SAFETY/VENTILATION | TECHNICAL
Many drives achieve ramp down using a brake resistor,
but this creates heat, limiting its braking ability. Drives with an active front end remain cool while braking, as they recover the electricity, enabling them to ramp down and reverse a fan motor more quickly. This cooler operating temperature also means that less air conditioning is required in the electrical room, providing savings throughout the system’s life.
SPECIFYING DRIVES FOR TUNNEL APPLICATIONS For tunnels up to around 500m in length, natural airflow is often sufficient for maintaining air quality. Longer tunnels depend on ventilation systems,
typically at 690V supplied by substations at either end for road tunnels, and at 400V supplied at stations for rail tunnels. For fire safety, however, emergency ventilation
is required for road tunnels longer than 150m. In applications where the ventilation system is used exclusively for fire safety purposes, a soft starter system provides a more cost-effective solution to a drive. However, in all other applications, a VSD is the right technology. Long cables connect drives to fans throughout the
tunnel. At these lengths, voltage drop is an issue, even with copper cables. Active front end drives can increase their voltage by up to 10% to compensate for this, ensuring that fan motors have sufficient power wherever they are located within the system. This also avoids oversizing of electrical equipment, like motors, VSDs, and cables. Drives also play a key role in tunnel excavation and
construction. They are used to control the temporary ventilation systems and the dewatering systems on drilling equipment, as well as manage systems like the high-pressure water supply and conveyors. In some applications, drives even control the drill.
DRIVES IN THE ALPS, INDIA, AUSTRALIA The Frejus road tunnel in the Alps connects France and Italy. It was constructed in 1980 and is 12km long. When its HVAC system was renovated in 2016, operators replaced 24 fans with new motors and drives. The new fans use huge 1MW motors controlled by VSDs. During normal operations, the fans remove vehicle
emissions to maintain high air quality. They are also essential to the fire safety system. In an extreme condition test, the motor-drive system withstood temperatures of 400⁰C for two hours without external cooling. In Chennai, India, the metro also uses drives for air
quality and fire safety. ABB ACH580 and ACS880 active front end drives compensate for voltage drop issues caused by the long cables in the tunnels, producing significant savings. Chennai metro also relies on the drives’ ‘firefighter’s
override’ feature, which enables a firefighter to run the drives at maximum speed while ignoring non-critical faults at the turn of a key. This feature buys time for the passengers to escape and firefighters to control the fire. In Australia, the recently opened WestConnex M4-M5
link tunnel is Sydney employs ULH drives to control the 19 axial fans and reduce harmonic content by 97%. Further, VSDs are used on its 168 egress passage pressurisation fans to provide safe evacuation route in case of an incident.
DRIVING FOR BETTER, SAFER TUNNELS VSDs enable tunnel operators – whether retrofitting an existing tunnel or fitting a new one – to maximise air quality and remain in compliance with strict safety standards. Drives also produce significant cost savings for operators, especially in terms of energy efficiency and right-sizing components. Considering these advantages, drives are a rational investment when it comes to tunnel ventilation.
Above: ABB supplied drives for ventilation at WestConnex road tunnel, in Sydney, Australia August 2023 | 19
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