CN106786385B - A kind of differential protecting method being suitable for adjustable frequency motor - Google Patents
A kind of differential protecting method being suitable for adjustable frequency motor Download PDFInfo
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- CN106786385B CN106786385B CN201611143355.1A CN201611143355A CN106786385B CN 106786385 B CN106786385 B CN 106786385B CN 201611143355 A CN201611143355 A CN 201611143355A CN 106786385 B CN106786385 B CN 106786385B
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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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Abstract
The invention discloses a kind of differential protecting methods for being suitable for adjustable frequency motor, combine using the phasor based on frequency-tracking is differential with sampling value difference, decide whether to issue tripping outlet after the two phase "AND".Sampled point is respectively set in the generator terminal and neutral point of adjustable frequency motor, acquire the instantaneous value of two sides electric current, running frequency and real-time sampling rate adjusting by current tracking Frequency Patterns detection motor, keep every cycle sampling number constant, then the electric current phasor of two sides is calculated using difference half-wave fourier, find out corresponding difference current and stalling current, differentiated according to certain acting characteristic, increase the sampling value difference not influenced by frequency variation simultaneously, the poor conductance of the differential generation of phasor causes malfunction when to avoid frequency discontinuity, improve the anti-interference ability of differential protection.
Description
Technical field
The present invention relates to the differential protection action logics that adjustable frequency motor how is realized in high voltage frequency conversion system, belong to electricity
Force system relay protection field.
Background technique
As factory's net such as is broken up the family, surfs the Net at a competitive price at the gradually implementation of policies, it is imperative that power plant reduces station service power consumption rate.Frequency conversion
Motor is widely answered in the fan-type and load of the pumps in power plant with its excellent speed regulation, starting and braking ability
With.High Pressure Frequency Conversion Technical is carried out to Auxiliary Machinery of Power Plant, can be realized motor soft-starting, reduces motor starting current,
Reduce the impact and mechanical wear to motor stator winding insulation layer.Meanwhile traditional mechanical flow restriction control mode economy
It is poor, it is changed to frequency control, can be effectively reduced station service power consumption rate, improves system motors efficiency.
Relative to Frequency Conversion Modification bring economic benefit, guarantee 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 are generated in operation, is made electronic
Machine is run under non-sinusoidal voltage, electric current.The problems such as frequency converter brings harmonic wave and fever to motor, to the long-term of equipment
Operation generates certain influence.Traditional motor differential protection is designed based on power frequency, power frequency after attached with frequency converters
Non- 50Hz, when converting operation, have to exit differential protection, and the protection of motor at this time only relies upon the included protection of frequency converter
Function.According to the regulation of national relay protection regulation, the motor of 2MW or more should all set differential protection, 2MW or less and quick-break
The lower motor protection of protection sensitivity should also install differential protection.Therefore, it needs to provide fastly for the operation of adjustable frequency motor
The reliable differential protection of speed.
Summary of the invention
Difference when motor power frequency that it is an object of the present invention to provide a kind of suitable for high voltage frequency conversion system and converting operation
Dynamic guard method, this method have movement threshold precision height, quick action, strong antijamming capability, adaptive frequency variation etc.
Advantage.
To achieve the above object, the technical solution used in the present invention is:
A kind of differential protecting method being suitable for adjustable frequency motor, which is characterized in that it includes following steps:
1) sampled point is respectively set in the generator terminal and neutral point of the adjustable frequency motor, acquires the instantaneous value of two sides electric current,
Running frequency and real-time sampling rate adjusting by current tracking Frequency Patterns detection motor, to guarantee the variable-frequency electric
Every cycle sampling number is constant when the running frequency variation of machine；
2) phasor calculation is carried out to the sampled value obtained in step 1), finds out the difference current of the adjustable frequency motor two sides
And stalling current, judge whether to meet operation condition according to the differential decision procedure of scheduled phasor；Synchronization is directly used simultaneously
The sampled value of adjustable frequency motor two sides electric current calculates instantaneous difference current and stalling current, according to scheduled 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 movement in
Tripping outlet, otherwise tripping outlet are failure to actuate.
Preferably, the current tracking Frequency Patterns in the step 1) become in the running frequency of the adjustable frequency motor
Zero-crossing examination algorithm, the implementation of the zero-crossing examination algorithm are used when change are as follows: choose former point in sampled data and adopt
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, does an oblique line by the two points, determine the exact time of zero crossing, calculate two neighboring zero passage
The time interval of point, obtains the half period of current signal, to quickly track the running frequency of the adjustable frequency motor.
Preferably, the current tracking Frequency Patterns in the step 1) are when the running frequency of the adjustable frequency motor is stablized
Using fourier Frequency Measurement Algorithm, the implementation of the fourier Frequency Measurement Algorithm are as follows: using variable-frequency electric described in all-wave fourier recursive calculation
The positive-sequence component of motivation generator terminal three-phase current, when Δ f variation occurs for frequency, then forward-order current phasor can be generated in each cycle
The phase difference of 2 π Δ f, obtains the variable quantity of frequency by the variable quantity of phase, to accurately measure the operation of the adjustable frequency motor
Frequency.
Preferably, the differential decision procedure of phasor in the step 2) are as follows: by the adjustable frequency motor generator terminal and neutral point
Electric current calculate respective fundamental phasors with difference Half-cycle Fourier Algorithmfor, then find out the phasor of two 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 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,The fundamental current phasor acquired for the half cycles sampled value based on current point through difference half-wave fourier
Real part, imaginary part,The fundamental current acquired for the half cycles sampled value based on former point through difference half-wave fourier
The real part of phasor, imaginary part.
Preferably, the phasor differential criterion uses ratio-restrained characteristic, to escape in starting process of motor or just
Often out-of-balance current when operation, expression formula are as follows:
Wherein,For the fundamental phasors of motor generator terminal generator terminal electric current,For the fundamental phasors of motor neutral point electric current,
IdsetFor phasor differential action electric current threshold, KsetFor phasor differential, ratiometric restraint coefficient.
Preferably, the sampling value difference decision procedure in the step 2) are as follows: directly by synchronization motor generator terminal and
The instantaneous sampling value of neutral point current is differentiated according to sampling value difference criterion, if there is S point satisfaction in continuous R sampled point
The criterion (R >=S) of setting, then sampling value difference meets operation condition:
Preferably, the sampling value difference criterion uses nonlinear braking characteristic, and expression formula is as follows:
Wherein, imFor the sampled value of motor generator terminal generator terminal electric current, inFor the sampling of identical times when motor neutral point current
Value, k1For the proportionality coefficient of sampling value difference stalling current threshold and phasor differential action electric current threshold, k2For sampling value difference ratio
Rate restraint coefficient.
The beneficial effects of the present invention are:
This method realizes the quick tracking of frequency by zero-crossing examination algorithm, realizes frequency by fourier Frequency Measurement Algorithm
Accurate measurement, can adapt to the running frequency variation characteristic of adjustable frequency motor, and differential protection uses the phasor based on frequency-tracking
For the dual criterion that differential and sampling value difference is constituted as operation condition, the difference Half-cycle Fourier Algorithmfor of the differential use of phasor is effective
Ground inhibits DC component and harmonic component, has taken into account the computational accuracy and movement speed of protection, while having sampling value difference
Strong antijamming capability, the advantages of not influenced by frequency variation, fast and reliable protective effect is played to adjustable frequency motor conscientiously.
Detailed description of the invention
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 applied to high voltage frequency conversion system.
Fig. 2 is the current waveform that single-phase fault occurs in 25Hz for adjustable frequency motor.
Fig. 3 is the current waveform that single-phase fault occurs in 60Hz for adjustable frequency motor.
Specific embodiment
The operation of high-tension motor is not influenced when breaking 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, bypass cabinet three parts,
Wherein phase-shifting transformer plays the role of isolation of system, and power frequency supply is transformed into the power supply of another frequency, bypass cabinet by frequency converter
For the switching of frequency conversion/power frequency operation mode.When motor power frequency operation, by-pass switch GD3 closure, GD1, GD2 are disconnected；Frequency conversion
When operation, by-pass switch GD3 is disconnected, GD1, GD2 closure.When considering motor power frequency operation, incoming switch to motor generator terminal
Cable can be protected by original comprehensive protecting device for motor, acquired under power frequency or conversion system by CT1 and CT2
Electric current constitute differential protection.
The electric current that motor generator terminal and neutral point acquire quickly is tracked motor by zero-crossing examination algorithm by the present invention
Running frequency, real-time sampling rate adjusting guarantees that each cycle sampling number is constant.For harmonic carcellation and the shadow of DC component
It rings, divides after motor is with stable frequency operation, then with the positive sequence of all-wave fourier recursive calculation motor generator terminal three-phase current
Amount is released the variable quantity of frequency by the variable quantity of phase, to accurately measure actual frequency.
The differential phasor that motor generator terminal and neutral point current are calculated using difference Half-cycle Fourier Algorithmfor of phasor, then find out 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；It adopts
Sample value is differential directly to carry out differential differentiation to the sampled value of synchronization motor generator terminal and neutral point current, if continuous R
There is S point 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 movement.
The differential protecting method is characterized in: fast and accurately frequency tracking algorithm can adapt to differential protection electronic
The wideband working characteristics of machine guarantees that fourier algorithm can be computed correctly electric current phasor；Phasor is differential to be calculated using difference half-wave fourier
Method restrained effectively DC component and harmonic component, have the advantages that act threshold precision height and quick action, sampled value
It is differential not influenced and strong antijamming capability by frequency variation, the two is combined, while taking into account rapidity, is greatly improved
The reliability of differential protection.
Simulation model is built, carries out RTDS l-G simulation test to using the device of the differential protecting method.Fig. 2 is variable-frequency electric
Machine operates under 25Hz the current waveform that single-phase fault occurs, and after about 45ms occurs for failure, protective device cuts off failure.Fig. 3 institute
Show, the time of failure removal is 35ms when 60Hz.Test result shows that differential protection can at different frequencies fast and reliablely
Cut off the short trouble of adjustable frequency motor.
Above-described embodiment only illustrate invention technical solution, this does not limit the scope of protection of the present invention, it is all according to
Technical solution proposed by the present invention is equivalently replaced or equivalent transformation, falls within the scope of the present invention.
Claims (6)
1. a kind of differential protecting method for being suitable for adjustable frequency motor, which is characterized in that it includes following steps:
1) sampled point is respectively set in the generator terminal and neutral point of the adjustable frequency motor, acquires the instantaneous value of two sides electric current, passes through
Current tracking Frequency Patterns detect the running frequency of motor and real-time sampling rate adjusting, to guarantee the adjustable frequency motor
Every cycle sampling number is constant when running frequency changes；
2) phasor calculation is carried out to the sampled value obtained in step 1), finds out the difference current and system of the adjustable frequency motor two sides
Streaming current judges whether to meet operation condition according to the differential decision procedure of scheduled phasor；Simultaneously directly described in synchronization
The sampled value of adjustable frequency motor two sides electric current calculates instantaneous difference current and stalling current, according to scheduled 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
Outlet, otherwise tripping outlet are failure to actuate；
The differential decision procedure of phasor in the step 2) are as follows: by the electric current difference of the adjustable frequency motor generator terminal and neutral point
Half-cycle Fourier Algorithmfor calculates respective fundamental phasors, then finds out the phasor of two sides electric current and makees as difference current, phasor difference
For stalling current, judge whether to meet operation condition further according to phasor differential criterion；The difference Half-cycle Fourier Algorithmfor is used and is passed
Return form, 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,For the reality for the fundamental current phasor that the half cycles sampled value based on current point is acquired through difference half-wave fourier
Portion, imaginary part,The fundamental current phasor acquired for the half cycles sampled value based on former point through difference half-wave fourier
Real part, imaginary part, N be a cycle sampling number.
2. the differential protecting method according to claim 1 for being suitable for adjustable frequency motor, which is characterized 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
State the implementation of zero-crossing examination algorithm are as follows: it is big less than zero, current point sampled value to choose former point sampled value in sampled data
Be more than or equal to zero, minus two points of current point sampled value in null two points or former point sampled value, by this two
A 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, to quickly track the running frequency of the adjustable frequency motor.
3. the differential protecting method according to claim 1 for being suitable for adjustable frequency motor, which is characterized in that the step 1)
In current tracking Frequency Patterns the adjustable frequency motor running frequency stablize when use fourier Frequency Measurement Algorithm, the fourier
The implementation of Frequency Measurement Algorithm are as follows: using the positive sequence point of adjustable frequency motor generator terminal three-phase current described in all-wave fourier recursive calculation
Amount, when Δ f variation occurs for frequency, then forward-order current phasor can generate the phase difference of 2 π Δ f in each cycle, by the change of phase
Change the variable quantity for measuring frequency, to accurately measure the running frequency of the adjustable frequency motor.
4. the differential protecting method according to claim 1 for being suitable for adjustable frequency motor, which is characterized in that the phasor
Differential criterion uses ratio-restrained characteristic, out-of-balance current when escaping in starting process of motor or operate normally, table
It is as follows up to formula:
Wherein,For the fundamental phasors of motor generator terminal electric current,For the fundamental phasors of motor neutral point electric current, IdsetFor phase
Measure differential action electric current threshold, KsetFor phasor differential, ratiometric restraint coefficient.
5. the differential protecting method according to claim 4 for being suitable for adjustable frequency motor, which is characterized in that the step 2)
In sampling value difference decision procedure are as follows: directly by the instantaneous sampling value of synchronization motor generator terminal and neutral point current according to
Sampling value difference criterion is differentiated that, if having S point to meet the criterion of setting in continuous R sampled point, wherein R >=S, then sample
Value difference is dynamic to meet operation condition.
6. the differential protecting method according to claim 5 for being suitable for adjustable frequency motor, which is characterized in that the sampling
It is worth differential criterion and uses nonlinear braking characteristic, expression formula is as follows:
Wherein, imFor the sampled value of motor generator terminal electric current, inFor the sampled value of identical times when motor neutral point current, k1For
The proportionality coefficient of sampling value difference stalling current threshold and phasor differential action electric current threshold, k2For sampling value difference ratio brake
Coefficient.
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| CN107181237B (en) * | 2017-07-07 | 2018-11-13 | 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 |
| CN108092234B (en) * | 2017-12-28 | 2019-12-24 | 长园深瑞继保自动化有限公司 | Differential protection method and device suitable for variable frequency motor |
Citations (4)
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|---|---|---|---|---|
| CN101908753A (en) * | 2010-07-06 | 2010-12-08 | 北方联合电力有限责任公司 | Current differential protection method automatically adaptive to variable frequency motor |
| CN101976820A (en) * | 2010-08-31 | 2011-02-16 | 南京南瑞继保电气有限公司 | Processing method of protection sampling signals of variable-frequency electric motor protection device |
| CN104993457A (en) * | 2015-07-21 | 2015-10-21 | 大唐三门峡发电有限责任公司 | Thermal power plant high-voltage variable frequency motor protection system |
| CN204761361U (en) * | 2015-07-28 | 2015-11-11 | 大唐三门峡发电有限责任公司 | System for protection high -voltage frequency converters motor |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101908753A (en) * | 2010-07-06 | 2010-12-08 | 北方联合电力有限责任公司 | Current differential protection method automatically adaptive to variable frequency motor |
| CN101976820A (en) * | 2010-08-31 | 2011-02-16 | 南京南瑞继保电气有限公司 | Processing method of protection sampling signals of variable-frequency electric motor protection device |
| CN104993457A (en) * | 2015-07-21 | 2015-10-21 | 大唐三门峡发电有限责任公司 | Thermal power plant high-voltage variable frequency motor protection system |
| CN204761361U (en) * | 2015-07-28 | 2015-11-11 | 大唐三门峡发电有限责任公司 | System for protection high -voltage frequency converters motor |
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