As a result of the changing and more demanding environment for duty of care, there is the need to improve the facilities for the evacuation of disabled, injured or incapacitated persons from public premises. Local Governments of the UK have embarked upon an initiative to provide purpose built standby power systems for dedicated emergency evacuation lifts to be installed in schools, libraries, hospitals, and other public buildings.

This EPS series of stand by power systems is designed to supply three phase traction motor driven hoisting units of emergency evacuation lifts in an evacuation emergency or when the public power supply has failed.

The EPS standby power system is a fully self contained, free standing high performance rectifier battery charger and an inverter with automatic bypass feature. The EPS system is provided with a valve regulated or AGM lead acid 10 years design life storage battery sized to support the inverter load for an autonomy period long enough to permit 10 upward and 10 downward lift car journeys within the one hour period as stipulated in the EN-British Standard specification.

In normal mode the control logic of the power system is energised so the rectifier will maintain the battery in a fully charged condition. The battery charging function will automatically revert to standby when the battery is fully charged.

The power consumption of the EPS standby power system in quiescent mode and with the battery in the fully charged condition does not exceed 100 Watts.

The operational mode is selected by means of a key switch with “local”, “remote” and “automatic” (EPS-B Version only) positions fitted to the control panel of the EPS system.

The normal operational mode is in “remote” position and permits the EPS to be enabled from an externally located “emergency control” switch usually fitted to the lift control panel in the lift car that will allow an authorised person to take control of the lift and to make the prescribed number of journeys.

This remote “emergency control” key switch is often supplemented by a parallel connected key switch sited close to the normal lift command station to be used if the lift doors are closed and access to the switch inside the lift car is not possible.

When the EPS unit is “enabled” and is providing power to the lift traction system it provides a contact closure signal that is used by the lift manufacturer to illuminate an “on emergency power” light on the lift control panel inside the lift car. This signal can also be delivered to a building management system and to an exterior indicator outside the lift entrance doorway if required.

When the EPS selector switch is turned to the local position, this allows the service engineer to make repairs and undertake routine maintenance on the EPS and make battery voltage measurements and cell testing. In this position the remote “emergency control” switch circuits are disabled.

In the “Automatic” position for the EPS “B” version, if normal mains power is still available during the emergency use, the remote “emergency control” switch actuation allows the use of the mains power source via the bypass circuit of the EPS to feed the lift traction system and preserves the stored energy in the batteries.

If, in this mode of operation the mains should subsequently fail, or if the mains power is switched off during the emergency evacuation process, the lift motor or traction drive system is automatically powered by the inverter using the stored energy of the battery.

The EPS systems are supplied with a wall mounting wrap around bypass unit that should be inserted into the mains power circuit feeding the lift traction system.

This mechanically operated wrap around bypass unit is fitted with a rotary handle operated changeover switch, input and output plugs and sockets and should be installed by the electrical contractor close to the intended location of the EPS unit.

The EPS system is supplied complete with flexible lengths of input and output cables. A Commando type plug is fitted to the input cable for inserting into a socket on the wall mounted bypass unit, the output cable from the EPS is fitted with a Commando type socket to be inserted into the plug on the bypass unit. The remote control, alarm terminations and status indication interface connections are within the EPS on a terminal block with compression type terminals and must be hard wired to the respective control switch and indicator lights by the electrical contractor.

The EPS standby power supply systems comply with BS EN 60146 and are specifically designed for use with lift hoisting systems fitted with VVVF traction drives and three phase induction motors as supplied by OTIS, Schindler, KONE, Mitsubishi etc.

The lift manufacturer must ensure the traction drive systems are fitted with harmonic correction compensation filters and be CE marked as compliant with the conducted and radiated EMC emission legislation of the appropriate EN Standards.

The product can also be supplied for the hydraulic lift hoisting mechanisms using three phase or induction motors and for lift hoisting systems with reverse energy load resistors and braking systems.

Summary points:

• The EPS20 in its normal mode has it's internal logic energised by means of a local key switch like the ignition switch in a car. The rectifier logic is on and it keeps the battery charged, the inverter is switched off, the system is in "cold" standby.
• Power for the lift traction system is fed through the bypass circuit of the EPS, the power flow through the EPS20 will be shown on the LED's in the small mimic panel on the front door of the equipment.
• The EPS inverter is of an advanced PWM technology design using IGBT power semiconductors oversized to handle the harmonics produced by VVVF traction drives and clear downstream faults using only its internal battery power source.
• The inverter overcurrent capacity enables the EPS to trip circuit breakers and rupture fuses using only the battery power source whereas an inverter in a conventional UPS system of the same kVA rating as the EPS cannot offer this capability or the harmonics produced by VVVF traction drives.
• The EPS20-B system logic can be switched into the hot standby (Automatic) mode by means of the local key operated switch or by an external contact closure command from auxiliary terminals on the remote located emergency lift evacuation switch.
• A remote evacuation control switch commands the logic in the EPS20 to start the inverter and it is then held in hot standby ready to power the lift traction equipment using the normal manual push button controls from within the lift car.
• The lift motor traction system and controller does not have a brain so it does not know if it is being fed from a mains power source or from the standby power system. We send a "ready" signal “emergency power on” to the lift control panel as soon as the EPS20 is ready for duty.
• We also signal to the remote evacuation switch by means of a contact closure in the EPS20 that it is "ready for duty", this signal is intended to illuminate a lamp adjacent to the remote evacuation