CN85108175A - Press the method for life loss protection motor overload - Google Patents

Abstract

" by the method for life loss protection motor overload " is a kind of method of finishing the electric equipment overload protection with electronic computer system; purpose is to develop to greatest extent the overload capacity of electric equipment; can be in order to protect the electric equipment that depends primarily on the insulating material operating temperature its useful life, as all kinds of motors and cable.During electric equipment overload to computer feed-in overload current information or temperature information; life loss amount β when computer then calculates electric equipment overload; if β meets or exceeds permission life loss amount (β), just send the overload action command, make the protection system action.Change the operation time limit that (β) value can change system.

Description

Press the method for life loss protection motor overload

The present invention relates to the method that an appliance computer system finishes the electric equipment overload protection.

The method of protection motor overload is more at present, and what domestic utilization was more general has:

1, adopts the bimetal thermal relay protection;

2, adopt GL series and time limit overcurrent relay protection;

3, adopt Analogical Electronics to protect, typical products is seen DW15 series air switch semiconductor release device;

4, adopt the temperature relay protection, temperature relay or temperature-sensing element are imbedded the motor hottest point.

More than these four kinds of modes all be that overload capacity with the specified temperature rise of motor restriction is the protection foundation except that 2.

Mitsubishi Electric Co. is developed into a kind of MS-K series magnetic starter that has electronic thermal relay in nineteen eighty-two, and it is to combine (seeing (day) " Mitsubishi Electric's skill newspaper " 1982, NO7 and 1983, NO1) by S-K Series AC Contactor and ET series electronic formula thermal relay.China publishes publication " low-voltage electrical apparatus " fifth phase nineteen eighty-three to be had and made brief of the introduction.ET series electronic formula thermal relay has adopted four microprocessor of monolithic, and more above-mentioned several protective devices have following obvious advantage:

1, adopted digital circuit, protective feature precision height, protection good reliability;

2, can have the kinds of protect function;

3, very wide Current Regulation scope is arranged.

But ET series electronic formula thermal relay also has significant drawback, is exactly that protective feature is undesirable.ET series electronic formula thermal relay has adopted specified time staged protective feature in protection during motor overload, with electric current as setting parameter.This protective feature is unfavorable for bringing into play the motor overload ability, and the influence that the overload that has taken place is caused does not have the accumulation effect of 1,3,4 these several overload protection methods as described above, and this has just influenced the validity of protection overload.

Purpose of the present invention:

1. utilize computer system protection to depend primarily on the electric equipment that insulating material moves temperature rise its useful life, as the overload of motor, generator, transformer, reactor, cable etc.;

2. develop the overload capacity of electric equipment to greatest extent;

3. obtain the inverse time protection characteristic curve that high accuracy, high-efficiency, operation time limit can be regulated arbitrarily;

4. digital circuit technique, the motor overload special protecting equipment with best protection performance are adopted in realization.

The present invention thes contents are as follows:

The hardware organization of computer system of the present invention has the structured flowchart shown in the figure (1) basically.

Behind motor overload analog signal (overload current or electric machine temperature rise) process signal transmitting and the processing unit, sample, through feed-in computer system behind the A/D conversion.Computer system is put (or curing) and is finished to having related parameter and control program to give before system works begins.Motor in the course of the work, the motor overload situation in the system monitoring of above-mentioned hardware organization, transships as motor, then computer carries out the life loss amount according to the overload signal of motor input by following formula and calculates:

β＝ ${\∫}_o^{\xi }$ Ae- (B)/(θ ₀+θ _X) dt……（1）

The life loss amount of β-motor overload in the formula;

The experiment coefficient of A-electrical machinery life depends on graded dielectric material, second ^-1;

The experiment coefficient of B-electrical machinery life depends on graded dielectric material, ° K;

θ ₀-ambient temperature, ° K;

θ _x-electric machine temperature rise, ° K or ℃;

e-2.7182818;

ξ-overload time, second.

In the formula (1)

The referential data of parameter A, B is as follows:

To the A class F insulation, A=5.308 * 10 ⁵Second ^-1;

B＝12642°K;

To the E class F insulation, A=22.895 second ^-1;

B＝9193.7°K。

If the life loss amount β during motor overload meets or exceeds the overload life loss amount (the overload life loss amount of adjusting) (β) of permission, just then computer system is sent the motor overload signal.Computer system is sent overload signal can three kinds of forms: the switching value that 1, acts on alarm or tripping relay; 2, feed back the analog quantity of carrying device in Reduction of Students' Study Load; 3, be used as the digital quantity of demonstration or other purpose.

Motor overload signal for sampling can be electric machine temperature rise θ _x, also can be current of electric I.Temperature sampling reliability height, and can prevent that motor from worsening because of cooling condition and failure and other reasons is damaged motor, but the optional equipment investment is high, and implement difficulty, and not as obtaining electric machine temperature rise θ by calculating again with current sample _xValue convenient.Electric machine temperature rise is to the overload delay of response of motor, not as current of electric is swift in response in addition.So adopt the scheme of current sample in the ordinary course of things, its result does not influence the usefulness of protection.Under demanding situation, adopt the way of the two combination, promptly with current sampling data as basis, with the means of temperature sampling as monitoring calculation.When the temperature rise of temperature sampling surpassed License Value, no matter motor overcurrent was denied, and life loss calculates and will not stop.

Calculate temperature rise θ by current sample _xFormula as follows:

${\theta }_{\mathrm{x\; i}}\mathrm{=［\theta }{}_e·\frac{{\mathrm{n\; +\; K}}^2{}_i{\mathrm{(1+\alpha \; \theta }}_{\mathrm{x\; i\; -\; 1}})}{\mathrm{n\; +\; 1}}{\mathrm{-\; \theta }}_{\mathrm{x\; i\; -\; 1}}\mathrm{］·(1-e}{}^{-\frac{\mathrm{△\; t}}{T}}\mathrm{)+}$

+θ _xi-1……（2）

In the following formula, θ _Xi-motor sampling temperature rise (or the sampling temperature rise of calculating), ℃;

θ _Xi-1The temperature rise of sampling-last time;

θ _eThe specified temperature rise of-motor, ℃;

The temperature coefficient of α-motor conductor material;

e-2.7182818;

The ratio of n-motor iron loss and copper loss;

T-the motor feels hot time constant, second;

The Δ t-sampling period, second;

K _iThe sampled value of-overcurrent multiple.

The protective feature curve of determining with (1), (2) formula is an anti-time limit characteristic curve.After surpassing the highest License Value, overcurrent multiple K also can utilize software to form the definite time protection characteristic.When the protection three phase electric machine, can utilize software to form multifunction protection characteristics such as single phasing definite time protection and the protection of anti-phase run timing limit.

The core concept of the method for protection motor overload of the present invention is the overload capacity that exchanges motor with minimum electrical machinery life loss amount for, and promptly the life loss amount of Yun Xuing is littler, and the motor overload ability is also little; Allow the electrical machinery life loss amount big, the motor overload ability is also big.In essence, allowing motor to do the short time operation above the specified temperature rise of motor exactly when overload moves until protection system.Setting value (β) span of life loss amount β is very big during motor overload, for example from 1 * 10 ^-4～1 * 10 ^-7, concrete value is decided on the machine operation situation.Result of study shows, when (β) value is 1,000,000/time, its overcurrent multiple-time response curve is similar to the protective feature curve (cold conditions) of bimetal thermal relay and above it.Transship and just lose one of electrical machinery life percentage 10,000 times, the life-span of this in fact harmless motor.

Compared with prior art; motor overload guard method proposed by the invention can be in the overload capacity that guarantees to develop to greatest extent under the motor prerequisite in useful life motor; and can provide very effective protection; also can provide effective protection to non-constant overload; and be of wide application; be applicable to various dutys, the protective feature curve has anti-time limit characteristic, and can change its time limit numerical value with the value difference of setting value (β).With relatively the seeing Table of other guard method (1).Adopt the motor of guard method protection of the present invention; when selecting capacity motor; can determine capacity motor by the highest operational efficiency of motor; life loss amount during again by motor overload is no more than License Value and checks capacity motor; this is especially suitable to the big motor of those load changes; owing to can press the preferred capacity motor of optimum operation efficient, this is to energy-conservation very favourable.

Table (1): " performance of different guard methods relatively "

The explanation of accompanying drawing drawing:

Figure (1), protection system hardware structure block diagram

Among the figure: 1, signal transmitting and processing unit;

2, sampling unit;

3, A/D conversion unit;

4, microprocessor system;

5, parameter is given and is put the unit;

6, program is given and is put the unit;

7, output circuit unit;

8, demonstration and print unit;

9, power supply.

The feasible method of figure (2), a kind of sample rate current direct currentization

Among the figure: I-motor overload current signal (interchange);

Ux-is for sampled voltage;

The 1-current transformer;

The 2-rectification circuit;

The 3-filter circuit;

The 4-potentiometer.

Implement the present invention two kinds of forms can be arranged: a kind of is to utilize the computer system that can make other purposes, and another kind is to aim at the electronic protection system that realizes the present invention and produce.

1, to the requirement of system hardware structure

Life loss amount during with overload is that the course of work of the computer protection system of setting value is exactly in fact to separate integral equation (1) on computers, obtains the process of upper limit of integral ξ.Getting Δ t is the sampling period, calculates the life loss amount Δ β i in the Δ ti time, and adds up the life loss amount sum β=∑ Δ β from i=1 to i=i, and (β) compares with setting value, just sends the overload action command if reach (β) value.To the protection system of protection separate unit motor, the sampling period is computing cycle just; To protecting the system of n platform motor simultaneously, n computing cycle is a sampling period.Guaranteeing to finish in a sampling period corresponding calculated necessarily requires computer to have enough computational speeds and sampling period to adapt.To overload signal is under the situation of AC signal, can not satisfy requirement to sample frequency as limited the sampling period because of the operational speed of a computer, and AC signal will be carried out the direct current processing, and to get its corresponding direct current signal be sampled input signal; Or input signal is handled to satisfy the requirement of computer to computing cycle with additive method.Figure (2) has provided a kind of feasible method of sampled signal current DCization.Should make it the numerical value that calculates into following formula by adjusting potentiometer by exchanging the converted direct voltage Ux of overload current signal:

Ux＝ (I)/(Ie) ·Ue ……（3）

In the formula, Ue-is input to the standard sample voltage (for example getting 1V) of computer, corresponding to the motor rated current;

Ie-motor rated current;

I-motor actual current.

When Ue=1V, Ux numerically promptly is overcurrent multiple K.(3) formula can be used as in the foundation of asking overcurrent multiple K with hardware.

In addition, computer involves more parameter and bigger number range in the life loss value process of calculating motor overload, therefore requires the numerical computations scope of computer to adapt with it.

2, the basic structure of software systems and program

Systematic error can be brought adverse effect to the system protection performance.The source of error of this protection system has three main aspects: 1 hardware error, i.e. system hardware error that operating accuracy own produces; 2. the degree of approximation of mathematical model and give the error that the accuracy of putting parameter causes; 3. protection system is under the continuous operation situation, with 1,2 two deviation accumulations that produced formed cumulative errors of getting up.Preceding two errors all can only influence the accuracy of the life loss amount of calculating; not influence of operate as normal to the whole protecting system; this is because the setting value of life loss amount β is artificial definite; itself there is no the requirement of precision; so the β value that computer is calculated only influences protection system operate time, and the system acting time there is no strict demand.But the 3rd error is the work that cumulative errors but can be destroyed system, makes it lose defencive function fully.Thereby when the software configuration of design system, prevent the formation of cumulative errors.When considering software configuration, 1. for preventing bigger cumulative errors appear in the computational process, only surpass License Value in overcurrent multiple K＞1(or temperature rise) after just begin loss amount mathematic(al) expectation, and calculate life loss evaluation work when not stopping this time overload after the beginning because of K in the sampling process＜1, have only when temperature rise drops to the life loss amount that License Value just stops this overload when following and calculate.2. for simplifying computational process, when the calculating of life loss amount is once transshipped in beginning, can establish motor and be in running under the specified temperature rise, and ambient temperature has been the highest License Value.

According to above consideration, the basic structure of software program is as follows:

00, starting up;

01, makes i=0, β=0, θ _Xi-1=θ _eΔ β=0;

02, overcurrent multiple Ki sampled value input;

03, Ki＞1? if carry out 04; If not, carry out 05;

04, Ki＞the highest License Value? if, output switching value, overcurrent relay action; If not, carry out 07;

05, i-1 〉=0? if carry out 06; If not, carry out 02;

06, temperature rise θ _Xi-1＞θ e? if carry out 07; If not, carry out 14;

07, takes out θ _Xi-1, calculate θ according to (2) formula _Xi;

08, ask Δ β,

Δβ＝Ae- (B)/(θ ₀+θ _xi) ·△t

09, asks ∑ Δ β, β=∑ Δ β;

10, β＞(β)? if carry out 13; If not, carry out 11;

11, counting i=i+1;

12, order. θ _Xi-1=θ _Xi, carry out 02;

13, send overload action command switching value, overload relay action;

14, overload frequency n=n+1;

15, calculate protection system action electrical machinery life loss amount β ' afterwards;

16, ask ∑ β=∑ (β+β ');

17, make i=0, β=0, θ _Xi-1=θ _e, Δ β=0;

18, carry out 02.

As having cut off current of electric after the protection system action, then the computational methods of β ' are as follows:

In the formula, t-∑ Δ t, electric machine temperature rise is by θ _XmaxReduce to θ _eTime, second;

θ _Xmax-motor overload maximum temperaturerise, θ _Xmax=θ _Xi;

θ _eThe specified temperature rise of-motor; T '-motor outage back time constant.

In the basic structure of above-mentioned software program, also can add the program that other add according to need of work, as demonstration, printing, current reversal protection, protection against single phasing, the energy-conservation automatic switchover of Y/ △, the calculating of load shedding controlled quentity controlled variable etc.

In fact, motor does not often transship when reaching specified operation temperature rise, therefore the life loss amount that in fact the electrical machinery life loss amount that calculates by the basic structure of above-mentioned software program takes place when being higher than motor overload far away needn't worry the useful life that the life loss amount of the repeatedly overload accumulative total of motor can the significantly sacrificing motor fully.The practical significance of the basic structure of above-mentioned software program is exactly to make the adjustable inverse time protection characteristic of time limit that adopts protective device of the present invention to obtain to have maximum feasible overload capacity.Use and to provide the body software program according to department of computer science's unified editing of being adopted when of the present invention and come into operation.

Claims (4)

1, the present invention is a kind of method that depends on the electric equipment overload of its operating temperature with the electronics computer system protection useful life basically, it is characterized in that the protective feature curve is an adjustable anti-time limit characteristic curve of time limit.

2, according to claim 1, protection system is that the life loss amount when calculating the protected object overload obtains inverse time protection characteristic.

3, according to claim 1,2; the overload signal that is input to protection system can be protected device current signal; it also can be protected device temperature signal; life loss amount β when protection system calculates overload according to overload signal; when β meets or exceeds when overload permission life loss amount (β); the protection system action, the time limit of action can the change by the numerical value of adjust (β).

4,, allow protected object when overload, to surpass its specified temperature rise operation and move until protection system according to claim 1.

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