TechArchive

Buzzwords in power protection technology

Spikes:high energy surges with a very short duration. Spikes can be generated by the local power companies load switching between transformers, as well as by modern office equipment, such as photocopiers, thermostats or any other hardware requiring high electrical currents. The most damaging type of spike is caused by a locally grounded lightning strike.

Electrical noise:high frequency interference which can occur in two forms – common mode and series mode. Common mode results in disturbances between earth and both mains supply lines. Series mode results in disturbances between neutral and the live supply. Electrical noise can be caused by lightning strikes, load switching, cable faults, office equipment, radio and welding equipment.

Surges:long-duration rises in the supply voltage which last for 1 cycle or longer. Surges are caused by a sudden reduction in demand on the local supply, by large power-hungry hardware applications.

Sags:long-duration drops in the supply voltage. Sags are most commonly noticed when local lighting suddenly dims. Sags are caused by large motor-driven hardware, such as electrical heaters and air conditioners, taking extra start-up loads. They place an instant demand increase on the local supply which causes the supply voltage to drop.

Brownouts:long-duration deep sags in the supply. Brownout conditions can last for long periods, especially in more remote areas and less developed countries.

Blackouts:both momentary and long-duration breaks in the mains supply.

Sinewave:a graphical representation of the supply voltage and frequency present in a normal mains supply. When selecting power protection, it is important to consider if the ICT hardware can be powered from anything other than a sinewave. Some hardware power supplies can only work to their specification when powered by a sinewave. Not all UPS produce a sinewave output. Off-line, standby and some line interactive UPS supply a step-wave, trapezoidal or square weave on mains failure.

Galvanic isolation: provided by low impedance and ferro-resonant transformers. They provide a physical barrier between the mains and the protected hardware which no spike or electrical noise can penetrate.

Off-line and standby UPS: use a simple filter to “clip” spikes and electrical noise levels. The output waveform on battery is a step-wave, trapezoidal or square-wave. The transfer time can be longer than 4ms. Off-line UPS usually have a poor input voltage window which can result in frequent battery use.

Line interactive UPS:designed to provide a superior transfer time to off-line UPS. The output waveform on battery is also typically a sinewave. Line interactive UPS normally have superior filtering capabilities than off-line UPS and may have a wider input voltage window. This allows the UPS to work down to lower mains voltages before battery power has to be used to power the load.

On-line UPS: designed to provide a zero transfer time supply, with far tighter voltage and frequency regulation than can be achieved by off-line and on-line interactive UPS. On-line UPS use a double-conversion process, whereby the alternating current (AC) of the mains supply is converted into two levels of direct current (DC). One feeds the inverter, whilst the other is used to charge the battery. The inverter changes the DC supply back into an AC pseudo mains supply to power the load. When the mains fails, the inverter instantaneously draws its DC supply from the battery. Spikes and electrical noise are normally removed through built-in EMI/RFI filters. The AC-DC-SC double conversion process eliminates sags, surges and brownouts. Additional benefits of on-line UPS include an automatic system bypass to protect the load from UPS failure and the UPS from overload by users. On-line UPS produce a sinewave output on both mains and battery.

No-break UPS: designed around a ferro-resonant transformer, no-break UPS provide the benefits of galvanic isolation, full-time power conditioning, a sinewave output and a break-free supply of battery power on mains failure. They offer bullet-proof protection for extreme electrical environments.