Page 58 - Energize September 2022

TECHNICAL

Testing energy storage modules

A case study from Megger

telecommunications company in preferable to lose the battery instead of Problem
Cambodia was having difficulty in the asset. Therefore, the battery needs to The telecommunication company needs
es
A ting their sets of batteries which be configured to open only in the case of to check and do a regular maintenance of
t
were connected in parallel. These batteries potential battery failure. their ESM. However, they are having some
were being used as energy storage modules This can still lead to an open battery challenges:
(ESMs) in a data centre. Ten sets needed string and a loss of backup. In critical • How can they check the status of the
testing and each individual set contained ten applications which use Li-ion batteries, individual cells within the ESM?
cells. The company needed a test set which a parallel string configuration is needed • Can they do online test of these
could do online battery impedance test with to provide redundancy. In stationary batteries as they cannot afford to have
cells connected in parallel and which could applications, the batteries are not unscheduled downtime?
withstand a 53 V DC system voltage. discharged and charged regularly, so they • Can any test set measure the
ESMs play an important role in a remain on float for extended periods of impedance of a battery string in parallel
telecommunication system. They supply time. connection with 53 V DC system
power to critical systems such as computers, In these applications, periodic testing is voltage?
meters and servers, and as a backup power recommended along with visual inspection.
source during a power failure. An ESM is The battery voltage and impedance should Furthermore, the EMS system was just
an energy storage unit composed of Li-ion be measured frequently. Trending test delivered less than a year ago and they
batteries. It features better charge and results over time will identify SEI build up. are mindful that they need to have
discharge performance, longer service The SEI layer, or solid electrolyte interphase baseline for impedance measurement of
life and less self-discharge loss than other layer, is a component of lithium-ion individual cell. The existing tester they
batteries. Besides the cells, an ESM contains batteries formed from the decomposition have can only handle up to 48 V DC and
an energy storage management unit (ESMU), materials associated with the electrolyte of cannot do parallel string without the
a fire control module, power and signal the battery. current clamp for escape current.
terminals and mechanical parts. It can be For some materials, the internal Figure 1 shows one set of ESM to test.
used as an independent 48 V unit, supporting resistance increase that occurs with age Table 1 lists the details of the specific
the mixed use of old and new batteries can be relatively small, and for others, a application.
as well as lithium and lead-acid batteries, doubling or tripling of internal resistance
and can collaborate with third-party power is not unusual.
systems.
BITE5
The Li-ion battery The BITE5 can perform the voltage and
Lithium-ion (Li-ion) batteries are a family of impedance measurements on all Li-ion
batteries with different types of chemistries, batteries. It will store the results and
each with their own unique characteristics allow you to trend them over time for
and configurations. Ageing of lithium-based each cell. You can also transfer the data
batteries is due to both calendar ageing to the Power DB PC-based software. This
and battery cycling. As Li-ion batteries age, will allow for automated analysis and
a reduction of available capacity occurs, customised report generation. To learn
which is known as fading, and an increase in more about the Li-ion batteries, please
internal battery impedance. For many Li-ion download and read the application from
technologies, the ageing will proceed at a Megger entitled “Lithium-Ion battery
relatively linear rate up to a certain point, maintenance”. Figure 1: ESM under test
typically 60 or 70 of rated capacity. At this
point the rate of ageing will accelerate. ESM voltage 53 V DC
Battery connection Parallel
Li-ion battery maintenance Maximum output 100 A; 4800 Wh per ESM
In stationary applications, the battery backs Battery type Li-ion
up the key asset. In these applications, it is Table 1: Application details

energize | September 2022 | 56