For too long, power supplies have been treated as an after-thought to the main design project. It is when all the other features and functions, as well as aesthetics, are finalised that the power supply is specified, and then has to be designed in. By that point, the desired specifications may be unattainable and/or the allocated space insufficient for the optimal power supply.
This can be avoided by putting power supply design higher up the design project criteria. Using the resources of specialists in power conversion can also benefit a project. Such specialists have access to products from different manufacturers, and the technical expertise to customise a power supply for a specific application can make all the difference to an effective project being delivered on-time and on-budget.
Emergency power systems
An example of sourcing application-specific products for the demanding rail environment is DC-AC inverters for emergency HVAC (heating, ventilation, air-conditioning) systems. A ventilation circuit is vital to ensure fresh air is supplied to passengers and staff in the event that a train should lose its main power source mid-route.
Relec’s portfolio includes single and three-phase DC-AC inverters from Premium – manufactured to be particularly suitable for operation in extreme temperature and humidity, shock and vibration conditions, yet in a compact size for use in small spaces.
All Premium DC/AC inverters comply with EN50155, guaranteeing performance for electronic equipment used in rolling stock.
Emergency HVAC systems are equipped with DC-AC inverters which are supplied by batteries that can range from 24V to 110V. The input power is converted into three-phase AC power, to allow the inverter to feed a three-phase motor which switches on fans in the carriages to maintain the ventilation system. Failures under extreme mechanical stress cannot be tolerated.
The conformally coated inverters withstand the harshest of environments, whether mobile or static, for example in ‘at seat’ power in carriages and network security systems.
In addition to the conventional 24V and 110V inputs, the company offers a variety of inverters operating from 12V, 36V, 48V or 72V battery systems, all approved to EN50155 and EN50121-3-2, with options to meet RIA 12 surges and transients.
Premium has supplied DC-AC inverters (ODX-1300) for the emergency fans in CAF´s Civity fleet of commuter and regional trains in the UK (Class 195, 196, 197, 331, 397). It has also supplied the ODX-3000 and ODX-6000 DC-AC inverters for HVAC emergency systems in Bombardier´s streetcars in Cologne, Germany.
Another series of DC-AC inverters is designed for trackside communications and to manage services on IP networks. The Cotek SR-1600 Plus series of modular, intelligent DC-AC inverters is available with Simple Network Management Protocol (SNMP) communication for use in trackside applications as well as data centres. The SNMP Internet standard gathers and organises data about managed devices, regardless of hardware and software variations, to monitor and modify device behaviour.
The DC-AC inverters offer true sine-wave output with minimal total harmonic distortion (THD) of less than two per cent, to ensure power factor, low peak currents and efficient operation. The standard 19-inch, 2U rackmount inverters are scalable, providing up to 6.4kVA per rack, based on 1600VA modules. They have redundancy and hot swap features as standard and DC or AC mode can be selected with zero transfer time for uninterrupted power supply. In DC mode, efficiency is 95 per cent.
The inverters are protected against reverse polarity connections and will also shut down, without damaging the systems, if the input levels rise outside specified parameters. Both AC and DC outputs are protected against overload, short circuit and over-temperature conditions.
For both series of DC-AC inverters, Relec provides technical and practical support for power design to ensure that exacting conditions for extreme environments are met, while balancing passenger comfort and operator efficiency.
Relec Electronics has been providing specialist power conversion and display products to support professionals for over 40 years. Its team of experts is able both to source and provide standard products and to use its technical expertise to deliver a power supply with bespoke features and benefits that can make a measurable difference by delivering optimum performance.
In addition to sourcing standard solutions, the company’s experienced engineers are able to understand an application and its specifications to source the most appropriate products. All members of the sales and technical support team are engineers and can help with modifications to standard products or features for power conversion.
Guest Editor: John Stone is sales director at Relec Electronics.