07-05-2012, 11:57 AM
Uninterruptible Power Supplies
[attachment=21448]
Introduction
The purpose of this article is to instruct the reader as to the various advantages and
disadvantages of installing a UPS system and to help guide him in ordering a system that is both
technically feasible and cost effective.
Various factors are considered when making a decision as to whether or not a UPS system must
be installed. The types of electrical loads must be considered as well as the appropriate amount
of back-up time that is required for a safe and effective operational shutdown. This article will
examine those loads and recommend the correct amount of backup time required.
This article will also examine the types of UPS systems that are available and will also look at the
pros and cons of each type. Not all types of loads are required to be placed on the same type of
UPS system. This article will make recommendations as to the appropriate system.
Finally, this article will guide the user through the steps required when specifying and purchasing
a UPS system and provide recommendations as to the construction and installation of the UPS
system.
Why Install a UPS?
Many of today’s sensitive electronic equipment and computer loads require an alternate source of
power in the event of a power system failure. These types of failures can vary from something as
little as a small power interruption (blip) to a large scale, long term power outage. Momentary
blips can be caused by wind (storms), lightning, rodents coming in contact with overhead power
lines, vehicles striking utility poles, etc. These types of incidents can cause the voltage to sag
below a point where most sensitive electronic equipment will begin to be affected.
More severe outages can occur as a result of storms or other natural and man-made
catastrophes such as equipment failures (transformers, high voltage cables, etc.) These types of
outages tend to last anywhere from several minutes to several hours, if not several days. UPS
systems need to be designed with the type of outages that the customer is likely to experience in
mind.
What types of loads should be placed on a UPS system?
Typically, any type of electrical load that is sensitive to momentary and long term power outages
should be placed on a UPS system. Most user PC’s, fax machines, computer servers, etc. are
placed on a UPS system. In addition, fire alarm systems, security and telephone communication
system are typical UPS loads. However, as of late, emergency egress lighting systems are being
connected to the UPS system as opposed to having individual battery backup.
How much is each minute of down-time costing you?
When making the decision as to whether or not purchasing a UPS system is worth while, you
need to consider the cost of not purchasing one. Each minute of lost production time costs your
company money. In order to help justify the cost of a UPS system, a cost benefit analysis needs
to be completed. This same analysis should also be used in determining the best type of UPS
arrangement that meets your company’s requirements.
How many 9’s of reliability do you need?
System reliability is usually calculated in terms of the amount of availability in the system. The
system availability is calculated and measured in terms of a %, with 100% being available all of
the time. As we all know, nothing is perfect or available 100% of the time. Usually, the
availability is calculated to anywhere in the range of 99.9% to 100%. The number of 9’s
determines how many decimal places we need to look for the availability. For example, 99.99%
availability has two 9’s worth of availability.
What types of UPS systems are available?
Stand-By Power System (SPS)
A stand-by power system (SPS) is often referred to as an off-line UPS system. It uses a transfer
switch for a system bypass between the utility power and the battery back-up. They also include a
rectifier (to convert AC to DC), a battery charger, a battery and an inverter (to convert DC to AC).
The system normally runs in bypass mode, i.e. no current running through the rectifier, battery
and inverter. When it senses an anomaly, the transfer switch switches position and starts to draw
power. In this scenario, protection is available only when the serving voltage dips to a
predetermined level. In addition, the ride through time required for transfer to battery power can
be significant.
[attachment=21448]
Introduction
The purpose of this article is to instruct the reader as to the various advantages and
disadvantages of installing a UPS system and to help guide him in ordering a system that is both
technically feasible and cost effective.
Various factors are considered when making a decision as to whether or not a UPS system must
be installed. The types of electrical loads must be considered as well as the appropriate amount
of back-up time that is required for a safe and effective operational shutdown. This article will
examine those loads and recommend the correct amount of backup time required.
This article will also examine the types of UPS systems that are available and will also look at the
pros and cons of each type. Not all types of loads are required to be placed on the same type of
UPS system. This article will make recommendations as to the appropriate system.
Finally, this article will guide the user through the steps required when specifying and purchasing
a UPS system and provide recommendations as to the construction and installation of the UPS
system.
Why Install a UPS?
Many of today’s sensitive electronic equipment and computer loads require an alternate source of
power in the event of a power system failure. These types of failures can vary from something as
little as a small power interruption (blip) to a large scale, long term power outage. Momentary
blips can be caused by wind (storms), lightning, rodents coming in contact with overhead power
lines, vehicles striking utility poles, etc. These types of incidents can cause the voltage to sag
below a point where most sensitive electronic equipment will begin to be affected.
More severe outages can occur as a result of storms or other natural and man-made
catastrophes such as equipment failures (transformers, high voltage cables, etc.) These types of
outages tend to last anywhere from several minutes to several hours, if not several days. UPS
systems need to be designed with the type of outages that the customer is likely to experience in
mind.
What types of loads should be placed on a UPS system?
Typically, any type of electrical load that is sensitive to momentary and long term power outages
should be placed on a UPS system. Most user PC’s, fax machines, computer servers, etc. are
placed on a UPS system. In addition, fire alarm systems, security and telephone communication
system are typical UPS loads. However, as of late, emergency egress lighting systems are being
connected to the UPS system as opposed to having individual battery backup.
How much is each minute of down-time costing you?
When making the decision as to whether or not purchasing a UPS system is worth while, you
need to consider the cost of not purchasing one. Each minute of lost production time costs your
company money. In order to help justify the cost of a UPS system, a cost benefit analysis needs
to be completed. This same analysis should also be used in determining the best type of UPS
arrangement that meets your company’s requirements.
How many 9’s of reliability do you need?
System reliability is usually calculated in terms of the amount of availability in the system. The
system availability is calculated and measured in terms of a %, with 100% being available all of
the time. As we all know, nothing is perfect or available 100% of the time. Usually, the
availability is calculated to anywhere in the range of 99.9% to 100%. The number of 9’s
determines how many decimal places we need to look for the availability. For example, 99.99%
availability has two 9’s worth of availability.
What types of UPS systems are available?
Stand-By Power System (SPS)
A stand-by power system (SPS) is often referred to as an off-line UPS system. It uses a transfer
switch for a system bypass between the utility power and the battery back-up. They also include a
rectifier (to convert AC to DC), a battery charger, a battery and an inverter (to convert DC to AC).
The system normally runs in bypass mode, i.e. no current running through the rectifier, battery
and inverter. When it senses an anomaly, the transfer switch switches position and starts to draw
power. In this scenario, protection is available only when the serving voltage dips to a
predetermined level. In addition, the ride through time required for transfer to battery power can
be significant.