Perfect Harmony SNG5100 Series High-Voltage Variable Frequency Speed Regulation System

SN6100 Internal Feedback Chopper Wave Speed Regulating Device
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Principle of energy saving for water pump (and fan) by speed regulation:
During the operation of water pump, the flux shall be frequently adjusted. The traditional way for flux adjustment is to change the opening of the valve. If the opening of the valve is smaller, the efficiency of valve operation will be reduced. As shown in the diagram, S1 is the lift-flux characteristics of rated operating water pump, R1 is the resistance characteristics in maximum valve opening, M1 is the rated operating point whose corresponding lift is H1 and the flux is Q1. The consumed power of motor is in direct proportion with the product of H and Q: P1=K H1 Q1; wherein, K is the proportionality factor. If the flux is reduced to Q2 by turning down the valve, the resistance characteristics of the pipe network is R2 and the operating point of the water pump is M3. At that time, the lift will be increased and the consumed power of the motor will be reduced slightly: P2=K H3 Q2; wherein, K is the proportionality factor. If the rotating speed is lowered, the lift-flux characteristics will be changed into S2, the resistance characteristics of pipe network is still R1 and the operating point of water pump is M2. At that time, the lift can be lowered more and the consumed power of motor can be greatly reduced: P3=K H2 Q2; wherein, K is the proportionality factor. Clearly from the diagram on the right, under the same flow Q2, the lift H2 when lowering the rotating speed is much smaller than the lift H3 when turning down the valve, so the consumed power of motor can be greatly reduced. This is the simple principle on energy saving of water pump by speed regulation.
Relationship between rotating speed and shaft power of fan (water pump):
(Based on the output power P base of the motor in 100% rotating speed)
Rotating Speed 100% Nn 90% Nn 80% Nn 70% Nn 60% Nn
Power of motor 100%P base 72%P base 51%P base 34%P base 21%P base
Note:
1. The Table above takes the full-opening baffle plate of fan and no change on other states of load when changing the rotating speed of motor as the condition;
2. When the number of revolutions is changed, the self-efficiency of fan shall not be reckoned in.
Analysis of energy saving:
The energy saving amount of water pump or fan depends on the peak change of the operating condition. According to the operating report on measurement of speed regulating device manufactured by our company for years in actual operation on site as well as self-measurement conducted by customers, the average minimum energy-saving rate is more than 41%, which is an energy-saving speed regulating device with less investment and quick returns.
Priority scheme on speed regulation of fan and water pump:
  • The outlet pressure of centrifugal water pump (or fan) decreases with the quadratic rotating speed; at that time, the output power of the motor decreases along with the cubic rotating speed. Therefore, there is a great potential to use speed regulation for energy saving;
  • The slip power of wire-wound motor is about 30% of the shaft power. The speed regulation of the motor can be achieved only by the internal feedback chopped wave speed regulating device through controlling the power of this part. Since the capacity of control device is small, the problems on idle harmonic can be resolved easily;
  • The voltage of wire-wound motor rotor is low voltage, which accordingly creates conditions good for work of power electronic elements. Within the power range of 200KW-4,000KW, the current of motor rotor is not too large and the devices in parallel connection can easily solve this problem;
  • When the control device is in failure, the speed regulating device can still ensure continuous and normal operation of the motor in full speed, and even can guarantee the function of soft startup of the motor;
  • The high-voltage internal feedback chopped wave speed regulating device has the advantages of high energy-saving efficiency, safety and reliability, simple maintenance, low price and less investment.
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