CN104993457A - Thermal power plant high-voltage variable frequency motor protection system - Google Patents
Thermal power plant high-voltage variable frequency motor protection system Download PDFInfo
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- CN104993457A CN104993457A CN201510429646.6A CN201510429646A CN104993457A CN 104993457 A CN104993457 A CN 104993457A CN 201510429646 A CN201510429646 A CN 201510429646A CN 104993457 A CN104993457 A CN 104993457A
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Abstract
The invention provides a thermal power plant high-voltage variable frequency motor protection system comprising a high voltage motor and a frequency converter connected to the high voltage motor. The frequency converter is connected to a factory high-voltage busbar through an incoming wire provided with an incoming wire switch QF. Power frequency bypasses are arranged under the frequency converter; one end of each power frequency bypass is connected to the high-voltage motor and the other end is connected to the incoming wire provided with the incoming wire switch QF. The power frequency bypasses are three groups of parallel circuits provided with bypass switches K3. The thermal power plant high-voltage variable frequency motor protection system has the advantages that the circuit structure is simple; during the operation of the high-voltage variable frequency motor, the reliability is stable and the utilization rate is high; the system can adapt to the power frequency mode operation or the variable frequency mode operation of the motor without manual interference.
Description
Technical field
The present invention designs thermal power plant's electric motor protecting field, is specially a kind of thermal power plants high-pressure frequency-conversion protection system for motor.
Background technology
Along with the requirement of national energy policy, energy-saving and emission-reduction launch in multiple industry as an important job, and at large-size thermal power plant, the reduction of station service power consumption rate is imperative.For the high-tension motor accounting for the station service overwhelming majority, the important technique measure of energy-saving field is exactly the application of High-voltage Frequency Conversion Technology.Along with the development of power electronic technology, the particularly development of domestic frequency converter producer, frequency converter price is more and more lower, frequency converter is obtained in power plant and applies more and more widely.Current new power plant construction, Important Auxiliary equipment, as blower fan, water pump etc., generally all requires to consider that configuration frequency converter drags; Increasing built power plant is carrying out or is completing the transformation that high-tension motor adopts frequency converter.After high-tension motor adopts frequency converter to drag, how motor protection configures guarantee unit safety is run reliably, becomes power plant, problem that designing institute, protection producer extremely pay close attention to.
High-voltage frequency conversion and speed-adjusting: in thermal power plant, the power consumption such as boiler induced-draft fan, forced draft fan, steam turbine electrically driven feed pump, condensate pump are large, and these water pumps and landscape place system need frequent and that amplitude is larger Flow-rate adjustment usually simultaneously.Conventional flow amount adjustment method be adjustment these system pipelines in air door or control valve opening.As long as these air doors or adjuster valve are not standard-sized sheets, the power that motor consumes is converted into regard to some the idle work overcoming these air doors or adjuster valve resistance.If air door or adjuster valve standard-sized sheet, by regulating electromotor velocity to regulate output power of motor, thus regulating fluid flow, just can realize the optimization of motor efficiency.
Existing general inverter motor relaying configuration has: motor protection measure and control device, motor differential protection (configuring with upper motor for 2000kW), tranformer protection measure and control device.The throwing that motor protecting device and protection equipment for transformer carry out function by by-pass switch is moved back: namely by-pass switch disconnects, and is now frequency converter drive motor mode, and protection equipment for transformer drops into, and motor protecting device and motor differential protection exit; When by-pass switch closes, be now the direct drive motor of common frequency power network, motor protecting device and motor differential protection drop into, and protection equipment for transformer exits.Mainly there is two problems in this kind of relaying configuration mode: for the motor of more than 2000kW, and regulations stipulate needs to configure differential protection, and therefore, in frequency converter drive motor situation, motor differential protection exits, and the reliability of protection is affected; Any time, protection equipment for transformer, motor protecting device only have one to come into operation, and reduce the service efficiency of device.
Therefore, change the protection system of existing motor, the reliability making it protect is more stable, and greatly improves the high-pressure frequency-conversion protection system for motor of service efficiency, has been a urgent problem.
Summary of the invention
In order to overcome above-mentioned deficiency of the prior art, the invention provides a kind of circuit structure simple, and at high-pressure frequency-conversion motor in running, can reliability be realized more stable, and the thermal power plant high-pressure frequency-conversion protection system for motor that service efficiency is high.
The object of the present invention is achieved like this:
Thermal power plants high-pressure frequency-conversion protection system for motor, comprises high-tension motor, the frequency converter be connected with high-tension motor, and frequency converter connects station-service high voltage bus by the inlet wire being provided with service entrance switch QF; The below of described frequency converter is provided with power frequency bypass, and described power frequency bypass one end connects high-tension motor, and the other end is connected with the inlet wire at service entrance switch QF place;
Described power frequency bypass is three groups of circuit with by-pass switch K3 be set up in parallel;
Described frequency converter comprises rectifier transformer and control cubicle, protection system for motor adopts differential assurance device, the electric current of described differential protection is provided with 3 groups of CT, is namely arranged on the CT2 and neutral side CT3 that increase above motor below the CT1 of switch-side, frequency converter and the power frequency by-pass switch contact simultaneously introduced;
Described CT2 is installed in frequency-charger cabinet, and be the electric current under same frequency with CT3, the two forms differential protection;
The guard method of described thermal power plants high-pressure frequency-conversion protection system for motor is:
When motor is run by power frequency bypass, now by station service mesohigh bus 10kV power-frequency voltage direct drive motor, the object of protection of service entrance switch QF place protective device is switch outlet and motor body; Now the requirement configuration motor protection of conveniently motor protection, has differential protection requirement, configuration motor differential protection;
When by-pass switch K3 disconnects, motor is dragged by frequency converter, the object of protection of service entrance switch QF place protective device is switch outlet and frequency converter, and because frequency converter comprises rectifier transformer and control cubicle, namely the object of protection of service entrance switch QF place protective device is switch outlet and rectifier transformer; Now motor becomes the load of the high voltage converter after isolating with station service bus, and thus the protection of motor is realized by the controller of high voltage frequency conversion system.
positive beneficial effect:the present invention is that circuit structure is simple; and at high-pressure frequency-conversion motor in running, can realize reliability more stable, service efficiency is high; can the operation of adaptive electric motor power frequency or conversion system, without the need to thinking the thermal power plant high-pressure frequency-conversion protection system for motor of intervening.
Accompanying drawing explanation
Fig. 1 is structural representation of the present invention;
Fig. 2 is protection act logic diagram one;
Fig. 3 is the operation curve figure of biased differential protection;
Fig. 4 is protection act logic diagram two.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described further:
As shown in Figure 1, thermal power plants high-pressure frequency-conversion protection system for motor, comprises high-tension motor, the frequency converter be connected with high-tension motor, and frequency converter connects station-service high voltage bus by the inlet wire being provided with service entrance switch QF; The below of described frequency converter is provided with power frequency bypass, and described power frequency bypass one end connects high-tension motor, and the other end is connected with the inlet wire at service entrance switch QF place;
Described power frequency bypass is three groups of circuit with by-pass switch K3 be set up in parallel;
Described frequency converter comprises rectifier transformer and control cubicle, protection system for motor adopts differential assurance device, the electric current of described differential protection is provided with 3 groups of CT, is namely arranged on the CT2 and neutral side CT3 that increase above motor below the CT1 of switch-side, frequency converter and the power frequency by-pass switch contact simultaneously introduced;
Described CT2 is installed in frequency-charger cabinet, and be the electric current under same frequency with CT3, the two forms differential protection;
The guard method of described thermal power plants high-pressure frequency-conversion protection system for motor is:
When motor is run by power frequency bypass, now by station service mesohigh bus 10kV power-frequency voltage direct drive motor, the object of protection of service entrance switch QF place protective device is switch outlet and motor body; Now the requirement configuration motor protection of conveniently motor protection, has differential protection requirement, configuration motor differential protection;
When by-pass switch K3 disconnects, motor is dragged by frequency converter, the object of protection of service entrance switch QF place protective device is switch outlet and frequency converter, and because frequency converter comprises rectifier transformer and control cubicle, namely the object of protection of service entrance switch QF place protective device is switch outlet and rectifier transformer; Now motor becomes the load of the high voltage converter after isolating with station service bus, and thus the protection of motor is realized by the controller of high voltage frequency conversion system.
When motor is run by bypass, now by station service mesohigh bus 10kV power-frequency voltage direct drive motor, the object of protection of service entrance switch QF place protective device is switch outlet and motor body.Therefore, now should the requirement configuration motor protection of conveniently motor protection, there is differential protection requirement, need configuration motor differential protection.
When by-pass switch K3 disconnects; when motor is dragged by frequency converter; the object of protection of service entrance switch QF place protective device is switch outlet and frequency converter; because frequency converter is generally made up of the part such as rectifier transformer, control cubicle, namely the object of protection of service entrance switch QF place protective device is switch outlet and rectifier transformer.Now motor becomes the load of the high voltage converter after isolating with station service bus, and thus the protection of motor should be realized by the controller of high voltage frequency conversion system.
1, inverter motor Differential Protection Theory
When using frequency converter drive motor, the reason that conventional motors differential protection cannot use is: motor machine end CT is that the power frequency of this two place of CT1 and motor neutral side CT and CT3 CT at Fig. 1 breaker in middle cabinet place is not identical.There is document to propose to adopt magnetic balance differential protection to realize, but there is Railway Project in reality:
1) motor that generation current factory uses all cannot provide the differential required neutral side cable of magnetic balance to draw substantially;
2) electric current that magnetic balance is differential is below frequency converter, non-power current, for Microcomputer Protection, under the definite value of adjusting according to power frequency 50Hz is not suitable for non-power frequency situation.
Because the both sides electric current of differential protection is necessary for electric current under same frequency, can consider below frequency converter, above motor, install one group of CT, i.e. CT2 additional, this group CT can be installed in frequency-charger cabinet, forms differential protection by CT2 and CT3 two groups of electric currents.
Conventional differential protection is that phasor is differential, and its principle is with fourier algorithm, calculates the real imaginary part of inflow and outflow electric current according to the sampled point of a cycle, then forms criterion by the mode that phasor compares after calculating the amplitude of differential current and stalling current, phase place.Due to the non-50Hz power frequency of electric current, therefore need when carrying out Fourier and calculating to ensure the correct of result of calculation by frequency-tracking, because no-voltage below frequency converter is introduced, therefore cannot be realized by conventional voltage-tracing Frequency Patterns.There is producer to propose to utilize current tracking frequency, but there is larger error due to current tracking frequency, easily cause the malfunction of protection, tripping, do not adopt in practice.For the sampling value difference adopted in differential protection, for channel sample all in Microcomputer Protection are the instantaneous value of electric current at synchronization: when protected equipment does not have horizontal internal fault, each sampled current value sum is zero; When there is internal fault, each sampled current value sum is non-vanishing.Sampling value differential protection utilizes sampled value electric current sum (also referred to as sampling value difference electric current) to form by certain operating criterion.
Compared with conventional phasor differential protection, the features such as sampling value difference has quick action, amount of calculation is lacked are breakthroughs in microcomputer differential protection field, in the protections such as mother is poor, transformer that oneself is applied to.Sampling value difference does not relate to fourier and calculates, and the harmonic wave that frequency converter brings also can not affect its computational accuracy, and therefore, to the high-pressure frequency-conversion motor working in 25 ~ 50Hz, its differential protection can utilize this algorithm realization completely.The input of differential protection electric current has 3 groups of CT, is respectively the CT2, the neutral side CT3 that increase above motor below switch-side CT1, frequency converter, introduces power frequency by-pass switch contact simultaneously.When by-pass switch junction closure, be now that conventional phasor is differential, adopt Fourier algorithm, differential current is CT1 and CT3 electric current; When by-pass switch contact disconnects, be now sampling value difference, adopt sampling value difference algorithm, differential current is CT2 and CT3 electric current.
2, inverter motor differential protection
The automatic identification of protected mode
By the protected mode of K3 position of the switch switching device shifter, when K3 closes, device is power frequency pattern, when K3 opens, is variable mode.Device by K3 switch co-bit contact or jump the automatic switchover that position contact realizes two kinds of protected modes:
1) when " co-bit " contact that K3 switch provides, this contact by " the motor mode switching " of hardwire introducing device open into, this open into for 1 time, under power frequency protection pattern; Open into for 0 time, under frequency conversion protected mode.
2) when " jumping position " contact that K3 switch provides, this contact by " the variable mode switching " of hardwire introducing device open into, this open into for 1 time, under frequency conversion protected mode; Open into for 0 time, under power frequency protection pattern." motor mode switching " and " variable mode switching " be device inside open into, device acquiescence provide " motor mode switching " open into, namely under default situations, " co-bit " contact of K3 switch please be access.If outside provides " jumping position " contact of K3 switch, can device open self-defined in be set to " variable mode switching ".
Unit protection function and principle
2.2.1 Differential Protection Theory
1) differential starting element
The differential quick-break of device and percentage differential adopt Sudden Changing Rate starting element and overcurrent starting element, when differential current is undergone mutation or the maximum of differential current is greater than corresponding overcurrent definite value, and starting element action broadening 10s, open starter relay.
2) differential current stalling current computing formula
Coexist according to Same Name of Ends the principle of side, carries out the calculating of differential current, be the vector of both sides electric current; Stalling current according to both sides current phasor and half calculate.
May be there is the inconsistent situation of no-load voltage ratio in motor both sides CT, utilize conversion to the coefficient of balance K of motor neutral side
ph1or K
ph2revise this impact.
Computing formula under power frequency situation
Differential current:
Stalling current:
Coefficient of balance:
Computing formula under frequency conversion situation
3) fast differential over current protection
Protection act logic diagram, as shown in Figure 2;
Protection act criterion
In formula, I
cdsd: fast differential over current protection operating current setting value (A)
4) biased differential protection
Device adopts tri linear percentage differential principle, and its operation curve is as shown in 3 figure, and the 3rd broken line slope is fixed as 1.Biased differential protection must motor not shut down state time, just now effectively.
Protection act logic diagram, as shown in Figure 4;
Protection act criterion
In formula, I
cdqd: biased differential protection operating current setting value (A)
I
e: motor running rated current two sub-value (A)
5) time delay CT broken string alarm function
Time delay CT breaks and differentiates that logic is: circuit either side three-phase current has a phase or biphase current to be less than 0.125 times of rated current, and other two-phase or a phase current are all greater than 0.2 times of rated current, then think that CT broken string occurs in this side.CT broken string time delay 2 seconds, sends CT broken string alarm signal, but any protection of not locking.
6) instantaneous CT breakage lock device function
CT broken string differentiates based on following hypothesis:
(1) CT broken string is not all mutually simultaneous;
(2) CT broken string is not simultaneous with fault.
Meet following arbitrary condition and do not carry out the differentiation of CT broken string:
(1) prestart side maximum phase current is less than 0.2Ie, then do not carry out this side CT broken string and differentiate;
(2) after starting, maximum phase current is greater than 1.2Ie;
(3) after starting, either side current ratio prestart increases;
Only after percentage differential element starts, just enter instantaneous CT broken string discriminating program, this also prevents the mistake locking that instantaneous CT breaks.
Certain side electric current meets following condition simultaneously and thinks that CT breaks:
(1) phase or biphase current is only had to be zero;
(2) other two-phase or a phase current equal with prestart electric current;
Dropped into or exit instantaneous CT to break lockable percentage differential by control word.
7) difference stream Threshold Crossing Alert
Device provides difference stream Threshold Crossing Alert function, detects that maximum differential electric current is greater than setting value, time delay 10s alarm, but not Blocking Differential Protection.
The present invention is that circuit structure is simple; and at high-pressure frequency-conversion motor in running, can realize reliability more stable, service efficiency is high; can the operation of adaptive electric motor power frequency or conversion system, without the need to thinking the thermal power plant high-pressure frequency-conversion protection system for motor of intervening.
Above case study on implementation is only for illustration of the preferred embodiment of the present invention; but the present invention is not limited to above-mentioned execution mode; in the ken that described exercising ordinary skill possesses; the any amendment done within the spirit and principles in the present invention, equivalent to substitute and improvement etc., the protection range of the application all should be considered as.
Claims (5)
1. thermal power plants high-pressure frequency-conversion protection system for motor, is characterized in that: comprise high-tension motor, the frequency converter be connected with high-tension motor, and frequency converter connects station-service high voltage bus by the inlet wire being provided with service entrance switch QF; The below of described frequency converter is provided with power frequency bypass, and described power frequency bypass one end connects high-tension motor, and the other end is connected with the inlet wire at service entrance switch QF place.
2. thermal power plants high-pressure frequency-conversion protection system for motor according to claim 1, is characterized in that: described power frequency bypass is three groups of circuit with by-pass switch K3 be set up in parallel.
3. thermal power plants high-pressure frequency-conversion protection system for motor according to claim 1; it is characterized in that: described frequency converter comprises rectifier transformer and control cubicle; protection system for motor adopts differential assurance device; the electric current of described differential protection is provided with 3 groups of CT, is namely arranged on the CT2 and neutral side CT3 that increase above motor below the CT1 of switch-side, frequency converter and the power frequency by-pass switch contact simultaneously introduced.
4. thermal power plants high-pressure frequency-conversion protection system for motor according to claim 3, is characterized in that: described CT2 is installed in frequency-charger cabinet, and be the electric current under same frequency with CT3, the two forms differential protection.
5. the guard method of thermal power plants high-pressure frequency-conversion protection system for motor as claimed in claim 1 is:
When motor is run by power frequency bypass, now by station service mesohigh bus 10kV power-frequency voltage direct drive motor, the object of protection of service entrance switch QF place protective device is switch outlet and motor body; Now the requirement configuration motor protection of conveniently motor protection, has differential protection requirement, configuration motor differential protection;
When by-pass switch K3 disconnects, motor is dragged by frequency converter, the object of protection of service entrance switch QF place protective device is switch outlet and frequency converter, and because frequency converter comprises rectifier transformer and control cubicle, namely the object of protection of service entrance switch QF place protective device is switch outlet and rectifier transformer; Now motor becomes the load of the high voltage converter after isolating with station service bus, and thus the protection of motor is realized by the controller of high voltage frequency conversion system.
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| CN201510429646.6A CN104993457A (en) | 2015-07-21 | 2015-07-21 | Thermal power plant high-voltage variable frequency motor protection system |
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| CN201510429646.6A CN104993457A (en) | 2015-07-21 | 2015-07-21 | Thermal power plant high-voltage variable frequency motor protection system |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106532648A (en) * | 2016-11-15 | 2017-03-22 | 国家电投集团河南电力有限公司技术信息中心 | Differential protection device and method for two mutual backup variable frequency motors |
| CN106704211A (en) * | 2015-11-18 | 2017-05-24 | 亿海天成(北京)科技有限公司 | Frequency change and energy conservation system of thermal power plant electric water feeding pump |
| CN106786385A (en) * | 2016-12-13 | 2017-05-31 | 南京国电南自电网自动化有限公司 | A kind of differential protecting method for being suitable for adjustable frequency motor |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106704211A (en) * | 2015-11-18 | 2017-05-24 | 亿海天成(北京)科技有限公司 | Frequency change and energy conservation system of thermal power plant electric water feeding pump |
| CN106532648A (en) * | 2016-11-15 | 2017-03-22 | 国家电投集团河南电力有限公司技术信息中心 | Differential protection device and method for two mutual backup variable frequency motors |
| CN106532648B (en) * | 2016-11-15 | 2019-07-02 | 国家电投集团河南电力有限公司技术信息中心 | A kind of differential protection and method of two mutual backup adjustable frequency motors |
| CN106786385A (en) * | 2016-12-13 | 2017-05-31 | 南京国电南自电网自动化有限公司 | A kind of differential protecting method for being suitable for adjustable frequency motor |
| CN106786385B (en) * | 2016-12-13 | 2019-01-18 | 南京国电南自电网自动化有限公司 | A kind of differential protecting method being suitable for adjustable frequency motor |
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