UPS Systems

Question 1

What is a UPS used for?

Answer 1

Supply clean or conditioned power to critical loads

Question 2

What two electrical values must be provided by the ups for the output to be considered clean (conditioned) AC?

Why is it important?

Answer 2

Rated Voltage
Rated Frequency

To keep critical loads energized with clean or conditioned power

Question 3

List 3 major components of a ups system

Answer 3

Rectifier
Inverter
Battery

Question 4

What interconnects the three major components of an ups system?

Answer 4

DC link
Aka DC bus, DC rail

Question 5

What’s a Brown Out?

Answer 5

Reduced power status

Question 6

During normal mode what two functions does the rectifier serve

Answer 6

Charge batteries
Supply inverter

Question 7

What two conditions will put the ups in battery mode?

Answer 7

Blackout no utility
Brown out under voltage

Question 8

State the normal battery operating time in a UPS system (ILM).

Answer 8

5–30 minutes

Question 9

Is there a time delay going from normal mode to battery mode?

Answer 9

No time delay

Question 10

During “On Battery Mode” operation, is the output voltage considered clean voltage?

Answer 10

Yes, clean AC (anytime through inverter)

Question 11

How many primary and secondary windings are in each of the output transformers of the redundant UPS systems?

Answer 11

• Primary: 3
• Secondary: 1

Question 12

Why is a partially redundant system used in a UPS system?

Answer 12

Cheap

Question 13

Q2 and Q3 produce a ________ pulse voltage.

Answer 13

Negative

Question 14

How is the output voltage varied?

Answer 14

Vary on time

Question 15

What is each pulse voltage responsible for?

Answer 15

Instantaneous Voltage

Question 16

How is the instantaneous voltage calculated?

Answer 16

V source × (On time ÷ Pulse period)

Question 17

How is the pulse period calculated?

Answer 17

T = 1 ÷ 60 Hz = 16.66 ms

Question 18

What is the purpose of an inverter?

Answer 18

Change DC into AC (convert)

Question 19

What are three applications for inverters?

Answer 19

UPS
VFD
DC to DC converter

Question 20

What is the most common type of inverter?

Answer 20

Pulse Width Modulation (PWM)

Question 21

What is each pulse voltage responsible for?

Answer 21

Instantaneous Voltage

Question 22

An inverter is basically ______ solid state switches.

Answer 22

4

Question 23

What is the other name for a Bypass switch and what component configuration does it utilize?

Answer 23

Static switch or inverse parallel SCRs / anti-parallel SCRs

Question 24

Is the AC waveform distorted during the transfer to Bypass mode?

Answer 24

No

Question 25

During “By-pass Mode” operation, what is the important circuit before changing over to by-pass mode and what is the reason for it?

Answer 25

Synchronous check — to ensure changeover voltage is in phase

Question 26

In order for the changeover voltage to be synchronized, what four conditions must be met?

Answer 26

•Phase position •Phase sequence •Terminal voltage •Frequency

Question 27

What are the two types of By-Pass Mode and state their purpose?

Answer 27

• Automatic — system failure • Manual — maintenance

Question 28

What are the two types of By-Pass Mode and state their purpose?

Answer 28

• Automatic — system failure • Manual — maintenance

Question 29

Why is it important to use air filters?

Answer 29

To remove dust, thermal blanket, and static electricity

Question 30

What must be done in order to test the RECTIFIER section of a UPS?

Answer 30

Isolate the rectifier

Question 31

What must be done to test the INVERTER section of a UPS?

Answer 31

MUST BE TESTED LIVE

Question 32

What is a load test used for?

Answer 32

To test the capacity of the batteries

Question 33

The output rating should be at least ______ to meet the critical output demands?

Answer 33

1.25 (125%)

Question 34

Why is the maintenance bypass system a make-before-break system?

Answer 34

To ensure the first make happens before the second break (maintain continuity)

Question 35

Give some examples of auxiliary equipment.

Answer 35

Cooling fans, air filters, display monitors

Question 36

Why would there be more than one cooling fan?

Answer 36

Reliability

Question 37

What type of battery is used in a UPS system?

Answer 37

Lead acid • Sealed (5–10 year life) • Vented (10–15 year life)

Question 38

Lead acid batteries are broken into two groups. What are they and what are their life spans?

Answer 38

• Sealed: 5–10 years • Vented: 10–15 years

Question 39

What is the ideal temperature for a battery to operate?

Answer 39

20°C to 25°C

Question 40

When installing the DC portion of a UPS system what kind of disconnect device must be used? WHY?

Answer 40

2-pole, single throw • Disconnect both the positive and negative • Rated for DC

Question 41

The two copper bars that interconnect the UPS DC section are called what?

Answer 41

DC Link

Question 42

Installation of a UPS system can be broken into FOUR AREAS. What are they?

Answer 42

Inputs, outputs, DC, auxiliaries

Question 43

When determining the input branch circuit capacity, what two things must be considered?

Answer 43

Input amps, charge demand

Question 44

The UPS must be on a _______ circuit.

Answer 44

Dedicated

Question 45

T OR F The static switch will turn off when the gate pulse is removed

Answer 45

False