Emergency back-up power at Lennox GS is provided by batteries which supply energy to critical functions at the facility - including to the emergency lighting system comprising around 1,200 fixtures. Efficiency is always a concern with lighting systems, so LED lights would seem to fit the bill, but most can’t operate at the higher DC voltages used in emergency systems in Ontario Power Generation (OPG) stations.
Many OPG generating stations use 125 VDC back-up power, but at Lennox the voltage is 250 VDC.
Batteries at Lennox GS
There are four individual battery rooms at the facility (one per unit), plus a fifth for the common plant area, each with 116 lead-acid cells which provide 250 VDC at 1173 AH (8-hour rate). Each battery room powers emergency backup DC motors for items such as pumps to lubricate the steam turbines in the event of power failure, 600V breaker trip and close control circuits, 4 KV breaker trip and close control circuits, and approximately 300 emergency light fixtures.
LEDs are low-power solid-state devices and are usually fed by specialized constant-current power supplies - LED Drivers. Typical LED bulbs operating from AC have built-in AC-DC LED drivers.
The application at Lennox requires 250 VDC input, while some other OPG facilities use 125 VDC, and for versatility, standard 120 VAC operation would be a bonus.
Battery systems also have output voltage fluctuations based on charging-levels, and DC systems must deal with voltage drop. Ideally, these bulbs would operate from 105 through 280 VDC and from 110 to 130 VAC.
LEDs are semiconductors, and their life is depleted by elevated temperatures. The junction temperature of these devices should be kept below 125 degrees Celsius.
Typical Fully-Enclosed Facility Fixture (with VCC LED Lamp)
Fully-enclosed fixtures are used throughout the emergency lighting system at Lennox GS, as is typical at OPG generating stations. Fully enclosed fixtures provide protection for the bulb, as well as for personnel - if a bulb should shatter - which is not uncommon for traditional incandescent lamps. These enclosures raise the temperature within when bulbs are operating, through self-heating, especially in the typical downward orientation. This heating can degrade the operating life of any bulb active within these enclosures.
Administration Building Fixture
OPG rightly requires safety authority listings for all applicable electrical components and systems throughout its facilities, and these systems and components are inspected by independent authorities.
VCC custom-designed the LED lamp for OPG considering all of the challenges and drawing on their years of experience in solid state indication and lighting for demanding applications. The LED driver had to accommodate the wide range of AC and DC voltages demanded and desired of this lamp. These electronics also incorporate the temperature sensing and fold-back circuitry to protect the LED from over-temperature conditions that are exacerbated by the enclosed fixture. VCC had extensive testing performed by a third-party authority and the design was revised and finally passed all requirements of UL 1993 (Self-Ballasted Lamps) for fully-enclosed fixtures.
The VCC replacement bulb has a standard E26 base, and a standard A21 shape, as well as being able to operate in the standard enclosed fixtures and with the range of input voltages that OPG uses. So, they are form, fit, and function compatible with the existing bulbs, and can be replaced on a fixture-by-fixture basis.
Lennox is using the VCC LED lamp to replace a mix of 100 W and 200 W incandescent light bulbs. The 200W bulbs had been used in the turbine hall where ceilings are high, and the fixtures are 25 feet above the floor. One-hundred-watt bulbs were used in corridors and other areas where fixtures are less than half that distance from the floor.
The VCC light bulb was noticeably brighter than the 100 W on replacement, and acceptably-so in the higher installations, in retrofitting the 200W ones. Part of this is due to the orientation and beam-angle. All fixtures at Lennox have the bulbs base-up, so the slightly narrower beam angle of the LED lamp suits this by shining most of its light downward, where it is required.
The VCC LED lamp is 9W, so it draws less than 1/10th the energy of the 100 W incandescent bulb and less than 1/20th of the power demanded of the 200 W bulb.
Figuring that the 200W bulbs are 10% of the installation, the total current draw for the emergency lighting at Lennox was 528 A (at 250 VDC) and is now 43.2A with the full implementation of 1200 VCC LED lamps.
This will translate into a much-increased hold-up time during a power-down situation, and more available energy for the other critical emergency systems, such as the DC pumps for lubrication of the steam turbines.
Emergency-Powered Lighting In-Action
The incandescent bulbs used at Lennox have a rated life of 1000 hours. Standard incandescent bulbs end their life with a flash - a worn-out filament breaks and arcs, usually on turn-on with the surge of power into a resistive and inductive load.
LEDs have no filament but are a solid-state device with a junction across which the light is generated. LED light output will degenerate over time but does not burn-out. LED life is rated, typically, to the number of hours from 100% to 70% output. The VCC LED lamp is rated at 50,000 hours. This means that where 50 bulbs may have been replaced in a given year, we may expect 1 in the future.
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