An uninterruptible power supply(UPS), is a device or system that maintains a continuous supply of electric power to certain essential equipment that must not be shut down unexpectedly. In simplistic terms, UPS is a device that provides battery back-up power to IT equipment should utility power be unavailable, or inadequate. UPSs provide power in such a way that the transition from utility power to battery power is seamless and uninterrupted. UPSs can range in size and capacity to provide power to small individual desktop computers, all the way up to large megawatt data centers. The UPS equipment is inserted between a primary power source, such as a commercial utility, and the primary power input of equipment to be protected, for the purpose of eliminating the effects of a temporary power outage and transient anomalies.

A UPS system provides power to equipment when commercial power goes offline. Some facilities will use a UPS system to power the entire facility, while others will only attach essential equipment. Either way, the point of this equipment is to ensure there are no unexpected outages due to power interruptions.

Large-scale data centers also use uninterrupted power supplies when performing maintenance on the electrical system. The electricians can manually allow the facility to run-off of the UPS while they perform their work.  This helps the equipment stays up and running during the maintenance. It also ensures that electricians or other professionals aren’t facing unnecessary risks.

Components of Uninterruptible Power Supplies

There are several types of uninterruptible power supplies, which will be defined below, but all UPS systems will make use of the following components.

Rectifier: The rectifier converts the input AC power into DC power. This DC power will be used to feed an energy storage system.

Energy Storage: Every UPS will use some type of system for storing energy in case of input power failure. This energy may be stored in the form of batteries, flywheels, or supercapacitors and is what allows a UPS to supply uninterrupted power.

Inverter: The inverter converts the DC power from the rectifier or the energy storage system into the required AC power to be used by the load.

Static Bypass Switch: This component is a safeguard in case there’s a failure within the UPS system. In the event of a UPS fault, the static bypass switch automatically connects the load to the mains supply, bypassing the rectifier, batteries, and inverter.

Other UPS Components

Depending on the size and type of UPS, there are several other common components that may be included, for example, fans or capacitors.

In addition, there are also components such as an External Maintenance Bypass switch, which enables the UPS to be removed and/or replaced without interrupting the load, Transient Volt Surge Suppressors (TVSS), and Simple Network Management Protocol (SNMP)-compliant monitoring and communications applications.

Form Factor

UPSs come in a range of form factors that fit into two master categories: rack-mounted and freestanding. The largest UPSs aren’t available in rack-mounted form factors, so companies with substantial power requirements almost always use freestanding devices. For companies with more modest needs, deciding between rack-mounted and freestanding UPSs is largely a matter of data center design philosophy. Some organizations use rack-mounted UPSs in an effort to consolidate as much hardware as possible in their enclosures. Others prefer to maximize the amount of rack space available for servers by using freestanding UPSs. From a technical and financial standpoint, neither approach is inherently superior to the other.

Rating

A UPS’s rating is the amount of load, in volt-amperes (VA), that it’s designed to support. UPSs are available with ratings as low as 300 VA and as high as 5,000,000 VA or more. Use this very basic procedure to determine the approximate UPS rating your organization requires:

1. Make a list of all the equipment your UPS will be protecting.

2. Determine how many volts and amps every device on the list draws. 3. For each device, multiply volts  by amps to arrive at a VA figure.

4. Add all of the VA figures together.

5. Multiply that sum by 1.2, to build in room for growth.

The UPS you buy should have a rating equal to or greater than the final number you arrived at in step 5, unless you have more precise load data for the equipment you are protecting. Here are a few additional considerations to keep in mind:

• Relying solely on nameplate ratings may lead you to oversize the UPS system, so always use your equipment manufacturer’s sizing calculator tools as well, if available. Most major manufacturers have Web-based or downloadable sizing tools that can closely estimate your equipment’s power draw based on the configuration you are using.
• When deploying a centralized power protection architecture, you typically deploy larger kVA UPSs than you would deploy using a distributed power protection scheme.
• If your UPS will be supporting motors, variable-speed drives or laser printers, add more VA capacity to your requirements to account for the high power inrush that occurs when those devices startup. Your UPS vendor can assist in applying the proper UPS and rating for these types of applications.
• Companies that anticipate rapid near- or medium-term growth should use a multiple higher than 1.2 when building in room for growth in the procedure above. So should organizations that expect to upgrade their server hardware soon, as newer servers tend to have higher power requirements than older models.

Remote Monitoring

The best way to address UPS problems is to prevent them from happening in the first place. Remote UPS monitoring applications continually watch for warning signs of future trouble, such as deteriorating performance or an overheating battery, and send real-time notification when potential issues develop. That enables technicians to make repairs before serious breakdowns have a chance to occur. Data centers can perform remote monitoring themselves or contract with an external provider to do it for them.

UPS Redundancies for High Uptime Requirements

A major purpose for data centers is to provide maximum uptime on all of their equipment. They achieve this by having redundant communications circuits whereas a UPS is one of the major component in this,

We will define the redundancy of UPS system based on the term “N” whereas N equals the amount of capacity required to power, backup or cool a facility at full IT load. A design of N means the facility was designed only to account for the facility at full load and zero redundancy has been added. If the data center facility is at full load and there is a component failure or required maintenance, mission critical applications would suffer.

N+1 Redundancy(Parallel Redundant)

If N equals the amount of capacity needed to run the facility, N+1 indicates an additional component added to support a single failure or required maintenance on a component. As you know “N” could stand for the number of uninterruptible power supply (UPS) modules needed. The “+1” would be one more module more than required. For example, if the total data center load is 1000kW and each UPS platform can handle 500kW. In this case we need three UPS systems of 500kW (N=1000kW, N+1=1.500kW). If one UPS is in maintenance mode we can ensure that the data center can deliver 1000kW of UPS power.

Having more power available than needed lowers the chance of downtime. Although N+1 is often called “parallel redundancy” these data centers are not fully redundant because they share common circuitry instead of being sourced from two separate fields.

2N Redundancy

Enterprise level IT equipment often supports dual power supply operation. This equipment can be connected to multiple power sources. In a data center, these two sources would be independent UPS systems. An “A side” and a “B side” can feed the computer equipment. Each side would be able to handle 100% load capacity. For data centers, having a 2N redundancy means you have twice the amount of equipment needed with no single point of failure. When extended power outages occur, 2N systems will be maintained without losing power to subsequent systems. This is referred to as 2N redundancy.

2(N+1) Redundancy

These two concepts can also be combined. Take for example having a 2N redundant power distribution system. Instead of a single module UPS on each side, there would be multiple modules. This provides N+1 redundancy on each side. For this reason, 2(N+1) data centers offer the highest guaranteed uptime. This is referred to as 2(N+1) redundancy.

The downside of 2(N+1) architectures is the high price that needs to be paid. Besides the initial component costs, as well floor space and as well the high operation costs. For better reliability data centers choose for 2N solutions, which provides more flexibility and easier operational management.

Benefits of an Uninterruptible Power Supply

When people think about the benefits of an uninterruptible power supply, they typically focus only on the fact that equipment won’t become unavailable during a power outage. While this is the most obvious advantage of having this type of system in place, there are several other benefits:

• Stopping Power Surges – A good UPS system has commercial power running through it and will intercept any potential power surges so that they don’t damage the equipment. This is especially important for sensitive electronic devices.
• Providing Even Electricity – Electricity doesn’t always come through an outlet at a perfectly consistent rate. The small power fluctuations won’t disrupt computer equipment, but over time, they can damage it. A UPS has the commercial power running through it, and in this process, it evens out the distribution to the equipment to prevent damage.
• Cut Back on Electrical Load – Large-scale data centers use a lot of electricity. Those that have a UPS system with a diesel generator can work with the commercial power company to operate on the generator during times of peak usage (usually very hot days in the summer). This earns the company significant credits from the power provider and helps the surrounding community avoid brown-outs.

Knowledge Credits: Eaton

Have a comment or points to be reviewed? Let us grow together. Feel free to comment.