Uninterruptible Power Supply (UPS) Systems

Vocabulary practice flashcards covering uninterruptible power supply (UPS) systems, power quality disturbances, static and rotary architectures, filters, standby diesel generators, and installation requirements.

Voltage Sag (Brownout)

A short-term decrease in voltage level (typically to $90\%$ or less of nominal voltage) caused by heavy starting currents of large inductive loads like motors or by utility load reduction during heavy demand, accounting for approximately $87\%$ of all power disturbances.

Blackout

A complete, prolonged loss of mains power caused by excessive grid demand, lightning storms, damaged power lines, or catastrophic events, resulting in the total loss of unsaved computer RAM/cache memory and the File Allocation Table (FAT).

Micro Cut (Micro Break)

A brief interruption of the mains power supply lasting less than one full cycle (typically $\le 10\text{ ms}$ to $20\text{ ms}$), which can cause computer systems to lock up and hard disk read/write heads to crash onto disk platters.

Voltage Spike

An instantaneous, rapid, high-amplitude voltage transition superimposed on the mains waveform, typically caused by locally grounded lightning strikes, switching heavy electrical currents, or utility switching.

Voltage Surge

A substantial short-term increase in voltage above normal mains levels lasting at least half a cycle, typically appearing immediately after large inductive loads (such as motors or air conditioners) are disconnected.

Transient Over-Voltage

A sudden, fast-dissipating rise in voltage or current caused by switching events or lightning that occurs between phase lines, between line and neutral, or between live conductors and earth.

Normal Mode Noise

Electromagnetic or radio frequency interference that appears across the active power feed conductors (between the live and neutral lines), quantified by the Normal Mode Rejection Ratio (NMRR).

Common Mode Noise

Electrical interference that occurs between the power supply lines (live or neutral) and the common earth/ground reference conductor, often exacerbated by earth ground loops and quantified by CMRR.

Voltage Dependent Resistor (VDR / MOV)

A surge suppression component with non-linear resistance connected across mains inputs that maintains an extremely high resistance until voltage exceeds its breakdown threshold, whereupon its resistance drops dramatically to clamp spikes to earth.

Voltage Regulator Tube

A gas-filled discharge tube operating with a fixed ionizing potential connected in series with a dropper resistor to maintain a virtually constant voltage drop across a protected load during voltage surges.

Radio Frequency (RF) Choke

An inductor made of insulated wire wound on a ferrite core designed to exhibit negligible inductive reactance at mains frequency ($50\text{ Hz}$) but extremely high reactance ($\approx 1\text{ M}\Omega$) at radio frequencies, blocking conducted RFI.

Autonomy Time

The duration for which a static UPS battery bank can continuously support its fully rated output load during a total mains failure, typically specified at $5\text{ to }15\text{ minutes}$ for standard setups.

Off-Line (Standby) UPS

A UPS topology where the load is normally powered directly from filtered mains while an off-line static inverter remains on standby, switching to battery power within $2\text{ to }10\text{ ms}$ upon detecting a power failure or sag.

Line-Interactive UPS

A UPS configuration that uses a constant voltage transformer (CVT / ferro-resonant transformer) to continuously regulate input voltage and utilizes the transformer's residual magnetic field to sustain load power during inverter changeover.

On-Line (Double-Conversion) UPS

A high-performance UPS topology where incoming AC is continuously rectified to DC to charge batteries and supply a static inverter, which generates clean AC power for the load at all times with zero transfer time during outages.

On-Line UPS with Static Transfer Switch

An on-line UPS topology equipped with a thyristor-based static bypass switch that can automatically transfer the critical load directly to an auxiliary AC mains supply without interruption if the inverter fails or experiences severe overload.

Rotary UPS System

A motor-generator power system combining an electric motor, a synchronous AC generator, and a heavy flywheel whose stored kinetic inertia sustains the generator output frequency during momentary outages and load changes.

Switched Mode Rotary UPS Connection

A rotary UPS configuration where secondary batteries are maintained on float charge by a dedicated charger and are only connected to the DC drive motor via a contactor/switch when the primary mains supply fails.

Diesel Rotary UPS System

A continuous standby system where an AC motor and flywheel drive a synchronous generator under normal mains conditions, and a diesel engine engages via an electromagnetic clutch once up to full speed to provide indefinite ride-through.

Static Transfer Switch (STS)

A high-speed solid-state switching circuit utilizing thyristors or transistors that senses out-of-tolerance conditions on the inverter and re-routes the load to the bypass mains in less than a microsecond.

Make-Before-Break Transfer

A synchronized switching operation wherein the static switch connects the bypass power line to the load before disconnecting the inverter output, ensuring an entirely seamless transition without any interruption in voltage.

Parallel Redundant System

A multi-module UPS installation containing one or more surplus modules ($N+1$ architecture) interconnected via ring-configured control cables to share load demand equally and maintain continuity if one unit trips.

Pulse Width Modulation (PWM)

An inverter switching technique where semiconductor pairs switch on and off rapidly throughout each half cycle to produce constant-amplitude pulses of varying width, synthesizing a sinusoidal wave without large output harmonic filters.

Third Harmonic Distortion

A zero-sequence harmonic component ($150\text{ Hz}$ in a $50\text{ Hz}$ system) produced by non-linear loads (e.g., switched-mode power supplies, rectifiers) that sums in the neutral conductor and can cause severe neutral overheating.

Rising Main Busbar Trunking

An all-insulated or sheet-steel enclosed vertical electrical distribution assembly rated between $100\text{ A}$ and $500\text{ A}$ used in multi-storey buildings, incorporating tap-off boxes, internal fire barriers, and expansion joints.

Thrust Unit

A heavy-duty internal mechanical mounting component provided in a vertical rising busbar trunking installation specifically to support the structural downward weight of the copper or aluminium busbars.

Peak Lopping

The practice of running an on-site standby generating set in parallel with the public electricity supply during periods of maximum tariff charges to reduce utility maximum demand penalties.

Composite Standby Power System

A comprehensive protection configuration combining a standby diesel generator, a computer-grade static on-line UPS with a $10\text{-minute}$ battery support time, and a separate DC standby battery power system.