JPS59115495A - Protective device for feed water pump - Google Patents

Abstract

PURPOSE:To prevent a feed water pump from overheating, by detecting a flow rate and a speed of rotation in the feed water pump, and performing the irreducible minimum of recirculating flow control, while checking a rise in the speed of rotation in time of said recirculating flow control or tripping the pump otherwise. CONSTITUTION:The output of a detector 8 for a speed of rotation in an output shaft of a hydraulic coupling 13 controlling the speed of rotation in a feed water pump 1 is converted into a minimum recirculating flow signal corresponding to the speed of rotation at that time in a flow setter 9 by way of a deviation operator 12 and impressed on a relay 10. On the other hand, as a feedback circuit, a signal out of the relay 10 is converted into the speed of rotation corresponding to a flow rate with a revolution operator 12, comparing it with the output of the detector 8, and when it comes to an expression of actual revolution > operation revolution, this signal is fed to a motor 14 and tripped. Next, when a pump speed is slowed down, a signal out of the deviation operator 12 is inputted into a control commander 16 and at this time the priority order of these signals is determined, transmitting this signal to a control drive 15, then the speed of rotation in the pump is slowed down to some extent whereby overheating and any damage are prevented.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a protection device for a water supply pump, and particularly to a protection device for a water supply pump suitable for preventing an increase in the rotational speed of the pump during recirculation flow rate control of the water supply pump. Regarding.

[Prior art]

Generally, when a water supply pump is in operation, if the pump discharge rate decreases excessively, most of the pump's power becomes heat, causing the water temperature inside the pump to rise rapidly, causing a seizure of the pump. Therefore, in order to prevent this, conventionally, as shown in Figure 1,
The flow rate of the pump is detected, and when the flow rate reaches a specified value, the recirculation valve (control valve) 3 is opened to protect the pump.

In addition, 1 is a water supply pump, 2 is a recirculation line, 3a is an actuator of a control valve, 4 is a booster pump, 5 is a flow rate detector, 6 is a flow rate transmitter, and 7 is a solenoid valve. However, as shown in Figure 2, in the method of
Since the minimum flow rate (a) at the rotation speed is determined and a certain point (b) on the square curve A is set as the set value, it is not possible to respond to the reduction of water supply fluctuations required by recent transformer plants. There is no situation.

It has also been considered that disturbances to the boiler side can be kept to a minimum by ensuring a sufficient circulating flow rate. In addition, 8 is a rotation speed detector, 9 is a flow rate setting device, and IO is a relay. However, even with this method, when the pump is being operated at a certain minimum flow rate (b) as shown in Figure 4, the number of revolutions of the pump suddenly increases due to some reason and the number of revolutions reaches the specified number of revolutions (N2).
(N+), the flow rate becomes (b)'. F) The minimum flow rate (a) at N+ rotational speed cannot be secured, and there is a risk of damaging the pump. This means that in an electrically driven water supply pump that uses a fluid coupling to control the rotational speed, if there is an incorrect operation or failure of the scoop tube, which is a device that changes the rotational speed, there is a risk that the pump will be damaged by overheating. Also, in a turbine-driven water pump, there is a risk similar to that of the electric water pump when considering a failure of the turbine speed governor.

[Purpose of the invention]

The present invention was invented in consideration of the above circumstances, and it detects the flow rate and rotation speed of the water supply pump, controls the recirculation flow rate to the minimum required amount, and also controls the recirculation flow section 1. The object of the present invention is to provide a device that prevents a water supply pump from overheating by suppressing an increase in rotational speed or tripping the pump.

[Summary of the invention]

The need to keep the minimum flow rate of the feed water pump as low as possible arises from the small capacity of the recirculation line and from the limited capacity of the boiler's feed water fluctuations, thus ensuring that the minimum required recirculation flow rate is achieved under all operating conditions. control is required. However, due to the characteristics of the pump, the flow rate changes in proportion to the rotational speed, so if the rotational speed increases rapidly, the flow rate also increases, but the recirculation valve opening operation cannot follow this, resulting in the pump overheating. Therefore, if the rotational speed increases for some reason, it is necessary to take measures to protect the pump by lowering the rotational speed or tripping the pump. The present invention has been made to address such motives.

[Embodiments of the invention]

Hereinafter, an embodiment of the water pump protection device according to the present invention will be described with reference to FIG.

A detector 8 for detecting the output shaft rotation speed of a fluid coupling 13 that controls the rotation speed of the water supply pump 1, a flow rate setting device 9, a rotation speed calculator 11, and a deviation calculator 12 for comparing the rotation speed with the actual rotation speed are provided. The output of the detector 8 is then passed through the deviation calculator 12 and converted by the flow rate setter 9 into a minimum recirculation flow rate signal corresponding to the rotational speed at that time, and is applied to the relay 10 as a set flow rate signal. At the same time, the suction flow rate of the water supply pump 1 is detected by a flow rate detector 5 and applied to a relay 10 via a flow rate transmitter 6.

The relay 10 compares the set flow rate signal and the suction flow rate, and when the suction flow rate ≦ the set flow rate, the solenoid valve 7 is de-energized, the actuator 3a fully opens the control valve 3, and the discharge flow rate of the water supply pump 1 is recirculated. Circulate to line 2. On the other hand, as a feedback circuit, the signal from the relay 10 is converted into a rotation speed commensurate with the flow rate by a rotation speed calculator 11, applied to a deviation calculator 12, and compared with the output of the detector 8 to calculate the actual rotation speed. When the number of rotations is reached, this signal is sent to the motor 14 and the motor 14 is tripped.

Next, an example of lowering the pump rotation speed without tripping the motor 14 will be explained with reference to FIG.

A signal from the deviation calculator 12 is input to the control command unit 16. Since the signal from the boiler ABC device is input to the control command device 16, this control command device 16 inputs the signal from the deviation calculator 12.
The priority order of the signals is determined by comparing the signals with those of the pump, and this signal is transmitted to the control drive 15 that operates the scoop tube of the fluid coupling 13, thereby making it possible to similarly lower the rotational speed of the pump.

According to the above example, even if the rotational speed of the pump increases rapidly, damage to the pump due to overheating can be prevented.

〔Effect of the invention〕

According to the present invention, the required minimum amount of recirculation flow rate can be obtained depending on the operating status of the feedwater pump, so disturbance to the boiler can be minimized, and overheating of the feedwater pump can be prevented even in abnormal situations. There is an effect.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing conventional recirculation flow rate control, Figure 2 is a diagram showing a conventional method of setting recirculation flow rate, and Figure 3 is a system diagram showing how to control recirculation flow rate by rotation speed and flow rate. , 4th
The figure is a diagram showing the operating state in FIG. 3, and FIGS. 5 and 6 are system diagrams showing the water pump protection device according to the present invention. 1... Water supply pump, 2... Recirculation line, 3...
Control valve, 5...Flow rate detector, 6...Flow rate transmitter, 8...Rotation speed detector, 9...Flow rate setting device, 1
o... Relay, 11... Rotation speed calculator, 12...
Deviation calculator, 16...control command unit. Agent Patent attorney Kata Usuda, -) ri7-1-no

Claims (1)

[Claims] A detector that detects the flow rate and rotation speed of the water supply pump, a computing unit that sets the recirculation flow rate of the water supply pump based on the signal from this detector, and a recirculation valve that controls the recirculation flow rate based on the signal from this computing unit. A recirculation flow rate control device for a water supply pump comprising: a feedback control circuit that reduces the rotational speed of the water supply pump or trips the water supply pump in response to a signal from the computing unit, thereby preventing overheating of the water supply pump. Water pump protection device.