FAQs - UPS Systems

UPS system information including sizing, battery runtimes and the types of UPS available.

Rotary UPS is an Uninterruptible Power Supply that converts Kinetic energy into electrical energy to power a load.

Volt Ampere (VA or kVA or MVA) is a measure of Apparent Power and the current drawing by a load at a given supply voltage.

A Static Transfer Switch is a solid state high-speed switching device that can transfer a load between two AC Power sources. The two AC power sources can be two AC mains power supplies, generators or uninterruptible power supplies or a mixture of these up to a maximum of two supplies. The two input can be out of phase as the STS ensure a single supply to the connected load(s). In a UPS installation the STS can provide the UPS with two power sources (A and B) drawn from separate supplies.

An on-line UPS has a static bypass built-into its design. The UPS inverter is always ‘on-line’ and its output waveform, voltage and frequency are monitored. If the output wave starts to collapse due to an overload and the overload is greater than the overload rating or there is an internal fault, the load is automatically transferred via the static bypass from the output of the inverter to the UPS bypass line. When the fault clears or the overload is reduced, the load us automatically transferred back to the output of the inverter. Some smaller on-line UPS below 10kVA may state in their specifications that they have an automatic bypass which will be relay rather than static technology based.

The rule of thumb is to achieve 80% recharge within 24hours. To make a quick calculate of the recharge time you divide the Ampere-hour (Ah) of the battery by the recharge current applied. The batteries in an uninterruptible power supply will be charged by the charger built-into the UPS and through its connection to the AC mains power supply. The charger may be part of the rectifier circuit or a separate battery charger. Where external battery cabinets are used, the battery cabinet may also have its own battery charger and require a separate AC mains power supply connection.

A UPS Break-Before-Make (BBM) Bypass is a bypass that introduces a break when transferring a load from the output of a UPS to the bypass supply, and vice-versa.

A Static UPS is an Uninterruptible Power Supply using solid state electronics and therefore no moving parts.

Series-Redundancy is a method of providing redundant power to a load whereby the output of one UPS module is used to supply the bypass of another. If one UPS fails the other automatically powers the load.

A Power Supply Unit (PSU) is the device within a piece of modern electronic hardware (e.g. file servers and desktop PCs) that converts an ac waveform into the various levels of dc required to power internal circuits.

Runtime, autonomy or backup time is  the amount of time (minutes or hours) that a battery set or other power source will support the load.

An Insulated Gate Bipolar Transistor (IGBT) is a high power switching device used in inverters and rectifiers.

An Uninterruptible Power Supply (UPS) is a system (either Static or Rotary) capable of maintaining power to a load (normally a critical IT server, network or PC) for a defined time period irrespective of the state of the mains power supply itself – also known as an Uninterruptible Power System.

Parallel-Capacity System is a type of parallel UPS system where the total load demand is met by operating a number of UPS in parallel without redundancy.

Parallel-Redundancy is a type of parallel UPS system where the total load demand is met by operating two or more UPS in an N+X configuration with all the UPS sharing the load between them equally. If one UPS fails the other supports the load.

An Automatic Bypass is a circuit within a UPS (or bypass panel) to transfer the load from and to a bypass supply, which may be relay or static switch-based.

Apparent Power is the current drawn by a load at a given supply voltage measured in VA.

Active Power (also known as Real Power) is measure of the actual power (Watts) dissipated by a load.

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