Txs Connections Flashcards
(20 cards)
In an Open delta what is the reduced VA percent ?
57.7%
Take total VA and divide 1.732
What’s most common transformer connection ?
Delta/Wye
Advantages of Delta/Wye connection ?
•Supply single and three phase( same panel)
•Balanced single phase=balanced three phase
•30 degree phase shift between primary/secondary line voltage
NGR are for impending e grounding. What are the low and high voltage ranges?
Low voltage 30V - 750V
High voltage 750V+
Ungrounded systems what happens ?
Code requires a device to be notified and if not corrected by second ground fault an overcurrent device and uncontrolled shutdown takes place
NGR advantages?
Fast response to where fault happened and reduce and prevent overheating and mechanical stress on conductors
Solidly grounded systems advantages?
•Fault to ground = breaker trips
•reduced over voltages
•improved system and equipment fault protection
•greater safety
Solidly grounded is for high voltage or low voltage?
Lower voltages
Impedance grounded systems characteristics
Primary connected in series to neutral and the resistor is connected secondary of grounding transformer
Which grounding system uses a CT?
Impedance grounded systems
Low resistance grounded neutral current limits ? And properties ?
•200-400A
•Can carry for 10seconds before overheating
•Commonly on high voltage systems
High resistance grounded neutral current limits and properties?
•5-10A
•used on low voltage systems under 750v
Advantage - eliminate dangerous flashovers to ground ( can occur on solidly grounded)
What voltage appears across NGR when single line to ground fault occurs on résistance system?
A voltage equal to the normal line to neutral voltage
What is purpose of NGR?
What system are they used in ?
•Limit ground fault current to a safe level
•impedance grounding of industrial power systems
Open delta reduced capacity percentages
Capacity reduced to 57.7%
Capacity compared to two txs 86.6%
Delta/Delta connection has to be ? What are rules ?
Paralleled
•same %iz
•same polarity
•same taps
•same secondary no load voltage
Wye/Wye connection problems ?
Third harmonic (180hz) can induce current into neutral causing heating in neutral
Advantage of primary neutral in Wye/Wye connection?
Elimination of voltage balancing problems
What is the phase displacement in Wye/Delta connection for primary and secondary voltage?
30degrees
If two transformers are connected in open delta, their output capacity will be _% of sum of their ratings ?
86.6%
