JPH01110886A - Abnormal operation preventing method for pump - Google Patents

Abstract

PURPOSE:To promote the improvement of reliability with less decision error by cutting off a driving current when an electric motor obtains a detection value of its input power not more than a predetermined abnormal operation condition value. CONSTITUTION:In a power detecting circuit 11, performing calculation containing a power factor being based on an input voltage value and active current value, a power value is obtained and given to a comparator circuit 12. Power in a racing condition or in an excessively small loaded condition is left as confirmed previously in the comparator circuit 12, and the critical power value of permissible limit is left as determined as the preset value. Comparing a detection power value, when it obtains not more than the critical power value, feeding a signal to a pump operation circuit 13, an electromagnetic relay 14 is excited cutting off a switch 7, and stopping an electric motor 1, a pump is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preventing abnormal operation of a pump driven by an electric motor.

[Conventional technology]

Abnormal operating states of the pump include idling state and underload operating state. The idling state is a state in which air is sucked into the pump and the load is almost zero, causing the pump to idle for a long time.The high-speed rotation can lead to accidents with the seals and mechanical seals.In the underload operating state, the load is small and the flow rate is low. When the pump is small, the pump continues to operate in a state close to its shut-off state, and the fluid being handled inside the pump is unnecessarily disturbed, leading to overheating and accidents such as sealing. Driving conditions must be avoided.

In order to avoid this abnormal operation state, conventional methods have been to detect abnormalities by detecting the flow rate and pressure using a flow rate switch, pressure switch, etc. on the discharge side of the pump, or by detecting the water level in the water tank on the suction side using electrodes. It was detected and the pump was stopped to ensure safety.

However, with this method, it is difficult to install switches in submersible pumps, for example, and there is a risk of electric shock, so conventionally, the input current of the pump drive motor is detected and the predetermined settings are set. When the value falls below this value, it is determined that the pump is idling or underloaded, and the pump is stopped.

[Problem that the invention seeks to solve]

However, with these conventional methods, when there are large fluctuations in the power supply voltage, the error in determining whether or not an abnormal operating state is present is extremely large, making it difficult to make reliable determinations and ensure safety. be. This is especially true for iron loss,
Fixed losses such as copper loss are high (and C as a pump load)
D" is small even at maximum load, and there is not much difference in the input current value of the motor between idling and maximum load (for example, a pump driven by a small-output single-phase motor)
Significantly.

In other words, in Fig. 2, the current value Ill as the idling state value for determining that the motor is in the idling state is set with reference to point A in a state where the power supply voltage is high Vmax (for example, 115 V). The power supply voltage decreases and Vmin
(for example, 85 V), even if it is in the normal operating range, if the voltage drops below point B, the pump will stop, significantly reducing the normal operating range and reducing the This caused some trouble.

In addition, in the same figure), if the current value 1+t as the underload state value for determining that there is an underload state is set with the 0 point as the reference in the state of Vmax where the electric voltage is high,
If the power supply voltage drops and enters the Vain state,
Even at point D of the flow iQmax, which is the maximum load, the value falls below the set value IN, causing the pump to stop, causing a major problem in practical engineering.

In addition, even in the case of a pump driven by a three-phase electric motor, if an attempt is made to determine an abnormal state based on the current value, an error in the current setting value due to imbalance between the three phases will cause an error in the determination, causing a practical problem. Met.

The present invention solves the problems of the conventional methods as described above, and provides a method for preventing abnormal operation of a pump that accurately determines the idling state or underload operation state, has high reliability, and can widen the normal operation range. The purpose is to provide the following.

Means for Solving Problem C] The present invention provides a method for preventing abnormal operation of a pump driven by an electric motor, in which the input power of the motor is detected, and the detected power value indicates a predetermined abnormal operation state. This method of preventing abnormal operation of a pump is characterized in that the pump is determined to be in an abnormal operation state when the value falls below a state value, and the drive current to the electric motor is cut off.

[For production]

Since the present invention detects the abnormal operating state using the electric power value, the determination error is small and the reliability is high.

That is, the relationship between the load state and the power value is as shown in Figure 2 (al), and between "idling" and "suction fully closed" and "
Between "flow rate zero" and "maximum flow i1QmaxJ", the ratio of change in power value to change in load state is large, and accurate determination can be made.

The reason why the power value shows such a large rate of change, unlike the current value, is that the power P is: P = Vlcos φ ■ Effective voltage value ■ Effective current value cos φ Power factor Unlike the effective current value shown in Figure 2 (bl), it is greatly affected by the load, and the no-load (
This is due to the large change between the idling state) and the maximum load (Qmax state).

Since the power value shows such a tendency, in order to avoid the idling state (normal operation even with zero flow rate except in the idling state), the power value P as the idling state value, When set with reference to point E at high voltage v max, even if the power supply voltage decreases to Vmin, F
Since the "idling state" is determined and the pump is stopped in the state of point G corresponding to the point G, that is, in a state extremely close to the actual idling state, the judgment error is small and reliability is high, and Vm
Even in the case of "in", the area to the right of the G point can be set as the normal operating region, and the operating range is widened, which is advantageous in practice. (Only to the right of the point Q in the same figure in the conventional example) In addition, in order to avoid the underload condition (including the idling condition), the underload condition value should be set as shown in FIG. When the power value PH is set based on the H point at high voltage V max, even if the power supply voltage decreases to Vmin,
Since the "underload state" is determined and the pump is stopped at the state corresponding to three points, that is, the load state close to zero flow rate, the determination error is small, the reliability is high, and the Vmin
Even in the case of , the area to the right of the point can be set as the normal operating area, and the operating range becomes wider, which is advantageous in practice. (Conventional model has no operating range) Also, the magnitude of the load is different during idling (zero load) compared to when the suction is fully closed or when the flow rate is zero.
Since the power factor cos φ is different and the power value is also different, different levels of setting values can be selected for the idling state value pH indicating the idling state and the underload state value PM indicating the underload state. Control based on the following can be performed in parallel.

This usage can be determined in advance because it can be classified depending on the usage status of the pump load.

Furthermore, the above set values PR and pH are not necessarily the same as the high voltage Vm.
It does not have to be based on the E point of idling during ax and the H point of zero flow rate, but may be based on any other suitable point.

Furthermore, for a three-phase motor, by looking at the power for the three phases, it is possible to improve detection accuracy through total power monitoring without having to consider setting errors due to unbalance between each phase.

〔Example〕

Embodiments of the present invention will be described using the drawings.

In Figure 1, l is a single-phase electric motor that drives the pump, and 2
is a power plug, and a current circuit 3 for driving the electric motor 1.
4 is incorporated into the control device 5. In the control device 5, an MCB 6 and a switch 7 are inserted in series in a current circuit 3.4, and a transformer 8 is connected in parallel. One current circuit 4 has a Hall element type current transformer 9 incorporated therein.

The secondary side of the transformer 8 is connected to the power supply circuit 10, and
A voltage value is given to the power detection circuit 11. In the current transformer 9, the operating current and power factor are converted into magnetic flux density, r cos
It is applied to the power detection circuit 11 in the form of an active current of φ. The power detection circuit 11 performs calculations including the power factor based on the input voltage value and active current value to obtain a power value and provides it to the comparison circuit 12 . In the comparator circuit 12, the power in the idling state or underload state is checked in advance, and the permissible limit power value (idling state value or underload state value) is determined as a set value, and the detected power value and When the detected power value is below the limit power value, a signal is sent to the pump operation circuit 13, the electromagnetic relay 14 is energized, the switch 7 is cut off, the electric ml is stopped, and the pump is stopped. It has become.

As shown in FIG. 2, the set value for the comparator circuit 12 is selected by obtaining data on the load to be used in advance.

〔Effect of the invention〕

The present invention detects the input power of the electric motor and determines whether it is in an abnormal operating state such as a idling state or an underload state, so it is less affected by fluctuations in power supply voltage and idling is detected. Or □It is possible to provide a method for preventing abnormal operation of a pump, which reduces the error in detecting the protection level against underload, is highly reliable, and allows a wide range of normal operation, which has an extremely large practical effect. play.

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention, and FIG. 1 is a circuit diagram, FIG. 2 (a) is a graph of the relationship between flow rate and power, and FIG.
bl is a graph of the relationship between flow rate and current. )1...
Electric motor, 2...power plug, 3, 4...current circuit,
5... Control device, 6... MCB, 7... Switch,
8...Transformer, 9...Current transformer, 10...Power supply circuit, 11...Power detection circuit, 12...Comparison circuit, I
3... Pump operation circuit, 14... Electromagnetic relay. November 29, 1988 Director General of the Japan Patent Office Yoshi 1) Moon Takeshi 1. Indication of the case 1988 Patent Application No. 69031 2. Title of the invention Method for preventing abnormal operation of a pump 3. Make amendments. Relationship with the case Patent applicant name Ebara Electric Corporation (one other person) 4. Agent 5. Date of amendment order August 30, 1985 (dispatch) 6. Subject of amendment Brief Explanation Column 7, Contents of Amendment (1) Page 10, Lines 10 to 11 of the Specification [Figure 2 (a) is...'' was replaced with ``Figure 2 is a flow rate. "There is a graph regarding the flow rate, and part (a) shows the relationship between flow rate and electric power, and part (b) shows the relationship between flow rate and flow."

Claims (3)

[Claims] (1) In a method for preventing abnormal operation of a pump driven by an electric motor, the input power of the motor is detected, and when the detected electric power value falls below a predetermined abnormal operation state value indicating an abnormal operation state, the pump is activated. A method for preventing abnormal operation of a pump, comprising determining that the pump is in an abnormal operation state and cutting off drive current to the electric motor. (2) The method according to claim 1, wherein the predetermined abnormal operating state value is a slipping state value indicating a slipping state. (3) The method according to claim 1, wherein the predetermined abnormal operating state value is an underload state value indicating an underload state.