Classification and Types of UPS – Part Two

In the previous article “Classification and Types of UPS – Part One”, We explained the following points:

• Applicable Standards for UPS Systems
• What is a UPS?
• Why do we need a UPS?
• UPS Rating
• Classification of UPS

 

In addition, we stated that UPS is classified according to:

1. Voltage range,
2. No. of phases,
3. Mobility,
4. Technological design,
5. Physical Size/capacity,
6. Form factor/ configurations,
7. Topology,
8. Distribution Architecture,
9. Use of transformers.

 

We already explained the first four classifications in the above-mentioned article and today, we will continue explaining the other classifications of UPS.

 

Fifth: According To Physical Size/Capacity

 

UPS Manufacturers design many UPSs that different in physical size starting from small UPS modules up to large sized UPS systems and with capacities ranges from 250 VA up to 3 MVA. The physical size and capacity available for data centers and the looks like applications are:   1- Desktop Systems that can be divided to: Micro Systems – up to 1000VA Mini-Systems – 500-2000 VA   2- Medium-Sized Systems – 3-20kVA   3- High-Power Systems (typically 30-500kVA)

 

5.1 Desktop Systems

 

 

5.1.1 Micro Systems – up to 1000VA   Modules in this power range are typically designed to supply a single personal computer (PC) workstation and are normally housed in a mini-tower case about half the size of a typical personal computer system unit. The UPS is connected to a standard utility mains supply outlet such as a three-pin 13A socket (UK) and due to their small weight and dimensions can be considered as being portable. Modules at this power level include on-line, off-line and line interactive designs and provide a single point solution to a particular power need. Load equipment is usually connected to a standard mains connector (IEC) on the back of the UPS which is usually protected by a circuit breaker or fuse. At this power level the batteries are usually integral to the UPS cabinet, and extended battery cabinets are unlikely to be offered as an optional extra. Because these modules are designed to be placed adjacent to the load equipment user, it is not generally necessary to provide any remote alarm facilities to warn the operator of the module’s operational status. However, current practice might include installing an automatic control interface between the UPS and computer e.g. SNMP (Simple Network Management Protocol) or automatic shutdown software.

 

 

5.1.2 Mini-Systems – 500 to 2000 VA   Modules in this power range are in many ways similar to the ‘micro’ UPS systems described above in that they are designed for office use and can be considered to be portable. However, the increased rating makes these modules suitable to supply a fileserver or a complete workstation comprising a PC and its peripheral equipment, such as printer (but not a laser printer), scanner etc. These modules are again connected to a standard utility mains supply outlet such as a three-pin 13A socket (UK) and can include on-line, off-line and line interactive designs. The load equipment is usually connected to standard mains connectors (IEC) on the back of the UPS which are usually protected by a circuit breaker or fuse, but it is likely that several supply outlets are provided to facilitate the connection of several small items of load equipment. At this power level the batteries are usually integral to the UPS cabinet, but some modules might have provision to connect to additional batteries contained in a purpose built extended battery cabinet to increase the total battery back-up (autonomy) time. Where this is the case the battery charger within the module is usually sufficiently rated to provide the additional battery charging current. However, in extreme circumstances the extended battery cabinet must include a dedicated charger system to cater for the additional batteries and will therefore also require connecting to the mains supply. As with the ‘micro’ UPS systems, it is not generally necessary to provide any remote alarm facilities for this size of UPS due to the close proximity of the system to the load operator. However, as with ‘micro’ systems, SNMP or automatic shutdown software may well be a requirement depending upon the criticality of the load.

 

 

5.2 Medium-Sized Systems – 3 to 20kVA   Modules in this power range are designed to offer more than the single point power provision afforded by the smaller desktop modules, being typically used to power a complete office network, small server farm or communications center. These modules, which cannot be considered as being portable (especially those in the upper end of the range), are permanently wired to the mains supply using medium power switchgear and may require some external input overload protection device as a standard part of the installation. The larger modules in this range may require a three-phase input supply – and indeed may even offer a three-phase output. The question of batteries varies across this particular power range. At the lower end the comments concerning the batteries fitted to the desktop systems are still valid, but when considering modules rated 15-20kVA it may well be that the batteries are housed in a separate cabinet which is positioned alongside the UPS module. In fact, most manufacturers offer a series of matching cabinets at this power level to provide a range of aesthetically appealing equipment that fits into an office environment. At the higher power levels the load equipment is either hard wired to distribution busbars fitted within the module cabinet or the UPS output is fed to a purpose designed distribution system. At the lower end of the power range it is possible that the UPS may be fitted with standard utility power outlet sockets in the same way as the desktop models. Most modules in this power range will include facilities for remote alarms and status indications.

 

 

5.3 High-Power Systems (typically 30 to 500kVA)   Modules of this rating can service a major data center but are not generally suited to an office environment due to the noise levels associated with their cooling fans and the heat generated when operating on high loads. Such modules are therefore usually located in a remote position such as a plant room, and their outputs connected to numerous loads using a dedicated mains distribution system incorporating external switchgear and protective devices. Modules in this power range are almost exclusively of an on-line design and invariably three-phase input and output. It is unlikely that the batteries are housed within the UPS module cabinet itself, and depending on the module rating and projected autonomy time, they may be housed in a separate cabinet(s) adjacent to the UPS module or, in the case of very large systems, rack-mounted in a dedicated battery room. Some of the larger modules in this range may employ a 12-pulse rectifier to reduce the amount of mains polluting harmonics generated within the UPS and reflected back to the utility mains supply. Where a 12-pulse rectifier is used it is usually contained in a separate cabinet which must be positioned immediately adjacent to the main UPS cabinet, increasing the required system footprint and weight. Single modules of up to 800kVA are available, however for the reasons of efficiency, availability and scalability, it is becoming increasingly more common for very large loads (300kVA to >1MVA) to be powered by UPS systems which comprise several “high power” UPS modules operating in parallel rather than by just one very large single UPS module. A standby generator may be incorporated into the system design to provide an alternative source of UPS input power during a utility mains failure. Such a generator must be self starting and be sufficiently large to maintain a stable output with the UPS on full load. When selecting a standby generator for this duty several features must be taken into account in order to ensure proper operation because the UPS input can present a hostile load to some generator systems. Due to the module’s location it is usual to include a remote alarm/control panel with this type of installation, and virtually all modules in this range offer this facility as a standard feature.

 

 

Comparison of UPS According to Physical Size/Capacity

 

 

feature	Micro Systems	Mini-Systems	Medium-Sized Systems	High-Power Systems
Capacity	up to 1000VA	500-2000 VA	3-20kVA	30 to 500kVA
Application	single personal computer (PC) workstation	fileserver or a complete workstation comprising a PC and its peripheral equipment, such as printer (but not a laser printer), scanner etc.	complete office network, small server farm or communications center.	major data center
Physical size	housed in a mini-tower case	housed in a medium-tower case	Separate cabinets	Large cabinets and racks
Mobility	portable	portable	Portable up to 15 KVA Stationary or fixed from 15 to 20 KVA	Stationary or fixed
Usability to Office environment	yes	yes	Yes, need a dedicated  space	No, due to the noise levels associated with their cooling fans and the heat generated when operating on high loads.
Mains Supply	outlet such as a three-pin 13A socket	outlet such as a three-pin 13A socket	medium power switchgear	a dedicated mains distribution system incorporating external switchgear and protective devices.
Topology	on-line, off-line and line interactive designs	on-line, off-line and line interactive designs	on-line, off-line and line interactive designs	on-line design only
No. of phases	Single phase (1/1)	Single phase (1/1)	Single phase (1/1) till 7 KVA or Three phase (3/1 or 3/3) above 7 KVA	Three phase (3/3)
Load equipment connection	a standard mains connector (IEC) on the back of the UPS	many standard mains connectors (IEC) on the back of the UPS	distribution busbars fitted within the module cabinet or the UPS output is fed to a purpose designed distribution system	purpose designed distribution system
Batteries	integral to the UPS mini tower	integral to the UPS tower	Up to 15 KVA: integral to the UPS cabinet 15 to 20 KVA: separate cabinet	Separate cabinet(s) adjacent to the UPS module or, in the case of very large systems, rack-mounted in a dedicated battery room.
Extended Battery	No	Some models	Yes	Yes
Remote alarm facilities	No	No	Yes	Yes
Need for A standby generator	No	No	No	May be

 

 

Sixth: According To Form Factor/ Configurations

 

 

UPS System Configurations Before listing the different UPS system configurations, let’s know the nomenclature “N” used in differentiating between different UPS system configurations

 

 

What is “N”? “Cupcakes Availability & Need”   UPS Design configurations are often described by nomenclatures using the letter “N”. “N” comes from the word “need”. Comparing the availability of power to the load need results in different combinations/configurations as follows:   1- For example, if you have a birthday party for your child and you have ten guests and ten cupcakes, since the available number of cakes (availability) equal to the number of guests (need) so, we have N system where the availability equal to the need. 2- But just in case you have that “unexpected” guest show up, you order eleven cupcakes.  “N” represents the exact amount of cupcakes you need, and the extra cupcake represents the +1.  Therefore, you have N+1 cupcakes for the party.  In the world of UPS, an N+1 system, also called parallel redundancy, and is a safeguard to ensure that an uninterruptible power supply (UPS) system is always available. N+1 stands for the number of UPS modules that are required to handle an adequate supply of power for essential connected systems, plus one more, so 11 cupcakes for 10 people, and less chance of downtime. Although an N+1 system contains redundant equipment, it is not, however, a fully redundant system and can still fail because the system is run on common circuitry or feeds at one or more points rather than two completely separate feeds. 3- Back at the birthday party!  If you plan a birthday party with a 2N redundancy system in place, then you would have the ten cupcakes you need for the ten guests, plus an additional ten cupcakes, so 20 cupcakes.  2N is simply two times, or double the amount of cupcakes you need.   a 2N system contains double the amount of equipment needed that run separately with no single points of failure.  4- If you plan a birthday party with a  2N+1, which is actually double the amount needed plus an extra piece of equipment as well, so back at the party you’ll have 21 cupcakes, 2 per guest and 3 for you!

 

 

Different Configurations of UPS System   Although UPS configurations found in the market today are many and varied, there are five that are most commonly applied. These five include:    1- “N” System Configuration   2- “N+1” System Configuration, which includes: Isolated Redundant Configuration (N +1) Parallel Redundant Configuration (1+1) Parallel Redundant Configuration (N +1) Parallel Redundant Configuration (N +2) and so on   3- Parallel Redundant with Dual Bus Configuration (N+1 or 1+1)   4- Parallel Redundant with STS Configuration, which includes: Parallel Redundant Configuration (1+1) + STS Parallel Redundant Configuration (N+1) + STS   5- System plus System 2(N+1), 2N+2, [(N+1) + (N+1)], and 2N

 

 

The Evaluation Criteria for Each UPS System Configuration Before starting explanation for each UPS System Configuration, we must know how we evaluate each configuration, so our evaluation criteria of these configurations’ capabilities will depend on 4 important factors as follows: 1. Reliability: Evaluates a configuration’s capability to maintain conditioned power to the load. 2. Complexity: Looks at the complexity of the configuration and the potential for single point failures. 3. Maintainability: The system configuration must allow for concurrent maintenance of all power system components – supporting the load with part of the UPS system while other parts are being serviced. 4. Functionality: The system configuration must be able to protect the critical load from a full range of power disturbances without transferring the critical load to external power sources, i.e. batteries or alternate power sources. A score between 1 and 5 has been assigned. A score of “5” indicates the highest degree of criteria capability, while a score of “1” indicates the lowest degree of criteria capability

 

 

6.1 “N” System Configuration   Other names for this :   Single Unit Configuration: It means using single module only, for example, a small UPS under an office desk is an N configuration.   Standalone Configuration: It means able to operate independently of other modules.   Capacity system Configuration: it means using appropriate number of modules with total rating as per the load need

 

 

An N system simply stated is a system comprised of a single UPS module, or a paralleled set of modules whose power capacity is matched to the critical load power need. For example, a computer room with a design capacity of 400 kW is an N configuration whether it has a single 400 kW UPS, or two 200 kW UPS paralleled onto a common bus. Another example three 100kVA units might be used to serve a 270kVA load. Under normal circumstances each module will supply a maximum of approximately 90kVA. However, if one module fails the remaining two modules will each be expected to supply 135kVA and would be substantially overloaded. In this situation the load will immediately transfer to bypass via the simultaneous operation of the static switch in each module.   If the faulty module is unable to operate its bypass-side static switch, the static switches in the remaining healthy modules will ideally be rated to sustain the full load supply (e.g. 135kVA), as illustrated in above Figure. When the faulty module has been repaired and all three UPS modules are again operational, the load is automatically transferred from bypass back to the inverters.

 

 

Criteria Score Comments Reliability 2 A negative most commonly associated with this configuration is the potential for a single point failure, i.e. a failure of the inverter results in the load being transferred to the alternate power source, which is generally not a clean, well regulated source of power, and whose reliability may be questionable Complexity 5 Simplest design and the least number of components Maintainability 2 The load must be transferred to the alternate source power whenever a system component is being maintained. Leaving the critical load on the alternate source, which may not be very reliable. Functionality 4 Provides protection to loads from all types of power quality issues Redundancy Level 0%     Advantages: Conceptually simple, and cost effective hardware configuration. Optimal efficiency of the UPS, because the UPS is used to full capacity. Provides availability over that of the utility power. Expandable if the power requirement grows (It is possible to configure multiple units in the same installation. Depending on the vendor or manufacturer, you can have up to 8 UPS modules of the same rating in parallel.)   Disadvantages: Limited availability in the event of a UPS module break down, as the load will be transferred to bypass operation, exposing it to unprotected power. During maintenance of the UPS, batteries or down-stream equipment, load is exposed to unprotected power (usually takes place at least once a year with a typical duration of 2-4 hours). Lack of redundancy limits the load’s protection against UPS failures. Many single points of failure, which means the system is only as reliable as its weakest point.

 

In the next Article, I will continue explaining Other Configurations of UPS System. So, please keep following.