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Level 3 Electrical, BCIT > Three Phase Systems > Flashcards

Three Phase Systems Flashcards

(70 cards)

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1
Q

Why are three phase systems necessary?

A

For power distribution to larger systems, transmission, and generation

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2
Q

What is the main advantage of using a three phase system over a single phase system?

A

More constant power distribution

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3
Q

What are the three advantages of three phase systems compared to single phase systems?

A
  1. Less material than a single phase system
  2. Three phase motors are smaller and more simple
  3. Delivers more constant power distribution
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4
Q

Theee phase motors provide how much more HP than single phase motors?

A

About 150% more

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5
Q

Coils are ____% apart

A

120°

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6
Q

What is voltage measured across a single winding or phase called?

A

Phase voltage

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7
Q

What is voltage measured across the load side lines called?

A

Line voltage

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8
Q

How is the Wye system connected

A

By connecting lower subscripts together.

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9
Q

How is the delta system connected?

A

By connecting windings end to end to form a triangle

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10
Q

El is higher than Ep by a factor of root 3 in which system?

A

Wye

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11
Q

What is the formula for finding El in a Wye system?

A

El=Ep x root 3

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12
Q

El and Ep are equal in which system?

A

Delta

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13
Q

What is the formula for finding El in a Delta system?

A

El=Ep

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14
Q

In which system are Il and Ip equal?

A

Wye

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15
Q

In which system is Il higher than Ip by root 3?

A

Delta

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16
Q

What is the formula for finding Il in a Delta system?

A

Il=Ip x root 3

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17
Q

What is the formula for finding VAt on both Delta and Wye systems?

A

Vat=El x Il x root 3

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18
Q

What is the formula to find total power on both a Wye and Delta system?

A

TP = El x Il x root 3 x Power Factor

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19
Q

In a delta connected load, the line current lags the phase current by how many degrees?

A

30%

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20
Q

In a delta connected supply, line voltage leads phase voltage by 90° T or F?

A

False

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21
Q

What is the relationship between the current flow in all three line conductors and the current in the neutral conductor.

A

The neutral conductor only carries unbalanced current.

In = Ia + Ib + Ic

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22
Q

What are the four reasons for grounding the common point in a Wye connected system?

A
  1. Limit V to ground
  2. Facilitate O/C protection
  3. Lightning protection is improved
  4. Prevents floating neutral
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23
Q

What are the two methods to indicate a ground fault in an ungrounded system?

What is the code rule?

A

Audible, and visual. Buzzer/horn

10-106

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24
Q

How is voltage to ground different in the high leg compared to other line voltages to ground?

A

The high leg is larger by a factor of root 3

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25
What is the formula to find power out?
I^2 x R
26
When does VAt = Pt?
When PF is 100% or at unity
27
Difference between total circuit power and total output power?
Total circuit power is rated, total output is what is output.
28
If only one voltage is given, assume it is ____
Line voltage
29
Formula for impedence given resistance and pf
Zp= R/PF
30
What formula would you use to find total power delivered?
Pt = El x Il x root 3 x PF
31
How much more is a delta connected load kVA than a wye connected load?
The VAt of a delta connected load will be three times as much as a wye.
32
Total circuit power is phase or line power?
Phase
33
When an ohmmeter is placed across two windings of a Wye system, what will the resistance read?
The two resistances added inversely.
34
When an ohmmeter is placed across two windings of a Delta system, what will the resistance read?
Two of the resistances added inversely, plus the remaining resistance added in parallel *number system
35
What is motor FLA?
Full load amps. Current at rated load. Iline.
36
Watts is _____ power
True
37
VARs is ______ power
Reactive
38
VA is _____ power
Apparent
39
Do all Delta and Wye systems need to be grounded?
No, only 4 wires. Ground the neutral.
40
What is the purpose of grounding a delta or wye system?
1. Limit voltage to ground 2. Facilitate O/C protection 3. Maintain phase voltage 4. **Prevents floating neutral.**
41
In an equation, when only one voltage is provided, assume it is 1. Line or 2. Phase?
1. Line.
42
Ground fault indicating lights are connected in delta or wye configuration?
Wye
43
In a delta supply, if there is a ground fault, will loads still run?
Yes
44
In a wye supply, if there is a ground fault, will loads still run?
No
45
1 wattmeter method is used for measuring ____ circuits
Balanced
46
What is the formula for the 1 wattmeter method?
Pt = W1 x 3 All lines will have equal power in a balanced system.
47
The 3 wattmeter method is used for measuring ______ loads
Unbalanced
48
What is the formula for using the 3 wattmeter method?
Pt = W1 + W2 + W3
49
The 2 wattmeter method measures ____
Il and El per wattmeter
50
What is the formula for using the 2 wattmeter method?
Pt = W1 + W2
51
Which wattmeter method can be used to determine PF?
2 wattmeter method
52
When using the 2 wattmeter method, if one wattmeter kicks downscale, the PF is _____
Less than 50%
53
What happens in the 2 wattmeter method if PF is less than 50%?
One wattmeter will kick downscale
54
When using the 2 wattmeter method, if one wattmeter reads zero, the PF is _____
50%
55
What happens in the 2 wattmeter method if PF is equal to 50%?
One wattmeter will read zero
56
When using the 2 wattmeter method, if both wattmeters read positive, the PF is _____
Over 50%
57
What happens in the 2 wattmeter method if PF is over 50%?
Both wattmeters will read positive
58
What happens in the 2 wattmeter method if PF is equal to 100%?
Both wattmeters read equal positive values
59
When using the 2 wattmeter method, if both wattmeters read the same value, the PF is _____
100%
60
In a 3 phase 3 wire Wye connection, when there is an open in the line, VAt will be ____ of rated VAt?
1/2
61
In a 3 phase 3 wire Wye connection, when there is an open in the line, the circuit is considered to be doing what?
Single phasing
62
In a 3 phase 3 wire Wye connection, when there is an open in the phase, VAt will be ____ of rated VAt?
1/2
63
In a 3 phase 4 wire system, when there is an open in line or phase, power will be _____
2/3 of rated
64
What are three signs of a motor single phasing?
1. Motor will sound different 2. Motors may stall 3. Motor will not be able to start
65
What is a floating neutral?
When neutral connection or ground connection becomes open.
66
In a delta 3 phase 3 wire system, when there is an open line, power will be ____ of rated
1/2 of rated
67
In a delta 3 phase 3 wire system, if there is an open phase, power will be _____ of rated
2/3
68
What is the angular displacement between phase voltage and line voltage in a balanced delta connection?
0°
69
How do you find angle theta of a delta system when given PF?
Inverse cos.PF
70
How do you find PF of a delta system when given angle theta?
CosAngle

Level 3 Electrical, BCIT (7 decks)

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