Uninterruptable Power Supply Systems Flashcards

1
Q

Many electrical and electronic devices are considered essential to human activities. These devices are called:

A

Critical Loads

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2
Q

Three key components in a basic UPS system:

A

The rectifier
The battery
The inverter

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3
Q

UPS System failures are typically due to what three common causes?

A

Overloading
High temperature
Faulty Inverter

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4
Q

What is often done to accomplish higher reliability in supplying power to critical loads?

A

Two independent UPS’s are used - a redundant system

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5
Q

Static switches, sometimes called solid state switches can operate in Nano seconds. T or F?

A

False. They can operate in microseconds

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6
Q

Each solid state contact of a static switch has what devices?

A

Two thyristors in anti-parallel (reverse paralell) configuration
Basically two SCR’s

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7
Q

What shape waveform does an inverter produce?

A

Square waveform

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8
Q

Name the three common switches associated with a PWM Inverter:
Which is the default?

A

SCR’s, IGBT’s, BJT’s

Default is IGBT’s

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9
Q

A PWM Inverter produces a true sinusodial waveform. T or F?

A

False. It isn’t a true sinusodial

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10
Q

The installation of a UPS system can be divided into what four areas?

A

Inputs
DC
Outputs
Auxiliaries

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11
Q

Batteries of a UPS can be lead acid or nickel cadmium type. T or F?

A

False. Can only be lead acid, N.C are not used because they require constant charging and discharging to maintain rated capacity.

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12
Q

As a good practice, you must ensure that the inverter or UPS system output rating is at least ____ % of the maximum critical load demand.

A

125%

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13
Q

To help prevent short circuits within an Output of an UPS, you should install a high degree of what sort of protection on the critical load wiring?

A

Mechanical.
Ex: installing cables in conduits

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14
Q

The maintenance bypass switch assembly is made up of three circuit breakers labelled what?

A

MB -Maintenance Bypass
UIP- UPS Input
UOP - UPS Output

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15
Q

Cool ambient air enters through the bottom of a UPS. T or F?

A

False. Its the lower part of the UPS air enters from

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16
Q

Why would a UPS have more than one cooling fan installed?

A

For redundancy, designed for quick replacement without UPS system shutdown.

17
Q

What would an additional UPS display panel be used to indicate?

A

Alarms such as high temperature and imminent shutdown warning

18
Q

What does a higher ambient temperature do to battery cells? And what does a lower ambient temperature do to battery cells?

A

Higher - rapid chemical deterioration
Lower - reduces battery output capacity

19
Q

A sealed cell battery has how many years of servicable life?

A

5 to 10
A vented cell battery has more at 10-15.

20
Q

What guideline should be followed when doing maintenance on an UPS printed circuit board?

A

Use an anti-static wristband

21
Q

What are the three seperate tests of a load transfer test on a UPS system?

A

Manual transfer test
Simulate a failure in the inverter test
Overload through a dummy load

22
Q

What sections of a UPS cannot be operated alone for testing purposes?

A

Inverter
Bypass Switch

23
Q

A static switch has two SCRS connected in anti-parallel. T or F?

A

True

24
Q

All four solid state switches of an inverter on at the same time would equal:

A

A short circuit condition.

25
Q

The best method to identify a failed solid state power device is by comparing the dc voltage between the ___________ & ___________ terminals.

A

Anode & Cathode

26
Q

True or False:
In 3-phase UPS systems, all line and phase voltages are balanced

A

True

27
Q

What is another name for a static switch?

A

Solid state switch or By-pass

28
Q

True or False:
There is a noticeable distortion in the waveform during a load transfer of a UPS.

A

False, though there is a slight distortion at the instant of transfer, it is considered to be negligible.

29
Q

How many solid state switches are in a basic single-phase PWM inverter? And how are the switches connected?

A

There are 4, and they are connected in two parallel “totem pole” configurations (basically the same configuration as a bridge rectifier)

30
Q

How do you calculate instantaneous voltage of a sine wave?

A

V ᵢₙₛₜₐₙₜₐₙₑₒᵤₛ = Vₚₑₐₖ x sin θ

31
Q

How do you determine the average voltage of single point of a PWM waveform?

A

Vavg = Vpeak x (time on/(time on+time off))