Today, we will start explaining the
UPS design and sizing calculations, and as we do usually, we will start by
explaining the components and main types of UPS systems.
First:
Applicable Standards for UPS Systems
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Throughout Our explanation of the UPS
systems, we will use the following standards:
1- Standards
Relevant to UPS Installations:
Standard
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Details
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CE
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Marking in compliance with the
following European directives:
• Low Voltage Directive 2006/95/EC
• EMC Directive 2004/108/EC
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ISO/IEC 27001:2005
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Information Security Standards
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BS 25999-1:2006
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Business continuity management. Part
1: Code of practice
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BS 7698-1:1993, ISO 8528-1:1993
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Reciprocating internal combustion engine
driven alternating current generating sets. Specification for application,
ratings and performance
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ER G59/1
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Recommendations for the connection
of embedded generating plant to the Public Electricity Suppliers distribution
systems. Energy Networks Association
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BS EN 60529:1992
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Specification for degrees of protection
provided by enclosures (IP code) BS EN 60439-4:2004: Low-voltage switchgear
and control gear assemblies
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BS 7671:2001
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Requirements for electrical
installations. IEE Wiring Regulations. Sixteenth edition
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BS EN 50310:2006
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Application of equipotential bonding and
earthing in buildings with information technology equipment
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BS EN 60439-4:2004
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Low-voltage switchgear and control
gear assemblies
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EN 60950:2006
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Safety of information technology equipment
including electrical business equipments
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2- Standards
Relevant to Lead Acid Batteries:
Standard
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Details
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BS 6133:1995
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Code of practice for safe operation
of leadacid stationary batteries
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BS 6290-4: 1997
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Lead-acid stationary cells and batteries.
Specification for classifying valve regulated types
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BS EN 60896-1:1992, IEC
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Stationary lead-acid batteries.
General requirements and methods of test. Vented type
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BS EN 60896-2:1996, IEC
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Stationary lead-acid batteries. General
requirements and methods of test. Valve regulated type
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BS EN 50272-2:2001
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Safety requirements for secondary
batteries and battery installations. Stationary batteries
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ANSI/IEEE 450-2002
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IEEE recommended practice for maintenance,
testing and replacement of vented lead-acid batteries for stationary
applications
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ANSI/IEEE 1184-1994
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IEEE recommended guide for selection
and sizing batteries for Uninterruptible Power Supplies (UPS)
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ANSI/IEEE 1188-1996
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IEEE recommended practice for maintenance,
testing and replacement of valve-regulated lead-acid (VRLA) batteries for
stationary applications
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What
is a UPS?
A
UPS is a combination of convertors, switches and energy storage devices (for
example, batteries), Constituting an alternate or backup source of power for
maintaining continuity of critical loads power in case of input power
failure.
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Why do we need a UPS?
The
two main functions of the UPS are:
- Ensuring
continuity of an alternate power source,
- Improving
the quality of the power source by keeping it within specified
characteristics.
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1-
Ensuring continuity of an alternate power source:
An
UPS can be considered as a source of standby power or emergency power
depending on the nature of the critical loads.
Typical
critical loads are:
- Computers
– e.g. data processing and control systems
- Industrial
process equipment – e.g. precision manufacturing
- Medical
equipment – e.g. life support and monitoring systems
- Telecommunications
network equipment – e.g. PABX
- Point
of sales (POS) terminals – e.g. retailing environment
- Online
business transactions – e.g. internet shopping.
- Emergency
lighting for evacuation,
- Emergency
perimeter lighting for security.
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2-
Improving the quality of the power source by keeping it within specified
characteristics.
- Any
power system may face a variety of issues either from generation,
Transmission & Distribution (T&D) or even within a customer facility
which cause disturbance in the quality of power.
- The
Power quality disturbance can be defined as the deviation of the voltage and
the current from its ideal sinusoidal waveform.
- The
Power quality disturbance can affect the uninterrupted operation of customer
loads, reduce the life of the connected loads and electrical equipment and
affect other loads within the facility or even outside the customer facility.
The
Power Quality Issues and Causes are summarized in the following table:
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Therefore,
The UPS can provides the following functions:
- Protection
of load against Line frequency variations,
- Elimination
of power line noise and voltage transients,
- Protection
of load against Voltage regulation.
- Safe
operation of equipment during sags and brownouts.
In
addition, some UPS or UPS/software combinations provide the following
functions:
- Automatic
shutdown of equipment during long power outages.
- Monitoring
and logging of the status of the power supply.
- Display the Voltage/Current draw of
the equipment.
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UPS
Rating
- UPS
manufacturers generally use VA (or kVA) to describe the UPS output ratings;
this rating determines the maximum load that can continuously be supported by
the UPS when the mains supply fails.
- When
selecting a UPS to service a particular load it is important that the
combined load does not exceed the UPS output rating, and if the load
equipment is specified in Watts it is necessary to convert this to VA in
order to assess the UPS/load rating compatibility.
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UPSs can be classified into many
types according to the following:
- Voltage range,
- No. of phases,
- Mobility,
- Technological design,
- Physical Size/capacity,
- Form factor/ configurations,
- Topology,
- Distribution Architecture,
- Use of transformers.
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First:
According to Voltage Range
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The IEC 60038 standard rates voltage
ranges as; low 0-1000v, medium 1000v - 35kv, and high as anything over 35kv.
Therefore, according to voltage
range, the UPS has two types:
- Low Voltage UPS,
- Medium voltage UPS.
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1-
Low Voltage UPS
- At low voltage system levels of 400
volts or 480 volts a maximum capacity of approximately 5 MVA at the common
bus is reached very soon.
- The limitation to 5 MVA is given by
the current capability of bus bars and breakers of about 6000 amps on one
side and the short circuit capability of the switchboards of typically 100 kA
on the other side.
- Higher ratings of both will let the
costs and the dimensions of the switchgear increase dramatically while the
component availability in the market is very limited. Additionally, high
currents require high copper cross sections and cause rather high resistive
losses, both resulting in increasing costs for power transmission. A way to
reduce the currents and to enable a further increase of the power is the move
to a medium voltage (MV) system level.
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2-
Medium voltage UPS
- A medium-voltage UPS is essentially
the same as a standard UPS but is designed for a medium-voltage range,
ranging from 1000v - 35kV. The major difference between a low voltage (LV)
UPS and a medium voltage (MV) UPS is the source voltage. Both systems will store
power in the event of a power outage. Both systems filter the incoming
voltage to provide clean source voltage to the downstream devices. A typical
MV UPS is used for data centers or any mission-critical facility requiring
clean, constant electrical power.
- For example, at a typical MV level
of 13.2 kV, the maximum system power rises up to 27 MVA using a standard MV
breaker size of 1200 amps and up to 57 MVA with a breaker size of 2500 amps.
Medium voltage levels go up as high as 34.5 kV, allowing a system power
rating of up to 70 MVA.
- The
transition from low voltage (LV) to medium voltage (MV) level is a natural
progression of power protection for large critical power facilities. The
approach offers three main benefits as follows:
- Increased
reliability because the MV design approach comes with larger protected load
blocks, lower switchgear count and the operating culture of medium voltage
systems.
- Reducing
the costs because installing the power protection at the MV level provides
the most energy efficient configuration as the lower currents at this voltage
result in smaller cables and lower losses.
- Reducing the floor space for
infrastructure equipment like power supplies results in additional space for
IT or manufacturing equipment. Often the available area for the UPS system is
given and limited, particularly in existing buildings, but the required power
is increasing.
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Second:
According to No. of phases
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The input/output phase configurations of UPS
systems are available in:
- Single-phase configuration (1/1) or
- Three-phase configuration (3/3 and
3/1).
The
common phase configurations for UPS are:
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1- Single Phase UPS System (1/1)
- A
single phase installation consists of two wires where AC voltage is a single
sine wave. The standard voltage of single phase varies in different countries
or regions. The standard single phase voltage in America is 120V and Europe,
Asia or other regions take 230V as a standard voltage.
- Single-phase uninterruptible
power supplies typically cover requirements up to 20 kVA and
are used for smaller installations such as rack-mounted servers, telecoms or
computer systems, and network switches, along with any device that runs
directly from a standard three-pin plug.
- A 20kVA output is generally the largest single phase UPS system
available. This is due to the output amperage and cable requirements.
20kVA=20,000VA / 230Vac = 86.9Amps.
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2- Three Phase UPS System (3/3 and 3/1)
The
three phase UPS can be subdivided into:
- Three
phase input/three phase output UPS system (3/3),
- Three
phase input/single phase output system (3/1).
- If
you need to connect to a three phase supply, you must need a UPS with a 3/x
configuration. A 3/1 UPS takes in 3 phase power but delivers single phase to
the downstream load while a 3/3 UPS not only takes in but also puts out 3
phase power.
- Three-phase
UPS are the standard choice for larger
installations with critical loads such as data centers, industrial
applications, and medical environments,
as well as protecting equipment with motors such as lifts, pumps,
and fans.
- With a three-phase system,
consideration should be given to phase load balancing and load power factors
to minimize the imbalance in the output voltage.
Three-phase power
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Single-phase power
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common in
most large businesses and high-density data centers with higher kVA and
rack applications.
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Used in most
residential homes and small businesses.
Used for a
wide range of general applications.
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Used for
applications requiring greater than 1000 watts.
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Is the most efficient for units up
to 1000 watts.
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Used to
balance the loads on the utility power of the building.
Is safer and
more cost effective to run.
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The standard
for locations where three-phase power is unavailable.
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Delivered in
a steady stream at a constant rate.
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Not delivered at a constant rate.
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Third: According to Mobility
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UPS
can be classified according to Mobility to:
- Movable,
- Stationary,
- Fixed,
- Building-in.
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1-
Movable UPS (transportable):
An
UPS that is either 18 kg or less in mass and not fixed comes usually with
wheels, castors or other means to facilitate movement by the operator as
required to perform its intended use in different locations.
2-
Stationary UPS:
An
UPS that that exceeds 18kg and is not provided with a carry handle or wheels.
3-
Fixed UPS:
An
UPS that is fastened to a support or otherwise secured in a specific
location, e.g. open Rack or Stand.
4-
UPS for “building in”:
An
UPS intended to be installed in a prepared recess such as a cupboards, closed
racks etc.
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Fourth: According to Technological Design
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The design technologies of ups
systems are different and can be classified into two main types:
- Static UPS,
- Rotary UPS.
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1-
Static UPS
- The static UPS is called
“static” because, throughout its power path, it has no moving parts (although
it has auxiliary moving parts, such as cooling fans).
- The rectifier inside of
the static UPS converts the incoming utility AC current to DC, and the
inverter converts DC back to clean sine-wave AC to supply the load.
- The DC current
interfaces with the “energy storage” medium – most commonly batteries, in
which case it charges the batteries and receives power from the batteries
when the utility power supply is distorted or fails.
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2-
Rotary UPS
- The rotary UPS is called “rotary” because rotating
components (such as a motor-generator) within the UPS are used to transfer
power to the load.
- Rotary technology has been utilized for many years especially
in the following conditions:
- When loads would commonly exhibit a low power factor
(which resulted in increased losses in the power distribution system and
thus, an increased energy cost),
- When loads would commonly exhibit high harmonics
(which prematurely shortened the life of transformers and capacitors),
- When loads would commonly exhibit high voltage dips
and sags for example when large motors turned on, Users would experience the
dimming of lights
Thus, the introduction of the rotary UPS to address this issues.
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2.1 Types of Rotary UPS
The rotary UPS has two main types as
follows:
- Motor-generator / battery rotary UPS,
- Engine-coupled rotary UPS.
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2.1.1 Motor-Generator / Battery
Rotary UPS
- When the utility power quality (voltage and frequency) falls
within an acceptable range, then the motor component of the rotary UPS is
driven directly from the utility. That motor then provides mechanical power
to the generator component of the motor-generator to support the critical
load with clean power. Also, the rectifier / inverter unit operates in
stand-by mode during the time the utility is stable. That is, the rectifier
is in “battery float” mode (the batteries get charged).
- When utility voltage and frequency parameters fall outside of
preset limits, then the rectifier / inverter unit begins to provide
controlled power to the motor which is coupled directly to the generator to
support the critical load. When a blackout occurs, the battery bank provides
necessary power via the inverter to the motor-generator to support the load.
The stored energy within the batteries provides sufficient ride-through to
sustain the load until the standby generator (outside of the UPS) comes up to
full operating speed.
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2.1.2 Engine-Coupled Rotary UPS
- The key components of an engine-coupled rotary UPS include the
following: a motor-generator, a choke, a flywheel, a mechanical clutch, and a
diesel engine.
- Under normal operation, the utility feeds power to the critical
load via the filter (made up of the choke and motor). The same motor also
provides the necessary power to the flywheel to retain kinetic storage of
energy in case of emergency.
- During
failure mode, power is supplied by the flywheel to the motor-generator unit,
which in turn supports the critical load for a few seconds before the diesel
engine runs up to full speed. The clutch is then engaged to provide
mechanical power to the motor-generator to supply continuity of power to the
load.
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2.2 Comparison Of Static and Rotary
UPS Architectures
The range of applications for static
UPSs is broad while the application ranges of rotary UPSs are more limited.
In the domain of the data center, static UPSs represent the technology of
choice. Rotary UPSs become more competitive in very large multiple megawatt
data centers.
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In the next Article, I will continue explaining other
classifications of UPS. So,
please keep following.
Thanks Eng. Hassan For All your Effort. Very Interesting Information. Hope you More Successful
ReplyDeleteQuite satisfactory. Well done.
ReplyDeleteI have learned some useful specifications details to consider when am planning on buying a UPS device. Thanks for sharing.
ReplyDeleteVery Useful technical Artical, Thanks Eng. Hassan.
ReplyDelete