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22     Chapter 3  Installation Of Parallel System 

NXr UPS Module And Parallel System 30kVA ~ 200kVA    User Manual 

Chapter 3   

Installation Of Multiple UPS cubicles 

This chapter details the installation and wiring of a system containing more than one UPS cubicles installed in either 
parallel and / or dual bus configuration. 

3.1   Overview 

Up to four UPS units can be connected in parallel to form a parallel system. Further, single or parallel configurations 
can form systems with independent output buses (“dual bus systems”). The parallel and dual bus system installation 
shall be carried out according to the installation procedures contained in chapter 1 for the single UPS cubicle and to 
the applicable requirements of this chapter. 

 

In addition to the Emergency Power Off (EPO switch provided on the operator control and display panel of each UPS 
module for controlling the EPO of each module respectively, the parallel system also provides remote EPO function 
for controlling all UPS modules to shut down simultaneously from a remote terminal, as shown in Figure 3-1. 

Note 

1. The remote EPO switch must provide dry contact signal, which is normally open or closed. 
2. The open circuit voltage provided is 5Vdc, <20mA. 
3. The external EPO device can be composed of another control system which can disconnect the UPS mains supply or the 
bypass input. 
4. Pins 1 and 2 of the normally closed EPO-J10 port on the bypass module have been linked in factory.   

 

UPS 1

J10: 3
J10: 4

J10: 3
J10: 4

UPS 2

UPS 1

Bypass module

Bypass module

J10: 3
J10: 4

Bypass module

 

Figure 3-1    EPO circuit diagram (single and parallel UPS) 

3.2   1 + N Parallel System 

The basic installation steps of parallel system are the same as those of the single UPS cubicle. The following sections 
describe the differences between the parallel system installation and single UPS installation. 

Summary of Contents for Liebert NXr

Page 1: ...Liebert NX Liebert NXr 8VHU 0DQXDO ...

Page 2: ...rt Users may contact the nearest Emerson local sales office or service center Copyright 2010 by Emerson Network Power Co Ltd All rights reserved The contents in this document are subject to change without notice Emerson Network Power Co Ltd Address No 1 Kefa Rd Science Industry Park Nanshan District 518057 Shenzhen China Homepage www emersonnetworkpower com cn E mail support emersonnetwork com cn ...

Page 3: ...ment is started should be taken into account in the selection of instantaneous residual current circuit breakers RCCBs or residual current detector RCD devices Note also that the earth leakage currents of the load will be carried by the RCCBs or RCDs The equipment must be earthed in accordance with the local electrical authority codes of practices Warning backfeeding protection This UPS is fitted ...

Page 4: ...onnected together the battery terminal voltage exceeds 400vdc and is potentially leathal Battery manufacturers supply details of the necessary precautions to be observed in working on or in the vicinity of a large bank of battery cells These precautions should be followed implicitly at all times Particular attention should be paid to the recommendations concerning local environmental conditions an...

Page 5: ......

Page 6: ... DC Currents Maximum steady state AC and DC currents 6 1 6 2 Distance From Floor To Connection Point On The Equipment 7 1 6 3 Cable Connection 7 1 7 Control Cables And Communication 12 1 7 1 Input Dry Contact Port Battery Environment ventilation Ground fault Temperature 12 1 7 2 Battery Circuit Breaker BCB Port 13 1 7 3 Maintenance Switch And Output Switch State Port 13 1 7 4 Backfeed protection O...

Page 7: ...Operating Theory 28 4 1 2 Static bypass Transfer Switch 28 4 2 1 N Parallel System 29 4 2 1 Parallel System Features 29 4 2 2 Requirements For Paralleling Of UPS Modules 29 4 3 Operation Mode 29 4 3 1 Normal Mode 30 4 3 2 Battery Mode 30 4 3 3 Automatic Restart Mode 30 4 3 4 Bypass Mode 30 4 3 5 Maintenance Mode Manual Bypass 30 4 3 6 Parallel Redundancy Mode System Expansion 30 4 4 Battery Manage...

Page 8: ...ures For Completely Powering Down The UPS 45 6 5 Procedures For Completely Powering Down The UPS While Maintaining he Power Supply To The Load 45 6 6 Isolation Procedures Of One UPS In A Parallel System 45 6 7 Insertion Procedures Of One UPS In A Parallel System 46 6 8 Emergency Power Off EPO Procedures 46 6 9 Automatic Restart 46 6 10 UPS Reset Procedures 47 Chapter 7 Service 48 7 1 Service Proce...

Page 9: ...8 8 Efficiency Heat Losses And Air Exchange 54 Appendix 1 Option List 55 Appendix 2 List Of Abbreviations 56 ...

Page 10: ...l is shipped with details of its own mechanical and electrical installation information Note 3 phase 5 wire input power required The standard UPS can be connected to TN TT and IT AC distribution systems IEC60364 3 of 3 phase 5 wire A B C N PE Warning battery hazards 1 Take special care when working with the batteries associated with the UPS When the battery is connected the battery terminal voltag...

Page 11: ...nt temperature is a major factor in determining the battery capacity and life The nominal operating temperature of the battery is 20 C Operation above this temperature will reduce the battery life and operation below this temperature will reduce the battery capacity If the average operating temperature of the battery rises from 20ºC to 30ºC the service life of the battery will be reduced by 50 If ...

Page 12: ...abinet shall have enough lifting capacity For the UPS weight refer to Table 8 3 2 Ensure that adequate personnel and lifting aids are available when removing the shipping pallet Note Take special care when moving the battery cabinet fitted with batteries in which case the moving distance shall be minimized The UPS can be moved by means of a fork lift or similar equipment 1 4 3 Clearance As the UPS...

Page 13: ...nd Parallel System 30kVA 200kVA User Manual 600 1396 843 80 586 794 1397 476 645 445 102 35 15 A amplified view A 145 Anchor hole Front view Side view Top view Bottom view 1400 843 1400 800 100 Figure 1 1 30kVA 160kVA UPS installation dimensions unit mm 350 ...

Page 14: ...00 825 Figure 1 2 200kVA UPS installation dimensions unit mm 1 4 6 Cable Entry The UPS uses top cable entry and bottom cable entry 1 5 External protective device External circuit breakers or other protective devices must be fitted at the input AC supply of the UPS This section provides a general guide for qualified installation engineers The installation engineers should have the knowledge of the ...

Page 15: ...ciated battery are protected against the effect of overcurrents through a DC circuit breaker provided by the external battery cabinet The rated voltage of the external battery overcurrent protective device is more than 500Vdc and its DC breaking current is more than 8kA 1 5 3 UPS Output The UPS output distribution shall be configured with a protective device The protective device shall be differen...

Page 16: ... current Do not form coils so as to minimize the formation of electromagnetic interference 3 For terminal location refer to Figure 1 4 Figure 1 6 Warning Failure to follow adequate earthing procedures may result in electromagnetic interference or in hazards involving electric shock and fire 1 6 2 Distance From Floor To Connection Point On The Equipment Table 1 1 Distance from floor to connection p...

Page 17: ... DRV FB OL GND 12V BAT_OUT GND N BAT BAT Battery input 1 2 3 4 1 2 3 4 UPS output Main input Bypass input BAT EXT Figure 1 3 UPS electrical connection 1 Verify that the UPS equipment is isolated from its external power source and all the UPS power isolators are open Check that these supplies are electrically isolated and post any necessary warning signs to prevent their inadvertent operation 2 Ope...

Page 18: ...Chapter 1 Installation Of UPS Module 9 NXr UPS Module And Parallel System 30kVA 200kVA User Manual Figure 1 4 30kVA NXr 30K B UPS power terminals ...

Page 19: ...e 1 Main input mA mB mC mN 2 Bypass input bA bB bC mN 3 UPS output oA oB oC oN 4 Battery input BAT BAT BAT N 5 Earth PE Figure 1 5 30kVA NXr 30K 160kVA UPS power terminals mN mA mB mC oN bA bB bC oA oB oC N PE Note 1 Main input mA mB mC mN 2 Bypass input bA bB bC mN 3 UPS output oA oB oC oN 4 Battery input N 5 Earth PE Figure 1 6 200kVA UPS power terminals ...

Page 20: ...hase rotation Warning For split bypass operation ensure that the linking busbars between the bypass input and maiin input are removed The main input and bypass input must be referenced to the same neutral point System output connection 5 Connect the system output cables between the UPS output terminals oA oB oC oN and the critical load Refer to Table 1 1 for the torque Ensure correct phase rotatio...

Page 21: ...ables must be routed separately from the power cables and parallel cables double insulated and of a typical 0 5mm2 to 1 5mm2 CSA for maximum runs between 20m and 30m respectively 1 7 1 Input Dry Contact Port Battery Environment ventilation Ground fault Temperature The input dry contact ports J7 and J8 provide environmental and battery ground and temperature fault contacts The ports are shown in Fi...

Page 22: ...B J10 OL GND FB DRV Aux N O Aux N O J6 Aux_N O Aux_N O BCB Figure 1 10 Connection between BCB port and BCB 1 7 3 Maintenance Switch And Output Switch State Port J9 is the maintenance switch and output switch state port The port is shown in Figure 1 11 and described in Table 1 4 EXT S CAB S CAB S J9 EXT_Q3 IN_S GND EXT_OUT Figure 1 11 Maintenance switch and output switch state port Table 1 4 Descri...

Page 23: ...EPO Input Port The UPS has an EPO function that operates by a button on the operator control and display panel of the UPS or by a remote contact provided by the user The EPO switch is under a hinged plastic shield J10 is the remote EPO input port The port is shown in Figure 1 13 and described in Table 1 6 J10 12V EPO_NO 12V 12V EPO_NC Figure 1 13 Remote EPO input port Table 1 6 Description of remo...

Page 24: ...rvice ports J2 and J3 Parallel connection ports used for control of two or more NXr UPS cabinets operating in parallel J4 Load Bus Synch LBS interface used to synchronize the outputs of two NXr UPS systems operating in dual bus mode RS232 RS485 maintenance ports used for programming commissioning and investigation by service engineers ModBus Card p n IS 485L preferred location port 3 SNMP WebBrows...

Page 25: ... time that is the time during which the battery can maintain supply to the load in the event of a mains failure is subject to the ampere hour capacity of the battery To achieve the capacity required subject to recommendation from the battery manufacturer several battery strings may be connected in parallel Batteries of different brand model and age should nottbe used together Except for the NXr 30...

Page 26: ... to move and hoist the battery so as to prevent any damage to human being or the battery terminals Severe damage to the battery may cause fire 4 The battery terminals shall not be subject to any force such as the pulling force or twisting force of the cable Otherwise the internal connection of the battery may be damaged and severe damage may cause fire 5 The battery shall be installed and stored i...

Page 27: ...If the UPS and battery cabinet are installed side by side on a solid floor these cables can be led into the UPS cabinet through the cable entry holes on the lower part of the battery cabinet 2 When multiple battery strings are used they shall be connected in series and then in parallel Before applying load and power up be sure to measure the total voltage of the battery strings and make sure that ...

Page 28: ...son complies with the safety requirements of IEC 62040 1 2008 For the battery maintenance and maintenance precautions refer to the relevant manual provided by the battery manufacturer and observe applicable local regulation e g AS2676 1993 IEEE Std 1188 2005 Note 1 Periodically check the screws of the battery terminals for loose connection If there is any loose screw tighten it immediately 2 Check...

Page 29: ...ble Cross Sectional Area CSA Table 2 7 Reference table for selection of BCB rated current and connection cable CSA minimum recommended Note the minimum CSA is adequate for batteries located up to 5 meters from the UPS For longer cable runs the CSA shall be increased so that the voltage drop remains less than 1 in order not to affect the battery run time significantly Item Unit UPS rating kVA 30 40...

Page 30: ...y 4 pole BCB and UPS 3 wire at battery side Figure 2 6 below shows connections to be carried out when using the UV trip controlled BCB box containing a BCB and a BCB control board made by Emerson Network Power X104 X105 X106 OUT P OUT N AUX1 AUX2 X101 X108 X102 X103 X100 UV 220VDC BCB Battery 12V 12V BAT T BAT T GND GND2 USE GND1 AUX DRV OL GND FB DRV NC 12V OUT GND TPM2 N Temp sensor W3 W2 W3 BCB...

Page 31: ...isplay panel of each UPS module for controlling the EPO of each module respectively the parallel system also provides remote EPO function for controlling all UPS modules to shut down simultaneously from a remote terminal as shown in Figure 3 1 Note 1 The remote EPO switch must provide dry contact signal which is normally open or closed 2 The open circuit voltage provided is 5Vdc 20mA 3 The externa...

Page 32: ...es side by side and make connection as shown in Figure 3 2 The output distribution consisting of external UPS output switches and maintenance bypass must be installed as shown in Figure 3 2 to facilitate maintenance and system testing Figure 3 2 Typical 1 N system schematic diagram with common input separate battery and output bypass distribution cabinet ...

Page 33: ...allel systems designed for redundancy with 3 or more UPSs it is recommended to install bypass load sharing inductors to optimize current sharing during static bypass operation 2 For parallel systems designed for capacity with 2 or more UPSs it is recommended to install bypass load sharing inductors to optimize current sharing during static bypass operation 3 2 2 External protective device Refer to...

Page 34: ...xt Distribution panel To load Figure 3 4 Auxiliary control wiring 3 2 5 Parallel Control Cables Shielded and double insulated parallel control cables available in lengths 5m 10m and 15m must be interconnected in a ring configuration between the UPS modules as shown in Figure 3 5 The parallel ports J2 and J3 are provided on the front panel of the bypass module as shown in Figure 3 6 The ring connec...

Page 35: ... the output of the two independent UPS systems or parallel systems in synchronization One system is designated as the master the other is designated as the slave The operation modes of the parallel system comprise master and or slave operation in normal or bypass mode Place the UPS modules side by side and interconnect the UPS modules according to the following instructions 3 3 2 External protecti...

Page 36: ... NXr UPS Module And Parallel System 30kVA 200kVA User Manual UPS 1 Bypass module LBS cable UPS 3 UPS 4 J2 J3 J4 J2 J3 J4 J2 J3 J4 J2 J3 J4 Bypass module Bypass module Bypass module UPS 2 LBS cable Figure 3 8 Connection of typical dual bus system ...

Page 37: ...nverts that DC power from the rectifier or the DC power from the battery into AC power and provides the AC power to the load The battery supplies the load through the inverter in the event of a mains failure The mains source can also supply the load through the static bypass If UPS maintenance or repair is necessary the load can be transferred without power interruption to the maintenance bypass M...

Page 38: ...tting down or starting up UPS modules in a parallel system can be done in any sequence Transfers between normal and bypass modes of operation are synchronised and self recoverable for example following overloads and their clearance 3 The total load of the parallel system can be queried from each UPS module s LCD 4 2 2 Requirements For Paralleling Of UPS Modules A group of paralleled modules behave...

Page 39: ...on if the inverter fails is overloaded or turned off the static transfer switch will perform a transfer of the load from the inverter to the bypass source with no interruption in power to the load Should the inverter be asynchronous with the bypass the static transfer switch will perform a transfer of the load from the inverter to the bypass with interruption in power to the load This is to avoid ...

Page 40: ...exceed 20 of the rated UPS kVA capacity If the load is less than 20 the automatic discharge cannot be executed The periodic interval can be set from 30 to 360 days The battery self test can be disabled Conditions battery at float charge for at least 5h load equal to 20 80 of rated UPS capacity Trigger manually through the command of Battery Maintenance Test in LCD or automatically Battery maintena...

Page 41: ... 08 1 0 3 1 1 2 3 0 3 6 1 5 0 kV A 3X3 单机 在线 正 常 旁路输入 主路输入 相电压 V 相电流 A 频率 Hz 线电压 V 功率因数 A AB 220 20 5 50 1 380 0 99 B BC 220 20 5 50 1 380 0 99 C CA 220 20 5 50 1 380 0 99 主路空开闭合 01 12 手动开机 主路逆变供电 01 22 交流输出 单机在 线 NXr 15 0 kVA 1 6 2 1 1 7 交流输出 A AB B BC C CA 相电压 V 相电流 A 频率 Hz 线电压 V 功率因数 220 220 220 20 5 20 5 20 5 50 1 50 1 50 1 380 380 380 0 99 0 99 0 99 F1 F3 F4 F5 F2 Figure 5 1 Operator control ...

Page 42: ...e kinds of sound listed in Table 5 3 Table 5 3 Audible alarm description Alarm sound Meaning A short beep Any key on the operator control and display panel is pressed Beep every other second The UPS has a general alarm for example AC input failure Continuous beep The UPS has a serious fault for example fuse or hardware fault 5 1 3 Control Keys The operator control and display panel provides five c...

Page 43: ...onds as shown in Figure 5 2 F1 F3 F4 F5 F2 Figure 5 2 Start screen 5 2 2 Primary Screen After the UPS starts and finishes self test the primary screen appears as shown in Figure 5 3 The primary screen is divided into four windows system information window data window menu window and keypad window 1 Liebert NXr 150 kVA L1 N L2 L2 N L3 L3 N L1 L N voltage V OutPut 220 6 220 0 220 0 0 0 0 0 0 0 50 1 ...

Page 44: ... up or F4 down key to select the desired language 4 Press the F5 enter key to confirm 5 Press the F2 ESC key repeatedly to return to the Output menu At this point the LCD displays in the selected language 5 4 Changing The Current Date And Time Use the following procedures to change the system date and time 1 On the Output menu screen press the F3 left or F4 right key to select the Settings menu 2 ...

Page 45: ...ge V Phase voltage L N current A Pahse current Frequency Hz Output frequency L L voltage V Line voltage Power factor Power factor TX Output L N voltage V Phase voltage L L voltage V Line voltage Load Sout kVA Sout apparent power Pout kW Pout active power Qout kVAR Qout reactive power Load level Load expressed in percentage of the UPS rating load Crest factor Output current crest factor System Sout...

Page 46: ...bout five seconds later to show the test result Stop testing Manually stops a battery maintenance test battery capacity test or system test Freshening charge Manually initiates a battery freshening charge Stop freshening charge Manually stops a battery freshening charge Modem auto answer enabled Manually enable the modem s auto answer function Version UPS version Provides UPS inverter rectifier an...

Page 47: ... in rectifier shutdown Check the rectifier input voltage and frequency Batt Charger Fail The voltage of the battery charger is too high Control Power 1 Fail The UPS is operating but the control power is abnormal or not available Mains Phase Reversed The AC input phase rotation is reversed Rectifier Fault Internal fault of a power module is detected and results in rectifier shutdown and battery dis...

Page 48: ...erload times out Note that 1 The highest loaded phase will indicate overload time out first 2 When the timer is active then the alarm Unit Over load should also be active as the load is above the nominal rating 3 When the time has expired the load transfers to static bypass The inverter shuts down and will restart after 10 seconds 4 If the load decreases to lower than 95 after five minutes the sys...

Page 49: ...E ON OFF button pressed Bypass Mode The UPS is in bypass mode Normal Mode The UPS is in normal mode Battery Mode The UPS is in battery mode Source share mode The inverter is supplied by the battery and rectifier at the same time UPS Shutdown UPS shutdown with no output power BCB Open BCB status open BCB Close BCB status closed Batt Float Charging Battery status float charge mode Batt Boost Chargin...

Page 50: ...rm at any time Warning hazardous mains and or battery voltage present behind protective cover The components that can only be accessed by opening the protective cover with tools cannot be operated by user Only qualified service personnel are authorised to remove such covers 6 1 Power Switches The UPS provides a maintenance switch only silkscreen MAINTAIN CB as shown in Figure 6 1 to Figure 6 3 The...

Page 51: ...gure 6 2 Location of maintenance switch of 30kVA NXr 30K 160kVA UPS Maintenance switch Figure 6 3 Location of maintenance switch of 200kVA UPS 6 2 UPS Startup Procedures It is assumed that the installation is complete the system has been commissioned by authorized personnel and the external power isolators are closed ...

Page 52: ...goes solid green After system initialization the bypass STS is closed The UPS indicator states are as listed in Table 6 1 Table 6 1 UPS indicator state Indicator State Rectifier indicator Green Battery indicator Off Bypass indicator Green Inverter indicator Off Output indicator Green Status indicator Amber 2 Press and hold the INVERTER ON button for 2s The inverter starts up and the inverter indic...

Page 53: ...r the inverter enters normal operation the UPS is transferred from bypass mode to normal mode 6 3 4 Transfer From Normal Mode To Maintenance Mode These procedures transfer the load from the UPS inverter output to the maintenance bypass supply but the precondition is that the UPS is in normal mode Caution Before making this operation read the information on the LCD to make sure that the bypass supp...

Page 54: ...pen both a c input switches In a parallel system at this point other UPSs report Parallel Comm Fail which is normal Other UPSs continue to power the load through the inverter All of the indicators and the LCD on the front panel will extinguish as the mains driven internal power supplies decay 3 Open the external a c output switch of the UPS 6 5 Procedures For Completely Powering Down The UPS While...

Page 55: ...t switches 3 Press and hold the INVERTER ON button of the UPS for 2s The inverter starts up and the inverter indicator starts flashing in green color When the inverter is ready the UPS transfers to parallel operation with other UPSs and the inverter indicator goes to a continuous on state The UPS is in normal mode and the UPS indicator states are as listed in Table 6 3 Table 6 3 UPS indicator stat...

Page 56: ...ULT CLEAR button to let the system exit the shutdown state 2 When the rectifier begins to operate normally rectifier indicator in solid green press and hold the INVERTER ON button for 2s Note 1 The rectifier will start and the bypass will begin to power the load The rectifier indicator flashes while the rectifier is starting up When the rectifier enters normal operation about 30s later the rectifi...

Page 57: ...s and bypass module should be serviced 10 minutes after they are removed 7 1 2 Service Procedures Of Power Module Provided that the UPS is in normal mode and that the bypass is normal 1 If the available UPS power modules have redundancy proceed to step 2 if not press and hold the INVERTER OFF button on the operator control and display panel for two seconds to manually turn off the inverters and th...

Page 58: ...onfiguration it is required to close both external a c input switches Two minutes later the bypass indicator on the operator control and display panel turns on indicating the UPS is operating in bypass mode 8 Open the maintenance switch press and hold the INVERTER ON button on the operator control and display panel for two seconds to manually turn on the inverters and the UPS transfers to normal m...

Page 59: ...50 Chapter 7 Service NXr UPS Module And Parallel System 30kVA 200kVA User Manual Fixing screw Fixing bar Air filter Fixing bar Figure 7 2 Replacing air filter of 200kVA UPS ...

Page 60: ...S60950 electromagnetic emission and immunity IEC EN AS61000 series and construction IEC EN AS60146 series and 60529 8 2 Environmental Characteristics Table 8 2 Environmental characteristics Item Unit Rated power kVA 30 40 60 90 100 120 150 160 200 Noise within 1m in the front dB 56 58 60 62 66 Altitude m 1000 derate power by 1 per 100m between 1000m and 2000m Relative humidity RH 0 95 non condensi...

Page 61: ...ectrical Characteristics Intermediate DC Circuit Table 8 5 Battery Item Unit Rated power kVA 30 40 60 90 100 120 150 160 200 Battery bus voltage Vdc Nominal 360 VRLA float charge is 405V range 300 576 Quantity of lead acid cells Maximum 40 x 6 cell 12V blocks Minimum 30 x 6 cell 12V blocks Float voltage V cell VRLA 2 25 selectable from 2 2V cell to 2 3V cell Constant current and constant voltage c...

Page 62: ... 5 Slew rate max change rate of synchronisation frequency Hz s 1 setting range 0 1 3 single unit 0 2 parallel system Note 1 Factory set to 380V 400V or 415V selectable by commissioning engineer 2 Factory set to 50Hz 60Hz selectable by commissioning engineer 3 IEC 62040 3 1 4 58 crest factor 3 1 4 IEC 62040 3 also for 0 100 0 load transient Transient recovery time return to within 5 of steady state...

Page 63: ...r 2 Factory set to 50Hz 60Hz selectable by commissioning engineer 8 8 Efficiency Heat Losses And Air Exchange Table 8 8 Efficiency heat losses and air exchange Item Unit Rated power kVA 30 40 60 90 100 120 150 160 200 Overall efficiency Normal mode double conversion Up to 96 Inverter efficiency DC AC battery at nominal voltage 432Vdc and full rated linear load Battery mode Up to 96 Heat losses air...

Page 64: ...ellislot 3 Battery temperature sensor UF SENSOR 02350174 Air filter 21120752 One air filter LBS cable 5m 10m 15m 5m cable 04118683 10m cable 04118684 15m cable 04118685 Two cables should be selected to achieve redundancy Parallel control cable 5m 10m 15m 5m cable 04118683 10m cable 04118684 15m cable 04118685 Two cables should be selected to achieve redundancy Bypass load sharing inductor UF NRBYP...

Page 65: ...rent circuit breaker RCD Residual current detector RFI Radio frequency interference EOD End of discharge CSA Cross sectional area PE Protective Earth SCR Silicon controlled rectifier EPO Emergency power off MCCB Moulded case circuit breaker CT Center tap BCB Battery circuit breaker LBS Load bus synchronizer PWM Pulse width modulation DSP Full digital control STS Static transfer switch VRLA Valve r...

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