Fan and water pump use speed regulation to reduce throttling loss
Fan and water pump speed regulation is a widely used energy saving measure. By adjusting the speed, the performance curve of the pump can be shifted into a state with many different capacity, so as to adapt to the load change, so that the pump is in a high-efficiency area or reduce throttling losses. There are many ways to regulate speed. The following two main measures are taken.
Mechanical speed change
Mechanical speed change uses mechanical methods to change the rotation speed of fluid conveying equipment. Specific examples include V-belt speed change, gear reducer, chain-type continuously variable transmission, multi-disc continuously variable transmission, and fluid coupling. Choose different conditions such as system, working environment, speed range, load characteristics and motor power. The most commonly used is a hydraulic coupling, which is a hydraulic machine that connects and transmits power through fluid kinetic energy. The main components are relatively installed concentric pump shafts and turbines with different shafts. When the pump wheel is driven to rotate, the internal working oil flows under the centrifugal force along the inner edge of the pump wheel to the outer edge, passes through the gap (working cavity) between the two wheels, and then flows from the outer edge of the turbine to the center. Impacting the turbine rotates it and the output shaft before returning to the pump impeller. This goes on and on. The adjustment of the output shaft speed is generally controlled by the spoon tube. Or use the control valve to control the oil inlet, or both, to achieve the most change in the working chamber of the coupling oil filling.
The main type of this coupling is variable charge type. The domestic production and use are two types of spoon tube interception type and rotary oil bag type. The former is a large and medium-sized device, suitable for transmitting large and medium power. The latter is a small device. Hydraulic coupling speed regulation has the following advantages: Even if the flywheel inertia is large, the motor can still start under no-load conditions and reduce the starting time. The book can reliably prevent the motor from overloading; it can absorb shock and torsional vibration, and it can run smoothly Significantly extend the life of the entire system; simple maintenance; stepless speed regulation can be achieved. If the speed regulation range is in a non-constant pressure system such as a dust removal fan, it can reach 2-0-985. In a constant pressure system (such as a boiler Water pump) can reach ... 3-0-985; transmission efficiency varies with working conditions, 0.96-0-985 under rated working conditions, which can simplify the fluid system and have high control accuracy. It is easy to realize remote control; the higher the drive speed, the larger the capacity, and the lower the motor speed, the larger the size and weight of the coupling; the hydraulic coupling with a power greater than 100k W requires additional coolers and piping systems. Magang uses Shanghai's YDT45 / 30 speed-regulating fluid coupling on the 300m state-of-the-art converter blower. The speed regulation range is 19% to 97% of the actual speed of the motor. The average hourly power saving is 292kw. It is recovered. The Y4-73-1122D dust removal fan at the blast furnace of Shougang blast furnace is equipped with YOTC-800 hydraulic coupling developed by Shougang, which can save 7.74 million kW · h of electricity annually.
2.Electrical speed regulation
The electric speed regulation is to change the speed of the electric motor by electric method. Generally, the speed of AC motors (squirrel-cage type, wire-wound type and synchronous motors) can be used to change the frequency f, the number of pole pairs, and the slip rate of the motor to achieve the purpose of speed regulation.
(1) Rotor circuit is connected with a resistor for speed regulation, that is, when the inductance of the rotor circuit is ignored: R / U is added, U and R are the rated rotor voltage and the rotor resistance, respectively. This speed regulation method is simple, but the speed regulation range is not large and the efficiency is low.
(2) Thyristor cascade speed regulation, that is, for a wound motor, the rotor voltage U2 = U, sw2 / w, can be changed, thereby changing s. The inverter voltage, which is the back-EMF of the motor rotor circuit, can be changed by changing the inverter's inversion angle. In order to change U, this method can be used to achieve smooth stepless speed regulation. Theoretically, the speed regulation can be above 1:10. In addition, it can feedback the slip to the power grid, which has a better power saving effect and facilitates the motor to large capacity. The development is very suitable for long-time low-speed equipment such as fans and pumps. The disadvantage is that the power factor is low. At present domestic equipment has KGJA. KGJF series and so on.
(3) Electromagnetic slip speed regulation. By adjusting the excitation current of the electromagnetic slip clutch, the slip between the driven part and the active part of the clutch is changed, so that the driven shaft can obtain different speeds.
This method is used for small-capacity motors that work for a long time and does not reverse. It can perform smooth stepless speed regulation, and the speed range can reach I: 10 or more. The disadvantage is that the efficiency is low, there is a runaway area, the speed cannot be adjusted when the load torque is less than 10% of the rated torque, and the time constant is large. The electromagnetic slip speed control motor is JZT series, which is generally used for motors below 100k W.
(4) commutator variable speed motor, three-phase rectifier motor has three windings, the primary winding is on the rotor, the secondary winding is on the stator, the tertiary winding is the adjusting winding for speed regulation on the rotor, and each winding is connected to the rectifier, The commutator has two sets of carbon brushes connected to the two ends of the secondary winding at every 1200 angles. The carbon brush set can adjust the speed of the commutator by moving back and forth relative to the commutator. This method is stepless speed regulation, with a range of I, above 3-10, constant torque characteristic efficiency and power factor are both high. The motor is a Jzs series, which is generally used on machinery that does not need to be reversed for a long time. The motor power is generally below look W.