JPS62293989A - Device for detecting secondary side imbalance of induction motor - Google Patents

Abstract

PURPOSE:To detect the imbalance on the secondary side, by taking out the primary current to detect its pulsation and by comparing it with the normal current. CONSTITUTION:A shunt 3 changes the current into a voltage signal and gives it to filters 4 and 7. The filter 4 removes pulsation frequency components. Out of the abovementioned voltage signal the pulsating voltage is takenby a maximum voltage detection circuit 5 and a minimum voltage detection circuit 6. These voltage is introduced into an arithmetic circuit 8 and is compared to 0.03 by a comparison circuit 9, where the voltage over this value only is outputted into a gate circuit 10. This is to prevent the malfunction by the fluctuation of supply voltage. The output of the gate circuit 10 is inputted to an alarm display circuit 11, so that the nonconformity is displayed.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Field of Industrial Application) The present invention relates to a detection device for secondary side unbalance of an induction motor.

(Prior art) Conventionally, secondary side imbalance of an induction motor can be detected by visually measuring the cycle of the pulsating current that appears on the primary side ammeter, or by checking the magnitude of fluctuations in the pulsating current or the motor This method uses vibration measurement to estimate rotor problems.

On the other hand, in patent publication No. 52-91123, only the pulsating component is extracted using a filter, this output is converted into pulses, and the number of erroneous pulses per unit time is counted and displayed to detect the secondary side unbalance of the induction motor. There is.

(Problems to be Solved by the Invention) If an induction motor has secondary side unbalance, that is, if the rotor bar or end ring is cracked or cut during operation of the induction motor, characteristics may deteriorate, abnormal vibration may occur, and proper operation may occur. The air gap cannot be ensured, leading to problems such as a gap between the stator and surface friction, which in the worst case may cause damage to the stator windings. On the other hand 1
This is also disadvantageous in that a pulsating current flows to the next side and has an adverse effect on the m source, so countermeasures must be taken immediately when unbalance occurs. In any case, it is impossible to accurately detect defects using conventional simple manual methods, and
! It is impossible to understand correctly without disassembling the IJ machine.

That is, conventionally, the pulsation period has been detected as described in Japanese Patent Publication No. 52-91123.

The present invention has been made in view of the above points, and an object of the present invention is to provide a secondary side unbalance device that quickly and reliably detects the secondary side unbalance of an induction motor.

[Structure of the invention]

(Means for solving the problem) In order to achieve this object, the present invention extracts the primary current of the induction motor and detects the presence or absence of pulsation in the primary current,
This is a secondary side unbalance detection device that detects secondary side unbalance by comparing it with the normal current. (Operation) It extracts the primary side current of the induction motor and detects the presence or absence of pulsation.

(Example) Next, an example of the present invention will be described. In Figure 1, 1
is a three-phase induction motor, and the motor primary current is taken out by a current transformer 2 installed on one phase of the primary sides m and sa, and is applied to a shunt 3 having a resistance value of RΩ. The shunt 3 converts the current into a voltage signal which is applied to the filters 4 and 7. The filter 4 removes the 2Sf component and takes out V=I・R. On the other hand, among the voltage signals of the shunt 3, Vmax=I raa
The pulsating voltages of x-R and Vmin=Imin-R are taken out by the maximum voltage detection circuit 5 and minimum voltage detection circuit 6, these voltages are input to the arithmetic circuit 8, and the output of is compared with 0.03 by the comparison circuit 9. Only when the value is greater than this value, it is input to the gate circuit 10 as an output. or.

Only the 2Sf component is extracted by the filter 7, and the gate circuit 1
Put it in 0. This is to prevent malfunctions due to fluctuations in power supply voltage, and it is sufficient to consider that the motor's slip S under normal load conditions should be 3% or less, and from this, the maximum pulsation frequency is about 4 or more. Therefore, in the case of secondary side unbalance, the pulsating frequency is one order of magnitude slower than the power supply frequency, so a highly accurate gate circuit is not required. Gate circuit 10
The output is input to the alarm display circuit 11 to display the malfunction.

FIG. 2 shows the primary current waveform when the secondary side of the induction motor is unbalanced. As can be seen from FIG. 2, due to the unbalanced secondary circuit of the induction motor, a current consisting of the power supply frequency f and the pulsating frequency 2·Sf flows on the primary side. Here S
is the slip of the motor at each load, and in Figure 2 it is 2Sf
is shown as f. Pulse for normal current (I)! It has been experimentally confirmed that the following equation holds true for the ratio of 21 J current.

I +nax -I min ■ ≧0.03 [Effects of the Invention] As described above, the present invention detects the secondary side imbalance by detecting the presence or absence of pulsation in the primary current of the induction motor.
Unlike conventional methods, this method is not ambiguous and can clearly detect the occurrence or non-occurrence of secondary side imbalance, and does not require work such as disassembling the motor. Moreover, since the detection can be performed automatically, the spread of an accident can be kept to a minimum, and it is also useful for investigating the cause when vibrations occur in the motor.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a secondary side unbalance detection device showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a primary current waveform of secondary side unbalance of an induction motor. 1...3-phase induction motor 2...Current transformer 3...
Shunter 4...Filter 5...Maximum voltage detection circuit 6...Minimum voltage detection circuit 710. Filter 8... Arithmetic circuit 9... Comparison circuit
10... Gate circuit 11... W hat display circuit f... Power supply frequency component f,... Pulsating frequency component I IIIax... Pulsating a current maximum value lm1n...
・Minimum pulsating current agent Patent attorney Noriyuki Chika Yudo Hirofumi Futamata

Claims (1)

[Claims] a signal forming device corresponding to the primary side current of an induction motor;
A voltage detection device obtains the output of this signal forming device and extracts the maximum and minimum values of the power supply frequency component, pulsation component, and the composite voltage of the signal, and the signal is input into an arithmetic circuit and the output is compared with a reference value. A secondary side unbalance detection device for an induction motor, comprising a comparison circuit and a gate circuit device operated by the output of the comparison circuit.