Phase, neutral, and earth are the three connections that make up an electrical system. For electrical energy to flow securely through the load, each wire connection is important.
In simple terms,
- A phase wire is utilized to carry the primary load current for the load
- A neutral wire is used for carrying the extremely small or even negligible return current back to the source, and
- An earthing wire is utilized for carrying the leakage current to the ground.
Specifically, a typical problem with the neutral wire exists and, if it is not fixed, it will quickly disrupt the electrical circuit. The problem is floating neutral.
What is Floating Neutral?
The phase voltage will not remain constant across each phase if the unbalanced load’s star point is not connected to the power source’s star point (generator or distribution transformer), but will consequently vary.
It is known as a floating neutral because the potential of a star point (or) neutral point that is so isolated is constantly changing and not fixed.
The neutral wire of a circuit is detached from the ground under the condition known as floating neutral. The neutral wire in an AC system is always grounded to the earth. However,
- Loose connection,
- Braking of the neutral flat,
- Bad circuit connection, or
- Short circuit
can all cause a floating neutral in a power system.
What is Neutral & why is it grounded?
The phase difference in a three-phase alternating current system is 120° for all phases. A central or common point is provided in the Delta-Star Transformer from which the identical potential difference with a phase angle shift of 120° is obtained for all three windings of R, Y, and B Phase.
The neutral point voltage is 0 during a balanced condition. If the phase angle of any phase changed due to an unbalance load or a fault condition, an unbalance voltage (or) current is generated at the neutral wire.
The neutral wire of each start winding transformer is securely grounded to protect the system. If there is an unbalance or a phase to ground at the load end, the unbalance (or) fault current will flow to the neutral wire via a close-loop using ground.
The protection relay functions by recognizing the neutral current and isolating the load.
Effects of the Floating Neutral
Floating neutral is extremely harmful in an alternating current(AC) system. Users may notice the following disturbances:
- Unbalanced voltage can occur at a neutral point, affecting the system’s and linked equipment’s stability.
- Because of floating ground unbalance (or) faulty current, the relay may not detect it, and the associated protection system will not operate.
Various factors causing Neutral Floating
Numerous elements are being identified as the root causes of neutral floating. Floating neutral’s effect is dependent on when neutral is broken.
1) Three-phase distribution transformer
Most transformer neutral failures are caused by a faulty neutral bushing.
It has been determined that the primary reason for the breakdown of the neutral conductor at the transformer bushing is the application of line tap. Vibration and temperature differences cause the nut on the line tap to loosen with time, resulting in a hot connection. The conductor began to melt, breaking off the neutral.
One of the causes of neutral failure is inadequate installation and technical personnel work.
Depending on how the system’s load is balanced, a damaged neutral on a three-phase transformer will allow the voltage to float up to the line voltage. Such neutral floating might damage customer equipment that is linked to the supply.
Current normally flows from Phase to the Load to the Load to the back to the source (distribution transformer) under normal conditions. Line to line voltage between the loads is created when the neutral is broken because current from the red phase switches to the blue or yellow phase.
Depending on the customer, they might experience low voltage or overvoltage.
2) A broken neutral conductor in the LV line
The result of a broken overhead The LV overhead distribution neutral conductor will be comparable to the broken at the transformer.
Instead of using phase voltage, the supply voltage floats up to the line voltage. Depending on the problem condition, linked customer equipment could be damaged.
3) Service Neutral Conductor broken
A damaged service conductor’s neutral will only cause a reduction in supply at the consumer’s point. There have been no damages to the customer’s equipment.
4) A Distribution Transformer with High Neutral Earthing Resistance
Low resistance path for the neutral current to discharge into the earth is provided by good earthing resistance of the neutral pit. High earthing resistance can provide a path with high resistance for neutral grounding at the distribution transformer.
Limiting earth resistance Low enough to provide sufficient fault current for immediate utilization of protective devices and to prevent neutral shifting.
5) Overloading and Unbalanced Loads
One of the most frequent causes of neutral failure is overloading combined with unbalanced load distribution.
Neutral should be suitably established to allow the flow of the least amount of current through the neutral conductor.The cancellation caused by the phase current’s 120° phase shift should theoretically result in zero current flow in the neutral.
IR<0 + IY + 120 + IB – 120 = IN
A lot of current flows in neutral in an overloaded, unbalanced network, breaking neutral at the weakest point.
6). Shared Neutrals
A single neutral is shared by two (or) three phases in some buildings’ wiring. The original plan was to mimic the four wire (three phases & a neutral) wiring of panel boards at the branch circuit level.Only the imbalanced current should theoretically return to the neutral. As a result, one neutral can complete the work for all three phases. With the rise of single-phase non-linear loads, this wiring workaround rapidly came to an end. The zero-sequence current is the issue.
Statistically adding up from nonlinear loads, especially third harmonic, will return on the neutral. The additional neutral current raises the voltage from the neutral to ground, which could be dangerous since it could cause an undersized neutral to overheat. The line to neutral voltage that is made available to the load is reduced by this neutral to ground voltage.
7). Poor maintenance and workmanship
The maintenance staff typically pays minimal attention to the LV network. Neutral continuity will be impacted by the looseness or insufficient tightness of the neutral conductor, which could result in floating neutral.
How can a Floating Neutral be tested?
The neutral is always grounded, under normal conditions, the voltage at neutral point with regard to the ground should always be zero. If the condition of floating neutral continues, there must be some voltage imbalance at neutral point with respect to the ground. It is possible to test the system by measuring the voltage between neutral & ground.
How to fix Floating Neutral?
1). Use a 4-pole breaker, an ELCB, or an RCBO in the distribution panel
A floating neutral is hazardous.
Consider having a breaker panel with the 3 Pole Breaker for 3 Phase &bus bars for neutral for 3 phase inputs and a neutral. Phase-to-phase voltage is 440V, and neutral-phase voltage is 230V. When feed 230V loads using single breakers. 230V loads have the one line fed by the breaker & a neutral.
And when the neutral gets loose, corroded, or disconnected in panel. However, 230V loads may be in trouble. This floating neutral condition will cause one line to go from 230V to 340V or 350V and the other to go down to 110V or 120V.
Overvoltage will damage half of the 230V equipment, while low voltage will damage the other half. Thus, avoid floating neutrals. In a 3ph supply system, ELCB, RCBO, (or) 4 pole circuit breakers will trip the entire supply if neutral opens.
2). Voltage Stabilizer
Due to floating neutral, three-phase loads will connect between phases when neutral fails. Depending on the load resistance between these phases, the voltage ranges from 230V to 400V.Protect equipment with a servo stabilizer with a wide input voltage range and high/low cutoff.
3). Standard workmanship and Maintenance
Maintaining the LV network should be given more priority. Apply sufficient torque to tighten the neutral conductor in the LV system.
Conclusion
A Floating Neutral fault condition is extremely hazardous because if an appliance isn’t operating, someone who is unaware of the neutral floating may easily touch the neutral wire to figure out why the appliance isn’t working when it’s plugged into the circuit and receive an electric shock. Single-phase appliances are made to operate at their usual Phase Voltage; if they are exposed to Line Voltage, they may become damaged.
Floating neutral fault is an extremely hazardous problem that needs to be fixed as soon as is practical by identifying electrical wires to check & then connect properly.
