UPS

Question 1

What does UPS stand for?

Answer 1

Uninterruptible Power Supply

Question 2

What defines a critical load?

Answer 2

Electrical and electronic devices that are concodered essential to human activities.

Question 3

What property’s do Clean and Conditioned power follow?

Answer 3

-Voltage is purely sinusoidal
-voltage is with in a narrow range, with no significant over or under voltage
-frequency is within a narrow range, with no significant over or under frequency
-3phase systems, all line and phase voltages are balanced and symmetrical

Question 4

UPS have similar routes to what other electrical equipment?

Answer 4

Transformers, both are rated in kVA

Question 5

What does the kVA rating of a UPS mean?

Answer 5

Maximum amount of load that can be connected to the unit with out causing an overload condition.

Question 6

What are the 3 main components to a UPS?

Answer 6

Rectifier, Dc Storage battery, Inverter

Question 7

What does the Recitifer do in a UPS?

Answer 7

An electronic device that converts single-phase or three-phase voltage in to a DC power source

Symbol is on page 5 of UPS mod

Question 8

What is the purpose of the DC Storage battery?

Answer 8

-Electrochemical device tua5 can store DC energy produced by the rectifier.
-will output DC power from the batteries in the even of an outage for critical loads.

Question 9

What is the purpose of the inverter?

Answer 9

An electronic device thats capable of changing DC power source to single-phase or three-phase Ac voltage and current.

Question 10

What is the most important thing about supplying power to critical loads?

Answer 10

The power must be clean and conditioned.

Question 11

What is the normal operation of a UPS?

Answer 11

1.Rectifier converts AC to DC and sends it to the DClink
2. Dclink- charges up batteries and stores energy. Provides DC power to the Invertor
3. Inverter changes the DC in to clean and conditioned AC, and sends it to critical loads.

Question 12

What is On-Battery mode?

Answer 12

When the utility power cuts out, and the batteries must provide the required power.

Question 13

Is On-battery mode limited?

Answer 13

Yes, the operation is limited. Systems commonly range from 5-30 minutes.

Pending the amount of batteries and number of generators, it could be hours-days.

Question 14

Is a UPS “dead” once you disconnect AC power?

Answer 14

No, the batteries will still be providing power to the UPS.

Question 15

What can cause a UPS to fail?

Answer 15

-Overload of the UPS
-High Temperature
-Components of the rectifier or inverter can fail.

Question 16

If a UPS has a Failure, what happens?

Answer 16

If the UPS cant clear the problem by switching to On-battery mode. It will immediately initiate a shutdown.

Question 17

If a UPS fails, what happens?

Answer 17

The system will immediately use a Bypass switch to energize through the utility power.

The bypass switch is a separate component from the UPS.

Question 18

Bypass switches are normally connected to?

Answer 18

An output transformer, the transformer provides filtering and isolation, while ensuring voltage matches the requirements for the load.

Question 19

What is the synchronizing circuit?

Answer 19

That circuit that synchronizes the inverters output phase sequence with the phase sequence of the power source connected through the bypass switch.

Question 20

Is the voltage through a bypass switch clean and conditioned?

Answer 20

No

Question 21

What type of switch is used in a bypass switch?

Answer 21

Static switches or solid state switches

Question 22

Do static switches have moving parts?

Answer 22

No

Question 23

Is a state switch phase dependent?

Answer 23

No, they can be used in single-phase or three-phase systems.

Question 24

How are the static switches connected?

Answer 24

They are 2 SCRs connected in an Anti-parallel configuration

Question 25

What is one disadvantage of a redundant UPS system?

Answer 25

They normally share battery banks, to cut down on cost and maintenance. Which means during any battery maintenance or failure of the common battery bank. No stored dc is sent to the investors.

Question 26

What shapes can an inverter output a waveform?

Answer 26

-Square -Triangle -Sine

Question 27

What are 2 basic types on inverters?

Answer 27

-Fixed frequency -Fixed Voltage output.

Question 28

In today's day and age, can inverters be programmable?

Answer 28

Yes, with high speed computers output voltage and frequency can be programmed

Question 29

What are the programmable ranges of the output voltage and frequency of the inverter?

Answer 29

Voltage- 0v- Same as peak value Frequency- 0Hz- several hundred MHz

Question 30

In a VFD, what is the normal output frequency range?

Answer 30

0-120Hz

Question 31

What is Pulse width modulation?

Answer 31

The inverter converts dc voltage into usable ac voltage. 4 solid state switches are programmed to turn on and off in pairs. Allowing power to fllow for a very small time. This happens hundreds to thousands of times a second. Making a blocky wave form

Question 32

What type of switches are used in a PWM circuit?

Answer 32

-SCRs(silicon controlled rectifier) -BJTs(bipolar junction transistors) -IGBT(insulated gate bipolar transistors)

Question 33

What happens when all four switches are "on" at the same time?

Answer 33

A short-circuit condition

Question 34

What is Carrier Frequency?

Answer 34

The rate that those switch pulse turn on and off.

Question 35

How do we calculate a PWM output?

Answer 35

Output= time on/ total conducting time × source

Question 36

Does a PWM inverter produce a true sinusoidal voltage direction?

Answer 36

No

Question 37

Hiw does a PMW inverter produce a smooth sine wave?

Answer 37

Through filtration, consisting of Coils and capacitors. Transformers can also be used to smooth out the sine wave output.

Question 38

What are the 2 categories of batteries a UPS uses?

Answer 38

Sealed and Vented

Question 39

What battery is becoming more common for UPS systems and why?

Answer 39

Lithoum-ion batteries: -higher energy storage capacity -reduced maintenance requirements -longer operating life span.

Question 40

What should UPS systems be rated for?

Answer 40

125% or greater of maximum critical load demand

Question 41

When using Maintenance Bypass circuit breakers, its important to remember?

Answer 41

Make-before-break

Question 42

Human Machine Interfaces can display what?

Answer 42

-UPS statues -Alarm history -voltage and current inputs and outputs -allows users to change functionality modes of the ups during maintenance tasks

Question 43

What are 3 ways to test a UPS?

Answer 43

-manual operation check -battery discharge test -load transfer check

Question 44

How do you test the Rectifier unit of a UPS?

Answer 44

Isolate it from the DClink and inverter.

Question 45

How do you test the Inverter of a UPS?

Answer 45

Check to make sure the rectifier and DClink are working correctly. Then connect all three back together and check output voltage.

Question 46

How do you test the bypass switch?

Answer 46

Perform a manual transfer test. Press the control button to force a loaf test transfer for the UPS

Question 47

What is the most common battery for UPS systems?

Answer 47

Lead-acid: -vented 10-15 years -sealed 5-10 years Aging cells should be replaced if the original storage capacity has decreased to 50%

Question 48

What ar ethereal 4 factors that affect energy release in a DC arc flash?

Answer 48

-voltage -current -arc duration -distance from the arc fault