Three Phase Transformer Connections Flashcards

1
Q

Describe a wye/wye transformer connection with a primary neutral

A
  1. Eliminates voltage balancing issues, so the transformer bank can supply a wye connected secondary with a neutral
  2. Even with a balanced load, the primary neutral contains a third harmonic (180hz) which can induce a current that causes excessive heating in the neutral
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe a wye/wye transformer connection without a primary neutral

A
  1. Rare
  2. Difficult to maintain balanced output voltages
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Advantages of a delta/delta

A
  1. The phase current is only 57.8% of the line current, so the conductors of the individual single phase transformers do not have to be as large as the the line conductors supplying a three phase load
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe a wye/delta connection

A
  1. 30 degree phase displacement between primary voltages and their secondary voltages
  2. The conductors of the primary do not need to be insulated for the full three phase
    Line voltage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe a delta/4 wire delta connection

A
  1. The fourth wire impact the secondary is a common conductor that is connected to the centre point of one of the windings
  2. Can feed a three phase, three wire panel board and a separate single phase three wire panel board
    3.CANNOT feed a three phase, four wire panel board
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe a delta/wye connection

A
  1. The common connection for three phase distribution
  2. 30 degrees phase displacement between the primary voltages and their respective secondary voltages
  3. The secondary can supply both single and three phase loads
  4. A four wire wye connection can feed a three phase, four wire panel board
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe an open delta/open delta connection

A
  1. Same as a delta/delta connection but one transformer is removed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the purpose of a neutral grounding resistor

A
  1. They are meant for impedance grounding of industrial power systems in low and high voltage distribution networks
  2. They protect power transformers and generators from damaging currents in the event of a ground fault
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe an ungrounded system

A
  1. A system that requires a ground fault detection device that can notify people when there is a ground fault situation
  2. These are used less because on inherent over voltages when the first fault intermittent
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe a solidly grounded system

A
  1. The grounding electrode and the equipment to the circuit conductor are connected using a low impedance conductor
  2. It is an improvement over ungrounded systems because it can speed up the process of locating faults.
  3. Only used in low voltage applications at lower power levels
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe an impedance grounded system

A
  1. A system that has resistance connected between the neutral of the system and the grounding electrode.
  2. The primary is connected in series to the neutral and the resistor is connected on the secondary.
  3. A CT is used to measure the ground fault current
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How does a neutral grounding resistor protect personnel and equipment from damage

A
  1. Limiting how long the fault lasts
  2. Limiting the faults magnitude
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

If a ground fault condition exists, what does the NGR limit the current to in a low resistance system

A

200-400A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does a high resistance grounding neutral limit the current to in a ground fault condition

A

5-10A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly