Protecting Batteries that Protect Your Power System

Wally Vahlstrom, Director of Technical Services
Emerson Network Power, Electrical Reliability Services

According to the US Department of Energy, reported electric emergency incidents and disturbances are on the rise with approximately 23 percent more events reported last year as compared to 2013. These outages or disturbances can cost facilities thousands or even millions of dollars if their emergency power systems do not immediately switch on and provide back-up power.

Ensuring that emergency power systems will provide reliable back-up power begins with battery management. Batteries are considered the most critical, yet vulnerable component of emergency power systems. Battery failure is one of the leading causes of back-up power system failure and the resulting outages and losses. Additionally, in the event of a power outage, a single bad cell in a string can leave a facility’s critical processes without protection.

Despite having this knowledge, many users do not have a proactive battery management strategy in place. Following are some key strategies and best practices that should be considered when determining the strategy that is right for your application and business.

Strategy 1: Comprehensive Battery Maintenance
A comprehensive preventive maintenance program for emergency power system batteries is one of the most cost-effective measures that can be taken to ensure reliability and prevent costly downtime.

MTBFChartAn effective preventive maintenance program should include regular inspections of batteries and battery charging equipment, thorough and well-documented battery testing, and proactive battery replacement to ensure batteries are capable of doing their job and supporting critical operations when needed.

In fact, one Emerson analysis involving more than 450 million operating hours for more than 24,000 strings of batteries revealed that an increase in the number of preventive maintenance visits substantially increased a system’s mean time between failures.

Preventive maintenance on batteries should be completed according to industry standards like the following from the Institute of Electrical and Electronics Engineers (IEEE):
•  IEEE 450 for vented lead-acid (VLA)
•  IEEE 1188 for valve-regulated lead-acid (VRLA)
•  IEEE 1106 for nickel-cadmium (NiCad)

Battery manufacturers often cite IEEE standards and require adherence in order to maintain a valid product warranty. All of these standards provide recommended practices for maintenance, testing and replacement of batteries for stationary applications. They address the frequency and type of inspection or measurements that need to be made to validate the condition of the battery.

The measurements needed such as string/cell voltage or battery float charging current are outlined in the IEEE standards based on monthly, quarterly, and annual inspections. The more frequent the inspection or testing intervals, the better. Gathering data on a more regular basis can be very helpful for trending battery performance and ultimately extending the useful life of these critical assets.

Capacity Tests
Recommendations for capacity testing of VLA and VRLA batteries are very similar. Both should be tested at installation, during periodic intervals (no greater than 25 percent of the expected service life), and annually when the battery shows signs of degradation or has reached 85 percent of the expected service life. The IEEE standard also suggests that VRLA batteries should be tested when internal ohmic values have changed significantly between readings or physical changes have occurred.

For these two battery groups, degradation is indicated when the battery capacity drops more than 10 percent from its capacity on the previous test or is below 90 percent of the manufacturer’s rating. For NiCad batteries, capacity/discharge testing should be done within the first two years of service, at five-year intervals, or annually if the previous test shows evidence of excessive capacity loss.

Both IEEE 450 and 1188 recommend replacing the battery if its capacity is below 80 percent of the manufacturer’s rating. And the replacement should be made expeditiously. Physical characteristics such as plate condition or abnormally high cell temperatures are often indicators that the complete battery string or individual cell should be replaced.

NERC Standards for Utilities
In addition to the IEEE standards, utilities also need to meet battery maintenance requirements stipulated by the North American Electric Reliability Corporation (NERC). NERC’s standard PRC-005-2, which went into effect in 2013, applies to electric utilities. This encompasses all electric utility functional entities, including substations and power generating plants.

It mandates certain minimum maintenance requirements for batteries that support equipment connected to the Bulk Electric System (BES), the electrical grid responsible for power across large regions of the US, within a certain amount of time. The PRC-005-2 standard does recommend service technicians use the best-practice battery maintenance procedures published by IEEE.

When it comes to preventive maintenance on batteries, unfortunately, common practices often replace best practices. Governed by real-world factors, many facility managers are often forced to take into account the cost of performing the recommended IEEE schedule as it relates to the criticality of the application.

While following the IEEE schedules is recommended, everyday pressures can push in the opposite direction. As a result facility managers are encouraged to consult manufacturer guidelines for recommended maintenance and potential cost-effective options.

Strategy 2: Battery Monitoring with Remote Services
Once a battery is operating properly, it’s important to proactively monitor daily performance trends to help detect battery failure. A continuous battery monitoring system assesses a battery’s true state of health. Instead of waiting for an inevitable failure or replacing batteries prematurely to prevent problems, monitors allow organizations to continue to utilize their batteries longer and with confidence by knowing the true condition of all critical battery parameters, such as cell voltage, internal resistance, cycle history, overall string voltage, current and temperature.

BatteryTestThe best way to determine a battery’s health without discharging it is to use a monitoring system that measures the internal resistance of all of the cells in the battery string. As the battery ages and loses capacity, the resistance of a battery cell’s internal conduction path increases. In an aged string, substantial increase of the resistance in one cell is typically considered end of life for a complete battery string.

Because 40 percent of the resistance in a battery cell is in effect paralleled with capacitance, DC resistance measurements are more accurate. With AC testing methods, the capacitance tends to mask the increase in resistance. DC resistance-based testing eliminates the capacitance considerations completely.

The information gained from battery monitoring should be analyzed and used to optimize battery life. For example, VRLA batteries are sensitive to temperature and float voltage settings. A battery monitor can provide ambient temperature, cell voltage, internal resistance, and data logging of the batteries monitored, allowing these conditions to be optimized, thereby utilizing the maximum available life and performance of the battery.
While there are many battery monitoring services available, the best solution to optimizing battery performance is to utilize an integrated service that combines state-of-the art battery monitoring technology with remote services.

Because managers have their plates full with responsibilities for running an efficient, reliable facility, battery monitoring may fall to the bottom of the list of priorities. In these cases, remote services, managed by an organization with resources devoted to battery monitoring, can provide great value. Remote services lift the burden of infrastructure monitoring from internal personnel. They allow for real-time diagnosis and near instant notification when a problem occurs.

When actual performance data falls outside of the established parameters, signaling performance degradation, an alert can be transmitted to remote power system engineers and/or product experts who assess the situation through data analysis. This in turn can generate a work order to inspect, repair, or replace the part that caused the alert, or it can initiate a notification process for key personnel if warranted. In either case, problems that have the potential to result in lost production or other losses can be avoided.

In addition to improved resource utilization, a dedicated monitoring organization can respond more quickly to larger infrastructure issues. For instance, in monitoring data across multiple facilities, they may be alerted to a problem caused by a certain part or component. Very quickly, the manufacturer can be notified so as to avoid a potential problem occurring across hundreds of sites, many of which contain similar parts or components.

A remote monitoring service provider may also have engineers on staff that systematically analyze data in real time. For example, they could recognize if an emergency generator has started and is providing power, but at the wrong time and for the wrong reason. The engineers would be alerted to this situation because when the uninterruptible power supply (UPS) is receiving utility power, the input power frequency is precisely 60 hertz. However, if the monitoring staff sees the input frequency vary within 58 to 61 hertz, engineers would immediately recognize that an emergency generator has started and is providing power. And because of other data they are receiving, they would know if there is a valid reason for the emergency generator to be running.

This exemplifies the importance of trended and historical data that can be collected with a remote monitoring service. Such data can help technicians identify conditions that deviate from normal operating conditions, but fail to trigger an alarm. Anomalies like these could indicate impending equipment issues, but are easy for technicians to miss when they lack access to trending data that can be compiled into equipment profiles.

Finally, telemetry-based monitoring enables remote management of systems where authorized, allowing the monitoring partner to control systems remotely. This is particularly valuable when a facility is undergoing changes and updates.

There’s an inherent benefit in having a centralized expert group that can conduct detailed analysis and proactively manage it. If a problem occurs, this group can immediately alert personnel of the situation, diagnose the problem, alleviate the problem prior to deterioration or failure, and dispatch a technician if needed.

Strategy 3: Proactive Battery and Capacitor Replacement
The actual life of emergency power system batteries is almost always shorter than the design life indicated by the manufacturer. The rate at which batteries will deteriorate depends not only on the type of battery used, but also on the specific application, how the battery is maintained, and the environment in which the battery operates. More specifically, there are several issues that can shorten the life of a battery string such as short circuit events on the incoming utility supply feeder (resulting in UPS engagement); high or improper room temperatures; high or low charge voltage; excessive charge current; manufacturing defects; overcharging and over-cycling; loose connections; strained battery terminals; and poor or improper maintenance.

Proactive replacement of batteries as they reach the end of their useful life is recommended to keep the power system running while minimizing risk of downtime. The same can also be said for UPS capacitors. Like batteries, capacitors used in UPS systems can fail unexpectedly. They too should be monitored and replaced before failure occurs.
Working through an experienced battery application engineer can help ensure a safe, reliable change-out of batteries, capacitors, or other deteriorated components.

Strategy 4: Mobile Power for Maintenance and Replacement
Performing maintenance on the emergency DC system can pose a risk to operations. If the utility source drops off line or suffers a power dip during the time when the battery is being serviced or tested, the results could be disastrous. For many critical facilities such as chemical plants, refineries, or power plants, disabling the emergency power system in order to perform required inspections, tests, and component replacements is not an option. Having access to a mobile power solution is hugely beneficial in these situations.
Mobile power means that facility managers receive dependable, temporary power with the added convenience of timely, on-site services. By working with a service provider with a mobile DC power option, facilities are able to support and back up critical loads, ensuring no business interruptions during battery maintenance.

As more and more emphasis is placed on availability and reliability of critical power systems, organizations need to understand that without properly operating batteries, no emergency power system can do its job. Batteries are the heartbeat of this system, and when well-managed, they protect critical operations and help facility managers avoid the high cost and detrimental impact of unplanned downtime.

Each of these strategies to maximize the availability and performance of battery systems can be adopted individually, but often provide even better reliability and performance when combined with others. The first strategy to consider is implementing a comprehensive battery maintenance program that utilizes industry best practices and is compliant with IEEE and/or NERC guidelines. Additionally, when facilities utilize a strategy of battery monitoring coupled with remote services, they can better optimize battery life and benefit from fast identification and correction of system issues. Regular maintenance and monitoring then allows for replacement of batteries (and other components) based on performance trending, instead of simply replacing based on battery age. Finally, utilizing a mobile DC power solution during battery maintenance is another strategy that will help ensure your facility stays up and running.

For more on determining a battery management strategy that is right for your business, watch the video on Emerson’s Mobile DC Power Services Unit or download the e-book entitled Battery Maintenance Solutions for Critical Facilities.

Wally Vahlstrom brings more than 40 years of electrical engineering experience to his position as the director of technical services for Emerson Network Power’s Electrical Reliability Services group, where he is responsible for failure investigation work, conformity assessment services, power system studies, and reliability analysis.

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