7 things to consider when implementing battery preventive maintenance practices
As of October 2019, 30% of your Bulk Electric System (BES) facilities needed to be compliant with PRC-005-6 (Protection System, Automatic Reclosing, and Sudden Pressure Relaying Maintenance). Since the introduction of the PRC-005 standard by the North American Electric Reliability Corporation (NERC), we have seen all electric power utilities engineering and operations departments reviewing and adapting their standardized protection control systems maintenance practices to meet the minimal maintenance requirements and implementation plan.
When it comes to outlining your companies’ new battery maintenance practices, you will be making important business decisions and you will need to consider the right insights. To help you out with that journey, we have put together the 7 things to consider when implementing battery preventive maintenance practices:
- NERC mandatory vs recommended maintenance
- Type of preventive maintenances (PM)
- Maintenance activities vs time intervals
- Data collection interventions: Manual or automated measurements?
- Comprehensive preventive maintenance workflows
- Data analysis, analytics and reporting
- Battery asset management: Centralized or decentralized?
1. NERC mandatory vs recommended maintenance
The NERC PRC‐005 standard was implemented following the devastating blackout of August 14 2003 where 50 million people lost power in the northeastern and midwestern United States as well as in Ontario. The PRC-005 standard is now enforced by NERC at all Electric power utilities located in Canada, US and Northern Baja California (Mexico) related to the mandated Protection System Maintenance Program (PSMP) for utility facilities connected to the Bulk Electric System (BES).
The PRC-005 standard is subdivided in 5 key discrete pieces of equipment:
1) Protective relays
2) Associated communication systems
3) Voltage current and sensing devices
4) Control circuitry
5) Station DC supply where the station batteries along with battery chargers make up the major part of the station DC supply
As for recommended maintenance, one should be looking at two key points when considering making modifications to company’s maintenance practices.
1) The manufacturer conditions and limitations, which can void the manufacturer’s warranty. Each manufacturer has different set of conditions such as operating temperature, design considerations and charging operation that pertain to their warranty. We recommended taking them in consideration to more easily support any warranty claims.
2) IEEE Standards for stationary batteries maintenance, testing and monitoring written by the ESSB – Energy Storage & Stationary Battery Committee. These standards provide comprehensive maintenance tasks and time intervals, their purpose and establishing specifications. The following are the mostly used maintenance and testing standards for VLA, VRLA and NiCad.
IEEE 1188-2005 : Recommended Practice for Maintenance, Testing, and Replacement of Valve-Regulated Lead-Acid (VRLA) Batteries for Stationary Applications. New guidance to users dealing with premature capacity failures with VRLA batteries and updated definitions are addressed in 2014’s amendment.
IEEE 450-2010 : Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead-Acid Batteries (VLA) for Stationary Applications.
IEEE 1106-2015 : Recommended Practice for Installation, Maintenance, Testing, and Replacement of Vented Nickel-Cadmium (NiCad) Batteries for Stationary Applications
2. Types of preventive maintenance
The goal of preventive maintenance is to prevent equipment failure before it occurs, ultimately eliminating strategic system component failure due to a power outage. There are 3 main reasons why we perform preventive maintenance and testing of batteries:
- To prevent unpredicted failures by tracking the battery’s health
- To ensure the supported equipment is adequately backed-up
- To plan when it is time to replace the batteries
There are different philosophies when it comes to battery maintenance and testing, some will just replace batteries when they die, some will replace the batteries after a certain period of time, other will have a comprehensive maintenance and testing program in place to extend useful life, ensure optimal battery operation and determine optimal time for replacement.
The NERC PRC-005 standard dictates that an established Protection System Maintenance Program (PSMP) be put in place that allows for two types of maintenance methods: performance‐based and time‐based methodologies.
The time-base method suggests that protection systems are maintained based on a defined schedule which is the process required for any stationary batteries. However, it is possible to automate the PRC-005 compliance for station DC supply.
The performance-based method enables the owner to extend the maintenance interval of a specific components based on archiving maintenance records and related statistics. However, stationary batteries are excluded from any performance-based method as there are too many variations due to the electrochemical process.
Some transmission substations can generate more than $10 million of revenue per hour and a $5k station battery is the last line of defense to keep critical system running when a power outage occurs. Is neglecting battery maintenance really a saving versus the potential risk of losing millions of dollars in revenue?
3. Preventive maintenance activities and time Intervals
The PRC‐005 standard mandates minimum maintenance requirements at maximum time intervals for stationary battery maintenance. These tasks and intervals are provided for Vented Lead‐Acid (VLA), Valve Regulated Lead‐Acid (VRLA) and Nickel‐Cadmium (NiCad) batteries. These requirements can be found in the PRC‐005 document in Tables 1‐4 a, b, and c.
For a complete listing of the mandatory activities, please consult the most recent PRC-005 standards version 6 available at NERC.com
IEEE stationary battery standards recommends maintenance practices through many standards where, 1188, 450 and 1106 are the one mostly recognized in Canada, United States and around the world.
The following is a high-level summary of the recommendations in 1188 and time intervals, these tasks and interval are subject to change, please refer to the original and most recent standard at IEEE.org.
Each and every battery manufacturer provides a list of conditions and limitations guidelines to follow in order to honor their warranty. They will also inform you on strategies to help you maximize the life expectancy of your battery assets. Please consult your battery manufacturer when implementing and designing the preventive maintenance programs.
4. Data collection intervention: Manual or automated measurements?
Based on the preventive maintenance activities and intervals, one can now consider what mechanism will be use to collect the data, it can either be a manual intervention, automated or a combination of both. It is generally understood that battery monitors do not completely replace manual maintenance but it can reduce its duration and extend the intervals between them, thus generating Operating Expense (OPEX) savings. On the other hand, the initial Total Cost of Ownership (TCO) for deploying a Battery Monitoring System (BMS) is still difficult to justify Capital Expenditure (CAPEX) due to the quantity of locations to serve. A partial implementation for remote locations, such as helicopter runs for example, is a good assumption.
By manual preventive maintenance type, we mean that a field technician or battery service company will be dispatched to each station or locations based on a pre-determined schedule and she or he will be tasks to perform repetitive tasks on every cell to measure and record battery data. One will have to aggregated all the data from digital voltmeters, hand held battery testers (Ohmic) or visual inspection to be logged and reported back to engineering department for subject matter expert verification and later archived for later auditing purpose. While this process repeats itself constantly, operation managers must control field technician schedules to ensure all locations and battery assets are inspected.
Few considerations for manual preventive maintenance:
- Field technicians performing these types of maintenance must be diligent and fully trained on the hand-held battery tester they are using, otherwise the data will not be usable.
- The maintenance workflow needs to make certain they are using the same hand-held tester model every time in order to trend the data over time. An impedance tester from two different vendors will not provide the same value as different induced signal and algorithms are used to make up the internal Ohmic measurement.
- Baseline for cell/unit internal Ohmic value must be established systematically and shall be retained somewhere in order to trend and compare new values against the baseline.
- Ensure field technicians can notify proper personnel of imminent corrective actions such as bad cell/unit to be replaced, new battery assets found on site (inventory adjustments), etc.
- NERC will audit from time to time, thus all information related to the completed maintenance, the data aggregated, and the data analysis is required. Fines can and most likely will be assessed for non‐compliance.
By automated preventive maintenance type, we mean that all measurements and inspection activities are performed continuously by a permanently installed battery monitoring system which is properly detecting and reporting alarm conditions. PRC-005 states that when no periodic maintenance is specified, one can assume it is not required, thus eliminating costly repetitive preventive maintenance activities. However, electric power utilities have the responsibility to analyze the readings and put in place corrective actions when needed.
Here are a few considerations for automated preventive maintenance:
- It is recognized that the use of permanently installed battery monitoring system can help you extend the maintenance intervals, while reducing the man hours involved.
- Permanent Battery Monitoring System (BMS) calibration should be verified yearly and remember they are not able to detect bulging cells, sign of corrosion, crack post and smell of sulfuric acid.
- Most battery monitoring system will provide remote IP connection; it is a good practice to select a model that conforms with your company’s IP/IT security requirements.
- Selecting a Battery Monitoring System (BMS) that only support proprietary protocols will make it hard to hard to integrate into your enterprise software/systems, look for open protocols like SNMP, Modbus, API, etc.
- Baseline for Ohmic value must be established and shall be retained somewhere in order to trend and compare new values against the baseline, some devices are capable of automatically establishing baselines;
- Battery Monitoring System (BMS) should have the ability to provide dry contacts for simple integration of house alarming where alarm verification should be tested periodically.
Note: The IEEE 1491-2012 – IEEE Guide for Selection and Use of Battery Monitoring Equipment in Stationary Applications provides best practices when employing these devices in you station DC supply network.
5. Comprehensive preventive maintenance workflow
The Preventive Maintenance Program can be seen as a workflow where the battery Principal Subject Matter Expert (SME) Engineer for substations and field technicians are the main actors. However, other participants such as: operations managers, strategic planning, system engineers, administrative and Management will be involved to address other related activities involved.
Depending on your companies’ philosophy, the preventive maintenance workflow can be automated using a specialized battery asset management and centralized maintenance software, which can provide the following benefits:
- Comprehensive asset tracking, on-demand visibility of asset condition, access to accurate maintenance historical and actual asset data eliminating silos between maintenance and engineering resources.
- Automated data transfer from most popular hand-held battery testers and battery monitoring systems to eliminate manipulation errors and reduce time spent on field by technician.
- Built-in approval process to validate field technician’s manual data entries and trigger abnormal data behavior.
- Monitor data behavior to trigger predictive warning to specific asset responsible to enable quick and consistent business decision in tune with your business rules.
- Automated calculation of backup power availability (percentage usage), actualize battery reserve time estimation along with State of Health (SOH) indication, predict maintenance budget and forecast battery replacement investment.
- Track maintenance program schedules by network area to improve equipment uptime; know when the maintenance is on time, coming due, or overdue.
- Quickly identify and report cell/unit which are eligible for warranty claims to allow quick return on investment.
- Simplified access to historical inspection forms, side notes, statuses, asset info, data analysis results and all relevant maintenance information is readily available for all executed maintenance.
6. Data analysis, analytics and reporting
Neither IEEE or NERC PRC-005 standards specifies the measured parameter able to determine that the battery will perform as manufactured as a substitute of conducting a full-blown discharge test (performance capacity test) which can ultimately demonstrate that a battery is able to deliver the energy required versus its actual state of health conditions and load consideration.
As recommended in the PRC-005-06 standard, the measurement indicative of battery performance should be cell internal Ohmic or float current. The three Ohmic measurement are: Impedance, Conductance and Resistance. All three technologies are deemed effective as per EPRI’s technical report No. 1002925. However, the interpretation of the requirement should not be focused on the individual cell pass or fail result, but rather on the assessment of the battery bank as a whole to perform as manufactured. The Ohmic value should be trended along the lifespan of the battery to see abnormal behavior of the trend, also it is established that any deviation below 85% of the baseline should trigger further investigation. At 65% and below, the cell should be replaced within a reasonable time (maximum 1 year).
Other battery parameters such as and not limited to voltage, float charging current, temperature and intercell connection resistance value must be collected and verified against a set of specifications (tolerances). Exceeding these tolerances should warn for further investigation and corrective actions. These specifications are normally provided by the battery manufacturer, hand-held battery tester manufacturers, battery monitoring system manufacturers or IEEE standards.
Battery maintenance data should be analyzed by hand or automatically by a software, a battery subject matter expert (in-house power engineers or battery services contractors) should carefully review the resulting analysis to establish the battery State of Health (SOH) based on knowledge and a set of common conditions to trigger when a battery replacement (Corrective action) must be performed.
7. Battery asset management, centralized or decentralized?
Based on the National Academies Press (NAP), the Electric Power Transmission and Distribution (T&D) in the United States is composed of approximately 3,000 power plants and 15,000 Transmission Substations and 60,000 Distribution Substations to practically power any building and facility in the continental US alone.
Still considering both options? Centralized or decentralized? Many companies have moved back and forth between these two models, we have seen both models do well and struggle. One should look at the advantages and disadvantages to help decide on the best organizational structure to implement.
However, in the event you are moving forward with a centralized battery asset management solution, one should look at the support and commitment of the organization top management over the long-term, picking an asset management leader with good communication skill allowing the Maintenance & Engineering responsible for station DC system reliability to work together toward common goals.
Any small or large electric power utilities will come to realize that the benefits and advantages of a centralized battery asset management solution will outdo the disadvantages. Still using Excel spreadsheet? What if it was possible to continuously and automatically collect, analyze, and trigger battery cell/unit replacements for all your critical battery assets network?
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