In the previous Article "Evaluation Criteria for Selecting an UPS-Part One”, we explained The process for selecting an UPS which consists of eight steps (see Fig.1). These steps are:
- Step#1: Determining the need for an UPS,
- Step#2: Determining the purpose(s) of the UPS,
- Step#3: Determining the power requirements,
- Step#4: Selecting the type of UPS,
- Step#5: Determining if the safety of the selected UPS is acceptable,
- Step#6: Determining if the availability of the selected UPS is acceptable,
- Step#7: Determining if the selected UPS is maintainable, and
- Step#8: Determining if the selected UPS is affordable.
Fig.1: The process
for selecting an UPS
Today we will solve an example for the use of this selection process described above.
Notes:
- Please note that no one example can serve as the model or template for every possible case. Each case in which an UPS is being selected for a specific facility is unique and the specifics of the process will vary.
- All figures are for purposes of the example and should not be considered indicative of actual costs.
|
Example:
Selecting an Uninterruptible Power Supply (UPS) |
|
The facility manager for a planet, want to
select the UPS to be installed in the plant. He used the 8 steps of the
selection process as follows: Step#1: Determine the need for UPS.  Fig.2: The
process for determining the need for a facility UPS The facility manager knows that many of the
electrical loads are critical. He is also aware of governmental regulations
that require that lighting for evacuations and for other functions must be
available in the event of a loss of power. By answering the question included
in Fig-2 we can determine the need for a facility UPS: Is the facility inhabited? No Are critical functions involved? Yes Is emergency power required by law? Yes Result of step#1: UPS is required. |
|
Step#2: Determine the purpose of UPS. The purpose(s) must be known before proceeding because it
determines many factors that will drive the amount of power required and the
type of UPS that will be needed. These factors are:
The facility manager identified the
following purposes for the UPS:
The facility manager knows that many of the electrical loads are critical and even a lapse in power of 5 seconds could result in damage to very expensive processing equipment and could lead to injuries to operators. The purposes of UPS has been determined and
the following factors need to be applied:
|
|
Step#3: Determine the power requirements. To determine the required power capacity, you need to get answers for the following questions: The first
question: how much power is needed? The facility manager calculated the total power requirements for the UPS to be 1000 kVA The Second
question: how much (if any) to oversize the unit? For future growth; the facility manager
decides to add a 12.5 percent to allow for growth and to cover over-voltages
and other anomalies. Result of step#3: The total power required is 1250 kVA. At a
power factor of .80, this is equivalent to 1000 kilowatt (kW). Note: Later we will explain in detail the
calculation steps for determining the UPS power requirements |
|
Step#4: Select
the type of UPS. Selecting a particular type and configuration of an UPS depends on the following factors:
The facility manger review the comparison
between different UPS types as shown in fig-3  fig-3
comparison between different UPS types Result of step#4: The facility manager decide that The UPS should be Double conversion on-line which is the best choice for providing the maximum possible protection for critical loads and provide high efficiency that means less heat will be generated by the UPS. The result will be increased battery life, higher reliability, and decreased cooling requirements. For example fro, the selected UPS from Schneider Electric will be: Galaxy VX 1250kVA, Double Conversion Online
UPS, Tower, Sine Wave,480V, Start up 5x8 – model: GVX1250K1250GS with
external battery  |
|
Step#5: Is
safety of selected UPS acceptable? The facility manager decide that Separate
HVAC for the battery room will be provided to ensure that the room is
properly vented to prevent Hydrogen
accumulation and that the battery will not be operated at temperatures
above 25 deg.C. Result of step#5: The UPS room has good ventilation and safety is acceptable. |
|
Step#6: Is
selected UPS availability acceptable? Normally, the
required availability for UPS is 98 percent. The
designed-in availability is usually expressed as follows: Ai = MTBF / (MTBF + MTTR) Where: Ai is inherent availability MTBF is mean time between failure (a measure of reliability) MTTR is mean time to repair (a measure of maintainability) The selected UPS has the following settings: The reliability of the UPS in previous
applications is equivalent to about a 200-hour mean time between failures
(MTBF). The average time to repair a failure is less
than 5 hours (MTTR) Ai = MTBF / (MTBF + MTTR) = 200/(200+5) = 0.9756 = 0.98 Result of step#6: The selected UPS availability (0.98) is
acceptable |
|
Step#7: Is
selected UPS maintainable? The facility manager reviewed the maintenance procedures in the facility and find the following
Result of step#7: The selected UPS is maintainable |
|
Step#8: Is cost
of UPS acceptable? See fig.4 that
describes the process for determining affordability. For an UPS, the total cost includes:
 Fig.4 the
process for determining affordability The purchase price and Installation cost:
So, the total acquisition cost is $310,000. Operating and support costs Operating and maintenance costs are
estimated by the facility manager to be $40,000 over 15 years. This estimate
is based on an MTBM of 200 hours, spare parts costs, labor costs of $25 per
hour, and a conservative forecast of 20 operating hours per year. Disposal costs Disposal costs are considered negligible,
since some of the costs can be recouped through sale of the UPS for parts and
scrap. The total budget The total budget for constructing and
outfitting the new UPS will be $350,000, the budget / year for 15 years life
time will be $23,333. For similar projects, the budget / year for 15 years life time was between $22,500 and $25,000. Result of step#8: The total acquisition cost is acceptable. |
|
Summary Report
|
|
UPS System
Ratings and Service Conditions |
|
In this part, we will know how to specify
the standard ratings and performance characteristics for UPS systems from the
IEC and from the American standards. |
|
First: from IEC
60146-4 |
1-
Specify the UPS model
Use the
following table to specify the UPS Model.
|
IEC 60146-4 reference |
Characteristic
of equipment |
Manufacturer's declared
values |
|
|
Model catalogue reference |
|
|
|
Model rating |
W or VA |
|
|
Dimensions length x depth x height |
mm |
|
|
Weight |
kg |
|
|
Weight with batteries if integrated |
kg |
1.1
Mechanical conditions to be identified
a)
Exposure to abnormal vibration, shocks, tilting or earthquakes
b) Special
transportation or storage conditions (purchaser should identify method of
handling equipment)
c) Space
and weight limitations
2-
Normal environmental and climatic service conditions
The UPS
shall be capable of withstanding the conditions defined here, unless other
values are agreed between manufacturer/supplier and purchaser. Use the
following table to specify the environmental conditions for UPS system
|
IEC 60146-4 reference |
Characteristic
of equipment |
Manufacturer's declared
values |
|
Environmental |
||
|
4.1.4 |
Ambient storage temperature range |
°C |
|
4.1.2 x |
Ambient storage temperature range |
°C |
|
4.1.1 |
Altitude |
m |
|
4.1.3 |
Relative humidity range |
% |
|
|
Degree of protection in accordance with IEC 60529 |
PI |
|
7.3
|
Acoustic noise at 1 m: - Normal mode - Stored energy mode |
dBA dBA |
Notes:
- The performance specifications are normally based on operating the UPS system under typical environmental conditions as shown in table-1.
- It may be necessary to derate the UPS if environmental conditions differs from the above typical ones.
- Using the UPS without derating and at the limits table-1 guarantees operation, but may affect the effective life of certain components, in particular the life endurance of the energy storage device and its stored energy time.
- Refer to the manufacturer for details on life limitations, or where the energy storage device is purchased separately, review the battery manufacturer.
|
ambient
temperature range |
0°
to 40°C |
|
relative humidity range |
0 to 95% non-condensing |
|
operating Altitude |
0 to 1000 meters |
|
audible noise |
<67 dB(A) at 1.5 meters |
In the IEC 62040-3, the Normal service
conditions will be as follows:
- Compatibility with public low-voltage supplies:
- Equipment conforming to this standard shall be capable of operating in normal mode of operation when connected to an input supply having the following conditions, if not otherwise specified.
a) Input
voltage variation ±10 % of nominal rated voltage
b) Input
frequency variation ±2 % of nominal rated frequency
c) For
three-phase inputs, the ratio of negative to positive sequence components shall
not exceed 5 % (see 2.5 of IEC 60146-1-1).
d) Input
voltage total distortion factor D ≤0.08 with the following maximum level of
individual harmonic voltages according to the table below (extract from table-1
of IEC 61000-2-2 for public low-voltage supplies) up to the 40th harmonic.
Note: The limit to order 40 is
conventional.
Table 2 - Compatibly levels for individual harmonic voltages in low-voltage networks - (Extract from IEC 61000-2-2)
2.1 Derating for
ambient temperature:
A UPS
conforming to IEC standard shall be able to operate under rated conditions in a
minimum temperature range from 0 °C to + 40 °C except for indoor office ambient
temperature range from +10 °C to + 35 °C.
If UPS KVA
rating is applicable at a higher ambient temperature than specified 40 deg.c, you
need to consider a derating factor of at least 1.5%/deg.c above the 40 deg.c
2.2 Derating for
Altitude:
A UPS
shall be designed to operate under rated conditions at a height up to and
including 1 000 m above sea level.
Note:
The
manufacturer can state on request a necessary derating of equipment to be
applied at a height exceeding 1 000 m. The following table-2 is provided for
guidance.
Table-2 derating factors for use at altitudes above 1000 m
Some examples from manufacturer’s data
sheets for Derating for Altitude:
2.3
Another Environmental conditions to be identified
a) Damaging
fumes
b)
Moisture
c) Dust
d)
Abrasive dust
e) Steam
f)
Explosive mixtures of dust or gases
g) Salt
air
h) Weather
or dripping water
i) Extreme
changes in temperature
j) Cooling
water containing acid or impurities which may cause scale, sludge, electrolysis
or corrosion of the converter parts exposed to the water
k) Strong
electromagnetic fields
l)
Radio-active levels above those of the natural background
m) Fungus,
insects, vermin, etc.
n)
Restriction of ventilation
o)
Radiated or conducted heat from other sources
p) Battery
service conditions
3- Electrical
characteristics – Input
|
IEC 60146-4 reference |
Characteristic of equipment |
Manufacturer's declared values |
|
Electrical
characteristics - Input |
||
|
5.2.2 and 6.3.2.1 |
Rated input voltage
and voltage tolerance |
V |
|
5.2.2 and 6.3.2.2 |
Rated input frequency
and frequency tolerance |
Hz |
|
5.2.2 and 6.3.10 |
Rated input current |
A r.m.s |
|
5.2.2 and 6.3.9.2 |
Maximum input current |
A r.m.s |
|
5.2.2 |
Input current distortion
at rated input current |
% THD |
|
5.2.2 and 6.3.10 |
Input power factor |
|
|
5.2.2 and 6.3.3 |
Inrush current |
p.u. of
rated current |
|
5.2.2 |
Number of phases |
Phase/s |
4-
Electrical output characteristics - Static & Dynamic characteristics -
Normal mode & Stored energy mode
|
IEC 60146-4 reference |
Characteristic of equipment |
Manufacturer's declared values |
|
Output
waveform |
||
|
5.3.1.2 |
Waveform - Normal mode |
|
|
5.3.1.2 |
Waveform - Stored
energy mode |
|
|
|
Transfer: Normal
mode/Stored energy |
Break . No Break
. |
|
|
Break time/Make time
(if applicable) |
ms |
|
Electrical
output characteristics - Static characteristics - Normal mode |
||
|
5.3.2 |
Rated output voltage |
V
r.m.s |
|
|
Output voltage
variation |
V r.m.s |
|
|
Output frequency
(nominal) |
Hz |
|
6.3.2.2 |
Output frequency
variation (synchronized if applicable) |
Hz |
|
6.3.6.3 |
Output frequency
synchronized phase error at change of mode |
Degrees |
|
|
Rated output apparent
power |
VA |
|
|
Rated output active
power across linear load |
W |
|
|
Rated output active
power across a reference non-linear load |
W |
|
6.3.4.2 |
Total voltage distortion
across a linear load |
% |
|
6.3.8.1 |
Total voltage
distortion across a reference non-linear load |
% |
|
6.3.4.2 |
Individual harmonics
voltage |
See separate declaration |
|
5.3.2 and 6.3.5.3 |
Short-circuit
capability |
See separate
declaration |
|
5.3.2 and 6.3.5.1 |
Overload capability |
See separate
declaration |
|
5.3.2 and 6.3.4 |
Range of load power
factor permitted - Linear load Number of output
phases |
Phase(s) |
|
5.3.2 and 6.3.4.5 |
Output voltage
unbalance at reference unbalance load (multiphase only) |
% |
|
5.3.2 and 6.3.4.5 |
Maximum phase angle
variation (multiphase only) |
degrees |
|
6.3.4.6 |
Output voltage d.c.
component - linear load |
% |
|
Electrical
output characteristics - Dynamic characteristics - Normal mode |
||
|
5.3.2 and 6.3.6.1 |
Output voltage dynamic
variation during transfer normal/stored energy
mode of and 6.3.6.2 operation
and vice versa |
See separate declaration declaration |
|
6.3.7.1 and 6.3.8.4 6.4.8.4 |
Output voltage dynamic
variation due to load changes |
See separate
declaration |
|
|
Maximum rate of change
of output frequency |
Hz/s |
|
Electrical output
characteristics - Static characteristics - Stored energy mode |
||
|
5.3.1 |
Rated output voltage |
V
r.m.s |
|
6.3.4.4 |
Output voltage
variation |
V r.m.s |
|
6.3.4.3 |
Rated peak output
voltage |
V |
|
6.3.4.4 |
Rated peak output
voltage variation V |
V |
|
5.3.1.2 |
Non-sinusoidal voltage
rise time 0.1 to 0.9 peak (if waveform exceeds 0.5 V/μs) |
V/μs |
|
5.3.2 |
Output frequency |
Hz |
|
5.3.2 |
Output frequency
variation |
Hz |
|
5.3.2 |
Rated output apparent
power |
VA |
|
5.3.2 |
Rated output active
power |
W |
|
5.3.2 |
Rated output active
power non-linear load |
W |
|
6.3.4.4 |
Total output voltage
distortion |
%
THD |
|
6.3.4.4 |
Individual harmonic
voltage-linear load |
See separate Declaration |
|
5.3.2 and 6.3.8.2 |
Individual harmonic
voltage-non-linear load See separate declaration |
|
|
5.3.2 and 6.3.5.4 |
Short-circuit
capability |
See separate
declaration |
|
5.3.2 and 6.3.5.2 |
Overload capability |
See separate
declaration |
|
5.3.2 |
Range of load power
factor permitted |
|
|
5.3.2 |
Number of output
phases (multiphase only) |
Phase(s) |
|
6.3.6.1 |
Output voltage dynamic
variation during transfer from stored energy mode to normal mode |
See separate declaration |
|
6.3.7.1 |
Output voltage dynamic
variation due to load changes |
See separate declaration |
|
Efficiency |
||
|
6.6.11 |
Efficiency
input/output |
% |
5-
Stored energy mode of operation
|
IEC 60146-4 reference |
Characteristic of equipment |
Manufacturer's declared values |
|
5.4 Stored energy mode
of operation |
||
|
|
Duration of maximum
permitted stored energy time at rated load |
min |
|
6.3.9.1 |
Stored energy time
(for integral batteries) at rated load |
min |
|
6.3.9.2 |
Restored energy time
to 90 % charge (for integral batteries) Battery rating and
quantity (for integral battery) Battery recharge profile |
H Ah and units See separate
declaration |
|
6.3.9.1 |
Battery cut-off
voltage |
V |
6-
Bypass characteristics
|
IEC 60146-4 reference |
Characteristic of equipment |
Manufacturer's declared values |
|
5.5.2 Bypass
characteristics |
||
|
|
Type of bypass |
Manual . Automatic . |
|
|
Mechanical/static |
Mechanical . Static . |
|
|
No break
transfer/break transfer |
No break . Break . |
|
|
Break time/make time |
ms |
|
|
Maintenance bypass |
Yes . No . |
|
|
Bypass protection fuse
or circuit-breaker rating |
A |
|
|
Galvanic isolation
fitted |
Yes . No . |
7- Other characteristics
|
IEC 60146-4 reference |
Characteristic of equipment |
Manufacturer's declared values |
|
Synchronization
(if applicable) |
||
|
6.3.6.4 |
Acceptable voltage
difference |
% |
|
6.3.2.2 |
Range of frequency
synchronization |
Hz |
|
6.3.6.4 |
Maximum phase error |
degrees |
|
5.8
Control and monitoring signals |
||
|
|
See separate
declaration for complete list of indications and remote alarm/monitoring or
interface devices |
|
|
5.7
Electromagnetic compatibility |
||
|
|
Immunity see IEC
62040-2 in preparation |
|
|
|
Emission see IEC
62040-2 in preparation |
|
|
Second:
according to American standards |
1-
The rectifier ratings
The rectifier acts as a load to the electrical mains and the following characteristic of the rectifier will decide the type of upstream infrastructure required:
- Input current distortion (THDI) : Harmonics,
- Input power factor,
- Input startup current,
- Number of wires (3ph or 3ph+Neutral),
- Efficiency (influences global efficiency),
- Maximum output power,
- Input voltage & frequency tolerances
- Generator compatibility
The
Typical rectifier/charger ratings are as follows:
|
a. Input
Voltage |
208,
220, 240, 380, 415, or 480 V, 10%, 3 phase / 120/220 V, ±10%, 1phase |
|
Frequency
|
50 or 60
Hz. ±0.5% |
|
Power
Factor (typical) |
0.8 |
|
b.
Output Nominal Voltage |
110 VDC,
220 VDC nominal 130VDC,
260 VDC nominal ±5%
adjustment |
|
Equalize
Voltage |
140 VDC,
280 VDC ±5%
adjustment |
|
Ripple
Voltage |
<2%
RMS with batteries |
|
Equalize
Timer |
1-100
hours, manual start, auto-reset |
|
Capacity |
Sized to
recharge the battery in 8 to 10 hours |
2-
The inverter ratings
The
inverter of the UPS System will be a source for the critical loads connected to
the UPS and based on the need of the load.
The following parameters decides the quality & capacity of the UPS:
- Nominal apparent power (VA)
- Nominal active power (W)
- Capability to support load Power factor (low power factor and Leading mainly)
- Inverter efficiency (influences global efficiency)
- Output voltage distortion (THDV, with different load types)
- Max load, current, crest factor
- Overload, Inrush current and short circuit capability,
- With or without galvanic isolation
The Typical inverter ratings are as
follows:
|
a. Input
Voltage (range) |
120, 220 V ± 20% |
|
b.
Output Voltage |
120 V,
single phase 280 V or 480 V, 3 phase, 3 or 4 wire |
|
Voltage
Regulation |
± 2% for
balanced load ± 3% for
100% unbalanced loads (3 phase only) |
|
Sync
range |
±0.5 Hz |
|
Load
Power factor |
0.8 to
1.0 |
|
Transient
Recovery |
± 3%
within 10 milliseconds ± 1%
within 30 milliseconds |
|
Harmonic
Distortion |
3%
maximum single harmonic 5% THD
maximum up to crest factor 2 3% THD
maximum for linear loads |
|
Frequency |
50 or 60
Hz ±0.1% |
|
Overload
Capacity |
500% for
1 cycle, 120% continuous |
|
Crest
factor |
3:1 at
full load |
3-
The battery ratings
The
battery is the heart of the UPS system and the selection of battery is more important
as it decides the duration of operation in the event of mains failure. The battery
also plays an important role in deciding the Capital and operation cost.
The following points has to be evaluated to have the right battery configuration:
- KW considered for battery sizing
- End cell voltage
- Ageing factor (in case of low backup time)
- No of battery banks in parallel
- Design life of the selected battery
- Requirement of charging current and its compatibility with UPS
4-
Static switch ratings
The Typical static switch ratings are
as follows:
|
Transfer Time |
0 s (Make-before-break) |
|
Overcurrent Transfer |
120% of rated full load current |
|
Overload Capacity |
1000% for 1 cycle |
In the next Article, we will explain
the UPS system KVA
sizing Calculations. So, please keep
following.
|
Subject Of Pervious
Article |
Article |
|
Applicable Standards for UPS Systems What is a UPS? Why do we need a UPS? UPS Rating Classification of UPS: 1-Voltage range, 2-No. of phases, 3- Mobility, 4- Technological design, |
Classification and Types of
UPS – Part One |
|
5- Physical Size/capacity, 6- Form factor/ configurations: 6.1- “N” System
Configuration |
Classification and Types of UPS – Part Two |
|
6.2- “N+1” System
Configuration, which includes:
6.3- Parallel Redundant with Dual Bus Configuration (N+1 or 1+1) |
Classification and Types of
UPS – Part Three |
|
6.4- Parallel Redundant with STS Configuration
6.5- System plus System 2(N+1), 2N+2, [(N+1) + (N+1)], and 2N |
Classification and Types of UPS – Part Four |
|
7- According to UPS Topology 7.1 Off-line or Standby UPS, 7.2 Line Interactive UPS, 7.3 Standby-Ferro UPS, 7.4 Online Double Conversion UPS, 7.5 The Delta Conversion On-Line UPS. |
Classification and Types of
UPS – Part Five |
|
8- According to UPS Distribution
Architecture 8.1 Centralized UPS Configuration, 8.2 Distributed (Decentralized) UPS Configuration, 8.2.1 Distributed UPS-Zonewise Configuration 8.3 Hybrid UPS Configuration. Conventional (Monolithic) Vs Modular
UPS System:
|
Classification and Types of UPS – Part Six |
|
Three Basic Configurations Of Mains And Bypass For A UPS System:
9-According to Use of transformers with the UPS
|
Classification and Types of
UPS – Part Seven |
|
Transformer Arrangements in Practical UPS Systems: 1-Transformer options for the “single mains” configuration 2-Transformer Options for the “Dual Mains” Configuration |
Classification and Types of UPS – Part Eight |
|
3-
Transformer options for “single mains without bypass” |
|
|
Components of Online Double Conversion UPS: 1- Rectifier, 2- Inverter, 3- Energy Storage system: 3.1 Battery |
Components of Online Double Conversion UPS– Part One
|
|
3.1.1 Battery
Configurations Serial
Strings, Parallel
Strings. 3.1.2
Battery Size and Location 3.1.3
Battery Transition Boxes 3.1.4
Battery Monitoring 3.2
Energy Storage System – Flywheel 3.3
Energy Storage system – Super Capacitors 3.4
Hydrogen Fuel Cells 4- Static
switch Earthing
Principles of UPS Systems |
Components of Online Double Conversion UPS – Part Two |
|
Evaluation Criteria for Selecting an UPS:
|
Evaluation Criteria for Selecting an UPS-Part One
|
No comments:
Post a Comment