Building regulations in the UK require that lift systems for evacuation meet the standards set out in BS 9999 Annex G. This requires that a secondary power source is available to power the lift in the event of a power outage, to ensure that the lift can still be used to evacuate the building.
Uninterruptible Power Supplies (UPSs) are a cost-effective choice as a secondary source of power for lifts, as they are easy to install and integrate into existing lift systems. However, standard UPS systems may not be suitable for lifts that produce regenerative power during normal operation. Regenerative power is energy that is generated by the lift motor and returned to the power supply. This power is different from traditional AC power and can cause damage to the UPS and affect the overall performance of the system.
To address this issue, manufacturers have developed specialized UPS systems that have been specifically designed for use with lifts that produce regenerative power. These systems, such as PowerPro EF LIFT, are equipped with features that can handle the unique characteristics of regenerative power and protect the UPS from damage.
Overall, the selection of a secondary power source for lifts is essential to meet the requirements of BS 9999 Annex G and ensure the safe evacuation of the building in case of a power outage. It's important to consider the type of power supply and the characteristics of the lift system when selecting a UPS, to ensure that it is able to provide reliable and efficient power backup.
Regenerative Load Operation
The EF LIFT UPS incorporates an intelligent braking system, using IGBT controllers to electronically absorb any regenerative back feed energy from the lift. Regenerative load causes reverse current to flow to the output of the UPS system. This reverse energy causes the internal DC bus within the UPS to rise above safe levels of the UPS design and can cause damage to the DC Capacitors, Rectifier, and Inverter.
The PowerPro EF Lift system has a separate IGBT Controlled Regeneration Box that connects directly to the UPS DC Bus. The DC bus voltage of the UPS typically floats at ±405Vdc and can boost up to 435Vdc. The Regen Box monitoring system continuously analyses the internal rise of the DC bus voltage. When the voltage increases over 435Vdc fast switching IGBTs connect DC resistors and dissipate the energy into heat, protecting the UPS components and Inverter operation. When the DC bus voltage decreases back down to an acceptable level, the Regen Box self-deactivates.