Why regulate the voltage?

The voltage supplied by electricity suppliers is supposed to be stable. In fact, a large number of factors may disturb its stability and take the voltage to levels which are excessive (over 260 volts) or inadequate (below 180 volts) for the proper operation of a computer system.

Voltage sags are mainly caused by the following factors:

the site is too far from the power station: in some parts of Southern Europe the voltage does not exceed 200 volts!

occasional, peak power demand: at the end of the afternoon, in winter, when workers return home and all turn on their electrical heaters at the same time.

the proximity of a power-hungry machine: a photocopy machine, a lift or a power-tool.
the voltage sag causes the computer system, or one of its sub-assemblies (keyboard), to crash on account of the lack of power.

Voltage spikes are mainly caused by the following factors:

sudden load-shedding on the mains power system: the shutdown of an electrical furnace located in the vicinity may result in a temporary voltage spike before the voltage can stabilise again at its rated value.

a general rise in mains voltage after heavy use by a large number of consumers: this phenomenon is common on winter nights after all the inhabitants of a neighbourhood have turned off their electrical devices. Local utility companies, for instance, supply a higher voltage under these conditions (about 250/260 volts) in order to cater for peak consumption until about 23.00.

The simplest solution is to use the UPS batteries as a voltage stabiliser, when the voltage exceeds a pre-set threshold.

Continuous voltage regulation, at 230 volts, on the battery output of the UPS, secures voltage stability. Pulsar ES2/ES4 UPS range operates in this way. This solution is adequate for protecting computer equipment in an office or commercial environment.

Advantages
simplicity
price
effective in low-disturbance environments

Drawbacks
risk of deep discharge of battery, in the event of extented voltage sags

Threshold regulation is not a recent invention: Merlin Gerin has been marketing entry-level voltage regulators for over ten years. It is based on a simple mechanism: when a certain threshold is passed, a relay suddenly changes the output voltage of the transformer. It is thus possible to raise or decrease the output voltage by 12 % compared with the input. By adding more relays, you can provide multi-level voltage regulation, shifting the value up or down.
This type of operation is not recommended for sensitive loads or fragile power supplies. There are genuine risks of damaging electrical components if they are subjected to this stress. Most Line Interactive (or Active Standby) UPSs use threshold regulation.
They only "interact" with the mains power supply in so far as they activate the transformer relays. This solution should be used in the same office and commercial environments as the previous one. In economic terms, it may represent a good choice in situations where voltage sags are chronic.

Merlin Gerin calls Booster an upward relay and Fader a downward relay.
On the most recent models to use this solution, the threshold values can be set to suit mains characteristics.

However, some care is required when changing the settings: as electro-mechanical relay technology is relatively straightforward, the values cannot be varied indefinitely, as is the case on a real electronic regulation system. On some booster UPSs, lowering the activation threshold results in a comparable reduction in the maximum permissible voltage!
This rudimentary electro-mechanical system cannot be compared with real electronic regulation, as implemented on most On-line UPSs, which delivers perfect output-voltage stability.

Advantages
useful for extented, low-amplitude voltage sag
efficient in low-disturbance environments

Drawbacks
inoperative for high-amplitude voltage sags
power supplies subjected to stress
does not avoid the risk of battery discharging

This solution can only be envisaged if the UPS regenerates the electrical current continuously (as with On-line UPSs). In this case, the output voltage can be more finely regulated (to within a few percent) without drawing on the batteries. The Pulsar EX series is even capable of delivering a continuous 230 volts without drawing on the batteries, with a mains voltage as low as 80 volts (Pulsar EX30 at 33 % of its rated capacity). This is a world record!

Advantages
only real, continuous regulation solution
never draws on batteries

Drawbacks
can only be implemented on real On-line UPSs
higher cost

Making the right choice

The following table shows the best choice as a function of the following two factors:

The duration of voltage variation
The percentages indicate the frequency of the corresponding power problems (average for Western Europe)