Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
Which type of loads use 3 phase 4 wire ac system of distribution?
Balanced
Unbalanced
Both (a) and (b)
None of these
Unbalanced
A 3-phase 4-wire system is used in secondary distribution to supply power to both single-phase and three-phase loads. The neutral wire provides a return path for unbalanced phase currents, allowing single-phase loads (connected between any phase and neutral) to be operated independently without affecting the system's ability to maintain a constant phase voltage.
A 3-phase 4-wire system is used in secondary distribution to supply power to both single-phase and three-phase loads. The neutral wire provides a return path for unbalanced phase currents, allowing single-phase loads (connected between any phase and neutral) to be operated independently without affecting the system's ability to maintain a constant phase voltage.
INтАЛ=IRтАЛ+IYтАЛ+IBтАЛ тАФ Net current in the neutral wire due to unbalanced loading
VphтАЛ=3тАЛVLтАЛтАЛ тАФ Relationship between phase and line voltage in star configuration
In a 3-phase system, if loads on all three phases are identical (balanced), the vector sum of currents is zero, and no current flows through the neutral wire (InтАЛ=IRтАЛ+IYтАЛ+IBтАЛ=0). In practical distribution, loads are randomly distributed, causing unequal current magnitudes and phase angles. The neutral wire carries the resultant residual current, ensuring that the phase voltage (VphтАЛ=VLтАЛ/3тАЛ) remains constant regardless of the load distribution.
The 4th wire is the neutral conductor connected to the star point of the transformer secondary.
Essential for domestic distribution where single-phase loads are common.
Reduces the cost of the system by allowing individual phase control without dedicated return paths per phase.
Unbalanced currents cause I┬▓R losses in the neutral wire.
Supports both single-phase and three-phase loads simultaneously.
Provides two different voltage levels (Line-to-Line and Line-to-Neutral).
Independent operation of phase circuits.
Additional copper cost for the neutral wire.
If the neutral breaks, phase voltages become unstable, potentially damaging equipment.
Increased line losses due to neutral current in unbalanced conditions.
Residential power distribution
Commercial office buildings
Small-scale light industrial setups
| Feature | Balanced Load | Unbalanced Load |
|---|---|---|
Neutral Current | Zero | Non-zero (INтАЛюАа=0) |
In a perfectly balanced system, the neutral wire theoretically carries no current, but in reality, residential load is never balanced.
Option A is incorrect because balanced loads do not require a neutral wire for operation, as the return path is provided by the phases themselves (e.g., in a Delta-connected system).
B is correct тАФ 3-phase 4-wire systems are specifically designed to handle unbalanced loads by providing a return path for neutral current through the fourth wire.
Always remember that while 3-wire systems can handle balanced loads, a 4-wire system is strictly required when the load is unbalanced to prevent voltage shifting between phases.