CN1652423A - Digitallisation implementing method for ac motor heat overload protection - Google Patents

Abstract

The digital method includes following steps: after power on, protector calculates value 1 of formula expressed in the invention; collecting current value at side of electromotor and calculating positive sequence current and negative sequence current; determining whether positive sequence current is larger than 0.06 time of rated current at secondary side of current transformer, and determining states of electromotor: in starting state or in operating state or stop state; calculating formatted heat value in each state respectively; cumulating formatted heat value in each state; determining whether the cumulated value is larger than or equal to value 2 expressed in the invention to decide whether to stop electromotor; after stopping motor, cumulating formatted heat value continuously; determining whether formatted heat value is smaller than value 3 to decide whether to restart motor is allowed. The method reduces quantity of real time computation and required calculation speed.

Description

A kind of Digital Realization method of ac motor heat overload protection

Technical field:

The present invention relates to a kind of Digital Realization method to the motor heating overload protection.

Background technology:

In the implementation method of traditional motor heating overload protection; the method that calculating, judgement and the protection of thermal overload fault often adopt once sampling to calculate is once carried out; this method is very high to the sampling and the arithmetic speed requirement of motor protection equipment, and the computational methods of electric motor overheating amount are difficult to realize with digitizer.Guard method involved in the present invention adopt sampling repeatedly, calculate a form of degree n n heat, and the criterion parameter relevant with the form heat be placed on carry out Calculation Method before real-time sampling calculates.This method has significantly reduced the real-time amount of calculation of motor digital protection device, has reduced the requirement to motor digital protection device arithmetic speed, is suitable for digital device and realizes.

Summary of the invention:

In order to overcome existing motor heating overload protection method, provide a kind of sampling and arithmetic speed ac motor heat overload protection method less demanding, easy to use to protection equipment to the sampling of protection equipment and the defective that the arithmetic speed requirement is high, use is inconvenient.The step of this method is as follows: motor protecting device powers on 101; Calculate respectively

With

Value 104; Per blanking time, Δ t gathered the current value 102 of motor machine end by current transformer; Per blanking time m Δ t calculating motor forward-order current and negative-sequence current one time 103; Judge that forward-order current is whether greater than 0.06 times Current Transformer Secondary side load current value I _n105; The result is for being, judges then whether motor is operated in start-up time 107; The result of step 105 is for not, then according to the form calorie value 106 in motor stop state time in the counting period m Δ t; The result of step 107 is for being, then according to the form calorie value 108 in the motor start-up state computation time interval m Δ t; The result of step 107 is for not, then according to the form calorie value 109 in the motoring counting period time m Δ t; The result of step 108, step 109 and step 106 sends to the form calorie value that adds up (the form calorie value of each computing gained being added up, if the result is for negative, then with zero setting as a result) 110; Judge that form calorie value after adding up is whether more than or equal to having calculated Value 111; The result is not for, judges that then form calorie value after adding up is whether more than or equal to having calculated Value 112; The result then returns the initiating terminal of step 102 for not; The result of step 112 then reports to the police 114 by warning device for being, and returns the initiating terminal of step 102; The result of step 111 is for being then to make motor quit work 113; Per again blanking time, Δ t gathered the current value 115 of motor machine end by current transformer; Per blanking time m Δ t calculating motor forward-order current and negative-sequence current one time 116; Then according to the form calorie value 117 in motor stop state time in the counting period m Δ t; The form that adds up again calorie value 118; Judge that form calorie value after adding up is whether less than having calculated Value 119; Step 119 result then returns the initiating terminal of step 115 for not; Step 119 result then allows motor to restart 120 for being, and returns the initiating terminal of step 102.Guard method of the present invention is, sampling repeatedly, calculate a form of degree n n heat, and the form heat Calculation is simple, and the criterion parameter relevant with the form heat be placed on calculate before real-time sampling calculates.This method has significantly reduced the real-time amount of calculation of motor digital protection device; reduced requirement to motor digital protection device arithmetic speed; and in being judged, the heating of motor considered the influence of starting state, running status and stop state to the motor heating process; the overall process that therefore can truly reflect motor work heating all sidedly; being suitable for digital device realizes; 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 powers on 101; Calculate respectively With Value 104; Per blanking time, Δ t gathered the current value 102 of motor machine end by current transformer; Per blanking time m Δ t calculating motor forward-order current and negative-sequence current one time 103; Judge that forward-order current is whether greater than 0.06 times Current Transformer Secondary side load current value I _n105; The result is for being, judges then whether motor is operated in start-up time 107; The result of step 105 is for not, then according to the form calorie value 106 in motor stop state time in the counting period m Δ t; The result of step 107 is for being, then according to the form calorie value 108 in the motor start-up state computation time interval m Δ t; The result of step 107 is for not, then according to the form calorie value 109 in the motoring counting period time m Δ t; The result of step 108, step 109 and step 106 sends to the form calorie value that adds up (the form calorie value of each computing gained being added up, if the result is for negative, then with zero setting as a result) 110; Judge that form calorie value after adding up is whether more than or equal to having calculated Value 111; Step 111 result is not for, judges that then form calorie value after adding up is whether more than or equal to having calculated

Value 112; Step 112 result then returns the initiating terminal of step 102 for not; The result of step 112 then reports to the police 114 by warning device for being, and returns the initiating terminal of step 102; The result of step 111 is for being then to make motor quit work 113; Per again blanking time, Δ t gathered the current value 115 of motor machine end by current transformer; Per blanking time m Δ t calculating motor forward-order current and negative-sequence current one time 116; Then according to the form calorie value 117 in motor stop state time in the counting period m Δ t; The form that adds up again calorie value 118; Judge that form calorie value after adding up is whether less than having calculated Value 119; Step 119 result then returns the initiating terminal of step 115 for not; Step 119 result then allows motor to restart 120 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 105, as the Current Transformer Secondary side load current value I of forward-order current greater than 0.06 times _nThe time, 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; The form calorie value of the form calorie value of the form calorie value of step 108 calculating motor start-up course, step 109 calculating motor running and step 106 and step 117 calculating motor stop state will pass through forward-order current I ₁With negative-sequence current I ₂Equivalent current I _EqThe value thermal process of coming simulating motor:

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

In the formula, K1 is the forward-order current coefficient; K2 is the 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 finishing, startup (is in running) or stop state, 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.

(1) after motor protecting device powers on, carries out initialize routine, read user's set point, comprise motor machine end Current Transformer Secondary side load current value (motor protector load current value) I _n, forward-order current COEFFICIENT K 1, negative-sequence current COEFFICIENT K 2, heating time constant τ ₁, the heat radiation timeconstant ₂Deng; If the user does not set, then read the default value of above-mentioned each amount.Calculate then

1.05 ²I _n ²With

Value (value of m generally can between 2 to 20).In the formula, τ ₁Be heating time constant, the thermal time constant when promptly electronic motivation is in starting state and running status; τ ₂Be heat radiation time constant, the thermal time constant when promptly electronic motivation is in stop state.τ ₁And τ ₂When dispatching from the factory, motor just determines.Distinguish τ ₁And τ ₂Purpose, be in order accurately to distinguish the Different Effects of the different running statuses of motor to the heat history value.I _nIt is motor machine end Current Transformer Secondary side load current value.

(2) the motor protection Equipment Inspection is calculated as follows the form heat Q in time interval m Δ t when motor is in starting state and running status _j

$Q_j=I_{\mathrm{eqk}}^2-{1.05}^2{I}_n^2----\left(2\right)$

In the formula, I _Eqk-equivalent electric the flow valuve calculated according to the k time actual current of obtaining of sampling;

I _n-motor machine end Current Transformer Secondary side load current value.

With formula (1) substitution following formula, have

$Q_j=K1\×I_1^2+K2\×I_2^2-{1.05}^2{I}_n^2---\left(3\right)$

In the formula (3), the value of the used forward-order current COEFFICIENT K 1 of form of calculation heat is different when motor is in starting state with running status: motor is in starting state, K1=0.5; Motor is in running status, K1=1; I ₁, I ₂Be respectively forward-order current, the negative-sequence current of motor machine end.

(3) the protection Equipment Inspection is calculated as follows the form heat Q of motor in time interval m Δ t when motor is in stop state _n

$Q_n=\frac{{\mathrm{\τ}}_1}{{\mathrm{\τ}}_2}(I_{\mathrm{eqk}}^2-{1.05}^2{I}_n^2)----\left(4\right)$

In the formula,

Calculate.With formula (1) substitution following formula, have

$Q_n=\frac{{\mathrm{\τ}}_1}{{\mathrm{\τ}}_2}(K1\×I_1^2+K2\×I_2^2-{1.05}^2{I}_n^2)----\left(5\right)$

In the formula (5), motor is in stop state, K1=1.

(4) protection equipment adds up the form heat that calculates, if accumulated value then is changed to accumulated value zero for negative.Carrying out the thermal overload action by following formula then judges

$Q_j+Q_n\≥\frac{I_n^2{\mathrm{\τ}}_1}{\mathrm{m\Δt}}----\left(6\right)$

Promptly satisfy following formula, think that electrical motors arrives the thermal overload operating value.

Carry out the thermal overload alarm decision by following formula

$Q_j+Q_n\≥0.75\frac{I_n^2{\mathrm{\τ}}_1}{\mathrm{m\Δt}}----\left(7\right)$

Promptly satisfy following formula, think that electrical motors arrives the thermal overload alarming value.

(5) after the motor stall, can start twice principle continuously according to motor, before the each startup of motor, its heat accumulation value should be greater than 50% thermal tripping value.Therefore, after the thermal overload protection action, protective device still continues the form of calculation heat.Restart judgement by following formula then

$Q_j+Q_n<0.5\frac{I_n^2{\mathrm{\&tau;}}_1}{\mathrm{m\&Delta;t}}----\left(8\right)$

Promptly satisfy following formula, think that motor can restart.

Claims (2)

1, a kind of Digital Realization method of ac motor heat overload protection is characterized in that it finishes by following steps: motor protecting device power on (101); Calculate respectively

With

Value (104); Per blanking time, Δ t gathered the current value (102) of motor machine end by current transformer; Per blanking time m Δ t calculating motor forward-order current and negative-sequence current once (103); Judge that forward-order current is whether greater than 0.06 times Current Transformer Secondary side load current value I _n(105); The result judges then whether motor is operated in start-up time (107) for being; The result of step (105) is for not, then according to the form calorie value (106) in motor stop state time in the counting period m Δ t; The result of step (107) is for being, then according to the form calorie value (108) in the motor start-up state computation time interval m Δ t; The result of step (107) is for not, then according to the form calorie value (109) in the motoring counting period time m Δ t; The result of step (108), step (109) and step (106) sends to the form calorie value (110) that adds up; Judge that form calorie value after adding up is whether more than or equal to having calculated

Value (111); Step (111) result is not for, judges that then form calorie value after adding up is whether more than or equal to having calculated Value (112); Step (112) result then returns the initiating terminal of step (102) for not; The result of step (112) then reports to the police (114) by warning device for being, and returns the initiating terminal of step (102); The result of step (111) is for being, then makes motor quit work (113); Per again blanking time, Δ t gathered the current value (115) of motor machine end by current transformer; Per blanking time m Δ t calculating motor forward-order current and negative-sequence current once (116); Then according to the form calorie value (117) in motor stop state time in the counting period m Δ t; The form that adds up again calorie value (118); Judge that form calorie value after adding up is whether less than having calculated Value (119); Step (119) result then returns the initiating terminal of step (115) for not; Step (119) result then allows motor to restart (120) for being, and returns the initiating terminal of step (102).

2, the Digital Realization method of a kind of ac motor heat overload protection according to claim 1 when it is characterized in that motor protecting device detects motor and is in starting state and running status, is calculated as follows form heat Q _j

$Q_j=K1\&times;I_1^2+K2\&times;I_2^2-1.05^2{I}_n^2$

The protection Equipment Inspection is calculated as follows the form heat when motor is in stop state

$Q_j=\frac{{\mathrm{\&tau;}}_1}{{\mathrm{\&tau;}}_2}(K1\&times;I_1^2+K2\&times;I_2^2-1.05^2{I}_n^2)$