019_generator (ups good)

GE Digital Energy Power Quality

UPS Application Guide Digital Energy Uninterruptible Power Supply

19 EMERGENCY GENERATOR 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

www.gedigitalenergy.com

Modifications reserved EMERGENCY GENERATOR V1.0 - Page 2/7

APG_019_GENERAT_XGB_V010.pdf UPS Application Guide

Title: EMERGENCY GENERATOR

Date of issue: November 2008

File name: APG_019_GENERAT_XGB_V010

Version: 1.0 Up-dating

Revision Concerns Date

Table of contents Page

19 EMERGENCY GENERATOR ........................................................................................................................................................... 1 19.1 INTRODUCTION......................................................................................................................................................................................3 19.2 UPS AND EMERGENCY GENERATOR.............................................................................................................................................4 19.3 LOAD STEP................................................................................................................................................................................................4 19.4 FREQUENCY SYNCHRONIZATION...................................................................................................................................................4 19.5 BATTERY CHARGING............................................................................................................................................................................4 19.6 SUMMARIZING........................................................................................................................................................................................4 19.7 GENERATOR SIZING .............................................................................................................................................................................5

19.7.1 Genset sizing example 1 (SG Series S1 Thyristor rect.) ........................................................................................................ 5 19.7.2 Genset sizing example 2 (SG Series S1 IGBT rect.) ................................................................................................................ 6 19.7.3 Genset sizing example 3 (SP500kVA vs SP500kVA with DCU) .......................................................................................... 6 19.7.4 Example UPS sizing ............................................................................................................................................................................. 7

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.

19.1 INTRODUCTION

In many installations an engine generator set is used to supply either non-critical load and/or UPS system. In this case the required batterys back-up time, in the event of a mains outage, could be only few minutes. There is no general rule, but a minimal backup time should be ca. 10 minutes in order to allow, even manual, start of the EG. The solution with an EG will reduce the investment in large batteries, nevertheless, a careful analysis of the specific characteristics of the installation it is recommendable in order to have the best price/reliability compromise and to eliminate possible problems that could arise when a UPS and an engine generator are put together in a system. An Emergency Generator (EG) can be considered as a separated electrical energy source, which does not comply with standard rules EN/IEC 61000-2-4. Furthermore we are confronted with the case where the Mains has an high impedance and a relatively low short circuit power. The output voltage of an EG depends on voltage regulation system of its alternator, which senses the output voltage and compares the value with a reference value. If the load applied to an EG generate a distortion, this would effect the voltage regulators. The current harmonics, generated by non linear loads, flowing in the line impedance generates voltage harmonics, which added to the fundamental wave, generates the voltage distortion. From this consideration it is evident that all non linear loads, like the UPSs Rectifier, or SMPS which can have a high harmonics distortion can cause serious EG operating problems like instability in the EG regulation and overheating in the EG alternator windings. Attention should be paid to the Sub-transient reactance (Xd) of the EG; its value varies between 10% and 30%, depending of EG type. It is convenient to operate with EG which have the lowest possible Xd-value, since the voltage distortion caused by current harmonics depends directly on this value. It follows that in order to maintain the voltage distortion low, it is necessary that: a)-THD (Total Harmonics Distortion) currents generated by non linear loads shall be low. b)-The sub transient reactance Xd of the EG should be < 15%. (For good EG is 8 to 12%) If points a) and b) are not satisfied the possibility to reduce the voltage distortion will be by over-sizing the EG, so that it is only partly utilized.

Xd



19.2 UPS AND EMERGENCY GENERATOR

If in the electrical installation an EG is used to supply a UPS, this could give rise problems which do not arise when they are installed separately. When there are problems becomes difficult to establish which of the two is the case. UPS manufacturer may say the UPS system is working perfectly and the problem is the EG. The EG manufacturer may say in turn that the problem is related to the loads and there is nothing that can be done with the EG. The ability of a UPS and an EG to operate properly together, requires special consideration concerning their compatibility. GEs long standing experience, have identified the following common problems and relative solutions when interfacing UPS and EG. As previously mentioned, UPSs Rectifiers generate current harmonics, which flowing through the line and EG impedances will cause voltage distortion.

19.3 LOAD STEP

When the EG is on, the instantaneous application of the load to the EG, result in high inrush currents which can cause voltage and frequency swings. To avoid such problems, GEs UPS has a soft start system so that the power draw from the UPSs Rectifier can gradually be applied to the EG. The power walk in is ca. 30 sec.

19.4 FREQUENCY SYNCHRONIZATION

EG have a limitation on how closely and how fast they can control frequency response due to sudden changing loads. On the other hand the frequency tolerance to synchronize to bypass, so that the critical load can be transferred to EG, can be much tighter. The result would be a continuous alarm: UPS not synchronized. Therefore a UPS system shall have the possibility to block the synchronization, modify the Slew Rate and/or to enlarge the synchronization window if the critical load would accept a wider frequency tolerance.

19.5 BATTERY CHARGING

The electrical energy produced by an EG is expensive. In UPS systems with large battery, it would be worth to recharge the battery whit the electrical mains. Therefore the UPS shall have the possibility to block the batterys charging when the Rectifier draw energy from an EG.

19.6 SUMMARIZING

In a system which includes UPS and EG a careful analysis should be made considering the electrical installation and the equipments compatibility. 1) UPS might have:

a) Soft start system. b) Different solutions to reduce the harmonics. c) Possibility, via bypass, to block the synchronization with EG. d) Possibility to automatically adapt the frequency slew rate. e) Possibility to block the recharging of the battery.

2) EG might have :

a) Power rating able to supply the UPS, other loads and a certain power reserve b) Small sub transient (

3) Cables might be sized considering currents harmonics and if the cables length is significant a voltage drops of 5% should be considered for the EG output nominal voltage. 4) For large installation must also to verify whether compensating power factor capacitors are installed. These capacitors form a resonant circuit with the mains a resonant circuit with one or more harmonics generating a distortion.

19.7 GENERATOR SIZING

The following information are useful to determine the size of an EG by means of its sub transient reactance Xd, the acceptable voltage distortion d and Rectifier input power. (Rectifier input power is ca. 10% more than UPS nominal power) Note: Norm EC/IEC 61000-2-2 allowed max. 8% THD voltage distortion. However, it is advisable to contact the EG supplier for the compatibility of the EG and the UPS system and other loads, if any, if the size of the EG is less than 2 times the applicable loads. A simplify and indicative formula to calculate the size of a GenSet is the following. PG = PR * C * Xd / d where - PG GenSet power; - PR Rectifier input power; - Xd GenSet sub-transient reactance; - d acceptable THDv voltage distortion at GenSet terminals; - C constant, which value depends from the number of rectifier pulses and the total line impedance

of the electrical system. Extrapolate values: thyristor rectifier C= 1.3 to 1.6 Clean Input Module C= 0.8 to 1 Given the GenSet, the formula can be used to calculate the maximum UPS applicable PR = PG *d /(C * Xd) An indicative evaluation of GenSet size related to UPS rectifier power is as follows: 6-pulse rectifier PG = 2.5 ~ 3 times PR CIM Clean Input Module PG = 1.5 ~ 2 times PR 19.7.1 Genset sizing example 1 (SG Series S1 Thyristor rect.)

Project data UPS type SG-CE S1 thyristor rect. UPS nominal power 300kVA Rectifier input power factor PFrect = 0,8 UPS efficiency EffUPS = 93,3% Acceptable voltage distortion d = 8% GenSet sub-transient reactance Xd = 12%

GenSet sizing

Load power Sload = 300kVA Load power factor PFload = 0,8 Load active power Pload = Sload x PFload = 300 x 0,8 = 240kW Rectifier input active power Prect = Pload / EffUPS = 240 / 0,933 = 257,2 kW Rectifier input apparent power Srect = Prect / Pfrect = 257,2 / 0,80 = 321,5 kVA GenSet sizing 6 pulses rectifier configuration SGenSet = Srect x C x Xd / d = 319,1 x 1,5 x 0,12 / 0,08

= 723kVA GenSet oversize (related to UPS load) SGenSet / Sload = 723 / 300 = 2,4 240%



19.7.2 Genset sizing example 2 (SG Series S1 IGBT rect.)

Project data UPS type SG-CE S1 IGBT rect. UPS nominal power 300kVA Rectifier input power factor PFrect = 0,99 UPS efficiency EffUPS = 92,3% Acceptable voltage distortion d = 8% GenSet sub-transient reactance Xd = 12%

GenSet sizing

Load power Sload = 300kVA Load power factor PFload = 0,8 Load active power Pload = Sload x PFload = 300 x 0,8 = 240kW Rectifier input active power Prect = Pload / EffUPS = 240 / 0,923 = 260 kW Rectifier input apparent power Srect = Prect / Pfrect = 260 / 0,99 = 262,7 kVA GenSet sizing IGBT rectifier configuration SGenSet = Srect x C x Xd / d = 262,7 x 0,85 x 0,12 /

0,08 = 334,8kVA GenSet oversize (related to UPS load) SGenSet / Sload = 334,8 / 300 = 1,11 111% Note: SG-CE Series Clean Input Module configuration has a double benefit effect on GenSet sizing respect to a traditional thyristors rectifier:

- higher rectifier input power factor 0.99 (respect to 0.8) - lower harmonics contents, that means a C factor lower (0.8-1) respect to thyristor

rectifier (1.3-1.6)

19.7.3 Genset sizing example 3 (SP500kVA vs SP500kVA with DCU)

Project data UPS type SitePro 500kVA 12pulses rectifier UPS nominal power 500kVA Rectifier input power factor PFrect = 0,8 UPS efficiency EffUPS = 90,1% Acceptable voltage distortion d = 8% GenSet sub-transient reactance Xd = 12%

GenSet sizing

Load power Sload = 500kVA Load power factor PFload = 0,8 Load active power Pload = Sload x PFload = 500 x 0,8 = 400kW Rectifier input active power Prect = Pload / EffUPS = 400 / 0,901 = 444 kW Rectifier input apparent power Srect = Prect / Pfrect = 444 / 0,8 = 555 kVA GenSet sizing IGBT rectifier configuration SGenSet = Srect x C x Xd / d = 555 x 0,85 x 0,12 / 0,08

= 707,5kVA GenSet oversize (related to UPS load) SGenSet / Sload = 707,5 / 500 = 1,41 141%





UPS type SitePro 500kVA 12pulses rectifier with DCU UPS nominal power 500kVA Rectifier input power factor PFrect = 0,98 UPS efficiency EffUPS = 89,7% Acceptable voltage distortion d = 8% GenSet sub-transient reactance Xd = 12%

GenSet sizing

Load power Sload = 500kVA Load power factor PFload = 0,8 Load active power Pload = Sload x PFload = 500 x 0,8 = 400kW Rectifier input active power Prect = Pload / EffUPS = 400 / 0,897 = 445.9 kW Rectifier input apparent power Srect = Prect / Pfrect = 445,9 / 0,98 = 455 kVA GenSet sizing IGBT rectifier configuration SGenSet = Srect x C x Xd / d = 455 x 0,85 x 0,12 / 0,08

= 580,12kVA GenSet oversize (related to UPS load) SGenSet / Sload = 580,12 / 500 = 1,16 116% 19.7.4 Example UPS sizing

Project data GenSet nominal power 300kVA UPS efficiency 92% Acceptable voltage distorsion d = 8% GenSet sub-transient reactance Xd = 15% UPS sizing rectifier sizing 6 pulses rectifier configuration PR = PG x d / (C x Xd) = 300 x 0,08/(1,5 x 0,15) = 107 kVA UPSsize S=PR / efficiency = 107 / 0,92 = 116kVA SGSeries 120kVA rectifier sizing IGBT rectifier configuration PR = PG x d / (C x Xd) = 300 x 0,08/(0,9 x 0,15) = 178 kVA UPSsize S=PR / efficiency = 178 / 0,92 = 193kVA SGSeries 200kVA

19 EMERGENCY GENERATOR19.1 INTRODUCTION19.2 UPS AND EMERGENCY GENERATOR19.3 LOAD STEP19.4 FREQUENCY SYNCHRONIZATION19.5 BATTERY CHARGING19.6 SUMMARIZING19.7 GENERATOR SIZING19.7.1 Genset sizing example 1 (SG Series S1 Thyristor rect.)19.7.2 Genset sizing example 2 (SG Series S1 IGBT rect.) 19.7.3 Genset sizing example 3 (SP500kVA vs SP500kVA with DCU) 19.7.4 Example UPS sizing

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