Variable Speed Unit Suction Height Calculation Method
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Solution Overview
Problem
Current methods for determining the suction height of variable speed units in pumped storage power stations are inaccurate and fail to meet the higher cavitation index requirements, as they rely on outdated statistical formulas that do not account for recent design and development advancements, and are not suitable for the variable speed operating range.
Innovation Solution
A method and device that acquire reference cavitation coefficients and specific rotation speed parameters from existing power stations to derive a target formula, which is used to determine the suction height of variable speed units by considering maximum and minimum lifts, speed variation range, and input force values at key working condition points, providing a more accurate calculation of cavitation coefficients and suction heights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If existing empirical formulas for constant-speed units are applied to variable speed units, then the calculation method is simple and easy to implement, but the calculation results cannot reflect the progress of unit design and R&D technologies in recent years and cannot accurately guide scheme argumentation and parameter optimization
Solution Approach 1:
The patent transforms the cavitation coefficient calculation from using static empirical formulas to a dynamic calculation method that incorporates specific speed parameters and their statistical relationships. By changing the calculation parameters to include nq (specific speed) as a variable and establishing statistical correlations between nq and σ (cavitation coefficient), the method achieves both computational feasibility and improved accuracy that reflects recent design progress.
2Ease of operation
If existing calculation formulas for constant-speed units are used, then the calculation process is straightforward, but the operating range of variable speed units is wide and the requirement for cavitation index is higher, which cannot be met by constant-speed unit formulas
Solution Approach 1:
The patent applies dynamics by making the cavitation coefficient calculation adaptive to variable operating conditions. Instead of using fixed formulas for constant-speed units, the method dynamically calculates σ based on the specific speed nq and its statistical relationship, allowing the calculation to adapt to the wide operating range of variable speed units and ensure cavitation-free operation across different operating points.
Solution Approach 2:
The patent introduces a new dimensional approach by incorporating the specific speed parameter nq as an additional dimension in the calculation. Rather than relying solely on traditional constant-speed formulas, the method adds the nq-σ statistical relationship dimension, enabling accurate cavitation assessment across the extended operating range of variable speed units while maintaining calculation simplicity.
3Loss of time
If statistical data or empirical formulas from existing units are used to estimate suction height, then the design process can proceed without actual operation parameters, but the cavitation performance of water pump turbine is worse than water turbine and comprehensive comparison and selection is required
Solution Approach 1:
The patent implements preliminary action by establishing statistical relationships between specific speed and cavitation coefficient before actual unit installation. By collecting and analyzing operational data from multiple power stations and creating the nq-σ statistical model in advance, the method enables accurate suction height estimation during the design phase without waiting for actual unit operation parameters, thus reducing design time while maintaining precision.
Data Source
AI summary
A method and device for determining a suction height of a variable speed unit is provided. The method includes: acquiring a reference cavitation coefficient and a reference specific rotation speed parameter corresponding to a target water head section in a preset number of power stations; conducting calculations on the reference cavitation coefficient and the reference specific rotation speed parameter by utilizing a target scheme to obtain a target formula; acquiring a maximum lift, a minimum lift, a speed variation range and a synchronous rotation speed value of a current target variable speed unit and input force values of the target variable speed unit at a plurality of key working condition points; and determining a target suction height of the target variable speed unit.