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Emergency power supply for the heavy rail rapid transit system in Washington

30 BENNING UPS systems set to provide more safety for one of the busiest metro rail systems in the United States.

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The Washington heavy rail rapid transit system is one of the busiest rail systems in the USA, covering a total area of around 1,500 km² including Washington DC, as well as surrounding areas in Maryland and Virginia. It is predicted that the region around the American capital will enjoy strong growth in the coming decades, therefore the government has formulated a strategic plan called Momentum as a long-term vision for the future. This plan is intended to ensure that the rail network will continueto meet the needs of the region, whilst maintaining its competitiveness.

ENERTRONIC I 120 kVA with optional IP21 cabinet
ENERTRONIC I 120 kVA with optional IP21 cabinet

Modernisation programme

Momentum describes the need for a modern and efficient transit system which, in the long-term, will be able to ensure a safe and reliable rail service for all passengers. To achieve this goal, a modernisation programme for the rail system has begun in order to, amongst other things, gradually replace the existing emergency power supply with a modern and efficient system. Due to the high loads placed on the public power supply (caused by disturbance effects from large-scale consumers, connections in peak usage periods and lightning strikes) it is not possible to avoid voltage dips, overvoltage and transient currents in the public mains electricity supply.

Accordingly, robust uninterruptable power supplies (UPS) can be deployed to guarantee the supply to critical consumers (e.g. process control computers, control rooms or SCADA systems), all of which require an independent electrical supply that does not suffer from any disruption in the public network. A static UPS system is not only intended to ensure a continuous and uninterrupted supply to connected equipment, but also to achieve a considerable improvement in voltage and frequency quality compared to the normal power supply system. By 2021, various lines of the rail network should be equipped with appropriate systems to ensure a reliable and uninterrupted electricity supply to the rail signalling system, control centres and stations.

Six UPS systems per year

As a leading quality supplier of industrial power supply systems worldwide, BENNING was awarded the contract to supply specially configured UPS systems based on the ENERTRONIC I type for various rail lines in Washington in late 2016. Over the next five years, six UPS systems will be delivered and put into operation each year, making 30 units in total. In order for the highly customer-specific requirements to be met as closely as possible, BENNING and the client have been in close contact from the outset. The specific product specifications were jointly established and the technical planning agreed. The delivery and launch dates were set at an early stage to ensure that the installation and commissioning process would be as short and seamless as possible. The first successful system tests took place in the first quarter of 2017 with the first delivery taking place just a few months later.

Maximum safety

The robust three-phase ENERTRONIC I 3-3 UPS systems ensure high availability and represent safety and cost-effectiveness. The equipment combines excellent output characteristics and high voltage stability, even under heavy load fluctuations, with an input power factor ≥ 0.99 and minimal current distortion. The product line has a comprehensive set of reporting and monitoring functions, and can be controlled both remotely via the customer’s network and from the display on the system.

ENERTRONIC I 120 kVA with optional IP21 cabinet

Redundant and scalable

Should the client wish to have the UPS system expanded in the future, for example, to scale up output capability for increased load or for redundancy purposes, up to eight units of the ENERTRONIC I product line can be used in parallel. As a series production range, the ENERTRONIC I rectifier consists of an IGBT semiconductor rectifier bridge with power factor correction (power factor = 1).

In accordance with the special customer requirements in this case, BENNING has produced a thyristor rectifier with additional THDi filters, which reduce distortion to less than 12%. It is designed in such a way that it can simultaneously supply the full load and recharge discharged batteries within around 12 hours after a power outage to approximately 95% of the battery capacity.

Ideal for non-linear loads

In the inverter, the dc current is converted into a three-phase alternating current using a sinewave generated from pulse width modulation through an IGBT semiconductor and output isolation transformer. The high-switching frequency compared to the basic frequency and optimum regulation of the pulse duration allows great efficiency under partial loads and very low THD with non-linear loads. This also provides excellent dynamic response with load changes. The consumers load will be automatically switched to the bypass network or a parallel system if the supply is no longer guaranteed by the inverter within the prescribed tolerances.

Robust system engineering

The resistance of the UPS systems to environmental conditions was a decisive factor in selecting the system. For example, there was a lot of brake dust in the air at sites where the system was to be installed. This largely consists of fine dust which, because of its small particle size and chemical composition, could lead to breakdowns. The system cabinets developed by BENNING have special air filter devices to prevent the infiltration of the finest particles into the system. This is another product feature that serves to meet high customer requirements during demanding 24/7 operations and continually ensures reliable operation of the heavy rail rapid transit system in the political capital of the USA.

Further Information

author/contact: Dietmar Papenfort
telephone: +49 2871 93 237

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