CN1622416A - AC motor thermal overload protection method - Google Patents

Abstract

The present invention discloses one kind of motor protecting method to avoid heat overload accident. The heat overload protecting method for AC motor includes the steps of: powering on the motor protector; acquiring the real-time current value in the motor end, calculating the positive sequence current and the negative sequence current, judging whether the positive sequence current is greater than 0.06 time the rated secondary side current of the current transformer and determining the motor state; calculating heat accumulation values of different states; accumulating the heat accumulation values of different states; calculating and displaying residual action time; judging whether the accumulated value is greater than or equal to 100 % to determine whether to stop the motor; further accumulating the heat accumulation value after stopping; and judging whether the accumulated value is greater than or equal to 50 % to determine whether to re-start the motor.

Description

A kind of ac motor heat overload protection method

Technical field:

The present invention relates to a kind of guard method to the motor heating overload fault.

Background technology:

In traditional motor heating overload protection method, detection, judgement and protection to thermal overload are often only carried out according to a kind of operating state of motor, judge according to the current value of motor start-up process that promptly or only the current value when perhaps only moving according to motor is judged; Do not consider the problem that starts once more after the motor stall, do not consider the difference of thermal time constant when motor is in different conditions yet, more show to remain operate time etc.Because the start-up course of motor, running and stop state are different to its heat effect; so only detect, calculate the electric current under a kind of operating state or use changeless thermal time constant all can not reflect the actual heating situation of motor all-sidedly and accurately; the user also can't predict thermal overload residue operate time, therefore use existing motor heating overload protection method protection motor to exist not meet motor actual operating mode, accuracy of judgement degree not high, use defective such as inconvenience.

Summary of the invention:

For overcome existing motor heating overload protection method accuracy of judgement degree not high, use inconvenient defective, a kind of accuracy of judgement degree height, ac motor heat overload protection method easy to use are provided.The step of this method is as follows: motor protecting device works on power 101; Gather the current value of motor machine end in real time by current transformer, per blanking time Δ t calculating motor machine end forward-order current and negative-sequence current one time 102, judge that forward-order current is whether greater than 0.06 times Current Transformer Secondary side load current value In 103; Step 103 result is for being, judges then whether motor is operated in start-up time 104; The result of step 103 is for not, then according to the heat history value 107 in motor stop state time in the counting period Δ t; The result of step 104 is for being, then according to the heat history value 105 in the motor start-up state computation Δ blanking time t; The result of step 104 is for not, then according to the heat history value 106 in time in the motoring counting period Δ t; The result of step 105, step 106 and step 107 sends to the heat history value that adds up (the heat history value of each computing gained being added up, if the result is for bearing then zero setting) 108; Calculate and show and remain operate time 109; Whether the heat history value after judgement adds up is more than or equal to 100%110; Step 110 result is not, and whether the heat history value after then judgement adds up is more than or equal to 75%111; The result of step 111 then reports to the police 112 by warning device for being, and returns the initiating terminal of step 102; The result of step 111 then returns the initiating terminal of step 102 for not; The result of step 110 is for being then to make motor quit work 113; Gather the current value of motor machine end more in real time by current transformer, per blanking time Δ t calculating motor machine end forward-order current and negative-sequence current one time 114; Then according to the heat history value in motor stop state time in the counting period Δ t (the heat history value that calculate this moment is for negative) 115; The heat history value that adds up again (results added that result that step 115 is calculated and step 108 calculate) 116; Whether the heat history value after judgement adds up is less than 50%118; Step 118 result then returns the initiating terminal of step 114 for not; Step 118 result then allows motor to restart 119 for being, and returns the initiating terminal of step 102.Guard method of the present invention has not only been considered start-up course but also considered running in the heating of motor is judged; also considered the influence of stop state to the motor heating process; and can show and remain operate time; the overall process that therefore can truly reflect motor work heating all sidedly; it is very accurate, easy to use to judge, has big promotional value.

Description of drawings:

Fig. 1 is the schematic flow sheet of the inventive method.

Embodiment:

Embodiment one: specify present embodiment below in conjunction with Fig. 1.The step of present embodiment is as follows: motor protecting device works on power 101; Gather the current value of motor machine end, the forward-order current of per Δ t blanking time (size of time value is at Millisecond) calculating motor machine end and negative-sequence current one time 102 in real time by current transformer; Judge that forward-order current is whether greater than 0.06 times Current Transformer Secondary side load current value In 103; Step 103 result is for being, judges then whether motor is operated in start-up time 104; The result of step 103 is for not, then according to the heat history value 107 in motor stop state time in the counting period Δ t; The result of step 104 is for being, then according to the heat history value 105 in the motor start-up state computation Δ blanking time t; The result of step 104 is for not, then according to the heat history value 106 in time in the motoring counting period Δ t; The result of step 105, step 106 and step 107 sends to the heat history value that adds up (the heat history value of each computing gained being added up, if the result is for bearing then zero setting) 108; Calculate and show and remain operate time 109; Whether the heat history value after judgement adds up is more than or equal to 100%110; Step 110 result is not, and whether the heat history value after then judgement adds up is more than or equal to 75%111; The result of step 111 then reports to the police 112 by warning device for being, and returns the initiating terminal of step 102; The result of step 111 then returns the initiating terminal of step 102 for not; The result of step 110 is for being then to make motor quit work 113; Gather the current value of motor machine end more in real time by current transformer, per blanking time Δ t calculating motor machine end forward-order current and negative-sequence current one time 114; Then according to the heat history value in motor stop state time in the counting period Δ t (the heat history value that calculate this moment is for negative) 115; The heat history value that adds up again (results added that result that step 115 is calculated and step 108 calculate) 116; Whether the heat history value after judgement adds up is less than 50%118; Step 118 result then returns the initiating terminal of step 114 for not; Step 118 result then allows motor to restart 119 for being, and returns the initiating terminal of step 102.The start-up time of motor, promptly motor can be measured with the method for measuring in advance from starting to the time span of normal operation, and this time span is deposited in the control circuit.In the process of step 104, when forward-order current during greater than 0.06 times Current Transformer Secondary side load current value In, start timer, utilize the timer timing, the timing time and the motor start-up time of timer are compared, if forward-order current is greater than 0.06 times Current Transformer Secondary side load current value, and the timing time of timer thinks then that less than the motor start-up time motor is in starting state at present; If forward-order current is greater than 0.06 times Current Transformer Secondary side load current value, and the timing time of timer thinks then that more than or equal to the motor start-up time motor is in running status, then stops the timer timing, and with the timer zero clearing; If forward-order current thinks then that less than 0.06 times Current Transformer Secondary side load current value motor is in stop state.In the process of step 115, according to the heat history value of time in stop state counting period Δ t, the heat history value that calculates is for negative.

Embodiment two: the difference of present embodiment and execution mode one is: the step of the heat history value of the heat history value of step 105 calculating motor start-up course, step 106 calculating motor normal course of operation and the heat history value of step 107 calculating motor stop state is as follows:

(1) calculates forward-order current I earlier ₁With negative-sequence current I ₂And equivalent current I _EqValue.Equivalent current I _EqValue draw by following formula:

$I_{\mathrm{eq}}=\sqrt{K1\×I_1^2+K2\×I_2^2}---\left(1\right)$

K1-forward-order current coefficient in the formula; K2-negative-sequence current coefficient.The value of K1 is decided by the running status of motor: K1=0.5 in the motor start-up process can make thermal overload protection escape the huge starting current of motor like this; After startup is finished, K1=1.Because the thermal effect of negative-sequence current far above forward-order current, so the value of K2 generally is taken as 3～10, is generally 6.

(2) the anti-time limit characteristic parametric t of calculating motor thermal overload again.T is drawn by following formula:

$t=\frac{\mathrm{\τ}}{{(I_{\mathrm{eq}}/I_n)}^2-{1.05}^2}---\left(2\right)$

The thermal time constant of τ-motor itself in the formula, this constant just determine that when motor dispatches from the factory when electronic motivation was in starting state and running status, τ got heating time constant τ ₁Calculate, when electronic motivation was in stop state, τ got the heat radiation timeconstant ₂Calculate, with the different running statuses of accurate differentiation motor Different Effects the heat history value; I _n-motor machine end Current Transformer Secondary side load current value.

(3) calculate interior heat history value Q ' of a time in sampling interval.Q ' is drawn by following formula:

$Q^{\′}=\frac{\mathrm{\Δt}}{t}--\left(3\right)$

Δ t-sampling time interval in the formula; T-anti-time limit characteristic parameter.And the heat history value that adds up is:

$Q=\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\frac{{\mathrm{\Δt}}_k}{t_k}\×100\%---\left(4\right)$

Δ t in the formula _k-sampling time interval; t _kK sampling instant of-Di be the anti-time limit characteristic parametric t of (2) motor heating overload of calculating by formula; N-is by the determined sampling time interval number of current sample number of times.

Embodiment three: the difference of present embodiment and execution mode one is: step 109 is calculated and is shown to remain in operate time and calculates residue Δ t operate time by following formula _Res(corresponding) with formula (4):

Δt _res＝(1-Q)t (5)

The I that the t-current time calculates in the formula _EqCorresponding anti-time limit characteristic parameter.So be provided with, the heat history value that can be given in motor under this current condition estimates to reach 100% in will how long, promptly motor will how long in generation thermal overload fault.If motor is in normal operating condition, then remain Δ t operate time _ResCan increase along with the increase of calculation times, this trend shows that motor the thermal overload fault can not take place when operate as normal.This uses the user is very easily.

Claims (4)

1, a kind of ac motor heat overload protection method is characterized in that it finishes by following steps: motor protecting device work on power (101); Gather the current value of motor machine end in real time by current transformer, per blanking time Δ t calculating motor machine end forward-order current and negative-sequence current once (102), judge that forward-order current is whether greater than 0.06 times Current Transformer Secondary side load current value In (103); Step (103) result judges then whether motor is operated in start-up time (104) for being; The result of step (103) is for not, then according to the heat history value (107) in motor stop state time in the counting period Δ t; The result of step (104) is for being, then according to the heat history value (105) in the motor start-up state computation Δ blanking time t; The result of step (104) is for not, then according to the heat history value (106) in time in the motoring counting period Δ t; The result of step (105), step (106) and step (107) sends to the heat history value (108) that adds up; Calculate and show and remain operate time (109); Whether the heat history value after judgement adds up is more than or equal to 100% (110); Step (110) result is not, and whether the heat history value after then judgement adds up is more than or equal to 75% (111); The result of step (111) then reports to the police (112) by warning device for being, and returns the initiating terminal of step (102); The result of step (111) then returns the initiating terminal of step (102) for not; The result of step (110) is for being, then makes motor quit work (113); Gather the current value of motor machine end more in real time by current transformer, per blanking time Δ t calculating motor machine end forward-order current and negative-sequence current once (114); Then according to the heat history value (115) in motor stop state time in the counting period Δ t; The heat history value that adds up again (116); Whether the heat history value after judgement adds up is less than 50% (118); Step (118) result then returns the initiating terminal of step (114) for not; Step (118) result then allows motor to restart (119) for being, and returns the initiating terminal of step (102).

2, a kind of ac motor heat overload protection method according to claim 1, it is characterized in that the step of heat history value of the heat history value of heat history value, step (106) calculating motor running of step (105) calculating motor start-up course and step (107) and step (115) calculating motor stop state is as follows: (one) calculates forward-order current I earlier ₁With negative-sequence current I ₂And equivalent current I _EqValue: $I_{\mathrm{eq}}=\sqrt{K1\×I_1^2+K2\×I_2^2};$ (2) again according to the actual residing operating state of motor, the anti-time limit characteristic parametric t of calculating motor thermal overload, $t=\frac{\mathrm{\τ}}{{(I_{\mathrm{eq}}/I_n)}^2-{1.05}^2};$ (3) pass through formula then $Q^{\′}=\frac{\mathrm{\Δt}}{t}$ Calculate the heat history value Q ' in the single time in sampling interval.

3, a kind of ac motor heat overload protection method according to claim 1 is characterized in that step (108) the heat history value that adds up passes through formula $Q=\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\frac{\mathrm{\Δ}{t}_k}{t_k}\×100\%$ Calculate;

4, a kind of ac motor heat overload protection method according to claim 1 is characterized in that step (109) is calculated and the demonstration residue is calculated residue Δ t operate time by following formula in operate time _Res: Δ t _Res=(1-Q) t.

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