It’s Just a Battery
Proactive Condition / Performance Monitoring and Preventative Maintenance
For NETA by
Rodrick J. Van Wart
Senior Consultant / Instructor
AVO Training Institute, Dallas Texas
Earthquakes, hurricanes, tsunamis, wild fires and the like do not occur with any predicted great frequency. None the less we have established precautionary programs that protect people and property from the physical threats posed by such violent events. In recent times we have witnessed all too well the impact that these occurrences have on the quality of our lives and businesses. Another threat even more sinister is that of the malicious intent of groups such as Al Qaeda and ISIS to disrupt the national electrical infrastructure through cyber terrorism. They have demonstrated that they understand the techniques to be employed. According to FBI information other countries such as China, Saudi Arabia, France and Spain have experienced such attacks. Additionally, major US companies have reported major breaches targeting their source codes.
Our world today has become highly and in many cases wholly dependent upon electricity. This energy source provides the drive in support of our global economy, e-commerce and communications. When the primary AC systems fail we have an established protocol in our DC storage systems in the form of uninterruptable power supplies. The prime source of this backup power is our battery. If it fails to deliver, as it did in the earthquake and subsequent tsunami that inundated northern Japan, we become witnesses to disaster. This places any reliance and reliability of these systems into question.
Estimates according to EPRI, the Electrical Power Research Institute, of losses due to power interruptions cost the US approximately $80 billion per year. Two thirds of these losses are momentary interruptions and weigh in at $52 billion. Power outages carry an enormous price tag and account for losses between $104 billion and $124 billion each year. Add to that another $15 to $24 billion to power quality issues. The annual downtime average for the utility grid in the US is currently 8 hours 45 minutes; with onsite generation equipment and UPS solutions, that downtime can be managed to an equivalent of 5 minutes per year.
Studies concur that for small businesses the financial implications start at about $10,000 an hour and extend to $1,000,000 and higher per hour for larger companies that rely on e-commerce.
The Eaton Corporation conducted a Root Cause Study that revealed that two-thirds of downtime events stem from preventable causes. Studies have also shown that approximately four percent of UPS failures are the result of component aging while up to 20 percent fail due to battery degradation. These studies show that:
Preventable downtime (67%) is attributed to:
- Poor Design
- Inadequate Redundancy
- Insufficient Maintenance
- Human Error
- Incorrect Procedure
Non-preventable downtime (33%) is caused by:
- Equipment failure (even with PM programs in place)
- Service and supply chain failure
- Cyber terrorism
Of the 67% of reported load losses identified by Eaton during an analysis of its own service data, failures resulting from preventable human error and site design attributed to:
- Error in operations
- Error in design (under sized)
- Technician error
- Factory Quality
- Defective Parts
- End of life
The good news is that routine established condition / performance monitoring coupled with the IEEE recommended periodicities of preventative maintenance will appreciably reduce downtime. In fact the same load loss report indicated that clientele without any PM were almost four times more likely to experience a UPS failure than those who complete the IEEE recommended maintenance visits. These findings alone validate the effective significance of routine UPS service as a highly effective means to reduce the potentially devastating effects of downtime.
There are different philosophies and ambition levels for maintaining and testing batteries. Some examples:
Just replace batteries when they fail or die. There is minimum or no maintenance and testing.
Obviously, not testing batteries at all is the least costly with considering only maintenance costs but the risks are great. The consequences must be considered when evaluating the cost-risk analysis since the risks are associated with the equipment being supported. Batteries have a limited lifetime and they can fail earlier than expected. Time between outages is usually long and if outages are the only occasions the battery shows its capability risk is high that reduced or no back-up is available when needed. Having batteries as back-up of important installations without any idea of their current health spoils the whole concept of a reliable system.
Replace after a certain time with minimum or no maintenance and testing. This might also be a risky approach. Batteries can fail earlier than expected. Also it is waste of capital if the batteries are replaced earlier than needed. Properly maintained batteries can and do live longer than the predetermined replacement time.
A serious maintenance and testing program in order to ensure the batteries are in good condition, prolong their life and to find the optimal time for replacement . A maintenance program including inspection, impedance and capacity testing is the way to track the battery’s state of health. Degradation and faults will be found before they become serious and surprises can be avoided. Maintenance costs are higher but this is what you have to pay for to get the reliability you want for your back-up system. The best testing scheme is the balance between maintenance costs and risks of losing the battery and the supported equipment. For example, in some transmission substations, there is upwards of $10 million per hour flowing through them. What is the cost of not maintaining battery systems in those substations? A $3000 battery is fairly insignificant compared to the millions of dollars in lost revenues. Each company is different and must individually weigh the cost-risk of battery maintenance
There are numerous reasons why a UPS fails. The most common causes are:
The heart of any UPS, batteries, requires inspection and maintenance regardless of their age or warranty status, even “maintenance free” batteries. Studies show that up to 20 percent of UPS failures can be attributed to bad batteries, with temperature and cumulative discharges cited as the primary culprits. When performing preventive maintenance, data is obtained from thorough testing procedures, during which impedance or conductance measurements trace the battery performance and identify any batteries with potential internal failures.
Each battery type, VLA / VRLA, has many failure modes, some of which are more prevalent than others. Some of them manifest themselves with use such as sediment build-up due to excessive cycling. Others occur naturally such as positive grid growth (oxidation). It is just a matter of time before the battery fails. Maintenance and environmental conditions can increase or decrease the risks of premature battery failure.
Positive grid corrosion is the expected failure mode of flooded lead-acid batteries. The grids are lead alloys (lead calcium, lead-antimony, lead-antimony-selenium) that convert to lead oxide over time. Since the lead oxide is a larger crystal than lead metal alloy, the plate grows. The growth rate has been well characterized and is taken into account when designing batteries. In many battery data sheets, there is a specification for clearance at the bottom of the jar to allow for plate growth in accordance with its rated lifetime, for example, 10 or 20 years.
At the designed end-of-life, the plates will have grown sufficiently to pop the tops off of the batteries. But excessive cycling, temperature and over-charging can also increase the speed of positive grid corrosion. Impedance will increase over time corresponding to the increase in electrical resistance of the grids to carry the current. Impedance will also increase as capacity decreases as depicted in the graph in figure 2. Sediment build-up (shedding) is a function of the amount of cycling a battery endures. This is more often seen in UPS batteries but can be seen elsewhere. Shedding is the sloughing off of active material from the plates, converting to white lead sulphates.
Sediment build-up is the second reason battery manufacturers have space at the bottom of the jars to allow for a certain amount of sediment before it builds-up to the point of shorting across the bottom of the plates rendering the battery useless. The float voltage will drop and the amount of the voltage drop depends upon how relatively hard the short is. Shedding, in reasonable amounts, is normal.
Corrosion of the top lead, which is the connection between the plates and the posts is hard to detect even with a visual inspection since it occurs near the top of the battery and is hidden by the cover. The battery will surely fail due to the high current draw when the AC mains drop off. The heat build-up when discharging will most likely melt then crack open and then the entire string drops off-line, resulting in a catastrophic failure.
Plate sulphation is an electrical path problem. A thorough visual inspection in VLA batteries can sometimes find traces of plate sulphation. Sulphation is due to low charger voltage settings or incomplete recharge after an outage. Sulphates form when the VPC voltage is not set high enough during recharge. Sulphation will lead to higher impedance and a lower capacity.
Dry-out is a phenomenon that occurs primarily in VRLA batteries due to excessive heat (lack of proper ventilation), over charging, which can cause elevated internal temperatures, high ambient (room) temperatures, etc. At elevated internal temperatures, the sealed cells will vent through the PRV. When sufficient electrolyte is vented, the glass matte no longer is in contact with the plates, thus increasing the internal impedance and reducing battery capacity. This failure mode is easily detected by impedance testing and is one of the more common failure modes of VRLA batteries.
Soft (a.k.a. dendritic shorts) and Hard shorts occur for a number of reasons. Hard shorts are typically caused by paste lumps pushing through the matte and shorting out to the adjacent (opposite polarity) plate. Soft shorts, on the other hand, are caused by deep discharges. When the specific gravity of the acid gets too low, the lead will dissolve into it. Since the liquid (and the dissolved lead) are immobilized by the glass matte, when the battery is recharged, the lead comes out of solution forming threads of thin lead metal, known as dendrites inside the matte. In some cases, the lead dendrites short through the matte to the other plate. The float voltage may drop slightly but impedance can find this failure mode easily.
Thermal run-away occurs when a battery’s internal components melt-down in a self-sustaining reaction. Normally, this phenomenon can be predicted by as much as four months or in as little as two weeks. The impedance will increase in advance of thermal run-away as does float current. Thermal run-away is relatively easy to avoid, simply by using temperature-compensated chargers and properly ventilating the battery room/cabinet. Temperature compensated chargers reduce the charge current as the temperature increases. Remember that heating is a function of the square of the current. Even though thermal run-away may be avoided by temperature-compensation chargers, the underlying cause is still present.
While the numerous components that comprise a UPS are clearly susceptible to failure, a preventive maintenance service plan ensures that these parts are regularly examined, greatly reducing the risk of a load loss while extending the overall lifespan of your UPS.
Because all manufacturers’ UPS’s are complex devices that perform several critical power conditioning and backup supply functions, they are all subject to failure. However, by implementing a comprehensive preventive maintenance service plan that is delivered by trained and certified technicians, you can significantly reduce your vulnerability to a load loss and extend the lifespan of your UPS. Through the completion of systematic inspections, a preventive maintenance plan ensures that the various electronic and mechanical components of a UPS are thoroughly evaluated, cleaned, tested and calibrated on a regular basis. Without proper maintenance, many UPSs will fail prematurely since critical components such as batteries and capacitors wear out from normal use. However, a solid maintenance plan identifies issues and greatly reduces this risk of failure.
Rodrick has over 18 years in the electrical utility industry. His expertise includes chairing the development of testing for the International Code Council’s residential, commercial, and plans examiner electrical exams for inspectors for three years; Conducting training for the State of Iowa Electrical Examining Board members and support staff in licensing, permitting and inspection programs. Additionally, Rodrick has an understanding of the theory and principles of electricity and electronics. He has working knowledge of the National Electrical Code® (NEC®) and its applications. He has performed electrical plans examinations and conducted highly complex inspections. Rodrick has the fundamental knowledge of adult learning precepts and instruction in a classroom setting. He has been awarded “Top Gun” status for instructor training. Designed, developed, and implemented new core curriculum subject matter. Graduated 634 Apprentice and 208 Third Class Nuclear Electricians with a total student contact time of 336,800 hours and rained Engineering Officers of the Kuwaiti Naval Forces.