Mining multistage centrifugal pump speed regulation is generally a deceleration problem. When the frequency conversion speed regulation is adopted, the operating parameters of the pump and the motor originally designed according to the power frequency state have undergone great changes. In addition, factors such as the pipeline characteristic curve and the fixed speed pump running in parallel with the speed governing pump will be The range of speed regulation has a certain impact. It is difficult to achieve energy saving by over-range speed regulation. Therefore, variable frequency speed regulation is impossible to adjust without limit. It is generally believed that the frequency conversion speed regulation should not be lower than the rated speed of 50%, preferably between 75% and 100%, and should be determined by calculation in combination with the actual situation.
Influence of process characteristics of mining multistage centrifugal pump on speed regulation range
In theory, the high-efficiency zone of the multi-stage centrifugal pump for mining is the intermediate zone OA1A2 of the parabola of two similar working conditions passing through the left and right end points of the power frequency high-efficiency zone. In fact, when the multi-stage centrifugal pump of the mine is too small, the efficiency of the pump Will be drastically reduced, affected by this, the mining multi-stage centrifugal pump speed control high-efficiency area shrinks to PA1A2 [2] (obviously, if the operating conditions have exceeded this area, it is not appropriate to use speed regulation to save energy.
The effect of fixed speed pump on the speed range
In practice, the water supply system is often a parallel supply of multiple multi-stage centrifugal pumps for mining. Due to the high investment, it is impossible to adjust all the multi-stage centrifugal pumps. Therefore, the variable speed pump and the fixed speed pump are generally used for water supply. In such a system, care should be taken to ensure that both the variable speed pump and the fixed speed pump can operate in the high efficiency section and achieve optimal system performance. At this time, the fixed speed pump has a great influence on the speed regulation range of the speed control pump that is running in parallel with it. Mainly divided into the following two cases:
When the same type of mining multi-stage centrifugal pump must be operated in parallel, although the scheduling is flexible, the range of the speed control operation is small because the high-efficiency working section of the speed control pump and the fixed speed pump cannot be considered. .
When different types of mining multi-stage centrifugal pumps must be operated in parallel, if the speed-regulated pump is at rated speed, the high-end segment head end lift and the fixed-speed pump high-efficiency segment left end lift are equal. The maximum range of speed control operation can be achieved. However, at this time, the speed control pump and the fixed speed pump are absolutely not allowed to be interchanged and run in parallel.
Influence of motor efficiency on speed regulation range
In the case of similar working conditions, there is generally N∝n3, so the shaft power will drop sharply as the speed decreases, but if the motor output power is excessively offset from the rated power or the operating frequency is excessively offset from the power frequency, the motor efficiency will be The decline is too fast and ultimately affects the efficiency of the entire multistage centrifugal pump unit for mining. Moreover, when the cold motor runs continuously at low speed, it will also affect the heat dissipation due to insufficient air volume, which threatens the safe operation of the motor.
