IEEE P3006.2-D5-2015 pdf download – Draft Recommended P ractice for Evaluating the Reliability of Existing Industrial and Commercial P ower Systems.
5.3 Control and protection One level below the configuration is the control and protection system. Even if the power system configuration is adequate to provide the required level of reliability, its performance can be compromised by failure of the control and protection system. Controls such as automatic bus transfer schemes and standby generator control systems must function properly to make alternate paths or sources of power available to the load on failure of the primary source. Protective devices must be selectively coordinated to isolate the load from faulted portions of the system and prevent faults on one path or in one portion of the system from causing interruption of multiple paths or sources. 5.4 Physical installation The physical configuration and location of electrical equipment should be reviewed. Is the equipment adequately protected from physical damage and environmental hazards? Are redundant paths provided with physical segregation so that a major failure of one piece of equipment cannot readily propagate to redundant circuits or equipment? 5.5 Operations and maintenance Finally, operations and maintenance (O&M) practices are critical to achieving the designed-in reliability of the system. Effective commissioning helps assure that control and protection systems function per design. Preventive maintenance can reduce failure rates and an adequate level of spare parts stocking can reduce repair times when failures do occur. Effective policies, procedures, documentation, and training of O&M personnel reduce outages due to human activity and improves operator response time when failures occur. (see IEEE Std 3007.1 Recommended Practice for the Operation and Management of Industrial and Commercial Power Systems and IEEE Std 3007.2 Recommended Practice for the Maintenance of Industrial and Commercial Power Systems)
The utility’s history of interruptions can be compared with recorded dollar losses in assessing process vulnerability. By assigning a dollar loss to each interruption, it may be possible to determine a relationship between the duration of a power loss and monetary loss for a particular facility. When the actual outage cost is higher or lower than would be predicted, the cause of the deviation should be determined. For example, a 15 min power loss at a shift change will be less costly than one during peak production. With a refined cost formula in hand, the cost of available options vs. projected losses can be evaluated. Occasionally a facility experiences problems at times other than during a recorded outage. These problems may be caused by power quality deviations such as voltage sags or, more rarely, voltage swells that are difficult to trace (Refer to IEEE Std 141 for definitions of acceptable voltage ranges). With problems such as these, it is necessary to begin recording the exact date and time of these occurrences and ask the utility to search for faults or other system disturbances at or near the specific times that they have been recorded. It would be wise to convey the fault times to the utility reasonably soon after the fault. It must be emphasized that unless these problems are significant in terms of dollars lost, safety, or frequency, it is not reasonable to pursue the cause of voltage dips since they are a natural phenomenon in the expansive system operated by a utility. Voltage sags can be caused by large motor starting, welder or electric furmace inrush, or faults on other distribution feeders supplied by the same substation bus as facility feeders.