At Powerguard, we are often asked questions in regards to emergency lighting. In this article, we’ll be discussing what a lighting inverter is, how it should be maintained, and what standards are in place that organisations must adhere to.
Before any emergency lighting, maintenance or standards are discussed, it’s a good idea to first understand the different kinds of lighting inverters, what they do and why they’re so crucial to the safety of an organisation.
A lighting inverter transforms DC battery power to standard AC voltage to offer backup power for lighting in the event of an emergency situation. Some inverters will provide constant, filtered power and are referred to as uninterruptible power supplies.
Emergency lighting inverters can actually be used in a variety of applications besides emergency lighting solutions. These include fire alarm systems, exit lighting and other crucial life saving safety-related equipment.
Lighting inverters vary in transfer time, voltage regulation and power conditioning. For example, some inverters may have a short delay, typically measured in milliseconds to respond to a power anomaly, while others may offer a seamless transfer. Seamless power is needed for lighting control and many kinds of alarm circuits.
Transfer time is the length of time it takes to recognise and deliver the emergency power when it’s needed. Zero transfer time means that there will no power lag, which is particularly important when power is required for high-pressure sodium lighting.
Voltage regulation ensures that power drops and brownouts won’t impact the overall lighting system. Voltage regulation also maintains lighting levels during normal operating conditions.
Power conditioning stops surges and transients from travelling to the electronic ballasts, thereby providing a longer lifespan for the light fixture or another protected asset.
There are two different installation solutions when it comes to lighting inverters:
A central lighting inverter provides a central solution to emergency lighting and power backup with a variety of options designed to minimise maintenance requirements and increase emergency lighting performance.
Central lighting has a higher initial investment but requires lower maintenance. This is because it is all placed in one central location and uses only one battery system that requires occasional test and discharge maintenance.
Dispersed lighting costs less than central lighting initially, but requires far more time and manpower to maintain each light, as you need to test each light’s individual functionality one at a time.
UPS Module – When operating normally, utility power is constant, so the lighting load is fed from the utility, similar to a standby uninterruptible power supply. The UPS module includes an inverter which is an electrical device that converts direct current (DC) to alternating current (AC). There are typically several other components within the UPS such as an AC distribution module with a circuit breaker, boost tap transformer, and control and monitoring subsystems. These added components may offer some power conditioning, but in the main, they are usually not intended for total power conditioning like a true, online UPS system.
Battery Module – The battery module contains the battery system that is required to produce the backup energy to supply the inverter during instances of low power supply.
Battery Charger – The charger converts AC voltage to DC current. With utility power present, the battery charge circuit sends voltage and current to the batteries. For most solutions, once the batteries have received a full-power charge, a consistent supply of energy is enough to keep the batteries at maximum power.
The inverter converts DC voltage supplied by the battery to AC voltage of the correct stability and frequency so that it is capable of powering most lighting loads. Typically, inverter output voltage is produced by sinusoidal pulse width modulation (PWM). The use of high carrier frequency for PWM and a dedicated AC filter consisting of a transformer and capacitors will ensure low distortion of the output voltage.
Output Power Transformer – A dry-type power transformer delivers the inverter AC output. Transformers are a crucial factor in electrical distribution equipment and factors to contemplate would be capacity, voltage rating, insulation system, core and coils and winding insulation system. Not all systems will include an isolation transformer, but if they do, most, whether built-in a UPS or a lighting inverter unit, will be built with copper wiring.
Display & Controls – This system provides operation monitoring and control, alarms and diagnostics. The front-mounted control panel features a display and keypad for user interface.
Battery Assembly – While battery assemblies can vary significantly in a lighting inverter solution, most will contain front access, sealed, lead-acid valve-regulated battery cells. These batteries are connected using buss bars and cables.