JPS6160996B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is characterized by a method for accelerating a pump, in particular, in the case of a momentary power outage, the pump is not tripped, and when the pump continues to operate as soon as the power is restored, the rotational speed is increased step by step to the rotational speed at which it should be restored. The present invention relates to an acceleration method. Conventionally, when a pump is driven by an induction motor and the rotational speed of the motor is controlled by a Serbius controller, even a momentary power outage (for example, a very short power outage of 0.1 seconds or 0.5 seconds) can cause an electrical malfunction. As with long-term power outages, the pumps have tripped. However, if the pump is tripped every time there is a momentary power outage, it will take time to restore the pump to its original operating state, and this tends to take a long time, especially in long-distance water supply systems, resulting in various inconveniences. When a pump trips, it can take 30 minutes, an hour, or even an entire day to restore normal operation, causing serious problems with water supply systems, such as water outages in households. Therefore, recent new Servius control devices incorporate special electrical controls to prevent instantaneous power outages, so that the pumps continue to operate without tripping in the event of a momentary power outage. However, when a countermeasure against instantaneous power outages is adopted in the Cervius device for pump operation control, in addition to the electrical countermeasures in the Cerbius device itself, the sudden increase in pump rotational speed during re-acceleration upon power restoration causes Water hammer that occurs in water pipes is becoming a serious problem. This invention is characterized in that, as a method for increasing the rotational speed to a target value when the power is restored, the rotational speed is increased stepwise at certain time intervals, thereby simplifying the configuration of the apparatus for carrying out the method. It is inexpensive, has general versatility, and is capable of suppressing the pressure rise that occurs in the water pipe when power is restored within an allowable range. To explain the diagram, Figure 1 shows changes in rotational speed and pressure changes in water pipes for the conventional method, with time t plotted on the horizontal axis and time t plotted on the vertical axis.
The pressure P and rotational speed N are taken. Assume that when the pump is being operated at a rotational speed Na and a pressure Pa, a power outage occurs at time _t0 , power is restored at time _t1 , and operation continues. After the power failure occurred at time t ₀ , the pump speed began to decrease from point A, and when power was restored at t ₁ , it decreased to point B, and the speed reached Nb. The pressure also begins to decrease from point A' at time _t0 , and decreases to point B' at time _t1 when the power is restored, and the pressure has reached Pb. As soon as the power is restored at time _t1 , the rotational speed also begins to increase and reaches the return target value Nc at time _t2 . This state is represented by point C. (This return target value Nc is normally the operating speed Na before the power outage.) At this time, because the speed increases rapidly, the pressure inside the water pipe changes rapidly, generating a pressure Pmax that is much higher than during steady operation. and may create a dangerous situation. This invention recovers the target value Nc (normally
This is a pump acceleration method that makes it possible to suppress the water hammer phenomenon when power is restored by increasing the rotational speed stepwise at certain time intervals when raising the power to Na). The method of this invention will be explained with reference to FIG.
The horizontal axis represents time t, and the vertical axis represents pressure P and pump rotation speed N, respectively. Until a power outage occurred at time t ₀ , the operation was at rotational speed Na and pressure Pa, and the point
Assume that power is restored at time t ₁ after △T ₀ from t ₀ . During a power outage, both the rotation speed and pressure decrease, and the pressure decreases at time t ₁ .
Pb, the rotation speed is decreasing to Nb. If △T ₀ exceeds the predetermined maximum power outage time Tmax, the pump is tripped. (It is also possible to trip when the pressure or pump rotation speed falls below a predetermined value.) If the trip is not within △T ₀ or Tmax, the return target is set in the following three stages in the figure. Value Nc
(Usually, the speed Na before the power outage is restored). Between B and D in the first stage, at the time of power restoration _t1 , the first stage pump rotational speed set value _N1 is given to the Cerbius speed control device. As a result, the electric motor generates accelerating torque, and the pump rotation speed changes to Nb (B in the diagram) when the power is restored.
The rotational speed increases from point ) to N ₁ as shown by B to C, and thereafter the rotational speed N ₁ is maintained from time t ₁ to t ₂ after ΔT ₁ . Note that the pressure is maintained at _P1 . During the second stage between D and F, at time _t2 , the pump rotational speed setting value given to the Servius speed controller is switched to _N2 . This causes the electric motor to generate an accelerating torque, and the rotational speed of the pump increases from N ₁ to N ₂ (between D and E) and maintains the speed N ₂ from time t ₂ to t ₃ after ΔT ₂ . The pressure holds _P2 . During the third stage between F and G, at time _t3 , the return target value Nc (usually the rotation speed Na before the power outage) is given to the Cerbius speed control device, and the pump rotation speed increases to Nc. (Between F and G). The pressure then rises smoothly to the target value Pc. After point G, the pump resumes steady operation. In the figure, for convenience of explanation, the process is explained as three stages, but in reality, it can be carried out in the same way in any number of stages. The number of stages is the amount of increase in pump rotation speed at each stage △
It is determined from N and the Servius speed control range. Rotation speed setting value maintenance time △T and raising width △N for each stage
is not necessarily constant at all stages.
The rotational speed setting value maintenance time ΔT and the raising width ΔN are determined by taking pressure fluctuations due to the water hammer phenomenon into consideration. FIG. 3 conceptually shows an apparatus for carrying out the method of the present invention. This has a rotation speed setter and a rotation speed set value switching circuit added to the conventional Cervius device. In Figure 3, 1
is the water tank, 2 is the pump, 3 is the water pipe, 4 is the water destination,
5 is a pressure gauge, and 6 is a flow meter. The pump 2 is driven by an induction motor 8 via a coupling 7.
10 is a rotational speed setting value switching circuit that has a built-in timer and a comparator;
Contains Sa. Although Sa is not particularly shown in the figure, it is a rotational speed setting value given by a rotational speed manual setting device, flow rate, pressure control device, etc. 11 is a plurality of rotation speed setting devices 11', 11''...
11 ⁿ outputs speed setting signals S ₁ , ^. 13 is a thyristor phase control circuit;
14 is a thyristor, 15 is a circuit breaker, 16 is a DC reactor, and 17 is a silicon rectifier. 20 is a power supply bus, 21 is an inverter transformer, 22 is an instantaneous power failure detector, 23 is a power failure time detection timer, and 24 is a circuit breaker. Figure 4 shows the pump rotation speed N, pump rotation speed setting value S, and instantaneous power failure detection signal corresponding to each stage.
Showing the SQ time chart. To explain the present invention with reference to FIGS. 3 and 4, each rotation speed setting device 11', 11''... ¹¹ⁿ is set in advance to a rotation speed of _N1 to Nn, and as mentioned above, the rotation speed is set in advance to prevent a momentary power outage. The speed Nb that decreased during the power outage is smaller than N ₁ , and the target value Nc of the pump rotation speed that should be restored at the end of the power outage is
Set it to be larger than Nn. Also, Ni _-1 <Ni. In FIG. 4, as described above, the horizontal axis represents time, and the vertical axis represents pump rotational speed detection value R, rotational speed setting value SR, and ON/OFF of instantaneous power outage signal SQ, respectively. The pump is in steady operation at the speed Na until the time t ₀ when the power outage occurs. A rotation speed set value Sa (corresponding to the speed Na) from a flow rate, pressure control device, or manual setting device is provided to the rotation speed set value switching circuit 10. At this time, since no instantaneous power outage has occurred again, the output SR of the switching circuit 10 is the set value Sa.
is output as is. Therefore, the rotation speed Na set by the set value Sa is applied to the speed control circuit 12, while the rotation speed detection value R from the rotation speed detector 9 of the electric motor is added to the circuit 12, where SR and R are They are compared and a phase output P corresponding to the deviation is output. P is applied to the thyristor phase control circuit 13, and the output gate pulse GP is applied to the thyristor 14, thereby controlling the thyristor so that the pump rotation speed becomes Na corresponding to the set value Sa. When an instantaneous power outage occurs at time t ₀ , the instantaneous power outage detector 22 is activated, and when the instantaneous power outage detection signal SQ from there turns ON, the pump rotation speed changes due to the power loss at the same time and the power is restored after the power outage time △T ₀ . At time t ₁ , it has decreased to Nb. When the power outage time △T ₀ (t ₁ - t ₀ ) exceeds the preset maximum power outage time Tmax according to the power outage time detection timer 23, a trip signal St is output from the timer 23 and the circuit breaker 24 is turned off. Trip the pump. In the first stage when the power is restored from time t ₁ to _{t 2} in FIG. 4, the output signal SQ of the instantaneous power failure detector 22 turns OFF due to the restoration of power, and the output SR of the rotational speed set value switching circuit 10 changes to the rotational speed. The setting device 11' is switched to output _S1 . As a result, the output S ₁ of the setting device 11' (which is set to the first stage rotation speed N ₁ ) is applied to the speed control device 12, and the pump rotation speed increases from Nb to N ₁ . . Here, the rotation speed switching circuit 10 switches the setting device 1 during a preset time width △T ₁ (t ₁ to _{t 2} ).
Since a timer is built in to keep the output S ₁ at 1', the pump rotation speed is
After increasing to N ₁ , the rotational speed of N ₁ is maintained until time t ₂ . When the set time ΔT ₁ of the first stage has elapsed and the time t ₂ is reached, the second stage between t ₂ and t ₃ occurs, and the output SR of the switching circuit 12 changes from the setting device 1 due to the action of a timer etc.
1'' output S ₂ (set at speed N ₂ ), and the pump rotational speed increases from N ₁ to N _2. Here, as in the first stage, the switching circuit 10 switches the speed
△T ₂ with preset output S ₂ of 11″ corresponding to N ₂
(between t ₂ and t ₃ ). Thereafter, the speed is similarly increased every preset time interval up to the nth stage speed Nn. When the duration ΔTn of the nth stage (speed Nn) has elapsed, the switching circuit 10 outputs the set value Sa corresponding to the target value Nc after recovery (normally equal to the speed Na before the power outage). The pump is accelerated from speed Nn to Nc. As a result, the pump enters steady operation at the rotational speed Nc, and a series of acceleration controls according to the present invention at momentary stop and power restoration are completed. As mentioned above, the set values _N1 to ^Nn of the rotation speed setters 11' to 11n are set in advance, but the pump rotation speed Nb and The target value Nc after power restoration is Ni~
It may fall within the range of Nn. In such a case, if you take the trouble to reduce the speed from Nb to Ni and then proceed through the steps N ₁ →N ₂ ... → Nn → Nc, it will not be possible to smoothly accelerate the pump. Also, when Nc is less than Nn, it is not only pointless to raise the speed to Nn and then reduce the speed again, but it also hinders smooth operation. So Nb,
Even when Nc is within the range of N ₁ to Nn, the speed Nb at the time of power restoration is set as a method for smooth acceleration after power restoration.
Judging from the target value Nc after recovery, when accelerating from Nb to Nc, the rotation speed is
It is sufficient that the number of stages within the range of Nb to Nc does not elapse. The number of stages to be elapsed after power restoration may be determined based on the judgments shown in Tables 1 and 2. In Table 1, Ns is the pump rotation speed given to the first stage when power is restored after a momentary power outage. That is, as shown in Figure 4
If Nb is less than or equal to N ₁ , Ns becomes N ₁ , and N ₁ ≦Nb ＜
If N ₂ , then Ns becomes N ₂ . In other words, Ns is a set speed that is larger than Nb among N ₁ to Nn and is closest to Nb. Also, N _L in Table 2 refers to the speed at the last stage when accelerating in several stages before reaching the final speed Nc, and as shown in Figure 4, when Nc is greater than Nn, N _L is Nn, and if Nc is Nn _-1 <Nc≦Nn (that is, if Nc is between Nn _-1 and Nn), then N _L is
Nn _-1 . In other words, N _L is the set speed that is smaller than Nc and closest to Nc. Therefore, referring to Tables 1 and 2, suppose that N ₁ Nb<N ₂ and Nn _-1
<NcNn, then Ns=N ₂ , N _L =Nn _-1 , and each step passing between acceleration from Nb to Nc is Nb→
N ₂ →…→Nn _-1 →Nc. In Tables 1 and 2, in cases marked with *, that is, when the rate of decline Nb upon power restoration is greater than Nn, or when the target value Nc to be restored is smaller than _N1 , Nb is set directly without going through any steps. You can accelerate from to Nc. Also, if the difference between Nb and Nc is small, for example, Tables 1 and 2
In the case where N ₂ ≦Nb<N ₃ and N ₂ <Nc≦N ₃ , Ns=N ₃ and N _L =N ₂ , and the steps are Nb→N ₃ →N ₂ →Nc. But in this case, Nb→
Should be accelerated directly to Nc. Therefore, according to Tables 1 and 2, when Ns>N _L , the acceleration is directly accelerated from Nb to Nc without going through any steps. Although the explanation above is based on NcNb, if the target value Nc of the rotation speed to be restored upon power restoration is less than or equal to Nb (i.e.
Nc<Nb) cannot occur in normal control and is not a desirable control, but if it were possible, the process would be reversed to the above method, that is, Nb→
There is also a method of reducing the water hammer phenomenon during deceleration by decelerating in stages Nn→...N ₁ →Nc.

【table】

【table】 [Brief explanation of the drawing]

Fig. 1 is a chart showing the relationship between time, rotational speed, and pressure in a conventional pump acceleration method, Fig. 2 is a chart showing time, rotational speed, and pressure in the present invention, and Fig. 3 is a chart showing the relationship between time, rotational speed, and pressure in the conventional pump acceleration method. Fig. 3 is a chart showing the relationship between time, rotational speed, and pressure in the conventional pump acceleration method. The apparatus, Fig. 4 shows the time and rotation speed in this invention,
This is a chart showing the relationship between set values and instantaneous power failure signals. Explanation of symbols 1...Water tank, 2...Pump, 3...Water pipe, 4...Water destination, 5...Pressure gauge, 6...Flow meter, 7...
Coupling, 8... Induction motor, 9... Pump rotation speed detector, 10... Rotation speed set value switching circuit, 1
1... Rotation speed setting device, 12... Speed control circuit, 13
...Thyristor phase control circuit, 14...Thyristor,
15... Circuit breaker, 16... DC reactor, 17... Silicon rectifier, 20... Power bus,
21...Inverter transformer, 22...Momentary power failure detector, 23...Momentary power failure time detection timer, 24...Circuit breaker.

Claims (1)

[Claims] 1. When a rotation speed control device that controls the rotation speed of the pump using a stationary Servius device is used to continue operating the pump during a momentary power outage, it is possible to control the power outage time, the number of revolutions of the pump, or the discharge pressure. The amount of decrease is detected, and if it is greater than a preset value, the pump is tripped, and if it is less than that value, the rotation speed is set to the target after power is restored to prevent water hammer phenomenon that occurs in water pipelines. A pump acceleration method characterized by increasing the pump rotation speed stepwise at certain time intervals when increasing the pump rotation speed to a certain time interval. 2. The pump acceleration method according to claim 1, characterized in that the rotation speed of each stage is set by a plurality of rotation speed setters in order to increase the pump rotation speed in stages as described above. 3. When increasing the pump rotational speed in stages as described above, the speed of the first stage is the speed that is higher than and closest to the speed at the time of power restoration among the speeds of each stage. A method for accelerating a pump according to claim 1. 4. Claims characterized in that when the pump rotational speed is increased in stages as described above, the speed of the final stage is a speed that is smaller than the target value after power restoration and is closest to the target value. The pump acceleration method according to item 1.