Cabinets, modules or units - what to choose for power management in the data center?

Modern data centers require a careful approach to power. It is necessary to simultaneously monitor the state of loads and manage the connection of equipment. This can be done using cabinets, modules or power distribution units. What type of power equipment is best suited for specific situations, we describe in our post using examples of Delta solutions.

Powering a dynamic data center is often a daunting task. Additional devices in the racks, the transfer of equipment to sleep mode or, conversely, an increase in load leads to unbalanced power supply, increased reactive power and non-optimal operation of the electrical network. The power distribution system helps to avoid losses, ensure efficient operation of the equipment and protect it from possible power supply problems.

When designing power networks, IT professionals often face a choice between cabinets, modules, and power distribution units. Indeed, in essence, all three categories of devices solve the same tasks, but at different levels and with a different set of options.

Power Distribution Cabinet

Power Distribution Cabinet, or PDC (power distribution cabinet), is a power control device at the top level. The Cabinet allows you to balance the power supply for dozens of racks in the data center, and the use of several offices at once allows you to control the work of large data centers. For example, similar solutions are used by cellular operators — more than 50 power distribution cabinets installed in the China Mobile Data Center in Shanghai were required to power the data center for 5,000 racks.

The Delta InfraSuite PDC cabinet, which is the same size as a standard 19-inch cabinet, includes two groups of single-pole circuit breakers, protected by additional switches. The cabinet can monitor the current parameters of each circuit with a separate switch. The power distribution cabinet has a built-in alarm system for uneven load sharing. As an option, Delta cabinets are equipped with additional transformers for generating various output voltages, as well as impulse noise protection modules, such as those created by lightning discharges.

For management, you can use the built-in LCD display, as well as external energy management systems connected via the RS232 serial interface or via SNMP. The device is connected to the external network through a special InsightPower module. It allows you to send to the central server alerts, data of the control panel and parameters of the state of distribution networks. This is the main component that makes remote management and monitoring possible, and also notifies system engineers of critical events via SNMP traps and email.

Specialists serving the data center can find out which phase is loaded more than others and switch some consumers to less loaded ones or schedule the installation of additional equipment in a timely manner. On the screen, you can monitor parameters such as temperature, leakage current to earth, the presence or absence of a voltage balance. The system has a built-in log that stores up to 500 cabinet event records, which allows you to restore the desired configuration or analyze the errors that preceded the emergency shutdown.

If we talk about the model number Delta, PDC is connected to a three-phase network and can operate with a voltage of 220 V with a deviation of no more than 15%. The line includes models with a capacity of 80 kVA and 125 kVA.

Power Distribution Modules

If the power distribution cabinet is a separate cabinet that can be moved around the data center in the event of its redevelopment or changes in the load arrangement, then modular systems allow you to place similar equipment directly in racks. They are called RPDC (Rack Power Distribution Cabinet) and are small distribution cabinets that occupy 4U in a standard rack. Such solutions are used by Internet companies that require guaranteed work of a small fleet of equipment. For example, distribution modules were installed as part of an integrated solution to protect the data center of one of the leading online stores in Germany.

If we talk about the equipment Delta, the power of one unit of RPDC can be 30, 50 or 80 kVA. Multiple modules can be installed in the same rack to provide power to all the loads of a small data center, or you can place RPDCs in different racks one at a time. The latter option is suitable for powering quite powerful servers that need power control and power redistribution depending on the configuration and load.

An advantage of the modular system is the possibility of increasing capacity as the data center grows and scales. Users often make their choice in favor of RPDC in the case when a full-fledged cabinet creates too much margin for the current configuration of 2-3 equipment racks.

Each module is equipped with a touch screen with almost the same control capabilities as a separate PDC, and also supports RS-232 interfaces and smart cards for remote control. Distribution modules control the current in each of the connected circuits, automatically inform about abnormal situations and support hot swapping of switching devices. Data on the state of the system are recorded in the event log, which can store up to 2,000 entries.

Power distribution units

Power Distribution Units are the most compact and economical systems in this category. They allow you to control the operation of equipment within one rack, providing information on the status of lines and load. For example, such units were used to equip the Miran data center in St. Petersburg and the demonstration center of the Digital Enterprise consortium in Chelyabinsk.

The blocks come in different formats, however, models made using Zero-U technology are placed in the same rack as the main equipment, but do not occupy individual “units” - they are mounted vertically or horizontally on the structural elements using special brackets. That is, if you use a 42U rack, after installation of the unit, just as many units will remain with you. Each distribution unit has its own alarm system: LEDs indicate the presence of a load or an emergency situation on each of the outgoing lines. Delta units have an RS232 interface and are connected to monitoring systems via SNMP, just like cabinets and power distribution modules.

Measuring and basic distribution blocks can be installed directly in the rack, and both in the standard Delta constructor, and in the racks of other manufacturers. This is possible due to the universal set of brackets. Power distribution units can be installed vertically and horizontally, used in the supply of electricity from single-phase and three-phase networks. The maximum current for the Delta distribution units is 32 A, the input voltage deviation is up to 10%. The connectors for the load can be 6 or 12.

The main thing is to create a comprehensive management system.

The choice between the cabinet, unit or module occurs depending on what kind of load you need to connect. In large data centers, distribution cabinets are necessary, which, however, does not preclude the installation of additional modules or units for branching off power to individual loads.

In a medium-sized server, most often one or two distribution modules are enough. The advantage of this solution is that the number of modules can be increased by scaling the power supply system along with the development of the data center.

In individual racks, distribution units are usually installed, which will be enough to equip a small server room. With a unified control system, they also provide the ability to monitor and control energy consumption, but do not allow for the dynamic redistribution of lines and hot-swappable contact elements and relays.

In modern data centers, you can simultaneously find both cabinets, and modules, and power distribution units installed at different times and for different purposes. The main thing is to combine all the equipment for energy management into one monitoring system. It will allow you to control any deviations of the power supply parameters and take prompt action: change equipment, expand power or move the load to other lines / phases. This can be done through software such as Delta InfraSuite or a similar product.