Voltage Stabilisation and Energy Storage Devices

Voltage stabilisation and voltage regulation are two inter-changeable terms referring to a power protection product set that includes power conditioners automatic voltage stabilisers (AVS) / automatic voltage regulators (AVR).
Power Protection

From a power protection perspective, power conditioners, AVS and AVRs provide protection when the mains power supply is present. The devices provide protection from mains related problems including sags, surges and brownout conditions. The devices will also provide spike and transient noise protection through some form of filtering device. The devices are normally connected directly to the mains power supply but may also be used to protect loads from generator supplies and other AC sources.

Voltage Stabilisation Technologies

One of the principle characteristics of a voltage stabiliser is its wide input voltage window. As well as protecting the loads connected, a voltage stabiliser widens voltage operational window when an AC power supply is present. A typical voltage stabiliser may operate on a voltage supply from +15 to -40%. Voltage stabilisers do not provide protection from changes in mains power supply frequency. Only devices with a built-in inverter can achieve this such as an uninterruptible power supply.

There are three main types of technology associated with voltage stabilisers. These include transformer based, electro-mechanical and electronic. Transformer-based voltage stabilisers may be pure transformer-based or a combination of transformer and electronics.

Constant Voltage Transformers and Power Conditioners

A pure transformer-based product would be a Constant Voltage Transformer (CVT). The device used a special type of transformer known as a ferro-resonant transformer with a primary and secondary output and a tank capacitor circuit. CVTs have a wide operating window and provide a regulated output supply to within ±3-5% of their nominal output.

CVTs are more commonly referred to as power conditioners. They ‘condition’ the electrical supply and protect their connected loads. The can provide momentary protection from millisecond breaks in electrical supply thanks to their tank capacitor circuit. This a tuning feature of a CVT power conditioner and the energy stored in the capacitor set provides a source of power when the mains power supply breaks momentarily.

CVTs also provide Galvanic isolation as an inherent part of their design. This is a physical separation between the primary and secondary transformer windings. Energy flows from the primary to the secondary via the flux magnetic field within the transformer design.

As constant voltage transformers are transformer based, they tend to be energy-inefficient and generate noise and heat. CVTs are also heavy and limited to applications below 15kVA single phase. Three phase designs can be manufactured but using three single phase transformers (one per phase) in a single cabinet.

Auto-Transformer-based Voltage Stabilisers

Another type of transformer-based voltage stabiliser couples an auto-transformer with an electronic control and filtering circuit. The transformer has a wide input voltage window and taps that are automatically selected according to the input voltage required. The output is again regulated for a given input voltage window and a filtering circuit provides protection from spikes and electrical noise

Electronic Automatic Voltage Stabilisers

This group of voltage stabilisation products uses no transformers and is based on static electronic technologies. Their design is more complex but the degree of control and speed of response to changes in mains power supply voltage is almost instantaneous. The systems are more energy efficient as there is no transformer and therefore no transformer-related energy losses. Electronic voltage stabilisers may not be as robust in their design as a transformer-based system, but they are more compact and quieter. They may rely on internal fans for cooling and may provide galvanic isolation as an option.

This type of more advanced automatic voltage stabiliser may again provide minimal protect from short break in the electrical supply through internal capacitor energy storage. The device may also include options for remote alarm monitoring in the form of signal contacts and possibly over an IP-network with a plug-in SNMP card.

Electro-mechanical Stabilisers

This type of automatic voltage regulator marries electronics and transformers. The most common type of electro-mechanical transformer-based regulator will use a toroidal or column-type transformer. These devices use brush position on the transformer to control the output voltage. As the input mains power supply voltage changes, so does the position of the roller and brush connection.

Electro-mechanical stabilisers tend to be very robust being based around a transformer design. They may provide Galvanic isolation as standard or an option. Being electro-mechanical they will require routine inspection and regular maintenance dependent. The frequency of this will depend on the application and country of use.

AVS and UPS System Combinations

In remote and third-world countries, voltage stabilisers can be used to provide additional protection to the input power electronics of uninterruptible power supplies. Installing an AVS or AVR before an uninterruptible power supply will also widen its input voltage range to reduce battery usage. The voltage stabiliser is installed upstream of the UPS system and will then also provide protection if the load is transferred to the bypass supply line of the UPS system, if the bypass supply is also taken from the same source. The stabiliser can also protect the UPS input from problems that can arise form a poorly maintained or specified upstream generator.

Voltage Stabilisation and Super Capacitor Energy Storage

One of the most interesting developments for voltage stabiliser technologies is the development of energy storage options which can extend the amount of time a stabiliser can fill-in momentary breaks in electrical supply. Lithium-ion and lead acid batteries cannot be used for this type of application as this would require an inverter. The solution is to use super capacitors as additional or replacements to the already built-in capacitor circuits.

Super capacitors can store larger amounts of electrical energy than a traditional capacitor and recharge far quicker than a conventional battery system. Whilst a traditional voltage stabiliser may cover 10-20ms breaks in electrical supply, one fitted with supercaps could see this extended to a minute or more, dependent on sizing and loads.

With greater demands being placed on electrical networks worldwide there is a growing need for voltage management and stabilisations. Areas of the world with poor and unstable mains power supplies will always be reliant on some form of voltage stabilisation technology. In more advanced countries, the need for super capacitor-based voltage management technologies could develop in line with the overall demand for electricity and Internet of Things connected devices.