Ensuring the continuity of power supply is a key task for many people responsible for the operation of ,,sensitive systems". Many of them use UPSs to guarantee power backup. They make sure that the equipment is fully operational by carrying out inspections and maintenance. They want UPSs to work trouble-free, for a long time, and to keep the cost of operation low.
In the overwhelming number of incidents that result in the loss of guaranteed voltage, the cause is the improper operation of batteries. Conducting regular measurements of these energy banks is one of the primary responsibilities of technical services.
On the quality of measurements and making the right diagnosis, regarding the condition of batteries, can depend on the high costs of the subsequent operation of the uninterruptible power supply system. Of the several test methods, battery discharge is the best to assess battery capacity.
At CES, a device was developed with which we can track , "on-line" the voltage on each battery separately during discharge as well as charging.
CASE STUDY - excerpts from a report on a study of 160 batteries
The measurements were to give an answer as to what the condition of each battery is at the halfway point of its service life as stipulated in the manufacturer's DTR
1.Conditions for conducting AKU_METRONOMEM CES tests
The contractor must ensure that the UPS and battery stack can be accessed (as for maintenance). In addition, it must specify the reserve charge level of the battery stack to be left. The lower this value is, the more authoritative the measurement will be. This value is important because after the measurement, the UPS backup time is lower until the battery is recharged.
2. Method of conducting the test
The measuring device is adapted to carry out direct voltage measurement on each battery of the UPS battery stack. The total duration of the measurement is determined by the amount of energy that can be drawn from the battery banks.
3. Safety of measurements with the device
The UPS service software used controls operation during battery stack discharge and does not allow battery operation when the battery stack voltage is too low. It ensures continuity of power supply to loads even in case of damaged batteries.
4. Advantages of carrying out the measurement by the method used by CES engineers
- no switching of the device to by-pass during the measurement (power supply is guaranteed all the time)
- no shutdown of UPS power supply, no connection of external load
- detection of damaged/exhausted/decreased capacity batteries
- measurement for the current UPS load
- verification of back-up time
5. Description of the study
Measurements were made for 4 UPS units in parallel operation, guaranteeing supply voltage for one of the office buildings in Krakow.
Each unit (Flexus 120kVA) has an individual battery consisting of 40 AML 100 Ah batteries.
The system was delivered and put into operation in late 2010 and early 2011 by the Centrum Elektroniki Stosowanej.
The test was performed without shutting down any component of the power system and with the assurance of the safety of power supply to the loads in the event of a power outage during the measurement. This was possible thanks to the redundant configuration (N+1) of the UPSs. In addition, thanks to the service software, the redundancy of the UPSs was maintained.
6. Summary
Among the 160 batteries intended to provide energy during a power outage, 2 pieces have been identified that are defective/have insufficient capacity and should absolutely be replaced. One unit was detected that had lost about 30% of its nominal capacity. Due to the nature of the system and the electrical dependencies that govern it, it was recommended that this battery be replaced as well.
