What is the flow of what letters that use several units of measurement how to convert how to convert into weight and formula A: The unit of time the volume of liquid discharged by the pump is called flow, flow Q said that the unit of measurement: cubic meters / hour (m3 / h) (L / s), L / s = 3.6 m3 / h = 0.06 m3 / min = 60L / minG = QÏ G is the weight Ï is the liquid specific gravity Example: When a pump flow rate is 50 m3 / h, The weight of water per hour Ï Ï 1000kg / m3. Solution: G = Qp = 50 × 1000 (m3 / h · kg / m3) = 50000kg / h = 50t / h what is what the head with what measure Unit and pressure conversion and formula A: The weight of liquid per unit weight obtained by the pump is called the head. The pump head including the suction stroke, approximately the difference between the pump outlet and inlet pressure. Head with H said that the unit is meters (m) The pressure of the pump is expressed by P in units of Mpa and H = P / Ï, H = (1kg / cm2) / (1000kg / m3) if P is 1kg / / (1000 kg / m3) = (10000 kg / m2) / 1000 kg / m3 = 10m1Mpa = 10kg / m2, H = P2- P1 / P2 (P2 = outlet pressure P1 = inlet pressure) How the efficiency formula A: refers to the ratio of pump effective power and shaft power η = Pe / P Pump power usually refers to the input The rate, that is, the power transmitted to the shaft of the prime mover, is also called the shaft power, expressed as P. The effective power is the product of the pump head and mass flow and the acceleration of gravity .Pe = Ïg QH (W) or Pe = γQH / 1000 (KW) Ï: Density of the liquid pumped by the pump (kg / m3) γ: Severe γ = Ïg (N / m3) of the liquid pumped by the pump g: Gravitational acceleration (m / s) Mass flow rate Qm = ÏQ Or kg / s) What is the rated flow rate, rated speed, rated head A: According to set the pump performance parameters of pump design, and to achieve the best performance, as the pump rated performance parameters, usually refers to product catalog or sample On the specified parameters such as: 50-125 flow rate of 12.5 m3 / h for the rated flow head 20m rated head speed of 2900 rpm / divided into rated speed What is the NPSH What is the suction unit of measurement units Letter A: When the pump is working, the liquid will generate vapor under the certain vacuum pressure at the inlet of the impeller. The vaporized bubbles will denude the impeller and other metal surfaces under the impact movement of the liquid particles, thus damaging the impeller and other metals. At this time Vacuum pressure is called vaporization pressure, NPSH refers to the pump inlet per unit weight of liquid with excess steam Pressure surplus energy unit marked with meters, with (NPSH) r suction stroke is required NPSH Δh: that is, the pump allows liquid suction vacuum, that is, the pump allows the installation height in meters suction stroke = Standard Atmospheric Pressure (10.33m) -Near NPSH - Safe Amount (0.5m) Standard atmospheric pressure can pressurize the pipe to a height of 10.33m. For example, if a pump has required NPSH of 4.0m, find the suction Δh Solution: Δh = 10.33-4.0-0.5 = 5.83 m What is the characteristic curve of the pump, including several aspects of what effect A: The curve that represents the relationship between the main performance parameters is usually called the centrifugal pump performance curve or characteristic curve, in essence, the centrifugal pump The performance curve is the external manifestation of the law of the movement of the liquid in the pump and is obtained by the actual measurement.The characteristic curves include: flow-head curve (QH), flow-efficiency curve (Q-η), flow-power curve - NPSH (Q- (NPSH) r). The performance curve is an arbitrary flow point of the pump. All the curves of the head, power, efficiency and NPSH can be found out. This group of parameters known as the working condition, referred to as working conditions or conditions point, the highest efficiency point of the centrifugal pump is called the best operating conditions point, the most Good working condition point is generally the design condition point.General centrifugal pump rated parameters that the design conditions point and the best conditions coincide or very close to the point in the practice of the election efficiency range operation, that is, energy saving, but also to ensure the normal operation of the pump , So it is important to understand the performance parameters of the pump What is the pump's performance test bench A: The equipment that can accurately test out all the performance parameters of the pump through the precision instrument is the full-performance test bench.The national standard precision is B. Flow precision Worm wheel flowmeter measurement, head with precision pressure gauge. Suction with a precision vacuum gauge. Power measured with a precision shaft power. Speed ​​measured with a tachometer. Efficiency according to the measured value: n = rQ102 calculation. Pump high-voltage motor speed control Transformation should pay attention to the problem With the continuous improvement of the level of industrial automation and power electronics technology, water projects using high-voltage variable frequency speed control technology more and more, Guangxi Branch intends to use water pump room 12-pulse voltage source type High-voltage inverter to control the power of the pump motor 355KW, the pump motor frequency control technology upgrade, in order to achieve the purpose of electrical energy-saving and process optimization, high-pressure frequency In engineering design should pay attention to: First, the motor characteristics of the test and technical specifications of the revisions When an ordinary motor from the inverter to provide power, the inverter output voltage and current harmonics will increase the loss of the motor, reducing efficiency , The increase of temperature.The increase of loss caused by higher harmonics is mainly manifested in the increase of copper loss, iron loss and additional loss of stator and rotor, among them, the rotor copper loss is the most significant, because the induction motor always approaches 1 State rotor, so the rotor copper consumption is very large in ordinary induction motor, in order to improve the motor starting performance, the skin effect of the rotor so that the actual impedance increases, resulting in increased copper consumption.On the other hand, due to the presence of the motor coils Distribution of capacitance, when the higher harmonic voltage input, the voltage between the coils is not uniform, this long-term repeated effect of a certain part of the stator coil insulation damage, resulting in coil aging, which in the ordinary induction motor insulation The structure is unacceptable.In addition, the motor can not be absolutely symmetrical electromagnetic circuit, so the output power of the inverter contains all the harmonic components and electromagnetic return The inherent space harmonic components interact to form a variety of electromagnetic pulsation.At the same time, the motor is easy to produce mechanical resonance with the mechanical parts of the motor due to the working condition that the frequency is constantly adjusted, resulting in damage to the mechanical parts of the motor.Therefore, Speed ​​?? transformation project, in order to avoid the frequency control system in the operation of the above problems, technology design must consider and motor manufacturers for technical cooperation, the motor characteristics of the governor speed test, re-amend the original motor specifications. Second, the main points of power cable selection and laying requirements Because the connection between the output of the inverter and the motor is cable attached, and each phase of the line there is capacitance to ground, so the capacitor current is not equal at run time line if Cable attached to a longer distance, and there is a high-order harmonic currents in the line, then in the event of single-phase ground, the fault capacitor current ignition of the arc extinguishing time is too long, will make this side of the cable heat, causing non-fault insulation. , In the frequency control project, for the output power cable, cable structure to consider the three-phase symmetry and shielding, the cable If the original output power cable is unshielded or if the cross-sectional flow capacity margin is less than 2, the power cables should be replaced as required. During construction on site, connect the power cables and controls Cables and signal cables laid separately to avoid the magnetic field generated by the high-frequency power cables interfere with other signals. Third, the basic working conditions of the inverter High-voltage inverter inverter part of the high-voltage IGBT and other power devices, the open, off Frequency greater than 100HZ, easy to form high-harmonic current, making the frequency conversion device will produce a certain amount of heat at work.Generally in the inverter cabinet top are equipped with exhaust fan, it will heat the cabinet discharge to the interior, which makes the indoor The ambient temperature continues to rise, and ultimately will affect the reliable operation of the various components inside the cabinet.Therefore, in the water works engineering design general frequency control device alone set in the frequency conversion speed control room indoors must be equipped with spare air conditioning facilities to control the indoor temperature In the required range of the inverter, at the same time with ventilation doors and windows, if necessary, use a dedicated duct for forced ventilation and cooling. Improve the technical control of outlet circuit breaker The high-voltage side of the transformer used in the inverter speed control device should be directly connected with the switchgear in the high-voltage system, but the protection scope of the switchgear is only the short circuit of the low voltage side of the power supply line and the transformer, The inverter's own detection and protection system is completed. When the frequency converter fails to issue a tripping signal, the circuit breaker should trip reliably. However, there is a situation where the tripping circuit disconnects or the DC control power disappears inside the ordinary circuit breaker high voltage switchgear. Happens to be fault (trip required circuit breaker), the tripping coil has been power failure, the circuit breaker refuses to act, resulting in damage to the power components within the inverter. So in the design selected with undervoltage trip coil circuit breaker, once In the event of a trip circuit disconnection or loss of control power, the circuit breaker trips automatically first to protect the safety of the inverter.