Technological developments and increasing numbers of electrical appliances are driving global electricity consumption. A further increase will result from the electrification of vehicles, which will require not only an upgrade to the existing power-grid infrastructure, but also an increase in power-generation capacities (additonal power sources). Electricity consumption will, therefore, only increase in the future, with the necessary provision of accurate and reliable measurements of electricity use. Nowadays, this involves electronic electricity meters, which have successfully replaced the mechanical/induction electricity meters.
This doctoral dissertation deals with the topic of an adaptive quality system with respect to the technical specifications of electricity meters and focuses on the manufacturing process. Conventional consumer-goods manufacturers are very sales oriented and focus on the fullfilment of customer requirements. However, a company that produces electricity meters operates differently and has to match customer expectations, regulatory frameworks, policies and recommendations from the metrology field and suppliers of the electricity meter's components. In order to achieve this compliance the adaptability of the meter's development and production process has to be ensured. The complexity of the components of an average electricity meter is very high due to the increased diversity and quantity of components, which exceeds several hundred per meter. If the meter manufacturer supplies globaly, it must organize the production process in such a way that the meter will 100% fulfill customer demands. This requires a sufficient quantity and quality of the meter components. Production is therefore not possible without different external suppliers of components, which are divided into different supplier levels. The quality of their processes and the supplied components has an impact on the quality of the produced meters and their technical specifications, such as accuracy class, meter drift and noise, lifetime and verification interval. The main issue with the existing quality system is in a reduced ability to adapt the development and production process to customer requirements, such as the meter lifetime, which varies between customers. This issue can be resolved by a flexible quality system that transforms the various customer requirements into a modified production process.
The dissertation deals with the topic of a flexible quality system for meters' development and the production process, focusing on the meter's lifetime and its verification interval. A flexible quality system is defined by the concept of a targeted adaptation of the meter's technical specifications to customer requirements, regulatory frameworks and policies from the field of metrology by applying the steps presented in the individual sections of the doctoral dissertation.
The concept of the targeted adaptation of technical specifications is based on three segments:
The first segment represents the adaptation of the meter's lifetime to the customer`s requirements or to the influence of environmental parameters on the meter's actual use (temperature and relative humidity), which can vary widely between countries. The lifetime of a meter depends on the reliability of the built-in components. Considering that a supercapacitor is one of the most significant components in the context of the meter's reliability, the dissertation is focused on the development of a method for determining the supercapacitor's lifetime. Since the temperature and relative humidity affect the supercapacitor’s lifetime, the main novelty of the dissertation represents the development of an improved model for the supercapacitor’s lifetime determination that simulates the environmental conditions and the voltage load to which the supercapacitor is exposed during the meter's operation. Since the environmental parameters vary widely between countries, it is in the interests of the meter manufacturer to use a supercapacitor with a lifetime that matches the customer's requirements. The supercapacitor's lifetime-determination model represents the first segment of the flexible quality system.
The second segment of a flexible quality system is developing an improved model for determining a meter's verification interval. According to current guidelines the validation interval is fixed and does not consider the environmental parameters to which the meter is exposed during operation. These parameters directly influence the trend in the meter's measurement error. The intersection point of this trend curve with the upper 1 % allowed limit of the meter's measurement error (B class) defines its verification interval. The proposed model for determining a meter's verification interval represents the second segment of the flexible quality system and an opportunity to modify the metrological guidelines. The model is defined by a flexible verification interval scheme that reflects the meter's conditions of use and is the opposite to rigid verification guidelines that are not optimal for all applications.
The third segment of a flexible quality system is represented by the technical procedures for the quality assurance of measuring instruments, focusing on their reliability or lifetime. Technical procedures are developed based on the findings of experimental research and can be applied generically by the end manufacturer and its suppliers. The ability to improve the quality level in order to meet customer requirements represents the third segment of the flexible quality system.
The dissertation defines the concept of a flexible quality system, which is based on the three previously described segments.