AVO New Zealand

A Practical Technique FOR Battery Condition Assessment and Capacity Monitoring.

ABSTRACT:

The management of the condition assessment of standby lead acid battery systems using impedance methods is now a highly regarded and mature technology delivering an accepted compliment to load discharge methods. Offering the significant attributes of being a non-invasive diagnostic method implemented at modest per-cell costs to in-service battery systems, impedance testing may be applied both to absolute or trended ( CBM ) condition assessment philosophies. Given the often sudden nature of battery failure mechanisms, the success of failure prediction is proportional to sampling intervals. Studies have expanded the scope of impedance technology to the determination of deterioration in battery capacity.

Full Paper (632KB PDF)

(1.0 ) INTRODUCTION:

Battery bank failure in emergency or standby power systems typically invokes consequences beyond all proportion to the value of the failed component. Losses of up to USD 2 million directly from battery failure-related causes have been documented in the literature [1].
Surprisingly, the concept of risk-assessed battery maintenance has only very recently been embraced in New Zealand and, even then, by only some of the power and communication industries. Many still continue to judge battery maintenance in terms of the ratio of maintenance cost vs. the investment in the battery system per se.

It is generally still the belief of the asset owner in New Zealand that the batteries will last a defined time in service ( agreed on a sliding scale of warranty assurance with the battery supplier ), and that this assurance permits an adequate security reserve to adopt a minimal maintenance regime and a timely calendar-based replacement schedule of the entire bank.

Whilst the latter maintenance concept offers a “first order” degree of reliability assurance, the experiences of the Industry ( especially with valve regulated lead acid installations ) in both New Zealand and internationally [2] document the flaws and severe cost implications in applying this maintenance assumption too literally, especially as regards the maintenance intervals adopted as the bank ages.

Experience [3] internationally suggests that batteries are the most unreliable component of emergency power systems: arguably, then, a more mature attitude to battery maintenance issues is merited, particularly in strategic installations.

Indeed, studies [8] presented at the 1995 Intelec Conference [11] confirmed that VRLA batteries appear to have a shorter-than-advertised life and that some manufacturers have shown a willingness to accept that observation.

By corollary, the realities of batteries subjected to such influences call for far more sophisticated condition monitoring processes than generally practiced if battery system reliabilities are to be assured.