015 transformers types

GE Digital Energy Power Quality

UPS Application Guide Digital Energy™ Uninterruptible Power Supply

15 TRANSFORMERS GE Consumer & Industrial

General Electric Company CH – 6595 Riazzino (Locarno) Switzerland T +41 (0)91 / 850 51 51 F +41 (0)91 / 850 51 44

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Modifications reserved Transformers – V1.0 - /9

APG_015_TRANSFOR_XGB_V010.pdf UPS Application Guide

Title: Transformers

Date of issue: November 2008

File name: APG_015_TRANSFOR_XGB_V010

Version: 1.0 Up-dating

Revision Concerns Date

Table of contents Page

15 Transformers..................................................................................................................................................................................... 1 15.1 INPUT ISOLATION TRANSFORMER.................................................................................................................................................3 15.2 TRANSFORMERS TYPE.........................................................................................................................................................................3 15.3 INPUT RECTIFIER ISOLATION TRANSFORMER...........................................................................................................................4 15.4 INPUT BYPASS ISOLATION TRANSFORMER................................................................................................................................5 15.5 INPUT BYPASS TRANSFORMER WITH EXTERNAL MAINTENANCE BYPASS ..................................................................6 15.6 AUTOTRANSFORMER...........................................................................................................................................................................7 15.7 BI-MONO TRANSFORMER..................................................................................................................................................................7 15.8 K-FACTOR .................................................................................................................................................................................................8

COPYRIGHT © 2008 by GE Consumer & Industrial

Data subject to change without prior notice. All brands and product names are Trademarks or Registered Trademarks of their respective owners. Reproduction only upon written consent by GE.



15.1 INPUT ISOLATION TRANSFORMER

Typically a UPS system is directly connected to the Input Mains. In some applications a galvanic separation between the UPS and the Input Mains or a dedicated grounding system for the UPS and its loads is required. In these cases an input isolation transformer on the UPS rectifier or bypass Input Mains shall be installed. This document shows the different transformers topology used, the possible configurations and the relative features.

15.2 TRANSFORMER TYPES

Three different transformer types, characterized by wiring connections, can realize the UPS galvanic separation. The tables here below show the different characteristics of the used type and relative applications: Type Symbol Wiring connections Voltage

displacement Characteristics

Dyn11 30°

L1,L2,L3 l1,l2,l3

L1

L2

L3

l1

l2

l3

n

30°

L1

l1

l2 L2

l3

L3

30 electrical degrees phase shift between primary and secondary wiring neutral on secondary wiring

Dd0 0°

L1,L2,L3 l1,l2,l3

L3

L2

L1

l3

l2

l1

L3 L2

L1

l2

l1

l3

0 electrical degrees phase shift between primary and secondary wiring

Dzn0 0°

L1,L2,L3 l1,l2,l3

l3

n

l2

l1L1

L3

L2

L3 L2

L1

l2

l1

l3

0 electrical degrees phase shift between primary and secondary wiring neutral on secondary wiring

Table 2-1 Transformers typology

Type Bypass input isolation transformer

Rectifier input isolation transformer

Dyn11 X X with neutral not connected

Dd0 - X

Dzn0 X X

with neutral not connected (solution not practically used)

Table 2-2 Transformers typology applications



15.3 INPUT RECTIFIER ISOLATION TRANSFORMER

NEUTRAL

INPUTMAINS

Lk

RECTIFIER

BATTERY

NEUTRAL

UPS

SSM

L1/L2/L3

POWERDISTRIBUTION

UNIT

INVERTERTRANSFORMER

RECTIFIERISOLATION

Fig. 3-1 Electrical configuration

Configuration The isolation transformer is installed upstream the UPS rectifier between the rectifier and the Input Mains; the transformer neutral shall be not ground (earth) connected. This configuration is also used with UPS in RPA (Redundant Parallel Configuration), to realize a phase shift displacement between/among the different UPS, to reduce the rectifier harmonic effects. Applications For safety reasons. To realize a galvanic separation between the Input Mains and the UPS rectifier. This configuration is typically used with PB battery (not VRLA) that require periodical check by service engineers who operate directly on the battery (e.g. filling in electrolyte in battery blocks or checking the electrolyte density). For more details please refer to fig. 3-2 and 3-3. Efficiency effect The total UPS efficiency is affected by the transformer of about 1÷2% .

INPUT MAINS

INPUT MAINSTRANSFORMER

CURRENT FLOWING THROUGH HUMAN BODY

RECTIFIER BRIDGE

BATTERY

INVERTER BRIDGE

INVERTER BRIDGERECTIFIER BRIDGE

TRANSFORMERINPUT ISOLATION

BATTERY

INPUT MAINS

GALVANICALLY SEPARATED FROM INPUT M

GALVANIC SEPARTIONBETWEEN INPUT MAINS

AND UPS RECTIFIER

TRANSFORMERINPUT MAINS

Fig. 3-2 UPS without input rectifier isolation transformer Fig. 3-3 UPS with input rectifier isolation transformer



15.4 INPUT BYPASS ISOLATION TRANSFORMER

MAINS

INPUT

UPS

Lk

RECTIFIER

BATTERY

SSM

+30°

NEUTRAL

PE (GROUND)

NEUTRAL

L1/L2/L3

BYPASSISOLATION

TRANSFORMER

POWERDISTRIBUTION

UNIT

INVERTER

Dyn11

current flowing in normal mode operation

current flowing in bypass mode operation

Fig. 4-1 Electrical configuration

Configuration Configuration realized by a transformer installed on the UPS bypass input. Two different transformers can be used:

• Dyn11 (30 el. degr. phase shift) for the applications where the transformer phase-shift has no influence on the UPS output. Standard configuration.

• Dzn0 (0 el. degr. phase shift) where an UPS input/output electrical phase shift is not allowed. Solution more expensive than the previous one, due to the zig-zag transformer winding. This configuration is used when an external maintenance bypass is installed, to avoid phase shift with the UPS bypass

Applications • For a local grounding arrangement, in order to realize the neutral wiring for the UPS and its

loads, different from the one available on the Input Mains. This is the case where the UPS Input Mains is distributed without neutral (3 wire + ground) or where the replacement of the existing neutral conductor with a larger one could be problematic or costly.

• to avoid the propagation of the UPS loads current upstream the UPS on the Input Mains, even when the UPS is running in bypass mode. In fact with the UPS in normal mode, with the loads supplied by the UPS inverter, the current is limited to the inverter transformer without any propagation on the Input Mains distribution (refer also to the fig. 4-1). When the UPS is running in bypass mode the load current is spread on the UPS input electrical distribution; this can cause problems on other load there installed specially when the UPS supply non-linear loads with high harmonics contents or with high unbalanced loads (with high 3rd and multiple harmonic contents specially on the neutral conductor).

Efficiency effect The introduction of a transformer on the bypass line has no influence on the UPS efficiency because not part of the UPS normal mode power conversion operation.



15.5 INPUT BYPASS TRANSFORMER WITH EXTERNAL MAINTENANCE BYPASS

NEUTRAL

INPUT

MAINS

0°

Lk

RECTIFIER

BATTERY

NEUTRAL

UPS

SSM

L1/L2/L3

POWER

EXTERNAL MAINTENANCE BYPASS

Dzn0

DISTRIBUTION

UNIT

INVERTER

TRANSFORMER

BYPASSISOLATION

PE (GROUND)

Fig. 4.1-1 Example of input bypass transformer with external maintenance bypass

In some UPS applications an external maintenance bypass for UPS and bypass transformer is required for maintenance reason or to allow the possibility to remove the UPS maintaining the loads active. With this configuration it must be taken into account to have no phase shift between the UPS and the external maintenance bypass circuits. If a bypass isolation transformer is required, it shall be realized by a Dzn0 (Delta zig-zag with 0 el. degr. phase shift). Special attention has to be given if a differential protection relay is installed upstream the UPS; this can have false trip if the grounding connection between the “Input Mains transformer” and the “Input isolation transformer” is not realized properly.

15.6 AUTOTRANSFORMER

Adding an autotransformer it is possible to adapt the input and (or) the output UPS voltage. The use of this one at the ups input is allow only if the neutral is available. Contrarily a Dyn transformer is mandatory. An Autotransformer is an electrical transformer with only one winding, thus there will be no galvanic separation. Because it requires both fewer windings and a smaller core, an autotransformer for power applications is typically lighter and cheaper than a two winding transformer.

15.7 BI-MONO TRANSFORMER

By using a bi/mono transformer is possible to supply a mono-phase load. The size of UPS will be 1,78 times the load applied. In fact: VAload mono /0,97 (ηtrasf.) /400V= Iphase-UPS

Iphase-UPS x 3 x 230V = Pmin-UPS

Anyway bypass is always available and only two phases will be loaded.

Example: Load (mono-phase) = 120kVA Iphase-UPS = 120kVA / 0,97 / 400V = 309A Pmin-UPS = 309A x 3 x 230 = 213kVA (213kVA / 120kVA = 1,78) Size UPS 213kVA Sgseries 250kVA

Note: It’s not allowed to use Bi/mono transformer with LP33 models.

mono phase load (kVA)

3 phase UPS (kVA)

additional cabinet (mm) 5 (max 5,5) 10 ---* 8 (max 8,2) 15 ---*

10 (max 11,2) 20 ---* 15 (max 16,8) 30 ---* 20 (max 22,5) 40 ---* 30 (max 33,7) 60 500 40 (max 44,9) 80 500 50 (max 56,2) 100 500 60 (max 67,4) 120 500 80 (max 89,9) 160 500

100 (max 112,3) 200 500 120 (max 140,4) 250 500 (SP 680) 160 (max 168,5) 300 850 (SP 680) 200 (max 224,7) 400 1100 250 (max 280,9) 500 1100

* additional cabinet for SP10/40kVA is not required ONLY if batteries are mounted in separate cabinet. In this case the transformer will be mounted in UPS battery cavity, otherwise a 500mm cabinet will be used. It’s possible to have in SP10/40kVA battery cavity both the transformer and the 5th harmonic filter, but an additional cooling kit is required (art. n° 12038).



15.8 K-FACTOR

K-Factor is a weighting of the harmonic load currents according to their effects on transformer heating, as derived from ANSI/IEEE C57.110 and K-Factor ratings are described in UL1561(5). A K-Factor of 1.0 indicates a linear load (no harmonics). The higher the K-Factor, the greater the harmonic heating effects:

∑=− hIhFactorK 22)(

∑ = 0.1)( 2Ih

where Ih is the load current at harmonic h, expressed in A per-unit basis such that the total RMS current equals one Amp, i.e.,

One problem associated with K-Factor calculation is the selection of the harmonic frequencies range. Someone use up to the 15th harmonic, someone else up to the 25th harmonic, others up to the 50th harmonic. For the same load, each of these calculations can yield significantly different K-Factors because even very small current levels associated with the higher harmonics, when multiplied by the harmonic number squared (e.g., 502 = 2500), may change significantly the result. Based on the underlying assumptions of C57.110, it seems reasonable to limit the K-Factor calculation to harmonic currents up to the 25th harmonic.

Factor transformers differ from standard transformers. They have additional thermal capacity to tolerate the heating effects of the harmonic currents. Beyond that, well-designed K-Factor transformers will also minimize the winding eddy current losses through the use of parallel conductors and other winding techniques. The K-Factor indicates the multiple of the 60 Hz winding eddy current losses that the transformer can safely dissipate: Transformer load losses consist of winding I2R losses plus stray losses. Using UL1561 test methods, stray losses are assumed to be primarily winding eddy current losses for transformers 300 kVA and smaller. For example, a transformer having winding I2R losses of 2000 watts and 60 Hz stray losses of 100 watts would, with a K-20 rating, be required to dissipate the 2000 watts of I2R losses plus 20 times the 60 Hz stray losses of 100 watts for a total load loss of 4000 watts without exceeding the maximum winding temperature rise. The result is a larger, more expensive transformer.

Standardized K factors K-1 : resistive load (no harmonics) K-4 : THDi up to 26% K-9 : THDi up to 45% K-13 : THDi up to 58% K-20 : THDi up to 81% K-30 : THDi up to 124% K-40 : THDi up to 208%





Example: Input isolation transformer for SitePro

Taking into consideration that the input isolation transformer is used to feed the rectifier and that the harmonics spectrum is:

5th 25.8% 17th 1.8% 7th 7.4% 19th 2.1% 11th 5.9% 23th 1.0% 13th 4.1% 25th 0.9% we have that the K-factor is: K = 1*1 + 52x0.2582 + 72x0.0742 + 112x0.0592 + 132x0.0412 + 172x0.0182 + 192x0.0212 + 232x0.012 + 252*0.0092 = 4.09

015 transformers types

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