Reference
UPS & power-protection glossary
86 terms, A–Z, searchable and deep-linkable — COMPACT's long-standing power-protection glossary.
A
- AC
- Alternating Current. Used to indicate that voltage or current in a circuit is alternating in polarity at some frequency, as in “230 Volts AC”.
- Ampere
- The ampere is a measure of current, which represents the flow of electrons through a wire.
- Apparent Power
- The mathematical product of the RMS current and the RMS voltage. Identical to the VA rating.
B
- Battery
- An energy storage system used in a UPS. The battery used in a UPS is rechargeable.
- Battery Management
- An umbrella term used by various UPS manufacturers to describe a suite of functions related to charging, testing, and maximising the life of a UPS battery.
- Bit
- A binary digit, which represents the smallest unit of computer information and indicates one of the two electrical states in a computer: off (0) or on (1).
- Black Out
- Total loss of utility power, bringing the operation to a standstill.
- Brown Out
- A condition, usually temporary, when the AC utility voltage is lower than its normal value.
- Bypass
- An AC power path around one or more functional units of a UPS. An automatic bypass is controlled by UPS control logic and activated when some part of the UPS malfunctions or intentionally shuts down.
- Byte
- A frame of eight continuous bits, representing the smallest addressable item of information in a computer system.
C
- Circuit Breaker
- A protective device that interrupts the flow of current when the current exceeds a specified value.
- Common Mode
- For AC power systems, the term common mode may refer to either noise or surge voltage disturbances that occur between the power neutral and the grounding conductor.
- Constant Voltage Transformer
- A device that changes AC voltage and provides isolation between input and output through magnetic coupling via transformer design.
- Converter
- A circuit which converts AC to DC.
- Crest Factor
- The ratio of the crest (peak, maximum) value of a current to the root-mean-square (RMS) value.
- Current Limit
- The function of a circuit or system that maintains a current within its prescribed limits.
D
- Decibels (dB)
- dB stands for decibels, a way to represent logarithmic ratios. Since a dB number is a ratio, it must always be a ratio between two things.
- Delta
- A wiring system for distributing and utilising three-phase electrical power. In this system, three power-carrying conductors are used.
- Differential Mode
- For AC power systems, the term differential mode may refer to either noise or surge voltage disturbances that occur between the power live and the neutral conductor.
- Distortion
- When used in relation to AC power distribution, this refers to deviations between the actual AC voltage waveform delivered to the user and the ideal sine wave of voltage.
E
- Efficiency
- A ratio of output power to input power expressed as a percentage. If a UPS has a specific efficiency, such as 80%, then the difference from 100% — 20% in this case — represents the fraction of input power wasted as heat.
- EMI
- Electro-Magnetic Interference. EMI usually refers to unwanted electrical noise present on a power line.
- Ethernet
- A popular networking standard used to physically connect nodes on a LAN (Local Area Network).
F
- Fault Tolerance
- The current that can flow in a circuit as a result of an undesired short circuit.
- Ferroresonant Transformer (Ferro)
- A special transformer which puts out regulated AC voltage even when the input voltage is variable.
- Float Charger
- The battery-charging technique for which sealed lead-acid batteries are designed. A float charger maintains a voltage on the battery known as the “float voltage”.
- Fuse
- A protective device that interrupts the flow of current when the current exceeds a specified value.
G
- Galvanic Isolation
- A characteristic of a UPS or transformer in which the output is completely electrically disconnected from the input.
- Ground
- Electrical ground in an AC power system is a wire which is actually connected to the earth, hence the name “ground”.
- Ground Loop
- A common wiring condition where a ground current may take more than one path to return to the grounding electrode at the service panel.
H
- Handshaking
- The method by which computers or other devices communicate their status. In RS-232 communications, handshaking signals are used by one device to inform the other that it is ready to accept data transmission.
- Harmonics
- In an AC power system, distortion of voltage or current waveforms may be expressed as a series of harmonics.
- Holdup Time
- The amount of time that a power supply can continue to supply the load after input power is terminated.
I
- Input Voltage
- The electrical force given to any equipment which is operating on electric current.
- Inrush Current
- A current higher than the nominal steady-state value which is drawn by a device when initially energised or activated.
- Inter-System Ground Noise
- Noise consisting of any AC voltage, noise voltage, or surge voltage that occurs between the grounding pins of AC receptacles in different parts of a building.
- Inverter
- An electronic converter used to convert direct current (DC) into alternating current (AC). All UPS systems incorporate an inverter.
- Isolation
- See Galvanic Isolation.
J
- Joule
- The joule is a measure of the amount of energy delivered by one watt of power in one second, or one million watts of power in one microsecond.
L
- Line Conditioner
- The term is not used consistently and its meaning has been blurred. It is sometimes used to describe equipment that provides some type of filtering or regulation to an AC power source.
- Line Interactive UPS
- A type of UPS that combines some of the performance benefits of an on-line UPS with some of the reliability and efficiency benefits of a standby UPS.
- Line Noise
- More technically referred to as electro-magnetic interference and radio-frequency interference — line noise causes electrical noise which disrupts the smooth sine wave expected from the utility power.
M
- MOV
- A Metal Oxide Varistor. A varistor is a very rugged voltage-clamping device capable of absorbing very large currents without damage.
N
- Neutral
- The return path / wire for the current carried by the live wire in an electrical system.
- Normal Mode
- See Differential Mode.
O
- Off-Line UPS
- Off-line UPSs monitor and regulate the incoming AC power to the load. The moment the power goes below or above the set limits, they transfer the load to the inverter.
- On-Line UPS
- One of the many types of UPS. In this type the load is supplied from a power converter that always operates and takes its input from a DC supply.
- Output Voltage
- Power-protection equipment takes the input voltage and discharges the defined or required output for the smooth running of the protected system.
P
- Phase
- In AC power systems, load current is drawn from a voltage source. In typical systems, the AC voltage is a sine wave.
- Power Factor
- A number between 0 and 1 which represents the portion of the VA delivered to the AC load that actually delivers energy to the load.
- Power Factor Corrected
- A characteristic of many newer computer power supplies. A power-factor-corrected supply draws low-distortion current from the AC source and typically exhibits a low crest factor.
Q
- Quasi Sinewave
- A modified square wave where the peaks and the RMS voltage are equal to a sine wave. Quasi sine wave is supplied by most off-line UPS systems.
R
- Reactive
- An AC load is called reactive when it draws a current from the AC receptacle which is not in phase with the AC voltage.
- Reboot
- A reset of a computer that is manually initiated or occurs due to a software crash or due to a power sag or surge.
- Rectifier
- A device for converting AC into DC. An AC-to-DC converter.
- Redundant
- An intentional repetition of a given function — usually intended to improve reliability.
- Regulation
- A term used to describe the degree to which the voltage of an AC power source varies.
- RFI
- Radio Frequency Interference. Electrical noise present in communications or computing equipment which results from some parts of the equipment or attached wiring acting as a radio antenna.
- RMS
- Root-Mean-Square. The square root of the average value of the squares of all the instantaneous values of current or voltage during one half-cycle of an alternating current.
- RS-232
- A standard for asynchronous transfer between computer equipment and accessories. Data is transmitted bit by bit in a serial fashion.
S
- Short Circuit
- A situation where two wires become connected, usually by accident, resulting in a system malfunction.
- Sinewave
- A clean, pure AC waveform. A good online UPS inverter provides sine wave power with low total harmonic distortion under linear load.
- Slew Rate
- The rate of change of frequency in Hz per second. In a UPS, slewing occurs when the frequency of the internal inverter is automatically adjusted to bring the inverter and the input utility power into synchronisation.
- SMPS
- An inbuilt power converter present in all computers, which basically works on pulse-width-modulation technology.
- SNMP
- Simple Network Management Protocol. A protocol which allows the management of networks; today mainly used for managing TCP/IP networks.
- Spike
- An impulse. A spike is an instantaneous, dramatic increase in voltage. Like a tidal wave, a spike can enter electronic equipment through AC, network, serial or phone lines.
- Square Wave
- A waveform similar to the sine wave except that the transitions from negative maximum to positive maximum are abrupt.
- Stabilizer
- There are various stabilisers — manual, automatic relay-controlled, transistor-controlled and servo-controlled.
- Standby Power System
- In common utility terminology, a system in which the normal power source is utility AC power and the backup source is an AC generator.
- Standby UPS
- A UPS configuration in which the normal power source is filtered utility AC power and the backup source is a DC/AC converter operating from battery power.
- Step Load
- The instantaneous addition or removal of electrical load to or from a power source.
- Surge
- An unwanted momentary transient over-voltage which may be present on an AC power circuit, data circuit, or telephone circuit.
- Surge Suppressor
- A device used to protect equipment from transient over-voltages present on AC power, data, or telephone circuits.
- Synchronization
- The process of bringing the UPS inverter output into phase and frequency alignment with another source (typically the bypass supply) so the load can be transferred between them without interruption.
T
- Three Phase
- A method of distributing AC power. Power is distributed using three wires (the delta configuration) or four wires where the fourth is the neutral (the wye configuration).
- Transient
- A momentary variation which ultimately disappears. Most power problems are transients.
- Transfer
- Used to denote the switching of load power from one power source to another.
- Transfer (Synchronous)
- Transfer of the load power between two sources which are synchronised.
- Transfer Switch
- A switch used to transfer a load from one power source to another.
- Transfer Time
- The interval of time between the instant transfer is initiated and the instant load power is transferred from one source to another.
- Transformer
- A device that can change AC voltage and/or provide isolation. A transformer that changes an AC voltage is called a step-down or step-up transformer.
U
- UPS
- Uninterruptible Power Supply (or System).
V
- VA
- A form of power measurement called “Volt-Amps”. A VA rating is the volts rating multiplied by the amps (current) rating.
- Volt
- The unit of electrical force, defined as the force needed to carry one ampere of current against one ohm of resistance.
- Voltage
- The electrical force given to any equipment which is operating on electric current.
W
- Watts
- A form of power measurement. For AC power systems, the watts rating is the volts rating multiplied by the amps rating multiplied by the power factor.
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