Facilities such as data centers, hospitals, airports, public companies, oil and gas facilities, and railways cannot function without 100 percent backup power reliability. Even standard commercial and manufacturing facilities have backup power systems for their emergency systems, alarms and controls, emergency lighting, and smoke and fire control Battery systems.
Most standby power systems use an uninterruptible power supply (UPS) and a set of batteries. The UPS serves as a backup to the Digital Control System (DCS) to maintain control of plant operations until it can be safely shut down or until the standby generator starts.
Although most batteries used in modern UPS systems are maintenance-free, they are still susceptible to deterioration from corrosion, internal shorts, sulfation, drying, and seal failure. This article establishes the recommended practices to maintain the optimal operation of these “Battery systems banks”, so that the reserve is ready in the event of a blackout.
The two main indicators of battery status
One: internal resistance of battery
Internal resistance is a test of service life, not capacity. The resistance of the battery remains considerably uniform until it approaches the end of its useful life. At that point the internal resistance increases and the battery capacity decreases. Measuring and recording this value helps to identify when the battery should be replaced.
Fluke 500 Series Battery Analyzer
Two: the discharge test
The discharge test is the best way to discover the actual available capacity of a Battery systems, but it can be difficult to carry out. During this test, the battery is connected to a load and discharges over a specified period of time. In addition, the current is regulated and a constant known current is established while the voltage is measured periodically. Details of the discharge current, the specified time period for the discharge test, and the battery capacity in amp-hours can be calculated and compared to the manufacturer's specifications. For example, a 12 V 100 Ah battery may require a discharge current of 12 A for eight hours. A 12 V battery is considered discharged when the terminal voltage is 10.5 V.
Batteries do not carry critical loads during a discharge test, or immediately after completion. Transfer critical loads to another Battery systems bank for a significant time after testing is complete and reconnect a temporary load, comparable in size, to the tested batteries. Also, before testing, prepare a cooling system to compensate for the rise in ambient temperature. When large batteries discharge, they emit a large amount of energy in the form of heat.
Good batteries must maintain a capacity greater than 90% of the factory ratings. Most manufacturers recommend replacing the battery if its capacity drops below 80%. When performing battery tests, look for the following fault indicators:
- More than 10% drop in capacity compared to baseline or previous measurements
- 20% minimum increase in impedance compared to reference or previous measurements
- Continuous high temperatures compared to manufacturer's reference and specifications
- Degradation in the condition of the plates