency after attached with frequency converters
Non- 50Hz, has to exit differential protection during converting operation, and the now protection of motor only relies upon the protection that frequency converter is carried
Function.According to the regulation of national relay protection code, the motor of 2MW and the above all should set differential protection, below 2MW and quick-break
The relatively low motor protection of protection sensitivity should also install differential protection.Therefore, need badly as the operation of adjustable frequency motor is provided soon
Fast reliable differential protection.
The content of the invention
It is an object of the present invention to provide difference when a kind of motor power frequency suitable for high voltage frequency conversion system and converting operation
Dynamic guard method, the method has action threshold high precision, quick action, strong antijamming capability, adaptive frequency change etc.
Advantage.
To achieve the above object, the technical solution used in the present invention is：
A kind of differential protecting method for being suitable for adjustable frequency motor, it is characterised in that it is comprised the steps of：
1) generator terminal and neutral point in the adjustable frequency motor are respectively provided with sampled point, gather the instantaneous value of both sides electric current,
The running frequency and real-time adjustment sample frequency of motor are detected by current tracking Frequency Patterns, to ensure the variable-frequency electric
It is constant per cycle sampling number when the running frequency of machine changes；
2) to step 1) in obtain sampled value carry out phasor calculation, obtain the difference current of the adjustable frequency motor both sides
And stalling current, judge whether to meet operation condition according to the predetermined differential decision procedure of phasor；Directly use synchronization simultaneously
The sampled value of adjustable frequency motor both sides electric current calculates instantaneous difference current and stalling current, according to predetermined sampled value
Differential decision procedure judges whether to meet operation condition；
3) when phasor is differential and sampling value difference meets corresponding operation condition simultaneously, last differential protection act in
Tripping operation outlet, outlet of otherwise tripping is failure to actuate.
Preferably, the step 1) in current tracking Frequency Patterns become in the running frequency of the adjustable frequency motor
Zero-crossing examination algorithm is used during change, the implementation of the zero-crossing examination algorithm is：Former point is adopted in choosing sampled data
Two points or former point sampled value of the sample value less than zero, current point sampled value more than or equal to zero are more than or equal to zero, current point sampling
It is worth minus two points, an oblique line is done by the two points, determine the exact time of zero crossing, calculates two neighboring zero passage
The time interval of point, obtains the half period of current signal, so as to quickly track the running frequency of the adjustable frequency motor.
Preferably, the step 1) in current tracking Frequency Patterns the adjustable frequency motor running frequency stabilization when
Using fourier Frequency Measurement Algorithm, the implementation of the fourier Frequency Measurement Algorithm is：Using variable-frequency electric described in all-wave fourier recursive calculation
The positive-sequence component of motivation generator terminal three-phase current, when frequency occurs Δ f changes, then forward-order current phasor can be produced in each cycle
The phase difference of 2 π Δs f, the variable quantity of frequency is obtained by the variable quantity of phase, so as to accurately measure the operation of the adjustable frequency motor
Frequency.
Preferably, the step 2) in the differential decision procedure of phasor be：By the adjustable frequency motor generator terminal and neutral point
Electric current calculate respective fundamental phasors with difference Half-cycle Fourier Algorithmfor, then obtain the phasor of both sides electric current and as differential electricity
Stream, phasor difference judge whether to meet operation condition as stalling current further according to phasor differential criterion.
Preferably, the difference Half-cycle Fourier Algorithmfor uses recursive form, and its expression formula is as follows：
Wherein, i (n) is current last samples value, and i (n-1) is the sampled value of former point, and i (n-N/2) is half week wavefront
Sampled value,It is fundamental current phasor that the half cycles sampled value based on current point is tried to achieve through difference half-wave fourier
Real part, imaginary part,It is fundamental current that the half cycles sampled value based on former point is tried to achieve through difference half-wave fourier
The real part of phasor, imaginary part.
Preferably, described phasor differential criterion uses ratio-restrained characteristic, to escape in starting process of motor or just
Out-of-balance current when often running, its expression formula is as follows：
Wherein,It is the fundamental phasors of motor generator terminal generator terminal electric current,It is the fundamental phasors of motor neutral point electric current,
IdsetIt is phasor differential action electric current threshold, KsetIt is phasor differential, ratiometric restraint coefficient.
Preferably, the step 2) in sampling value difference decision procedure be：Directly by synchronization motor generator terminal and
The instantaneous sampling value of neutral point current is differentiated according to sampling value difference criterion, if having S points to meet in continuous R sampled point
The criterion (R >=S) of setting, then sampling value difference meets operation condition：
Preferably, described sampling value difference criterion uses nonlinear braking characteristic, and its expression formula is as follows：
Wherein, imIt is the sampled value of motor generator terminal generator terminal electric current, inIt is the sampling of identical times when motor neutral point current
Value, k1It is sampling value difference stalling current threshold and the proportionality coefficient of phasor differential action electric current threshold, k2It is sampling value difference ratio
Rate restraint coefficient.
The beneficial effects of the invention are as follows：
The method realizes the quick tracking of frequency by zero-crossing examination algorithm, and frequency is realized by fourier Frequency Measurement Algorithm
Accurate measurement, can adapt to the running frequency variation characteristic of adjustable frequency motor, and differential protection is using the phasor based on frequency-tracking
The dual criterion that differential and sampling value difference is constituted is used as operation condition, and the difference Half-cycle Fourier Algorithmfor of the differential use of phasor is effective
Inhibit DC component harmony wave component, taken into account protection computational accuracy and responsiveness, while having sampling value difference
Strong antijamming capability, the advantage not influenceed by frequency change, fast and reliable protective effect is played to adjustable frequency motor conscientiously.
Brief description of the drawings
The present invention is described in more detail with reference to the accompanying drawings and detailed description.
Fig. 1 is the motor differential protection schematic diagram for being applied to high voltage frequency conversion system.
Fig. 2 is that adjustable frequency motor occurs the current waveform of single-phase fault in 25Hz.
Fig. 3 is that adjustable frequency motor occurs the current waveform of single-phase fault in 60Hz.
Specific embodiment
The operation of high-tension motor is not influenceed when being broken down in order to ensure frequency converter, Frequency Conversion Modification uses frequency converter substantially
The structure of processing frequency bypass.Shown in Fig. 1, high voltage frequency conversion system mainly includes phase-shifting transformer, frequency converter, the part of bypass cabinet three,
Wherein phase-shifting transformer plays a part of isolation of system, and power frequency supply is transformed into frequency converter the power supply of another frequency, bypass cabinet
For the switching of frequency conversion/power frequency operation mode.During motor power frequency operation, by-pass switch GD3 closures, GD1, GD2 disconnect；Frequency conversion
During operation, by-pass switch GD3 disconnects, GD1, GD2 closure.When considering motor power frequency operation, service entrance switch to motor generator terminal
Cable can be protected by original comprehensive protecting device for motor, gathered by CT1 and CT2 under power frequency or conversion system
Electric current constitute differential protection.
The electric current that motor generator terminal and neutral point are gathered quickly is tracked motor by the present invention by zero-crossing examination algorithm
Running frequency, real-time adjustment sample frequency, it is ensured that each cycle sampling number is constant.It is harmonic carcellation and the shadow of DC component
Ring, after motor is run with the frequency of stabilization, then divided with the positive sequence of all-wave fourier recursive calculation motor generator terminal three-phase current
Amount, releases the variable quantity of frequency, so as to accurately measure actual frequency by the variable quantity of phase.
The differential use difference Half-cycle Fourier Algorithmfor of phasor calculates the phasor of motor generator terminal and neutral point current, then obtains two
The difference current and stalling current of side electric current, judge whether to meet operation condition further according to certain ratio braking characteristic criterion；Adopt
The differential sampled value directly to synchronization motor generator terminal and neutral point current of sample value carries out differential differentiation, if continuous R
There are S points to meet sampling value difference criterion in point, then sampling value difference meets operation condition；Above-mentioned two condition meets simultaneously, poor
Dynamic protection exit action.
The differential protecting method is characterized in：Fast and accurately to cause that differential protection can adapt to electronic for frequency tracking algorithm
The wideband working characteristics of machine, it is ensured that fourier algorithm can be computed correctly electric current phasor；The differential use difference half-wave fourier of phasor is calculated
Method, restrained effectively DC component harmony wave component, have the advantages that to act threshold high precision and quick action, sampled value
It is differential not influenceed and strong antijamming capability by frequency change, both are combined, while rapidity is taken into account, greatly improve
The reliability of differential protection.
Simulation model is built, RTDS l-G simulation tests are carried out to the device using the differential protecting method.Fig. 2 is variable-frequency electric
There is the current waveform of single-phase fault under operating in 25Hz in machine, after there is about 45ms in failure, protection device excision failure.Fig. 3 institutes
Show, the time of failure removal is 35ms during 60Hz.Result of the test shows that differential protection can at different frequencies fast and reliablely
Cut off the short trouble of adjustable frequency motor.
Above-described embodiment only illustrates the technical scheme of invention, it is impossible to limit protection scope of the present invention with this, it is every according to
Technical scheme proposed by the present invention carries out equivalent or equivalent transformation, each falls within the scope of the present invention.
Claims (8)
1. a kind of differential protecting method for being suitable for adjustable frequency motor, it is characterised in that it is comprised the steps of：
1) generator terminal and neutral point in the adjustable frequency motor are respectively provided with sampled point, gather the instantaneous value of both sides electric current, pass through
The running frequency and real-time adjustment sample frequency of current tracking Frequency Patterns detection motor, to ensure the adjustable frequency motor
It is constant per cycle sampling number when running frequency changes；
2) to step 1) in obtain sampled value carry out phasor calculation, obtain the difference current and system of the adjustable frequency motor both sides
Streaming current, judges whether to meet operation condition according to the predetermined differential decision procedure of phasor；Simultaneously directly with described in synchronization
The sampled value of adjustable frequency motor both sides electric current calculates instantaneous difference current and stalling current, according to predetermined sampling value difference
Decision procedure judges whether to meet operation condition；
3) when phasor is differential and sampling value difference meets corresponding operation condition simultaneously, last differential protection is acted in tripping operation
Outlet, outlet of otherwise tripping is failure to actuate.
2. the differential protecting method for being suitable for adjustable frequency motor according to claim 1, it is characterised in that the step 1)
In current tracking Frequency Patterns when the running frequency of the adjustable frequency motor changes use zero-crossing examination algorithm, institute
The implementation for stating zero-crossing examination algorithm is：Former point sampled value is big less than zero, current point sampled value in choosing sampled data
In null two points or former point sampled value more than or equal to zero, minus two points of current point sampled value, by this two
Individual point does an oblique line, determines the exact time of zero crossing, calculates the time interval of two neighboring zero crossing, obtains current signal
Half period, so as to quickly track the running frequency of the adjustable frequency motor.
3. the differential protecting method for being suitable for adjustable frequency motor according to claim 1, it is characterised in that the step 1)
In current tracking Frequency Patterns the adjustable frequency motor running frequency stabilization when use fourier Frequency Measurement Algorithm, the fourier
The implementation of Frequency Measurement Algorithm is：Using the positive sequence point of adjustable frequency motor generator terminal three-phase current described in all-wave fourier recursive calculation
Amount, when frequency occurs Δ f changes, then forward-order current phasor can produce the phase difference of 2 π Δs f in each cycle, by the change of phase
Change measures the variable quantity of frequency, so as to accurately measure the running frequency of the adjustable frequency motor.
4. the differential protecting method for being suitable for adjustable frequency motor according to claim 1, it is characterised in that the step 2)
In the differential decision procedure of phasor be：By the electric current of the adjustable frequency motor generator terminal and neutral point difference Half-cycle Fourier Algorithmfor meter
Respective fundamental phasors are calculated, the phasor of both sides electric current is then obtained and as difference current, phasor difference as stalling current, then root
Judge whether to meet operation condition according to phasor differential criterion.
5. the differential protecting method for being suitable for adjustable frequency motor according to claim 4, it is characterised in that the difference half
Ripple fourier algorithm uses recursive form, and its expression formula is as follows：
Wherein, i (n) is current last samples value, and i (n-1) is the sampled value of former point, and i (n-N/2) is adopting for half week wavefront
Sample value,It is the reality of the fundamental current phasor that the half cycles sampled value based on current point is tried to achieve through difference half-wave fourier
Portion, imaginary part,It is fundamental current phasor that the half cycles sampled value based on former point is tried to achieve through difference half-wave fourier
Real part, imaginary part.
6. the differential protecting method for being suitable for adjustable frequency motor according to claim 4, it is characterised in that described phasor
Differential criterion uses ratio-restrained characteristic, the out-of-balance current to escape in starting process of motor or during normal operation, its table
It is as follows up to formula：
Wherein,It is the fundamental phasors of motor generator terminal generator terminal electric current,It is the fundamental phasors of motor neutral point electric current, Idset
It is phasor differential action electric current threshold, KsetIt is phasor differential, ratiometric restraint coefficient.
7. the described differential protecting method for being suitable for adjustable frequency motor is required according to right 1, it is characterised in that the step 2)
In sampling value difference decision procedure be：Directly by the instantaneous sampling value of synchronization motor generator terminal and neutral point current according to
Sampling value difference criterion is differentiated, if having S points to meet the criterion (R >=S) of setting, sampled value in continuous R sampled point
It is differential to meet operation condition.
8. the differential protecting method of adjustable frequency motor is suitable for according to claim 7, it is characterised in that described sampling value difference
Criterion uses nonlinear braking characteristic, and its expression formula is as follows：
Wherein, imIt is the sampled value of motor generator terminal generator terminal electric current, inIt is the sampled value of identical times when motor neutral point current,
k1It is sampling value difference stalling current threshold and the proportionality coefficient of phasor differential action electric current threshold, k2It is sampling value difference ratio
Restraint coefficient.
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| CN201611143355.1A CN106786385B (en) | 2016-12-13 | 2016-12-13 | A kind of differential protecting method being suitable for adjustable frequency motor |
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Cited By (3)
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| CN107181237A (en) * | 2017-07-07 | 2017-09-19 | 南京南瑞继保电气有限公司 | A kind of pump-storage generator Back To Back Startup Procedure differential protecting method and system |
| CN108092234A (en) * | 2017-12-28 | 2018-05-29 | 长园深瑞继保自动化有限公司 | Suitable for the differential protecting method and device of adjustable frequency motor |
| CN110120655A (en) * | 2018-12-28 | 2019-08-13 | 江苏金智科技股份有限公司 | A kind of frequency-tracking system and method for frequency converter back end current channel |
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Cited By (3)
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| CN107181237A (en) * | 2017-07-07 | 2017-09-19 | 南京南瑞继保电气有限公司 | A kind of pump-storage generator Back To Back Startup Procedure differential protecting method and system |
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| CN110120655A (en) * | 2018-12-28 | 2019-08-13 | 江苏金智科技股份有限公司 | A kind of frequency-tracking system and method for frequency converter back end current channel |
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| CN106786385B (en) | 2019-01-18 |
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