3-Phase Star + Delta Connections
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14 Terms
How is 3-PH star connection wired up?
What is the formula to find VL from VP in a star system?
VL = -/3 * VP
What are the 5 types of loads in a 3-PH 4-wire supply?
3-PH delta, 3-PH star, 2-PH load (older installations), 1-PH 415V, 1-PH 240V
What kinds of applications are 3-PH delta loads used for?
3-PH motor, 3-PH industrial oven elements, primary coil of 3-PH distribution transformer, anything current- and phase angle-balanced with same impedance in each phase
What kinds of applications are 3-PH star loads used for?
3-PH industrial, commercial e.g. large unbalanced sites I work on
What is 1-PH 240V used for, what is 1-PH 415V used for?
240V for building power, lights. 415V used for motor, welder, flood light
In a star supply to delta load system, how is IL and IP defined?
Why is a neutral required on out-of-balance current loads and how is the current calculated? (star)
Draws unbalanced current away, keeps phase voltages equal on unbalanced loads. Unbalanced current draw is equal to phasor sum of the individual phases
How much load should 1-PH and 3-PH neutral conductors be able to handle?
1-PH should handle same as active, 3-PH should handle equal or more than maximum out-of-balance current of circuit
How is a phasor diagram affected if the phase sequence is reversed?
Phasor diagram is flipped, phase sequence flips angle’s lead/lag
What happens when a neutral is disconnected or broken? (star)
Star point shifts due to poor connection, no longer at zero/earth potential, meaning supply voltages + 120 degree displacement unaffected but star load phase voltages + displacement likely unequal.
What are the dangers of a broken/disconnected or high impedance neutral? (star)
Excessive voltage across 1 or 2 phases could damage load; dangerous voltage between offset star point and zero/earth potential could be danger to personal safety
Which system can have a neutral: star or delta?
star has neutral, delta runs between phases and cannot have neutral
How much does line current lag phase current by? (delta)
30 degrees
