General Frequently Asked Questions
What is the value of a preventive maintenance contract?
Preventive maintenance benefits you by:
- adding another layer of protective redundancy by overlaying your high-quality equipment with dedicated, regularly scheduled service upkeep;
- extending the life cycle of your critical equipment product and optimizing your capital expenditures;
- providing risk management at a fixed cost, which helps you make sound financial forecasts; and
- enabling you to better control of your business environment through proactive management rather than emergency reaction.
Why use centralized lighting inverters?
Centralized lighting inverters provide a single point source of power for all emergency lighting and exit signs. This offers simple maintenance and provides for a controlled, logical, wiring scheme. The output of the inverter is fed to a dedicated lighting panel, which provides only the power for the emergency lighting system.
How can power problems be avoided?
While power problems cannot be eliminated, you can help prevent the damage they cause by connecting sensitive electrical equipment to power conditioners, surge protectors, or uninterruptible power systems.
If my UPS is in storage how often should I charge the batteries?
The batteries should be charged every three or four months to prevent loss of capacity.
Is there any difference between the batteries used by smaller UPSs, from 250 VA to 3 kVA, and the ones used by larger UPSs?
While basic battery technology, and the risks to battery life, remains the same regardless of UPS size, there are some inherent differences between large and small applications. First, smaller UPSs typically have only one VRLA battery that supports the load and needs maintenance. As systems get larger, increasing battery capacity to support the load gets more complicated. Larger systems may require multiple strings of batteries, introducing complexity to battery maintenance and support. Individual batteries must be monitored to prevent a single bad battery from taking down an entire string, and putting the load at risk. Also, as systems get larger wet-cell batteries become much more common. The differences in battery maintenance between VRLA and wet-cell batteries discussed earlier in this handbook apply.
What are the most common types of UPS?
The Standby UPS is the most common type used for personal computers. The transfer switch chooses the filtered AC input as the primary power source and switches to the battery/inverter as the backup source should the primary source fail. When that happens, the transfer switch operates to switch the load over to the battery/ inverter backup power source. The inverter only starts when the power fails, hence the name “standby.”
What is a UPS?
An uninterruptible power system, or UPS, is a power source that provides a steady flow of power to an electrical load without interruption until the system can be safely shut down.
The Line-Interactive UPS is the most common design used for small business, Web, and departmental servers. The battery-to-AC power converter (inverter) is always connected to the output of the UPS. Operating the inverter in reverse during times when the input AC power is normal provides battery charging. When the input power fails, the transfer switch opens and the power flows from the battery to the UPS output. With the inverter always on and connected to the output, this design provides additional filtering and lessens the potential for switching transients when compared with standby UPSs. Line-Interactive UPSs also usually incorporate a tap-changing transformer, which regulates voltage by adjusting transformer taps as the input voltage varies, guarding against premature battery failure.
The Standby On-Line Hybrid is characterizes many UPSs under 10kVA that are labeled “on-line.” The standby DC-to-DC converter from the battery is switched on when an AC power failure is detected, just like in a standby UPS. The battery charger is also small, as in the standby UPS. Due to capacitors in the DC combiner, the UPS will exhibit no transfer time during an AC power failure. This design is sometimes fitted with an additional transfer switch for bypass during a malfunction or overload.
The Standby-Ferro UPS, usually produced for the 3-15kVA range, depends on a special saturating transformer that has three power connections. The primary power path is from AC input, through a transfer switch, through the transformer, and to the output. In the case of a power failure, the transfer switch is opened, and the inverter picks up the output load. In the standby-ferro design, the inverter is in the standby mode, and is energized when the input power fails and the transfer switch is opened. The transformer has a special “Ferroresonant” capability, which provides limited voltage regulation and output waveform “shaping.” The Ferro transformer provides isolation from AC power transients equal in quality to filters.
The Double-Conversion On-Line UPS is the most common type of UPS above 10kVA, is the same as the standby, except that the primary power path is the inverter instead of the AC main. Failure of the input AC does not cause activation of the transfer switch, because the input AC is the backup rather than the primary power source. As a result operation during an input AC power failure results in no transfer time. A double-conversion on-line UPS will exhibit a transfer time when there is a large load step or inrush current when transferring the load from the UPS inverter to the bypass line. Generally, the transfer time is very brief, usually 4-6 milliseconds.
Three-Phase UPSs are available in single-module, multi-module, and redundant configurations and are ideal for safeguarding mission-critical, continuous-availability applications from 12kVA.
What are the consequences of power problems?
Even minor power problems can delay work in progress, resulting in valuable loss of time. Power problems also can corrupt data files and permanently damage electrical equipment and systems.
What are some common power problems?
Blackouts, or outages, are usually caused by faults on the utility power system. Blackouts can result in unexpected and potentially damaging shutdown of all electrical equipment.
Frequency variations are usually caused when backup generators take over from utility power and can cause system crashes and equipment damage.
Harmonic distortion manifests itself as a multiple of the standard power wave generated by common electronic systems such as computers, network peripherals, factory equipment, or utility power. Harmonics can result in communications errors and hardware damage.
Noise is characterized by a jittery sine wave that can be caused by normal computer operation. Noise can lead to keyboard/mouse/monitor lockups, program freezes and crashes, data corruption, printing errors, and incorrect data transfer.
Overvoltages are increases in line voltages that last for extended minutes to a few days. They may be caused by lightning strikes and generally result in data loss or hardware damage.
Sags are short-term decreases in voltage level. They are generally caused by the starting up of large loads or utility power line faults. They can cause workstations and servers to freeze, hard drives to garble or misplace data, and motor parts to wear faster.
Spikes, or transients, are instantaneous, dramatic increases in voltage. They are most often caused by lightning, and sometimes by power coming back on after a blackout. Transients can damage electronic circuitry and corrupt stored data.
Surges are short-term increases in voltage. They are usually caused by drops in electrical demand and widespread equipment shutdown. They can lead to electronic wear and premature equipment failure.
Undervoltages, or brownouts, are characterized by reduced line voltage for extended periods ranging from a few minutes to a few days. They can result from rolling power outages created by utility companies on peak-use days or other heavy loads that exceed line capacity. Undervoltages often lead to equipment failure.