By Todd J Stukenberg, Midtronics executive director of marketing, Chicago, US.
The installations of uninterruptible power supplies (UPS) are typically a forgotten piece of insurance.
Most system options include batteries as the primary device for storage of the critical energy. More and more UPS systems, and therefore batteries, have been deployed in increasing numbers by a wide variety of organisations.
This increasing population of batteries has created a requirement for training, tools and equipment to ensure systems meet the designed requirements. Most organisations that rely on batteries for back-up power recognise consistent and effective testing or monitoring is a requirement for system integrity.
In the past, this routine has included regular battery discharge, known as load testing. This testing, while quite conclusive, can be somewhat impractical for modern operations. To address these weaknesses, electronic testing and monitoring has been enhanced with cutting edge electronics to offer an effective alternative.
Battery conductance is a measurement of a battery’s ability to produce current/power – measured through the injection of an AC signal of a pre-determined level and capturing and assessing the conducted yield. The resultant output produces a numeric value in the form of either Siemens or Mhos.
Conductance can be described as the equivalent measurement/approximation of the battery plate and reaction sites/surface area available within the battery for chemical reaction and exchange.
Through the standard ageing/degradation and use process, the battery’s plate surface will form sulfate, shed active material, and can be altered chemically; of which all adversely affect the battery’s ability to perform. This expected ageing/degradation process forces battery conductance to decrease gradually as the battery service life is consumed and therefore a predictive trending pattern can be established. The higher a registered conductance value (or lower internal resistance), the more healthy the battery.
The data in Figures A and B illustrate the conductance technique has a dependable capability in identifying the suspect cells. Because of these characteristics, it can be presumed conductance provides considerable value and support in preventing system failures that negate the expected insurance benefit of the UPS/back up system, but can also create highly dangerous, or even catastrophic, situations for personnel, equipment and other assets.
By incorporating a defined and consistent program of testing or monitoring of the entire string of batteries (including inter-cell connections, charging systems and other elements) in a stationary power system, gross deviations among batteries or the system can be quickly and easily identified and appropriate corrective actions taken prior to the system being relied upon or a serious event occurring.
An associated benefit from routine system maintenance and battery conductance testing is increased service life and ensure full use of the consumable service life. By monitoring or testing a battery site with conductance-enabled equipment, warning signs can be detected and rectified prior to a catastrophic loss. Making corrections to the power system means battery life can be extended. Another benefit of measuring conductance from the time of installation, related loss of capacity can be observed and trended, allowing effective management of time for replacement.
The IEEE advise Ohmic testing of all valve-regulated, lead acid batteries once per quarter. By using the measured conductance value of an optimised cell, or the average conductance signature of a battery type as a benchmark, an operator can easily develop a replacement strategy. Many organisations have successfully reduced battery related failures and unnecessary costs.
Enhanced, yet simplified battery management.
To further understand Ohmic testing or monitoring programs it is important to analyse its attributes compared to discharge testing:
• Fast: Conductance tests produce measurements in a matter of seconds rather than the hours of time required for discharge testing. Conductance technology enables battery monitoring full-time, on-line, and automated – eliminating costly labour. Conductance monitoring systems can provide remote access to current battery conditions that is readily available at the touch of a button.
• On-Line testing: The latest conductance technology monitors power systems on-line without any system disruption or downtime and these tests are passive and do not alter or cycle the battery to cause premature ageing.
• Accurate: Conductance testing and monitoring has proven accurate to the level that a few Australian telecom companies have discontinued most discharge testing.
• Safety issues: The passive nature of the latest conductance technology makes it substantially safer than discharge testing. Eliminating the potentially hazardous circumstances posed by heat, produced hydrogen gas and electrical arcing during the load testing process.
• Repeatable: Passive conductance testing or monitoring results are fully repeatable, without waiting for a recharge cycle.
• Simple: Ohmic testing can also be very simple. The newest conductance testers are menu-driven and provide absolute measurements with no further mathematical calculations needed.
• Affordable: Ohmic/conductance technology equipment is relatively inexpensive when compared to older technologies, both from a capital investment standpoint as well as the aforementioned savings in time.
This is an extract from a more detailed article by Todd Stukenberg. Contact Hot Wire to receive the full article.
