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Seven Steps to Online UPS Strategy for Power Protection of Three Phase Critical Systems |
| Our natural tendency is to solve a current problem by applying what seems to be the most straightforward and cheapest approach. The natural instinct when we are in need of a UPS is therefore to contact a UPS supplier, asking for a solution that meets our immediate requirement. Generally, you contact the vendor which supplied the previous UPS, and that provides also maintenance services to the existing equipment |
876
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| A Guide to Build an Effective Strategy to meet UPS Protection level and UPS Size Requirements for Achieving a Cost Effective Power Protection. |
This approach doesn't always render the best results. The current solution may restrict the ability to meet your future
requirements, because the contacted supplier, although honest and trustworthy, may not be able to offer the equipment that
serves best both our present and future needs.
To solve the problem, UPSonNet introduces High Power UPS Strategy Guide aimed to help building a Power Protection
strategy for UPS systems from 10kVA up to 600kVA, in order to meet current requirements and to provide guiding map for
future use, whenever additional power is required.
The strategy considers three following main points:
A. Required UPS Protection
First the required protection that the UPS needs to provide should be decided. The Guide presents UPS systems from major
UPS companies; all generally providing output voltage with the quality needed to protect the critical equipment which
the UPS powers. If a UPS would never fail, the load would be protected 100% of the time. Unfortunately UPS systems do
fail and protection is unavailable during the repair time.
The major term of interest should therefore be UPS Availability, which is defined as the ratio of the mean time when the
UPS operates correctly, or Mean Time Between Failures (MTBF), to the total time, which includes also the Mean Time
To Repair ( MTTR), or replace a Failed UPS, as presented by the following Formula:
AVAILABILITY (A) = MTBF/(MTBF + MTTR)
Knowing the Availability figure enables also to derive the Unavailability or Down Time figure. The annual Mean Down Time
(MDT) figure in minutes is expressed by the Formula:
MDT = 525,600 x ( 1-A)
where 525,600 is the number of minutes in one year.
Companies that supply online service generally require MDT of less than one hour per year which means 4 nines (99.99%)
availability, whereas most Data Centers strive for MDT of 5 minutes, which requires availability of 5 nines (99.999%).
The best way to meet these requirements is to use a redundant system. Most popular is the N+1 system, which means that
you use N systems in parallel to supply the required UPS capacity with an additional one spare UPS. In case of any single
UPS failure the system continuous to operate at full capacity.
First, you will have to decide the required Availability figure, which can be calculated either by estimating the losses you
may incur during UPS down time based on MDT figure, or according to the typical availability figure in your industry.
Next, based on MTBF information presented in the guide, and the Availability equation, calculate the MTTR value which
your service provider should provide in order to meet the Availability figure. The result dictates also whether a single UPS
may suffice, or a redundant system comprising at least 2 units (1+1) i s required.
The calculation of system MTBF of redundant systems is quite complicated. The resulting MTTR which you should require
from your service supplier, in a redundant system are presented in the Guide. These should be considered before a decision
is made.
B. Required current and future UPS Size
Grow as you Go approach is the most reasonable UPS protection strategy for a growing enterprise. The idea is to start with
a small system that meets current capacity and redundancy requirements, and add UPS units in parallel when more power is
required. Some additional things should however be considered if this path is decided.
Firstly, you should know that the possible scaling depends on the particular UPS size, make and type selected initially. Only
UPS systems of the same size make and type can be connected in parallel, whereas the maximum number of allowed parallel
UPS systems depends on the particular UPS initially selected. A 20kVA system of a UPS type which allows maximum 4
systems in parallel can be increased up to 80kVA for a non redundant configuration, or up to 60kVA for a redundant N+1
system.
UPS Strategy Guide indicates the maximum allowed parallel units, of UPS systems from Major UPS manufacturers, as well
as the maximum capacity, which can be achieved in a parallel or redundant system.
Secondly, increasing power by adding parallel systems decrease UPS availability. In order to maintain the availability
requirements, when more systems are paralleled, you will have to specify shorter MTTR times from your service provider,
add redundancy to a non redundant system, or increase the redundancy of a redundant system by one more redundant UPS
unit, thus forming a N+2 system.
Complex calculations are required to derive availability of redundant units. The results are presented in the Guide. Use it in
order to see the MTTR needed to meet availability of requirements of redundant systems, and the effect when more UPS
systems are connected in parallel.
Thirdly, when selecting UPS capacity, both UPS active power presented in Watt units and total power presented in VA (Volt
Amperes) units should be taken in account. New Green oriented computers, such as Energy star labeled servers, use input
power factor correction, which require almost unity power factor.
The Guide presents major UPS systems both in VA and in Watt Units. Make sure that the total power required now and
which will be required in the future is lower then the UPS Watt and VA rating.
C. UPS Cost for Cost Effective Solution
To calculate the total UPS cost both equipment and running costs should be considered. In both cases you will overpay if
you don't see the entire picture and implement a smart cost oriented approach.
Initial UPS system cost versus power can be deduced from UPSonNet Market Price Directory. You can reduce the initial
cost considerably, gaining thousands of dollars by implementing the suggested smart UPS selection approach.
Running costs are generally higher and therefore more important than the initial investment. These costs depend mainly on
UPS efficiency.
The Guide indicates that the efficiencies of different three phase UPS types in online operation vary from 90% to 95%. A
UPS with 90% efficiency rating dissipates twice the power of a 95% efficient UPS. A simple calculation shows that saved
electricity cost (including modest 30% for the added cooling expenses) when UPS with efficiency of 95% is preferred over
90%, returns the total initial investment within less than 5 years.
UPS systems are generally designed to provide maximum efficiency at full load, which drops when partial load is applied.
Redundant systems never operate at full load. Each UPS system with 1+1 redundancy and 20% power margin is loaded
with 40% of its rating during normal operation. The loading percentage grows when more UPS units are paralleled. Thus
UPS loading in a 2+1 redundant system is 53% and 63% in 3+1 redundant case.
To enable assessment of UPS power consumption at reduced loads, each presented type in the guide shows both full load
and half load efficiencies.
To estimate the annual Electricity running cost you should asses first the annual power in kWh (kilo Watt Hours) that the
UPS system dissipates (P), using to the following formula :
P = Load Power x 8760 x (1- Efficiency) / Efficiency
Load Power is the total load power in kW ( kilo Watts)
8760 - is the number of hours in one year.
Efficiency - is the Efficiency expressed in decimal fractions ( Efficiency expressed in percentage divided by 100)
Next calculate the cost taking in account the cost you pay per kWh and possible additional expenses.
For Instance: if a load of 70kW, is supplied by a redundant N+1system, comprising four UPS units of 30kW each , with
92% Full Load efficiency and 90 % Half load efficiency, the total annual Power consumed by the UPS system equals:
P= 70x 8760x ( 1- 0.91)/0.91 = 60,646 kWh
Assuming electricity cost of $0.12/ kWh and 30% additional cooling expenses, annual running cost results in $9,460.
Guiding Steps
Next, build your UPS strategy by implementing the following steps:
1. Decide or get the following information, needed to build your UPS strategy.
2. Select the size of the UPS systems that meets your current power requirement (with 20%-30%margin), and calculate
how much parallel UPS systems will be needed to supply future load.
3. Log -In to the Three Phase UPS-Guide and calculate the current and future MTTR for non redundant system by
entering the typical non redundant MTBF figures from the guide in the Availability equation. ( Non UPSonNet member?
Sign-UP to get unrestricted site access).
If Your service provider can meet the current and future MTTR requirements. Proceed to step 5.
4. For N+1 Redundant solution, Use the Guide for checking and refining the UPS size and number of parallel systems (
including the redundant unit) selected in step 2. Check meeting Availability, MDT and supported MTTR ratings, by using
presented above formulas entering the data from Reliability Parameters Table in the Guide.
5. Select from the displayed UPS systems in the Guide the specific types that meet your current and future Watt/ VA power
and redundancy requirement, prefer the types with the higher efficiencies.
6. Estimate investments costs using Market Price Directory , and running costs as described in item C above.
7. Select two to three preferred UPS systems presented in the guide and ask quotation from service providing distributors
in your region. Check also price of alternative parallel units as guided in UPSonNet article : Getting the Most for Your
Money when Buying a UPS
requirements, because the contacted supplier, although honest and trustworthy, may not be able to offer the equipment that
serves best both our present and future needs.
To solve the problem, UPSonNet introduces High Power UPS Strategy Guide aimed to help building a Power Protection
strategy for UPS systems from 10kVA up to 600kVA, in order to meet current requirements and to provide guiding map for
future use, whenever additional power is required.
The strategy considers three following main points:
- Firstly, the required UPS Protection level should be decided in order to select the needed system configuration.
- Secondly, the current UPS Size and expected future UPS capacity needs should be defined in order to select UPS
systems that meet the requirements.
- Finally UPS Cost should be considered, and a proper specific UPS make and type should be decided based on
equipment price and UPS running costs.
A. Required UPS Protection
First the required protection that the UPS needs to provide should be decided. The Guide presents UPS systems from major
UPS companies; all generally providing output voltage with the quality needed to protect the critical equipment which
the UPS powers. If a UPS would never fail, the load would be protected 100% of the time. Unfortunately UPS systems do
fail and protection is unavailable during the repair time.
The major term of interest should therefore be UPS Availability, which is defined as the ratio of the mean time when the
UPS operates correctly, or Mean Time Between Failures (MTBF), to the total time, which includes also the Mean Time
To Repair ( MTTR), or replace a Failed UPS, as presented by the following Formula:
AVAILABILITY (A) = MTBF/(MTBF + MTTR)
Knowing the Availability figure enables also to derive the Unavailability or Down Time figure. The annual Mean Down Time
(MDT) figure in minutes is expressed by the Formula:
MDT = 525,600 x ( 1-A)
where 525,600 is the number of minutes in one year.
Companies that supply online service generally require MDT of less than one hour per year which means 4 nines (99.99%)
availability, whereas most Data Centers strive for MDT of 5 minutes, which requires availability of 5 nines (99.999%).
The best way to meet these requirements is to use a redundant system. Most popular is the N+1 system, which means that
you use N systems in parallel to supply the required UPS capacity with an additional one spare UPS. In case of any single
UPS failure the system continuous to operate at full capacity.
First, you will have to decide the required Availability figure, which can be calculated either by estimating the losses you
may incur during UPS down time based on MDT figure, or according to the typical availability figure in your industry.
Next, based on MTBF information presented in the guide, and the Availability equation, calculate the MTTR value which
your service provider should provide in order to meet the Availability figure. The result dictates also whether a single UPS
may suffice, or a redundant system comprising at least 2 units (1+1) i s required.
The calculation of system MTBF of redundant systems is quite complicated. The resulting MTTR which you should require
from your service supplier, in a redundant system are presented in the Guide. These should be considered before a decision
is made.
B. Required current and future UPS Size
Grow as you Go approach is the most reasonable UPS protection strategy for a growing enterprise. The idea is to start with
a small system that meets current capacity and redundancy requirements, and add UPS units in parallel when more power is
required. Some additional things should however be considered if this path is decided.
Firstly, you should know that the possible scaling depends on the particular UPS size, make and type selected initially. Only
UPS systems of the same size make and type can be connected in parallel, whereas the maximum number of allowed parallel
UPS systems depends on the particular UPS initially selected. A 20kVA system of a UPS type which allows maximum 4
systems in parallel can be increased up to 80kVA for a non redundant configuration, or up to 60kVA for a redundant N+1
system.
UPS Strategy Guide indicates the maximum allowed parallel units, of UPS systems from Major UPS manufacturers, as well
as the maximum capacity, which can be achieved in a parallel or redundant system.
Secondly, increasing power by adding parallel systems decrease UPS availability. In order to maintain the availability
requirements, when more systems are paralleled, you will have to specify shorter MTTR times from your service provider,
add redundancy to a non redundant system, or increase the redundancy of a redundant system by one more redundant UPS
unit, thus forming a N+2 system.
Complex calculations are required to derive availability of redundant units. The results are presented in the Guide. Use it in
order to see the MTTR needed to meet availability of requirements of redundant systems, and the effect when more UPS
systems are connected in parallel.
Thirdly, when selecting UPS capacity, both UPS active power presented in Watt units and total power presented in VA (Volt
Amperes) units should be taken in account. New Green oriented computers, such as Energy star labeled servers, use input
power factor correction, which require almost unity power factor.
The Guide presents major UPS systems both in VA and in Watt Units. Make sure that the total power required now and
which will be required in the future is lower then the UPS Watt and VA rating.
C. UPS Cost for Cost Effective Solution
To calculate the total UPS cost both equipment and running costs should be considered. In both cases you will overpay if
you don't see the entire picture and implement a smart cost oriented approach.
Initial UPS system cost versus power can be deduced from UPSonNet Market Price Directory. You can reduce the initial
cost considerably, gaining thousands of dollars by implementing the suggested smart UPS selection approach.
Running costs are generally higher and therefore more important than the initial investment. These costs depend mainly on
UPS efficiency.
The Guide indicates that the efficiencies of different three phase UPS types in online operation vary from 90% to 95%. A
UPS with 90% efficiency rating dissipates twice the power of a 95% efficient UPS. A simple calculation shows that saved
electricity cost (including modest 30% for the added cooling expenses) when UPS with efficiency of 95% is preferred over
90%, returns the total initial investment within less than 5 years.
UPS systems are generally designed to provide maximum efficiency at full load, which drops when partial load is applied.
Redundant systems never operate at full load. Each UPS system with 1+1 redundancy and 20% power margin is loaded
with 40% of its rating during normal operation. The loading percentage grows when more UPS units are paralleled. Thus
UPS loading in a 2+1 redundant system is 53% and 63% in 3+1 redundant case.
To enable assessment of UPS power consumption at reduced loads, each presented type in the guide shows both full load
and half load efficiencies.
To estimate the annual Electricity running cost you should asses first the annual power in kWh (kilo Watt Hours) that the
UPS system dissipates (P), using to the following formula :
P = Load Power x 8760 x (1- Efficiency) / Efficiency
Load Power is the total load power in kW ( kilo Watts)
8760 - is the number of hours in one year.
Efficiency - is the Efficiency expressed in decimal fractions ( Efficiency expressed in percentage divided by 100)
Next calculate the cost taking in account the cost you pay per kWh and possible additional expenses.
For Instance: if a load of 70kW, is supplied by a redundant N+1system, comprising four UPS units of 30kW each , with
92% Full Load efficiency and 90 % Half load efficiency, the total annual Power consumed by the UPS system equals:
P= 70x 8760x ( 1- 0.91)/0.91 = 60,646 kWh
Assuming electricity cost of $0.12/ kWh and 30% additional cooling expenses, annual running cost results in $9,460.
Guiding Steps
Next, build your UPS strategy by implementing the following steps:
1. Decide or get the following information, needed to build your UPS strategy.
- Required UPS Availability level - based on item 1 above.
- Required UPS size based on Current (or initial) UPS Watt and Volt Amperes Requirement.
- Future UPS Size based on future Watt and Volt Ampere Requirements.
- MTTR supported by your service provider.
2. Select the size of the UPS systems that meets your current power requirement (with 20%-30%margin), and calculate
how much parallel UPS systems will be needed to supply future load.
3. Log -In to the Three Phase UPS-Guide and calculate the current and future MTTR for non redundant system by
entering the typical non redundant MTBF figures from the guide in the Availability equation. ( Non UPSonNet member?
Sign-UP to get unrestricted site access).
If Your service provider can meet the current and future MTTR requirements. Proceed to step 5.
4. For N+1 Redundant solution, Use the Guide for checking and refining the UPS size and number of parallel systems (
including the redundant unit) selected in step 2. Check meeting Availability, MDT and supported MTTR ratings, by using
presented above formulas entering the data from Reliability Parameters Table in the Guide.
5. Select from the displayed UPS systems in the Guide the specific types that meet your current and future Watt/ VA power
and redundancy requirement, prefer the types with the higher efficiencies.
6. Estimate investments costs using Market Price Directory , and running costs as described in item C above.
7. Select two to three preferred UPS systems presented in the guide and ask quotation from service providing distributors
in your region. Check also price of alternative parallel units as guided in UPSonNet article : Getting the Most for Your
Money when Buying a UPS