The investigation was carried out at the UEB Fuse and Disconnect Factory belonging to the Electromechanical Productions Company. It addresses the concepts most used in planned preventive maintenance and their importance.
The current situation and suitability of the maintenance process are described, and based on the existing contradiction between the objectives of this process and the indicators used to measure its effectiveness, the use of new objectives and indicators is proposed.
Based on the importance of the organization's flagship product, the K-type medium-voltage fusible link, for the production and quality of the organization, the reliability study of the A20B automatic lathe is carried out, with the aim of predicting the exact moment with greater accuracy. in which preventive maintenance must be carried out, and allowing these studies to be generalized to the rest of the installed equipment.
To carry out the reliability study, the Statistical Package for the Social Sciences (SPSS) was used.
INTRODUCTION
The UEB Factory of Fuses and Disconnectives was created in January 2000 by the Company of Generators and Electric Services (GEYSEL) and since April 1, 2007 belongs to the Company of Electromechanical Productions (EPEM) of the Ministry of Basic Industry (MINBAS).
Annex 1 shows the organizational structure, which has seven departments, a calibration laboratory for electrical energy meters and electrical tests, and six work brigades directly linked to production.
Its corporate purpose is the wholesale production and marketing of electrotechnical and electromechanical components, as well as the provision of calibration services and electrical tests for electrotechnical components to the entities of the Unión Eléctrica.
Its main products include the 15 kV and 34 kV type K medium voltage fusible link, the drop-out circuit breakers, single-pole and three-pole disconnectors, test chains, thimbles, calibration of energy meters, the assembly of street lighting luminaires and cabinets for electric energy meters (see annex 2), and its main clients are the Basic Electric Organizations (OBE) of the fourteen provinces of the country and the special municipality of Isla de la Juventud.
The organization has implemented and certified an integrated management system that includes the quality management system based on the NC-ISO 9001: 2008 standard, the occupational health and safety management system based on the NC 18001 standard.: 2005 and the environmental management system based on the NC-ISO 14001: 2004 standard.
It has also accredited the Laboratory for the Calibration of Electric Energy Meters based on the NC-ISO / IEC 17025: 2006 standard and works on the design, implementation and integration of the requirements of standard NC 3001: 2007 (Integrated Management System for Human Capital) to the integrated management system, as well as the certification of its main products and the accreditation of the Electrical Testing Laboratory. Within this integrated management system, the organization's policy is to satisfy the needs and expectations of customers, preserve the environment and guarantee the safety and health of workers.
The mission of the organization is to produce and commercialize competitive electrotechnical and electromechanical components in a wholesale manner, that satisfy the needs and expectations of national clients, to improve electrical networks, using for this purpose a highly trained and professional human resource that allows improvement. Continues its processes and creates the conditions for insertion in the international market; while its vision is to be an organization recognized for its leadership and business competitiveness, with cutting-edge technology and an excellent human resource, with a sense of belonging, motivated and qualified that diversifies and integrates quality products with management that anticipates and adapts to change, learn from experience and innovate permanently.
where:
represents the total number of maintenance carried out; and the total number of planned maintenance.
- If ≥100 the indicator is evaluated OK.If 90≤ <100 the indicator is evaluated REGULAR.If <90 the indicator is evaluated NOR.
2.1.2 Average real availability ()
where is the actual availability and is determined as:
where:
it is the actual service time; it is the real time of the maintenance;
it is the planned production; and
is the production capacity.
- If ≥90% the indicator is evaluated as OK. If 75% ≤ <90% the indicator is evaluated as REGULAR. If <75% the indicator is evaluated as NG.
2.1.3 Average maintenance effectiveness (
- If ≥90% the indicator is evaluated as OK. If 75% ≤ <90% the indicator is evaluated as REGULAR. If <75% the indicator is evaluated as NG.
2.1.4 Average cost of maintenance (
where is the cost of each maintenance performed and is determined as:
where:
is the maintenance cost;
it is the value of the realized production;
it is the real time of the maintenance;
it is the real time worked; and it is the unit cost of production.
- If ≥90% the indicator is evaluated as OK. If 75% ≤ <90% the indicator is evaluated as REGULAR. If <75% the indicator is evaluated as NG.
2.2 Reliability study of the A20B automatic lathe
The absence of a procedure that determines the reliability of the equipment used for the production process, means that compliance with the preventive maintenance plan is affected by failures and unexpected interruptions, which deteriorates the availability indicator and, at the same time, compliance of the maintenance plan.
For this reason, a feasibility study was carried out with the aim of forecasting more precisely the exact moment in which preventive maintenance should be carried out.
2.2.1 Selection of the equipment for the reliability study
The organization has 42 installed equipment that are part of the production process, however not all have the same importance within it, mainly due to the volume of production and the time of exploitation, aspects that differ considerably in many cases.
Therefore, it was necessary to carry out the reliability study on equipment that will be of vital importance in the production volume and that its incidence on product quality would be high.
The list of equipment with its degree of mechanical (RM) and electrical (RE) complexity is shown below.
From the importance it has for the production and quality of the medium voltage fusible link type K, for its complexity and the high exploitation that it has been subjected to for years, and for being the equipment that has the most damage due to breakdown in the organization., it was decided to carry out the reliability study on the A20B automatic lathe. Below are two photos of the A20B automatic lathe.
Photo # 1 View of the main mechanism of the A20B automatic lathe.
Photo # 2 General view of the A20B automatic lathe.
The fundamental characteristics of the A20B automatic lathe are:
- Denomination: Automatic lathe Model: A20B Country of origin: Czechoslovakia Year of manufacture: 1975 Year of installation: 1975 Inventory number: 19907 Revolutions per minute: 1720 rpm Consumption: 4 kW Weight: 1250 kg Mechanical complexity degree; 15.5 Degree of electrical complexity; 2.5 Power supply voltage: 220 V Supply voltage frequency: 60 Hz
2.1.1 Selection of the method and input data for the reliability study
To carry out the reliability study, the Statistical Package for the Social Sciences (SPSS) was used.
The selection of the input data for the reliability study was made from the data that appears in the equipment folder, where the breaks presented and the work carried out are collected.
The data used (Figure 1) correspond to the time elapsed between failures from June 2006 to December 2009 and are considered to follow a normal distribution.
To determine the distribution that best fits the input data, we assume as null hypothesis H 0 that the distribution used indicates the level of coincidence between the fit and the input data, so if the significance level is less than 0, 05 we reject H 0 and we will conclude that said distribution does not indicate the coincidence between the fit and the input data, while if the significance level is greater than 0.05 we accept H 0 and we will conclude that said distribution does indicate the coincidence between the setting and input data.
Figure # 1 Times elapsed between failures from June 2006 to December 2009 on the A20B automatic lathe.
2.1.2 Selection of the optimal model for the reliability study
Considering that the input data represents a continuous sample, the Chi-square and Kolmogorov-Smirnov statistics were used. These statistics indicate the level of agreement between the fit and the input data, and the level of confidence you can have that the data has been produced by the distribution function. For each of these statistics, the lower the value, the better the fit.
When calculating using the Exponential and Weibull distributions, it was found that they did not fit the hypothesis, which was fulfilled by using the Lognormal distribution (Figure 2). All calculations were performed for a 90% confidence interval.
Figure # 2 Model used to determine the level of agreement between the fit and the input data.
The Lognormal distribution is also applicable since:
- represents the evolution over time of the failure rate, that is, the probability that a component that has worked until time t fails between t and t + In this case the independent variable of the distribution is time; it allows setting times component repair, in this case also being the time the independent variable of the distribution; and
describes the dispersion of component failure rates, caused by different data sources, different operating conditions, environment, different data banks, etc. In this case, the independent variable of the distribution is the failure rate.
From the importance it has for the production and quality of the medium voltage fusible link type K, for its complexity and the high exploitation that it has been subjected to for years, and for being the equipment that has the most damage due to breakdown in the organization., it was decided to carry out the reliability study on the A20B automatic lathe. Below are two photos of the A20B automatic lathe.
Photo # 1 View of the main mechanism of the A20B automatic lathe.
Photo # 2 General view of the A20B automatic lathe.
The fundamental characteristics of the A20B automatic lathe are:
- Denomination: Automatic lathe Model: A20B Country of origin: Czechoslovakia Year of manufacture: 1975 Year of installation: 1975 Inventory number: 19907 Revolutions per minute: 1720 rpm Consumption: 4 kW Weight: 1250 kg Mechanical complexity degree; 15.5 Degree of electrical complexity; 2.5 Power supply voltage: 220 V Supply voltage frequency: 60 Hz
2.1.1 Selection of the method and input data for the reliability study
To carry out the reliability study, the Statistical Package for the Social Sciences (SPSS) was used.
The selection of the input data for the reliability study was made from the data that appears in the equipment folder, where the breaks presented and the work carried out are collected.
The data used (Figure 1) correspond to the time elapsed between failures from June 2006 to December 2009 and are considered to follow a normal distribution.
To determine the distribution that best fits the input data, we assume as null hypothesis H 0 that the distribution used indicates the level of coincidence between the fit and the input data, so if the significance level is less than 0, 05 we reject H 0 and we will conclude that said distribution does not indicate the coincidence between the fit and the input data, while if the significance level is greater than 0.05 we accept H 0 and we will conclude that said distribution does indicate the coincidence between the setting and input data.
Figure # 1 Times elapsed between failures from June 2006 to December 2009 on the A20B automatic lathe.
2.1.2 Selection of the optimal model for the reliability study
Considering that the input data represents a continuous sample, the Chi-square and Kolmogorov-Smirnov statistics were used. These statistics indicate the level of agreement between the fit and the input data, and the level of confidence you can have that the data has been produced by the distribution function. For each of these statistics, the lower the value, the better the fit.
When calculating using the Exponential and Weibull distributions, it was found that they did not fit the hypothesis, which was fulfilled by using the Lognormal distribution (Figure 2). All calculations were performed for a 90% confidence interval.
Figure # 2 Model used to determine the level of agreement between the fit and the input data.
The Lognormal distribution is also applicable since:
- represents the evolution over time of the failure rate, that is, the probability that a component that has worked until time t fails between t and t + In this case the independent variable of the distribution is time; it allows setting times component repair, in this case also being the time the independent variable of the distribution; and
describes the dispersion of component failure rates, caused by different data sources, different operating conditions, environment, different data banks, etc. In this case, the independent variable of the distribution is the failure rate.
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