User:Thomasl1971/Grounded B Phase
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Grounded B Phase (3-wire Corner-grounded delta) is one of many types of three-phase electric power systems. It is used to supply three-phase electric power while providing protection from lightning strikes, electric shock, fires, line surges and ground faults without the need for specialized equipment. It is not a common system, but can be found in older industrial buildings and some high rise commercial buildings.
Details[edit]
A grounded B phase system uses three conductors. All three conductors are current carrying phase conductors and are normally designated A, B and C respectively. Conductors A and C are ungrounded. In addition to being a current carrying phase conductor, the B phase is grounded and is referred to as the grounded phase conductor. There are many reasons for intentionally grounding a phase conductor. One of the primary purposes for grounding this conductor is ground fault protection, should such an event occur on the ungrounded phase conductors. Ground faults occurring on the B phase conductor are not detected or cleared. The grounded conductor should not be confused with a neutral conductor. No neutral exists in this system. This differentiates a corner-grounded delta system from the related High-leg delta system.
The RMS voltages phase to phase: A to B: 240v, A to C: 240v and B to C: 240v. The voltage of each individual phase is 138v.( add formula here and cite.) However, the voltage from each phase to ground: A to ground: 240v, B to ground: 0v, C to ground: 240v. No potential voltage difference exists between the B phase conductor and ground.
Advantages[edit]
Stabilizes voltages of all the phases to ground including the ungrounded phases.
Inhibits transient over-voltages.
Protects electrical distribution systems and equipment.
Detects ground faults without the use of additional equipment. In ungrounded three phase systems, an expensive Zigzag transformer is required for ground fault protection.
Disadvantages[edit]
The system cannot supply dual service for lighting and power loads.
The grounded phase conductor cannot be interchangeably substituted for another phase. It must be positively identified and separately maintained.
Higher phase to ground voltages present on two of the phases compared to High-leg delta systems.
Most distribution equipment is not rated for use on this system.
Usage[edit]
Fuses are not allowed in the grounded phase conductor except at a motor controller. A fuse must be installed in this case. No over-current device is permitted to be used to disconnect the grounded conductor, unless this device simultaneously disconnects all conductors of the circuit, including the ground.
See also[edit]
- High-leg delta
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References[edit]
External links[edit]