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Totally Integrated Power

Technical Series Edition 3

Modeling of systems for Uninterruptible Power Supply (UPS) in SIMARIS® design for application in data centers

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Technical Series Edition 3

Modeling of systems for Uninterruptible Power Supply (UPS) in SIMARIS® design for application in data centers

1. Basics

Uninterruptible power supply to the servers is of fundamental importance for data centers in order to have those

available 24hours a day and 365days a year. To achieve this goal, the power supply must be thoroughly planned.

This includes the coordination between the components to be used, taking into account that the selection and integration of UPS systems in the power supply concept is

essential in this process.

Meaning of the code elements:

AAA

The characteristic value describes the dependency of the UPS output supply in normal operation in case of change of voltage and fre-

quency at the input AC supply.

"VFD" (Voltage and Frequency Dependent):

UPS systems with VFD classification must pro-

tect the load against power failure.

In this case, the UPS output is influenced by changes of the input AC voltage and the frequency, and it is not suitable for assuming additional correction functions which may arise from the application of an

autotransformer.

Characteristic values dependent on the voltage curve. A difference is made between

the following operating modes:

• Normal or bypass operation (first character)

• Energy storage operation (second character)

"S": The voltage curve is sinusoidal.

In case of linear and non-linear reference load (the exact specification can be found

in IEC62040-3), the total harmonic distortion is lower than 8%. The curve shape is defined as sinusoidal.

"X": The curve shape is only sinusoidal in case of linear load. In case of non-linear refe-

rence load, the curve shape is no longer sinusoidal, as the total harmonic distortion

exceeds the limit value of 8%.

"Y": The voltage curve is not sinusoidal, neither for linear nor for non-linear reference

loads. The limit value of 8% is exceeded in both cases.

In accordance with the IEC 62040-3 standard (DINEN62040-3; VDE0558 Part 530), UPS manufacturers

can designate their devices according to the classification

described therein. The assessment criteria are shown

hereafter as an excerpt:

Designation code: AAA BB CCC

e.g.: VFI SS 111 (highest classification)

"VI" (Voltage Independent):

Like UPS systems with VFD, UPS systems with VI classification must protect the load against power failure, and also additionally ensure the supply in case of

• undervoltage permanently applied to the input

• overvoltage permanently applied to the

input.

The output of a UPS with VI classification depends on the frequency of the AC voltage input, and the output voltage must remain

within the prescribed limit voltage values.

"VFI" (Voltage and Frequency Dependent):

UPS systems with VFI classification are independent of (mains) supply voltage and frequency fluctuations, and must protect the load against negative effects of such fluctuations without discharging the energy storage

system.

CCC

Characteristic values for the dynamic behavior of the UPS output voltage:

• First numeral: in case of change of the operating mode

• Second numeral: in case of linear load step in normal or battery operation (specification for the worst case)

• Third numeral: in case of non-linear load step in normal or battery operation (specification for the worst case)

"1": required operating behavior for sensitive, critical loads.

The UPS output voltage remains within the limit values of curve 1 (see IEC62040-3)

in this section.

"2": permissible operating behavior for most of the critical loads.

The UPS output voltage remains within the limit values of curve 2 (see IEC62040-3)

in this section.

"3": permissible operating behavior for most of the general IT loads, e.g. switched-mode

power supplies.

The UPS output voltage remains within the limit values of curve 3 (see IEC62040-3)

in this section.

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Technical Series Edition 3

With SIMARIS design, electrical networks can be dimensioned with minimum input effort on the basis of real products – from the medium-voltage level down to the power consumer (which in the case of a data center means down to the rack where the ICT equipment (ICT: Information and Communication Technology) is supplied with

power). This reduces your efforts for the overall planning

of the power distribution a lot, and thus the time for selecting and dimensioning the electrical equipment –

with a high level of planning security.

When UPS systems are integrated for planning the power distribution, the functionality is structured in SIMARIS design, both

• as a load for selecting the components of the infeed

(transformers, generators, cables, busbars, switching devices)

• and as a power source to depict the effects on the

downstream network regarding the maximum short-circuit currents in case of transformer infeed, as well as the minimum short-circuit currents in case of inverter opera-

tion mode.

Following the standard EN 50600-2-2, Clause 6.3.2, the

functional elements of a power distribution system must be selected in accordance with the selectivity and shortcircuit withstand strength requirements in all operating

modes and during different operating phases.

To supply the connected loads, the

• supply via the UPS

• supply via a UPS bypass

must be considered. Infeed takes places either through a supply network (e.g. primary infeed for VFI operation and

secondary supply in case of internal bypass operation of

the UPS), or through an additional supply (e.g. generator).

With SIMARIS design it is possible to verify – for the downstream network – the compliance with the electrotechnical conditions according to the standard, such as the switch-

off condition according to IEC60364-4-41 (DINVDE0100 Part410), as well as the selectivity.

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Technical Series Edition 3

2. Integration of UPS systems in power distribution networks

In power distribution networks, UPS systems are installed to protect critical consumers for which an interruption of the power supply or failures of the supply quality would lead to serious consequences such as data loss, production

breakdown, or safety problems. The purpose of use usually

determines the functionality of a UPS, and thus the associ-

ated UPS classification. When the UPS is integrated in the

power distribution network, the functionality of the UPS must be observed in order to avoid malfunctioning and

undesirable effects in case of fault or operational changes.

UPS systems with double instrument transformers (mostly with UPS classification VFI) offer the maximum safety by

decoupling the load supply from the UPS input (see Fig.1), and are taken as a basis for the following considerations.

The integration of a static UPS system in a concept for a power supply network will be shown in the following by means of a specific planning example, including the simu-

lation of the UPS in SIMARIS design.

Based on the assumption that the input for the static bypass is supplied by the NPS busbar (transformer infeed, low-voltage main distribution LVMD of the normal power

supply NPS) and the rectifier input is supplied by the SPS busbar (generator, LVMD of the safety power supply SPS), the resulting conditions from the perspective of the UPS

output side (main distribution SDUPS) are shown in a simplified way in Fig.2.

The static bypass is supplied by the LVMDNPS (transformer). This considers the high short-circuit currents of a transformer supply.

In double conversion operating mode, the UPS rectifier

supply through the LVMDSPS (generator) is decoupled

from the inverter output, which means that, in inverter operation, the fault currents at the UPS output are exclusively determined by the inverter, and must be taken into

account in accordance with the manufacturer data.

Fig. 1: Integration of UPS systems with DC link (double conversion)

Normal

power supply

Normal loads

Manual bypass

Safety power supply

UPS UPS

UPS

Fig. 2: Supply of a short circuit on the output side by the

transformer through the bypass or/and through the inverter

LVMD NPS LVMD SPS

Safety loads

Static bypass

Externeral manual bypass

Rectiﬁer

Inverter

Load

SD UPS

Battery

UPS loads

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3. Simulation of UPS systems in SIMARIS design

Technical Series Edition 3

SIMARIS design offers various options for simulating UPS systems, of which only the detailed simulation according

to Fig. 3 is represented. In this context, it must be

observed that the UPS function modes are simulated together via SIMARIS design elements and the setting of

various operating modes.

In Fig. 3, the essential components required for the functionality of the UPS are identified by means of color boxes.

The red box marks the UPS as a symbol:

Yellow: Internal, static UPS bypass at one outgoing

circuit-breaker from the LVMDNPS to the UPS output

Green: Inverter as power source connected to the UPS output

Dark red: Rectifier as load for rectifier supply and battery charging at the incoming distribution from the generator busbar

Fig. 3: Detailed simulation of UPS systems in SIMARIS design

MV-CB 5.1 Circuit-breaker

CB-f NAR In (switch) = 630 A Trans. current = 75/1A 7SJ8011

MV-C/L 5.1 N2XS2Y 5 m XLPE 3 x 35

Transformer 1 Sn = 2,000 kVA / AN ukr = 6 % 20/0.4 kV Dyn5

CB 31.1a Circuit-breaker In = 630 A 3VA24635HN320AA0/LSI

B 31.1 Busbar 50 m BD2A-3-630

TN-S Un = 400 V

Load SD NPS Dummy load In = 451 A Un = 400 V 3-pole

SD NPS

4GX63643E

S 1 Busbar 25 m LI-AM32005H-55

LV-CB Transformer Circuit-breaker In = 3,200 A 3WL12402NG611AA2/LSING

External bypass CB 1 Circuit-breaker In = 2,000 A 3WL11202EB611AA2/LSIN

S 1.1 Busbar 5 m LI-AM20005H-55

External bypass CB 2 Circuit-breaker In = 2,000 A 3WL11202EB611AA2/LSIN

LV-S 1 Busbar 5 m LI-AM32005H-55

Coupling NPS/SPS Circuit-breaker In = 3.200 A 3WL12402NB711AA2/LSIN

LVMD NPS

TN-S Un = 400 V

Internal Bypass Circuit-breaker In = 2,500 A 3WL12322NB711AA2/LSING

S 1.2 Busbar 5 m LI-AM25005H-55

Internal bypass

Dummy bypass output Circuit-breaker In = 2,500 A 3WL12322NB711AA2/LSIN

UPS output Circuit-breaker In = 2,000 A 3WL11202EG711AA2/LSING

S 3 Busbar 5 m LI-AM20005H-55

UPS CB 1 Circuit breaker - 3VA with ELISA characteristics In = 630 A 3VA24635HK320AA0/LI

S 24.1 Busbar 25 m

BD2A-3-630

UPS load 1

TN-S Un = 400 V

Fu-SD 24.2a Fuse Switch Disc. In = 300 A 3 x 3NA3250 Size 2 3NJ41333BF01 Size 2

C/L 24.2 Cable/line 25 m Cu 1(3x240/240/120)

Total load 1 Inner zone In = 241 A Un = 400 V 3+N-pole

Remark: Regarding the rectifier requirements, not only the battery charging, but also the UPS losses in operation must

be considered.

Moreover, Fig. 3 shows the three types of power supply via

the corresponding sub-distributions:

• Normal power supply NPS (sub-distribution SDNPS)

• Safety power supply SPS (sub-distribution SDSPS)

• Uninterruptible power supply (sub-distribution SDUPS)

In addition, Fig. 3 shows a comparison between a molded-

case circuit-breaker 3VA with the ELISA tripping unit and a 3VA circuit-breaker with an LSI tripping unit at the UPS

sub-distribution. The advantages of adjusting the ELISA tripping characteristic to the one of a fuse are suggested.

The example can also be found in the enclosed SIMARIS

design file. Please contact your TIP partner at Siemens for more information.

Generator 1 Pn = 1,800 kW Sn = 2,250 kVA Un = 400 V

S 2 Busbar 10 m

NPS/SPS SD Non-automatic CB In = 2,500 A 3WL12252AA711AA2

UPS OUT

TN-S Un = 400 V

UPS load 2

TN-S Un = 400 V

UPS

Inverter Rectiﬁer input &

UPS inverter output In = 1,732 A Un = 400 V

Dummy inv. output Circuit-breaker In = 2,500 A 3WL12252NG711AA2/LSING

UPS CB 2 Circuit-breaker - 3VA with LSI characteristics In = 800 A 3VA25805KQ320AA0/LSIG

S 29.2 Busbar 25 m

BD2A-3-800

Fu-SD 29.2a Fuse Switch Disc. In = 300 A 3 x 3NA3250 Size 2 3NJ41333BF01 Size 2

C/L 29.2 Cable/line 25 m Cu 1(3x240/240/120)

Total load 2 Inner zone In = 241 A Un = 400 V 3+N-pole

2x2x

LI-AM40005H-55

Generator switch Circuit-breaker In = 4,000 A 3WL12402NG711AA2/LSING

Output switch to rectiﬁer Circuit-breaker In = 2.500 A 3WL12322NG711AA2/LSING

S 2.1 Busbar 5 m LI-AM25005H-55

battery charging

Rectiﬁer + Battery Inner zone In = 1,890 A Un = 400 V 3-pole

TN-S Un = 400 V

SD UPS

TN-S Un = 400 V

UPS CB 3 Circuit-breaker In = 630 A 3VA24635HN320AA0/LSI

S 4.2 Busbar 10 m BD2A-3-630

Total load 3 Inner zone In = 577 A Un = 400 V 3+N-pole

LVMD SPS

TN-S Un = 400 V

CB 30.1a Circuit-breaker In = 400 A 3VA23405HN320AA0/LSI

B 30.1 Busbar 25 m BD2A-3-400

UPS IN

SD SPS

TN-S Un = 400 V

Load SD SPS Dummy load In = 271 A Un = 400 V 3-pole

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Technical Series Edition 3

For the different functionalities of the UPS, individual operating modes can be defined and calculated in SIMARIS

design (Fig. 4):

• Normal UPS operation VFI ①:

Double conversion operating mode of the UPS via rectifier and inverter fed by the transformer

• Normal UPS operation VFI via generator ②:

• Internal bypass operation of the UPS ③:

The rectifier and inverter of the UPS are bypassed; the UPS sub-distribution MDUPS is supplied through the

transformer

• External bypass operation for UPS service purposes ④:

The UPS is isolated and all loads are supplied through the

transformer.

Double conversion operating mode of the UPS via rectifier and inverter fed by the generator

Fig. 4: Functional UPS simulation by determination of operating modes in SIMARIS design

Operating mode ①: UPS in VFI double conversion operating mode, infeed from transformer

Operating mode ②: UPS in VFI double conversion operating mode, infeed from generator

Internal bypass

UPS

Inverter Rectiﬁer &

battery loading

Operating mode ③: Internal bypass operation, infeed from transformer

Internal bypass

UPS

Inverter Rectiﬁer &

battery loading

Internal bypass

UPS

Inverter Rectiﬁer &

battery loading

Operating mode ④: External bypass operation, infeed from transformer

Internal bypass

UPS

Inverter Rectiﬁer &

battery loading

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Technical Series Edition 3

To illustrate the correlations between the operating modes and the calculations in SIMARIS design, the different

operating modes are itemized in Tab. 1 and Tab. 2:

• Tab. 1 shows the relevant circuits for dimensioning in the

• Tab. 2 shows the current paths for determining the

selectivity and the switch-off conditions, and assigns them to the respective operating modes (illustration in

Fig. 6).

respective operating mode (illustration in Fig. 5)

Tab. 1: Observance of operating mode determination when dimensioning with SIMARIS design

Dimensioning of products and systems (x identi󹪝es operating modes to be considered during dimensioning)

Circuit (see Fig. 5)

① ② ③ ④ ⑤ ⑥ ⑦ ⑧

Operating mode

UPS VFI operation via transformer

UPS VFI operation via generator

Internal bypass operation

External bypass operation

Fig. 5: Illustration of circuits for dimensioning during UPS simulation

x x x x x

x x x x

x x x x x

x x x x

①

②

④ ⑤ ⑥

Internal bypass

Inverter Rectiﬁer &

⑦

UPS

① Transformer infeed

③

② NPS-SPS coupling ③ Generator infeed ④ External bypass ⑤ Feeder to internal bypass of UPS ⑥ Feeder to UPS rectiﬁer ⑦ UPS output feeder ⑧ UPS distribution

battery charging

⑧

2x2x

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Technical Series Edition 3

Tab. 2: Observance of operating mode determination for considerations of selectivity and switch-o󹪜 conditions with SIMARIS design

Selectivity and switch-o󹪜 conditions (x identi󹪝es current paths to be observed)

Current paths (see Fig. 6)

UPS VFI operation via transformer

① x x x

② x

③ x

④ x

⑤ x x x

⑥ x

⑦ x

⑧ x x

UPS VFI operation via generator

Internal bypass operation External bypass

operation

Fig. 6: Illustration of current paths for considerations of selectivity and switch-o󹪜 conditions during UPS simulation

Transformer infeed - NPS distribution

①② ③④⑤

Internal bypass

Inverter Rectiﬁer &

⑧

UPS

①

② Transformer infeed - external bypass - UPS distribution

③ Transformer infeed - internal bypass - UPS distribution

④ Transformer infeed - NPS-SPS coupling - Rectiﬁer infeed

⑤ Transformer infeed - NPS-SPS coupling - SPS distribution

⑥ ⑦

⑥ Generator infeed - Rectiﬁer infeed

⑦ Generator infeed - SPS distribution

⑧ Inverter infeed - UPS distribution

battery charging

2x2x

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Technical Series Edition 3

4. Technical UPS data for simulation in SIMARIS design

For the example shown in here, manufacturer information

for a specific UPS with an apparent power of 1,200kVA was taken as a basis (see Tab. 3).

Tab. 3: Technical data for the example UPS1) (used in the enclosed SIMARIS design 󹪝le)

Rated value of the apparent power in kVA 1,200

Rated active power in kW 1,200

Rated voltage in V 400 (380/415 selectable, 3ph + N)

Rated frequency in Hz 50 (60 selectable)

Rated output current in A 1,731

Maximum input current in A 1,890

Maximum short-circuit current (short-circuit withstand strength of the UPS) in A

Minimum short-circuit current (overload capability of the UPS2)) in A 2,597

1) The UPS dat a corresponds to a L iebert® Trin ergy™ Cube of Ver tiv™ with an appa rent power of 1,200kVA

2) Informat ion of Vertiv™: 150 % ove rload at rated ou tput voltage for 1 m in

3,877

5. Critical issues regarding the integration of UPS systems in power supply networks

Regardless of the simulation of a UPS in SIMARIS design, the following issues must be especially observed when integrating UPS systems in power supply networks:

• Faults on the SDUPS are critical and must be avoided

preventively – using high-quality components (busbar

trunking systems including design verified connection; SIVACONS8 in rootless design, ...)

• In inverter operation, faults on the SDUPS can be a problem for switching off according to IEC60364-4-41 (DINVDE0100 Part410) if the fault currents are almost as high as the rated currents. In case of 1-pole faults to earth, high-quality circuit-breakers with G releases (e.g. Siemens 3WL circuit-breakers with ETU45B, ETU76B and 3VA circuit-breakers with ETU550/560, ETU 850/860) can

be the solution

• When switching off according to IEC60364-4-43

(DINVDE0100 Part430) and in order to implement

selectivity, it is advisable – due to the UPS short-circuit behavior – to limit the rated currents of the switching

devices in the outgoing feeders of the SDUPS to 30% of

the UPS rated output current

6. Sample file for SIMARIS design

• For low-range UPS systems (<100kVA), RCDs can be used for 1-pole faults to earth. In case of unfavorable design of the SDUPS, an optimized calculation of the

minimum short-circuit currents under consideration of the regular UPS behavior can be an advantage for the design

• In case of short circuit at the UPS output, the permissible load of the static bypass must be compared with the information of the UPS manufacturer

• If the UPS manufacturer uses a a semiconductor fuse for protecting the static bypass, this must be observed in the selectivity considerations

• When integrating the UPS systems in a TN-S system, the central earthing point and the number of poles of the switching devices (3- or 4-pole) must be defined, among others

• In case of UPS systems connected in parallel, a fault analysis in the downstream distribution network can

reveal a possible additional protection requirement.

Enclosed with the document you will find the SIMARIS

design model network (.sdx) with a static UPS system for integration in your own projects. The file has been created with SIMARIS design10.

Further information as well as the SIMARIS suite, which allows you to access planning tools such as SIMARIS design 10, can be found at

siemens.com/simaris.

Page 10

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Published by: Siemens AG

Smart Infrastructure Distribution Systems

Mozartstr. 31 c 91052 Erlangen, Germany

E-mail: [email protected]

For the U.S. published by Siemens Industry Inc.

100 Technology Drive Alpharetta, GA 30005

United States

Subject to changes and errors. The information given in this document only contains general descriptions and/or perfor-

mance features which may not always specifically reflect those described, or which may undergo modification in the

course of further development of the products. The

requested performance features are binding only when

they are expressly agreed upon in the concluded contract.

SIMARIS® is a registered trademark of Siemens AG. Any

unauthorized use is prohibited. All other designations in

this document may represent trademarks whose use by third parties for their own purposes may violate the proprie-

tary rights of the owner.