It is suitable to stop the pump during the zero-flow water supply

.Introduction
    In order to save energy and reduce cost, variable frequency water supply usually adopts multiple pumps in parallel with constant pressure variable water supply. This is because: ①a variable frequency pump is connected in parallel with multiple power frequency pumps, which can realize constant pressure and variable flow water supply, but the variable frequency pump is required to be the largest of them; ②the price of the frequency converter is proportional to its power, and multiple pumps Parallel water supply reduces the power of each pump and the power of the frequency converter accordingly, which can reduce the cost; ③Multiple pumps in parallel water supply reduces the power of a single pump. When a pump provides water with variable frequency, it can significantly improve its energy-saving effect.
    2. The best solution for variable frequency speed regulation feedwater stop pump control
    Judging from domestic and foreign literature reports and product samples, the best solution for multi-pump parallel constant pressure water supply pump control solution is:
    when the water flow is less than the rated flow of one pump , The same pump provides constant pressure water supply. According to the centrifugal pump theory, under similar working conditions, the hydraulic power of the pump is proportional to the cubic speed. When the water flow is close to zero (but at constant pressure), the pump has the lowest speed and its power. For commonly used centrifugal pumps, the power consumed by the variable frequency constant pressure water supply at zero flow is about /4 or less of the rated power of the constant speed pump of the same size (related to the Q and H external characteristics of the pump, the constant pressure value, etc.) , But the variable frequency pump runs at zero flow for a long time and consumes energy in vain is a shortcoming after all. This shortcoming is more prominent when the pump power is large.
    In order to stop the variable-frequency pump when it is not using water, so as to save energy and reduce the wear and tear of the pump, foreign inverters (with multi-pump parallel constant pressure water supply control function) adopt such a control scheme: when the variable-frequency pump speed (frequency) When it drops to close to the zero flow threshold, the inverter sends an instruction to stop the variable-frequency pump for a rest. A small air pressure tank is connected to the pipe network system. When the variable frequency pump stops, the air pressure tank maintains the water supply; when the water supply pressure drops to a certain set value, the frequency converter receives this pressure information to start the variable frequency pump and restore the constant Pressure water supply. In the actual water supply, it is not desired to stop the pump immediately when the speed of the variable frequency pump decreases to the zero flow threshold, but after a certain period of time, the pump is stopped after judgment and confirmation that there is no water. To this end, a judgment program can be set in the computer control program to achieve this goal. Specific method: When the rotation speed (frequency) of the variable frequency pump is reduced to the zero flow threshold and lasts for T time (T is the judgment time, which can be set as required), the computer sends out the instruction to stop the variable frequency pump to make the variable frequency pump stop automatically. This function is called Frequency conversion pump automatic sleep function. During the stop of the pump, if someone uses water and causes the pressure of the pipe network to drop, when it drops to the pump-on pressure (pressure value can be set as needed), the computer will accept this pressure information and issue a command to automatically start the variable frequency pump and restore constant pressure water supply , This function is called the automatic wake-up function of the variable frequency pump.
    It is understood that most domestic manufacturers of variable frequency water supply equipment have set up a small air pressure tank and a small power frequency in the water supply system in order to enable the variable frequency water feeder to better save electricity when water is supplied at a small flow rate and to stop the pump when no water is used. Pump.
    The author believes that there are many problems with the scheme of using small power frequency pumps and small air pressure tanks. It is better to adopt the automatic sleep and automatic wake-up scheme of variable frequency pumps. The intelligent variable frequency water supply equipment developed and produced by our company has successfully applied the automatic sleep and automatic wake-up scheme of variable frequency pumps, which proved to be very successful after testing and delivery to users.
   When the power of the variable frequency constant pressure water supply pump is large, for example, the power of a pump is 20kW. When the water flow is close to zero, the actual energy consumption of the variable frequency pump is about /4×20=30kW. At this time, when a small flow of water is used, a large variable frequency pump will consume a lot of electric energy. From the perspective of energy saving, a small pump should be used to supply water when the flow of water is small. In order to save energy, a small frequency conversion pump can be used. The control system is designed as follows:
    () When water is used for a small flow, the frequency of the large pump when water is supplied with a constant pressure and a small flow is calculated and set as (Hz) Qmin.
    (2) When the large pump is supplying water at a constant pressure and a small flow rate, when Hz≤(Hz)Qmin, an output relay (programmable) of the frequency converter works and sends a message to the dedicated PLC.
    (3) After the PLC receives the above information:
    (a) Control the inverter to stop working;
    (b) After the inverter stops, perform switching operations on its output side: first disengage the AC contactor of the variable frequency large pump, and then enable the low power (such as 30kW) The small pump is connected;
    (c) After switching on the output side of the inverter, restart the inverter to restore the constant pressure variable water supply.
    (4) A small pump (such as 30kW) is driven by the frequency converter to provide small flow and constant pressure water supply. At this time, the small pump has automatic sleep and automatic wake-up functions, which has the best energy-saving effect of small flow water supply.
    (5) When the water flow increases, the output frequency of the inverter rises. When Hz=(Hz)Qmin, a programmable output relay of the inverter works. As described in (2) and (3) of the entire water supply system, the water machine is still supplied by a small pump with variable frequency and constant pressure.
    (6) When the water flow continues to increase, the output frequency of the inverter continues to rise, when Hz=(Hz)Qmin+ΔQ another programmable output relay of the inverter works and sends a message to the dedicated PLC.
    (7) After the PLC receives the above information
    (a) Control the inverter to stop working;
    (b) After the inverter stops, perform the following switching operations on its output side: first disengage the variable frequency AC contactor of the small pump, and then enable the 20kW large pump Connect frequency conversion;
    (c) After switching on the output side of the frequency converter, restart the frequency converter to restore the constant pressure variable water supply.
    (8) A 20kW large pump is driven by a frequency converter to provide small flow and constant pressure water supply. For example, if three large pumps are connected in parallel, the maximum water supply power can reach 20×3=360kW.
    3. Application of ABB intelligent frequency conversion water supply equipment
    The automatic sleep and automatic wake-up control scheme of the variable frequency pump has been applied to the ABB frequency converter with PFC macro (pump and fan control). During automatic sleep, the water pump stops automatically without consuming electric energy at all, which has the best energy-saving effect. In order to maintain the water supply during the stop of the pump, a small air pressure tank is provided in the system. During the automatic sleep period of the variable frequency pump, the water supply is maintained by the small air pressure tank. When the pressure of the air tank drops to a certain set value, the variable frequency pump will automatically wake up and resume constant pressure water supply.
    Utilizing the above-mentioned functions of ABB frequency converter can be designed into the following series of intelligent frequency conversion water supply equipment:
    () YLD-BP-S series of intelligent life frequency conversion water supply equipment.
    When the water flow is less than the rated flow of a pump, the variable frequency and constant pressure variable water supply is provided by the variable frequency pump B; when the water flow is greater than the rated flow of a pump in the power frequency situation, the power frequency pump B2 is automatically connected in parallel with the variable frequency pump B Constant pressure variable water supply (when quasi-variable pressure variable water supply is used, every time a power frequency pump is put in, the constant pressure value rises by a step ΔP, ΔP can be set as required).
    When the water flow is further reduced, the speed of the variable frequency pump B will automatically drop to maintain the constant pressure water supply. When the water flow is close to zero (the degree of proximity is determined by the debugger), the variable frequency pump runs at a low speed close to zero flow. When running at low speed for T time (T value can be set and changed), the variable frequency pump automatically stops (sleeping), and the air pressure tank maintains water supply; when the pressure of the air pressure tank drops to a certain set value, the variable frequency pump automatically starts (wake up) To maintain constant pressure water supply.
    The ABB inverter with constant pressure (quasi-constant pressure) water supply control function (ABB inverter with PFC application macro) has the above control functions. A programmable output relay of the frequency converter can drive a power frequency pump. When the number of power frequency pumps is more than the number of programmable output relays, the ND0 module can be used for expansion.
    (2) YLD-BP-X series of intelligent variable frequency stabilized power frequency fire-fighting water supply equipment.
    B0 is a variable frequency stabilized pump, which is controlled by a frequency converter with constant pressure water supply control function.
    B, B2, and B3 are power frequency fire pumps, which are controlled by PLC
    Usually, the fire-fighting pipe network is filled with water and stabilized by the variable-frequency stabilized pump to make it ready for fire fighting. When the pipe network stabilizes to the set pressure, the flow rate of the stabilized pump is close to zero and maintains for a time T (T can be set), the variable-frequency stabilized pump will automatically stop (sleep) and rest, and the pressure tank will maintain the stabilized pressure; When the pressure of the fire pipe network drops to a certain set value, the variable frequency stabilized pump will automatically start to restore constant pressure and stabilized pressure (automatically wake up). The variable frequency voltage stabilization works intermittently, and the rest time is very long. There is no need to set up a backup pump to reduce the cost.
    When the fire signal is received, the main fire pump (the first one) is controlled by PLC to start at power frequency and put into fire fighting. The other fire pumps (including standby pumps for fire fighting) are controlled by the electric contact pressure gauges installed on the fire pipe network to automatically switch on or exit automatically. The specific control method is as follows: Under the condition that the main fire pump has been put into operation, if the pipe network pressure is insufficient (below the minimum fire pressure set by the electric contact pressure gauge), it will be controlled by PLC, and the next fire pump (including the standby pump) ) Automatic input to provide sufficient fire fighting flow.
    After the fire fighting is over, the PLC can accept manual instructions to stop the fire fighting (all fire pumps stop pumps).
    3. Application of ABB’s intelligent variable frequency water supply equipment The
    automatic sleep and automatic wake-up control scheme of the variable frequency pump has been applied to the ABB frequency converter with PFC macro (pump and fan control). During automatic sleep, the water pump stops automatically without consuming electric energy at all, which has the best energy-saving effect. In order to maintain the water supply during the stop of the pump, a small air pressure tank is provided in the system. During the automatic sleep period of the variable frequency pump, the water supply is maintained by the small air pressure tank. When the pressure of the air tank drops to a certain set value, the variable frequency pump will automatically wake up and resume constant pressure water supply.
    Utilizing the above-mentioned functions of ABB frequency converter can be designed into the following series of intelligent frequency conversion water supply equipment:
    () YLD-BP-S series of intelligent life frequency conversion water supply equipment.
    When the water flow is less than the rated flow of a pump, the variable frequency and constant pressure variable water supply is provided by the variable frequency pump B; when the water flow is greater than the rated flow of a pump in the power frequency situation, the power frequency pump B2 is automatically connected in parallel with the variable frequency pump B Constant pressure variable water supply (when quasi-variable pressure variable water supply is used, every time a power frequency pump is put in, the constant pressure value rises by a step ΔP, ΔP can be set as required).
    When the water flow is further reduced, the speed of the variable frequency pump B will automatically drop to maintain the constant pressure water supply. When the water flow is close to zero (the degree of proximity is determined by the debugger), the variable frequency pump runs at a low speed close to zero flow. When running at low speed for T time (T value can be set and changed), the variable frequency pump stops automatically (sleeping), and the air pressure tank maintains water supply; when the pressure of the air pressure tank drops to a certain set value, the variable frequency pump automatically starts (wake up) To maintain constant pressure water supply.
    The ABB inverter with constant pressure (quasi-constant pressure) water supply control function (ABB inverter with PFC application macro) has the above control functions. A programmable output relay of the frequency converter can drive a power frequency pump. When the number of power frequency pumps is more than the number of programmable output relays, the ND0 module can be used for expansion.
    (2) YLD-BP-X series of intelligent variable frequency stabilized power frequency fire-fighting water supply equipment.
    B0 is a variable frequency stabilized pump, controlled by a frequency converter with constant pressure water supply control function.
    B, B2, and B3 are power frequency fire pumps, which are controlled by PLC. The
    variable frequency stabilized pump is usually filled with water to stabilize the fire pipe network to make it ready Fire status. When the pipe network is stabilized to the set pressure, the flow rate of the stabilized pump is close to zero and maintained for a time T (T can be set), and the variable-frequency stabilized pump will automatically