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UPS Maintenance Planning Article

23rd, November 2012

Companies very often rely on an uninterruptible power supply (UPS) to deliver continuous power eliminating any disruption to their business. To ensure that UPS systems perform as expected it is critical a maintenance plan is put into place. Workspace Technology’s service team recently reviewed data collected by industry experts to help end users understand the importance and consequences of downtime.

In the UK it is estimated the national cost of power interruptions is approximately £10bn per year, with momentary interruptions accounting for two-thirds of the total cost at £6.6bn. Furthermore, the annual downtime average for the utility grid in the UK is currently eight hours and 45 minutes. However, with on-site power generation equipment and UPS solutions, this downtime can be reduced to the equivalent of five minutes and 15 seconds per year.

The cost of network downtime can be crippling to a company with financial implications starting at about £5,000 an hour for smaller companies and extending to £750,000 per hour for those that rely heavily on applications such as e-commerce.

Root Causes of Downtime

It is estimated that two-thirds of downtime events are a result from preventable issues. It has been shown that about 4% of UPS failures are the result of age related components wearing out, with up to 20% failures due to batteries. Studies into the causes of downtime reveal the following:

Causes of preventable downtime (67%)

  • Human error
  • Poor processes
  • Procedural Error
  • Poor design
  • Inadequate redundancy
  • Insufficient maintenance

Causes of non-preventable downtime (33%)

  • Equipment failure (despite proper maintenance and testing)
  • Supply chain/service chain failure
  • Cyber terrorism

Common Causes of UPS Failures 

There are numerous reasons why a UPS fails. The most common causes are detailed below:

Batteries – The heart of any UPS, batteries require inspection and maintenance, regardless of age or warranty status. Studies show that up to 20% of UPS failures can be attributed to bad batteries, with temperature and cumulative discharges cited as the primary culprits. During a preventive maintenance visit, data is obtained from thorough testing procedures, during which impedance or conductance measurements trace the battery performance and identify any batteries with internal potential failures.

Fans – Some fans fail because of their own electrical or mechanical limitations, or when their ball bearings become dried out. Fans may perform well for more than 10 years of continuous use, while others run for only short periods before locking up for mechanical reasons.

Transient Spikes – Damage may be caused to the input side of the UPS (filter/rectifier) when a transient spike occurs. During a preventive maintenance call, these parts are checked for any impairment.

Other factors that lead to UPS failure:

Lightning – A common misconception is that a UPS constantly protects the equipment load from lightning, but it primarily depends on the amount of energy in the transient. Preventive maintenance inspections can readily identify lightning damage and any appropriate repairs.

UPS Internal Connections – These may be affected by vibrations from the building or machinery close to the UPS. It is recommended that the UPS be scanned every three months to check for hot spots, as well as checked annually with a complete mechanical revision on the full UPS and battery cabinets.

Capacitors – A typical UPS contains a dozen or more electrolytic capacitors of different types and size, which smooth out and filter fluctuations in voltage. Like batteries, electrolytic capacitors degrade over time. While a typical capacitor might be rated by the manufacturer for five years of round-the-clock use, it could potentially deliver up to eight to ten years of useful life under favorable operating conditions. When a capacitor fails, there might not be any immediate visible effects, but other capacitors must compensate for the additional workload, which shortens their useful lives. In many cases, a capacitor failure will trigger the UPS to switch to bypass mode, at which time it is unable to protect downstream loads. Inspection of capacitors during preventive maintenance helps optimise their operation whilst also enhancing their lifespan.

Air Filters – Because dust may block air filters and cause a UPS to shut down due to overheating, they must be inspected every month. Replacing filters is an inexpensive component of an effective UPS maintenance plan.

Power Supplies – Although a UPS may have redundant power supplies, it is possible for the power supply to suffer from input voltage surges, which can cause unexpected stress and overheating. Regular inspection is recommended to detect potential issues.

Input Filters – Currents, parameters and physical conditions of input filters need to be reviewed and inspected. The input filter helps to reduce total harmonic distortion (THD) from the UPS to the input line. However, depending on the amount of input line electrical noise, the filter may attempt to correct harmonic distortion for the entire installation, causing overheated cables and chokes.

Contactors – Because they may collect fine dust and other resistive coatings, inspections and cleaning can prevent premature failures.

Sticking or Welded Relays – These may go unnoticed until emergency change-of-state events occur. Periodic inspections can detect potential problems before they occur.

Motor Operators – These should be checked for proper operation while disengaged from the breaker – a measure completed during a routine preventive maintenance visit.

Firmware Upgrades – Because upgrades incorporate the latest operational enhancements, they should be completed to ensure compatibility with new load devices, and to guarantee that the UPS is performing at optimum levels. A technician can complete these upgrades during routine service.

Transient Voltage Surge Suppression (TVSS) Integrity – It is important to verify that Metal Oxide Varistor (MOV) devices are functional and have not been compromised by excessive transients.

Overcoming Failures

Routine preventive maintenance significantly reduces the probability of a load loss event. 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. A solid maintenance plan identifies issues and greatly reduces this risk of failure.

With an effective preventive maintenance plan, your business will have access to more reliable, higher quality and more cost-effective power – all of which minimize the risks of downtime and disruption to your business. Preventive maintenance is crucial in order to achieve optimal performance from your equipment.

Systematic inspections, testing and cleaning by trained technicians ensure that the various electronic and mechanical components of a UPS are functioning to their maximum potential. When problems are detected and repaired before they evolve into significant – and often costly – issues, your UPS is able to deliver the level of performance you expect.

An Effective Preventive Maintenance Plan

There are a number of measures that are recommended to ensure the ongoing integrity of your UPS, including:

  • Annual scheduled preventive maintenance for both the electronics and battery
  • Access to rapid emergency response from trained technicians on the specific UPS models
  • On-site parts inventory or local field technicians with van-stocked required parts
  • Access to technical support and design engineering resources during escalation
  • Remote monitoring with monthly trended reporting, 7x24 alarm notification and rapid response linkage to field technician
  • Adherence to recommended parts replacement cycles, especially items that wear out more quickly, such as batteries and capacitors
  • Understanding of the UPS lifecycle, expansion features and total cost of ownership
  • Access to 7x24 call center specialists and local technicians
  • Maintaining accurate records

Since most batteries wear out every three to five years, it is critical that they are regularly inspected. And, considering the fact that the failure of a single battery jar can cause an entire UPS to fail, battery testing and replacement as needed are a fundamental component of a proper UPS maintenance plan, with most customers opting for semi-annual VRLA, or quarterly wet cell battery preventive maintenance.

A new trend in battery and UPS maintenance plans is to deploy a battery-monitoring system to constantly measure and report if any individual battery is out of factory specification. Load loss reports from customers who intended to self-monitor often reveal that the monitoring output was either not being viewed or had been misinterpreted. The load loss reports also show that many times there was not an effective process to link the bad battery alarm to a timely replacement.

A successful maintenance plan takes into account the age and actual wear of a UPS to determine where a specific device is relative to its expected lifespan. It also helps customers budget for major replacement items such as batteries or capacitors – items that customers may also choose to add into an appropriate maintenance agreement. A maintenance strategy should also include an understanding of where an organisation is headed, as well as its priorities for continuous operations. For example, are systems lightly loaded? Is the business experiencing unusual growth? How resilient must your operation be and what do you consider a fast response? Is it the next day, the same day or in two hours? Once you have assessed your basic needs, you can prioritise which equipment requires maintenance agreements and what level of service is appropriate.

Typical Maintenance Replacement Cycles

The following guidelines will help you determine the optimal replacement period for various UPS components:

Battery life 

Standby Use – Three to five years for VRLA batteries; wet cell battery life is variable

Cycle Use – 1200 cycles at 30% of discharge; 550 cycles at 50% of discharge; 250 cycles at 100% of discharge

Capacitors – Inspect annually. Replace every seven years or as needed


Fans – Replaceable with unit online if redundant or on bypass. Verify annually, replace every seven years

Lug Terminals – Crimp and mechanical power lugs, annual visual and thermal inspection

Air Filters – Replace annually or as needed

Common UPS Tests to Optimise Availability

The most successful UPS installations, which are measured by system availability or uptime, include prescriptive maintenance programs that are rigorously enforced. Within an effective maintenance strategy are a number of functional tests and component checks that should be conducted regularly.

Transfer to bypass and return to UPS – This test checks the static switch and bypass breaker motor operator or contactor. The test interval should be at least annually and can be performed with the load on maintenance bypass.

Battery operation and return – Sometimes coupled with a transfer-to-generator support and return to normal, this test is typically performed monthly and tests the UPS, generator and automatic transfer switch (ATS) functions.

Load balancing evaluation – This test checks for loads on any phase that may be approaching 100%. To limit potential overloads, loads may be redistributed as necessary. It is important to note that any one phase may be overloaded and trigger an unexpected alarm or transfer, even if the other two phases are only lightly loaded.

Phase rotation/site wiring checks – This test inspects for out-of-limit bypass alarms or site wiring faults that may have occurred as a result of normal site wiring changes or maintenance. These problems can go undetected until a transfer to bypass is attempted.

Listening tests – An experienced technician should listen for abnormal operational sounds, particularly arcing, fan-bearing noise or synchronisation problems, including hunting sounds or beat frequencies. These subtle hints can easily go unnoticed by users unfamiliar with the warning sounds.

Operator refresher training – Since most power interruptions are a result of human error, constant attention should be paid to ensuring and documenting that all personnel with access to the UPS and associated switchgear have a solid understanding of the operation of the system and the consequences of any incorrect actions.

Every UPS contains life-limited components that must be replaced according to the manufacturer’s specifications. To ensure these parts are properly cared for and replaced when needed, regular maintenance is critical. An effective preventive maintenance strategy can be one of the most cost-effective measures you can take to ensure the ongoing health of both your critical equipment and your overall business.

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