Assessing the sufficiency indicators of a set of spare parts, tools and accessories for uninterruptible power supplies of a data centre using data sheet specifications
Authors: Zhadnov V. V. 
Published: September 2022

Aim. To suggest a method of estimating the parameters of a set of spare parts, tools and accessories (SPTA) according to data sheet specifications for industrial uninterruptible powers supplies (UPS) of data centres using state-of-the-art techniques.

Methods. The paper uses methods of the dependability theory, the Markov process theory and the optimisation method.

Results. Using the suggested approach, the stages of parametric synthesis of an SPTA kit were defined for mainline modular UPS that feature redundancy with repair and limited SPTA. For each stage, the application of mathematical models required for calculating the dependability characteristics and parameters of power module components based on UPS dependability indicators is substantiated along with the mathematical models that associate the sufficiency indicators of an SPTA kit with its parameters. Those models allow calculating the failure and recovery rates of UPS power modules, as well as the mean time to failure and restoration based on the data sheet specifications of reliability, maintainability and availability. In turn, the obtained dependability characteristics are the input data for calculating the SPTA sufficiency values (average delay in meeting a request). Using the value of average delay in meeting a request with an SPTA kit as a criterion for the mean time to power module restoration allows suggesting that it is, in principle, possible to ensure the specified dependability indicators in the course of its operation, and, therefore, such UPS can be used. Should the latter be possible, then using the value of average delay in meeting a request as a restriction, while taking into account the restrictions on the initial SPTA inventory, will allow synthesising the SPTA kit (select a replenishment strategy and define its parameters (delivery time, etc.). Comparing the logistical capabilities and the resulting data for the selected replenishment strategy will allow making a final conclusion regarding the capability to maintain the specified UPS dependability characteristics throughout the operation period. Using the above method, the parameters were synthesised of a single kit of spare parts, tools and accessories, using the Protect 3.M UPS as an example.

Conclusion. The approach suggested in the paper allows estimating both the general feasibility of ensuring the specified dependability, and the economic expediency of using industrial mainline modular UPS with redundancy and recovery. Additionally, if ensuring the UPS dependability is possible, but the operating costs of its maintenance are unacceptable, the possibility of reducing the number of repair teams (reducing the cost of their deployment) and/or using more efficient redundancy methods (mixed redundancy, mixed redundancy with rotation, etc.) should be evaluated. However, it should be taken into consideration that the proposed approach based on the use of mathematical models does not guarantee a 100% accuracy of SPTA parameter estimation, as the mathematical models that it uses, like any other models, have a limited accuracy and the results obtained with their help require experimental confirmation by means of testing or controlled operation.