Frequency Converter Control for Fire Pump Motor Pressure Regulation
Solution Overview
Problem
Existing fire protection systems, such as high-pressure water mist extinguishing systems, are complex, large, and expensive due to the need for separate water tanks, unloading valves, and standby pumps, which also suffer from mechanical hysteresis and water circulation-related issues.
Innovation Solution
The use of a frequency converter to control AC electric motors, allowing for variable voltage and frequency control, eliminating the need for separate water tanks and standby pumps, and simplifying the mechanics by optimizing electricity and water consumption while minimizing starting-current peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate water tanks, unloading valves, and standby pumps are used in prior-art pump units, then the system can maintain standby pressure and handle flow requirements, but the system becomes complex, large, and expensive
Solution Approach 1:
The patent combines the functions of the standby pump, water tank, and unloading valves into a single integrated pump unit. The pump unit directly connects to the water mains system and uses a frequency converter to control motor speed, eliminating the need for separate standby pumps and water tanks. This merging of functions reduces system complexity while maintaining the ability to maintain standby pressure and handle flow requirements.
Solution Approach 2:
The pump unit is designed to perform multiple functions: it can maintain standby pressure, respond to fire flow demands, and regulate pressure dynamically. By using a frequency converter-controlled motor, the single pump unit can adapt its operation to different system conditions, replacing the need for specialized standby pumps and unloading valves. This multi-functionality reduces the number of components needed while ensuring reliable fire protection.
2Stress or pressure
If mechanical unloading valves and water circulation are used in prior-art systems, then pressure regulation is achieved, but mechanical hysteresis and warming issues occur
Solution Approach 1:
The patent replaces mechanical pressure regulation mechanisms (unloading valves) with an electronically controlled system using a frequency converter. The frequency converter adjusts the motor speed to match the required flow and pressure demands, eliminating mechanical hysteresis associated with unloading valves. This substitution of mechanical control with electronic control prevents both mechanical hysteresis and warming issues while maintaining effective pressure regulation.
3Ease of operation
If AC electric motors are directly connected to the electricity network, then simple control is achieved, but large starting-current peaks occur
Solution Approach 1:
The patent uses a frequency converter to dynamically control the motor starting process. Instead of direct connection to the electricity network, the frequency converter gradually increases the motor speed from zero to the required operating speed, smoothing out the starting current. This dynamic control allows the motor to start without large current peaks while maintaining ease of operation through automated speed control.
4Use of energy by moving object
If frequency converter control is implemented, then starting-current peaks are minimized and operation is optimized, but device complexity increases
Solution Approach 1:
The frequency converter acts as an intermediary between the electricity network and the motor. It provides smooth starting current control and optimized operation while isolating the motor from direct network connection. Although the frequency converter adds a component, it eliminates the need for other complex mechanical systems (standby pumps, unloading valves, water tanks), resulting in overall system simplification.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution results in a cost-effective, mechanically simple, and compact pump unit with reduced hysteresis and warming issues, achieving efficient pressure control and optimized operation.
Implementation Method 1
one of the electric motors (102) is connected to the supply network (106) via a frequency converter (108), by means of which variable frequency and variable amplitude three-phase AC voltage (109) can be obtained
Data Source
Figure 1
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Figure 3
AI summary
Control method and control apparatus of the electric motors of a pump unit of a fire protection system, which fire protection system comprises spray nozzles (112), a pump unit, a control system with pressure-measuring means, and piping (105) for conducting extinguishing medium from the pump unit to the spray nozzles, which pump unit comprises pump drives, each of which comprises a pump (101 ) and an AC electric motor (102, 203a-203f) rotating it, which AC motor can be connected to an AC electricity network via a contactor device (206a-f), in which pump unit the AC electric motors are controlled on the basis of the pressure to be measured in the piping, and in which one of the electric motors (102, 203a-203f) at a time is controlled by means of a frequency converter (108, 204) such that the motor to be controlled with the frequency converter operates as a motor that under the control of the frequency converter steplessly adjusts pressure and the others are started up into the network as steplessly adjusting motors.