Thermal challenges of a compact power entry module with 7,000 W output in a telecom system

The subject system is the first terabit high-availability router which occupies a half rack space. The PRO/8812 high-availability router is a high-capacity system that is designed for performance scalability. The fully loaded router delivers 480 Gbps full-duplex throughput. A standard NEBS-compliant 7-foot rack can accommodate up to two systems. While the power to port density ratio is lower than the other routers, the absolute power consumption is high because there are twice the port count and are packed densely together in half the space. At the early stages of product development, the original power target for the system was 5.5 kW. However, it was increased to 7 kW to provide headroom for future hardware upgrades in order to be consistent with the company´s marketing message of hardware and software scalability and upgrade to provide investment protection incentive for the IP network providers. Similar to the system package, this PEM has the densest packaging for a Telecom product that is in production. The 7 kW PEM is the version that is currently in production, but most of the research and development were performed for the 5.5 kW PEM. In this paper, the detailed thermal analysis and testing are discussed for the 5.5 kW PEM, as well as the incremental evolutionary changes that were implemented to increase the power output to 7 kW without the need to change any boundary conditions at the system level, such as increasing airflow or changing the layout by physically relocating the PEMs to cooler zones in the system. There are two PEMs in each system; however, each PEM has to be able to provide 100% of the load due to power supply redundancy requirement. The design constraints and the thermal design implementation will be discussed in the following sections, as well as the thermal analytical predictions and empirical work.