INTRODUCTION TO UNINTERRUPTIBLE POWER SUPPLY(UPS)SYSTEMS
GENERAL
The Emerson electric UPS equipment is designed to furnish a well regulated output voltage
with high frequency stability. The system is unaffected by variations in the mains supply and
, during periods of power failure, will continue to supply power for a period sufficient to allo
w an orderly shutdown of load equipment or start-up of standby generator.
Design concept
To allow the UPS equipment to continue to supply power after the mains supply has failed,
a standby power source is needed. This consist of a large battery of lead acid or nickel cadmi
um cells. These cells have a large discharge capability, rapid recharge rates and require little
maintenance.
As battery supply only Dc voltage, the circuit to the UPS must convert this to a three phase A
C sine wave voltage. The three phase sine wave input to the UPS must also be connected via
UPSS circuitry to the battery. The way in which this is achieved is shown in the simple block
diagrams.
UPS Block diagram description(figure2-1)
The three phase mains supply is connected to the UPS module. It is rectified by the r
ectifier section of the UPS module to 405v DC. The battery is connected in parallel wi
th the rectifier output and is charged at 405v DC float charge voltage.
The 405v DC bus is also applied to the inverter section which consists of three pairs o
f inverter phases converting the DC voltage into square waves at the correct frequen
cy, and at 120 apart to form three phases. The UPS output voltage is controlled by ad
justing the firing angle between the two inverters within a phase. The output of each
phase is connected to the filter section.
The filter section consists of a series conductor and the 5th and 7th harmonic traps wh
ich convert the outputs from the inverters into sine wave suitable for connection to t
he computer load.
UPS Block diagram description(figure2-2)
Should the mains supply fail, current is drowned from the battery to supply the converter se
ction which will continue until the battery is discharged.
Bypass Supply
To further improve reliability and facilitate ease of maintenance, a bypass system may be ins
talled. Figure 2-3 shows a typical installation. The UPS is shown connected to the mains supp
ly by means of CB1 (the “input” breaker) and connection between the UPS and critical load
made via CB2 (the “output” breaker). A third breaker (CB3) is shown connecting the mains s
upply directly onto the load-this is known as the “Bypass” supply.
N.B- The bypass supply need not necessarily be from the same source as the UPS unit, but
many come from a generator or other form of standby supply.
Normal operation is with CB1 and CB2 closed and CB3 open. Thus the UPS is continuously su
pplying the critical load and maintaining a float charge 405v on the battery. If the UPS devel
ops a major fault, its controlled circuitry will open CB2 and close CB3, transferring the critica
l load to the bypass supply. Transfer between UPS and bypass is also possible under manual
control to facilitate maintenance of the UPS module. N.B-When operating on bypass, the UP
S module is not completely isolated.
LETHAL VOLTAGE STILL EXIST WITHIN THE CABINET- Refer to the safety instructions (sectio
n1)and the main circuit schematic diagrams.
It should be noted that if both CB2 and CB3 are energized simultaneously, the UPS module is
connected in parallel with the bypass supply. This condition will blow the series output fuse
s which presents damage to the module.
Static Bypass
When the module automatically transfers the load to bypass, CB2 is opened and CB3 is close
d. However, due to the mechanical nature of the circuit breakers, a slight delay is probably b
etween these two actions and a brief period will exist where both breakers are open and the
critical load unsupplied.
The static bypass overcomes the problem. The assembly of two SCR’s connected in parallel
across CB3 contacts, and whenever the UPS transfers the load to bypass, the SCR’s are turne
d on for a few seconds. These action effectively short circuits CB3 contacts during the transf
er period, and provides a true “no break’ supply to the critical load.
N.B- When manually transferring between CB2 and CB3, a slight overlap is incorporated into
the control circuit, making it unnecessary to operate the static bypass assembly.
UPS
PERSONNEL
It is recommended that eye protection be worn to prevent eye damage, should an electrical
ark by mishandling or severe electrical fault.
Replacements power components can be very heavy. If removal is required, use adequate m
echanical handling equipment.
Personnel should not work alone on any equipment when high voltage is present. A second
person should be standing by to assist, and help in case of an accident. This is particularly tr
ue when work is performed on the battery bunk.
CAUTION
Safety covers are designed to avoid the possibility of accident content with high voltages an
d do NOT render it impossible to make contact with high voltages if probing with fingers.
HORN TEST
EMERGENCY SHUTDOWN
NOTES
The state of the circuit breakers are indicated by LED’s:
GREEN=OPEN
RED=CLOSED
The static bypass isolator also has LED indicators:
RED=CLOSED .i.e. Static bypass available unless inhabited.
GREEN=OPEN OR Static Bypass Inhabited.
GREEN AND RED= although selected, the static bypass is inhabited.
It should be noted that RED switches, pushbuttons etc. will affect the system and should not
be operated, without careful consideration of their effect. (.i.e. CB1, CB2, PB1, PB2 etc.)
Block switches or pushbuttons perform monitoring function and can be operated without af
fecting the system.
The static bypass isolator should always be left ON during normal run.
Manual circuit breaker CB1 has three operational positions:
ON=indicated “I”
OFF=indicated ”O”
RESET=indicated “X”
The circuit breaker trips to the “RESET” position and must be turned to the OFF position figu
re before it can again be turned ON. It is impossible to turn a circuit breaker ON directly fro
m the RESET position.
Before starting the UPS, check that S9, static bypass isolator, is in the OFF position.
S1 selects the function of the meters M1, M2, M3 to monitor either input or output.
START-UP
Switch on power to UPS from distribution panel. Close S3-controls switch located behind mo
dule door:



Check CB1, CB2 and CBB have GREEN (open) indication.
Check input voltages on M2 are correct.
Check that the “CBB OPEN” alarm is indicated.
NOTE: CB3 may be open or closed, depending on its state when the module wass switched
OFF.
Close CB1 input circuit breaker.
The DC voltage will rise over approximately 15 seconds to 405v dc. When the DC is above 36
0v dc.the AC will rise to normal output voltage.
A. Check CB1 on mimic-Red (closed)
B. Check module output voltage for correct level and balance M1.
Close S9-Static bypass isolator.
Check that the mimic LED”s change from Green to Red OR Green and Red.
Close remote battery circuit breaker CBB.
A. Check CBB on mimic-Red (closed)
B. Check battery charge current-M5, to ascertain battery charge stage.
C. Reset battery circuit breaker alarm.
LOADING 1-CB2 AND CB3 OPEN








Close CB3 using transfer switch S8
Observe CB3 mimic diagram LED’s charge from Green to Red.
Loads may now be switched ON-see note 1.
To receive a smooth transfer when changing from CB3 (bypass) to CB2 (UPS) set UPS
volts above bypass volts where possible 10v above bypass on 415v or 380v output
UPS.
Operate transfer switch S8 to UPS to close CB2- see note 2.
Observe CB2 mimic diagram LED’s change from Red to Green.
Slowly adjust UPS output voltage to required nominal value.
Switch on load if not switched on at 12.
LOADING 2-CB3 CLOSED, LOAD ON BYPASS
Operate transfer switch to bypass. This will have n o visible effect but will reset UPS circuit b
reaker logic.
Wait at least 10 seconds and then follow procedure 2.3.3 to 2.3.8
TRANSFER OF LOAD UPS TO BYPASS
To achieve a smooth transfer from UPS to bypass, check that the UPS volts and bypass volts
are matched.
Operate transfer switch S8 to bypass, observe CB3 mimic diagram LED’s change from Green
to Red and CB2 LED’s change from Red to Green.
SHUTDOWN
A. Transfer load to bypass the following above procedure.
B. Switch OFF module using the following procedure.




Press CBB trip pushbutton on module mimic.
Turn CB1 to OFF(‘o’)
Turn OFF S3-control switch
Turn OFF S9- static bypass isolator.
NOTE 1
Where large amounts of reactive load are to be switched, it may be advantageous to connec
t them while on the bypass supply.
NOTE 2
There is a 10 second delay period after operating either CB2 or CB3, during it is impossible t
o manually close the other breaker.
EMERGENCY STOP
Pressing the emergency stop pushbutton will completely shut down the UPS, opening all circ
uit breakers.