Overview of Uninteruptive Power Systems (UPS)
A. Bhatia, B.E.
The critical applications
such as computers, servers, instruments or life saving equipments require 100%
redundancy in every aspect to ensure high degree of reliability and operation.
Although the power supply is available from commercial power supply sources,
it is subject to disturbance of various types like brownouts, voltage spikes,
frequency instability and harmonic distortion, all of which can disturb the
smooth functioning of the modern equipments. The UPS can protect the electrical
and electronic loads from the damages caused by the utility power supply malfunction
and power disturbance of electric loads in the building, etc.
This 4-hour course is a summary extract from the Technical Manual of Department of Army: TM 5-693: Uninterruptible power Supply System Selection, Installation, and Maintenance for Command, Control, Communications, Computer, Intelligence, Surveillance and Reconnaissance (C4ISR) Facilities.
The course includes
a glossary and multiple-choice quiz at the end, which is designed to enhance
the understanding of the course materials.
At the conclusion of this course, the reader will:
This course is aimed at students, electrical engineers, facility managers, architects, H &S professionals, and energy auditors, technical and sales representatives.
An UPS is a device
that sits between a power supply and a device (e.g. a computer) to prevent undesired
features of the power source (outages, sags, surges, bad harmonics, etc.) adversely
affecting the performance of the device. It is designed to automatically provide
power, without delay or transients, during any period when the normal power
supply is incapable of performing acceptably. UPS provides reliable protection
against short-term power outages by accessing a battery source as backup. It
not only ensures a supply of power in the event of a black or brown out, many
of the latest UPS systems actually "condition" the power coming into
your system right from the utility source. A UPS, therefore, has the ability
to eliminate surges, noise, spikes, and waveform distortions.
This course discusses some basic fundamentals of uninteruptive power systems in detail.
The course content is in a PDF file Overview of Uninteruptive Power Systems (UPS). You need to open or download this document to study this course.
A UPS is ideal equipment, which provides continuous power to critical connected electrical and electronic loads even in the event of blackout or variations in voltage. It regulates the voltage to the constant range that is safe for its loads. The principle of the UPS is to keep the connecting loads continuously working without any interruption. Whenever power problems occur, the UPS still supplies power by regulating, or drawing backup power from the storage battery, converts it back to AC power and supplies to the loads. These can be broadly classified into two categories namely: Static UPS and Rotary UPS.
A static UPS consists of
1) Charger or Rectifier
- takes the utility AC power and converts to DC power and then charges the batteries
2) Inverter - takes the DC power from the batteries and converts to AC power for electrical and electronic loads
3) Battery - backs up power to supply during the power problems. It can supply DC power to the inverter in case of the UPS cannot take the utility AC power.
4) Stabilizer - regulates the voltage to the constant range that is safe for the electrical and electronic loads
Not every UPS is
the same. There are different designs and technologies based on the type of
equipment you need to protect and the amount of power, or the load, the unit
will be required to handle. Typically, with stand alone PCs offline UPS may
suffice the needs. Also known as a standby UPS, this device turns on backup
battery power in the event of a power failure. The next level of UPS protection
is line-interactive. Its called interactive because, unlike the off-line technology,
it filters a line current to the power load and converts a trickle of DC power
to the battery to keep it fully charged at all times. When the power fails,
this UPS doesn't need to turn on, but rather switches from the standard utility
source to the backup battery. The highest level of protection is the on-line
UPS. This UPS continually charges the battery source so that if the power goes
down, backup is instantaneously available, with no start up or switching required.
A rotary UPS consists
of a synchronous motor driving a synchronous generator with a large flywheel.
During normal operation the motor drives the flywheel and the synchronous generator
at constant speed proportional to the power supply frequency. When input power
is momentarily lost or degrades, the flywheel supplies its stored energy to
the generator and the frequency is maintained within the required tolerance
for duration depending on the flywheel inertia. Rotary UPS systems are typically
outdated now days due to rapid advances made in the field of electronics; the
static UPS have become very popular since it has no moving parts. Rotary UPS
are more costly for small capacities but become competitive with static units
UPS may be needed
for a variety of purposes. Before proceeding for the selection and sizing of
UPS, the purpose(s) must be clearly known. The factors influencing the selection
are evaluating critical loads, switchover time, acceptable delay, backup time
and the criticality of the load that the UPS must bear. All critical loads shall
be connected to the UPS. If you get a UPS that's too big, then you've overpaid,
but your equipment can survive a longer outage. If you get a UPS that's too
small, your equipment might not be protected. Therefore, you have to be a little
conservative in sizing your requirements. Unfortunately, this costs money and
the decision shall be best made in consultation with a professional.
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.