3 phase motor
An alternating current (AC) generates a voltage that varies over time, reversing direction and then returning. This means that the voltage between them fluctuates from maximum to zero in opposite directions during each cycle on a 2-wire system. This variation is not noticeable in heating applications and is acceptable for many lighting systems due to the speed of 50 or 60 times per second.
As indicated in the image below, a three-phase electric supply produces three wires that all produce the same cycle, but each one a little later. (More phases are conceivable, but three is the most common.) A fourth wire, which corresponds to the zero line in the diagram, is frequently used as a neutral wire. A conventional AC system can be created by connecting any phase to the neutral wire, such as Phase 1.
A three-phase induction motor is a low-maintenance, high-reliability rotating electrical unit that turns a shaft using three-phase power (or, do mechanical work). Three-phase motors are used in a wide range of applications nowadays, including industrial electric drives, locomotive drives, car propulsion (such as in the Mahindra e2o and e2o plus), and some medium-power home applications such as water pumps and pedestal fans (Such fans are generally driven by single phase motors)
What happens if a 3 phase motor loses a phase?
The conditions are as follows:
- Stand Still Condition
- Running Condition
At standstill, meaning even if the motor is not running, this failure might be dangerous because, depending on the load, the Motor may or may not be able to start even if only two phases are connected. In most case it may not be able to start because a single phase motor is not a self-starter and because a three phase motor includes a safety system to protect it from overheating. And if it starts, trust me it will burn out.
How to detect the single phasing fault?
The operator must be aware of whether the motor has gone single phasing. For single phasing detection, a three-phase induction motor is commonly equipped with an overload detection mechanism. Still, a machine can fail at any time, and as an electrical engineer, she or he must be familiar with the motor's typical sound, feel, and operation.
When completing tests on a motor, it's critical to have all senses alert in order to spot problems connected to single phasing:
The motor makes an unusual humming noise.
The motor is vibrating at a higher than normal frequency.
The odor of heated, charred copper (insulation) ( Find out how insulation testing using megger meter helps to prevent any accident)
 Light smoke/fumes seen from the motor casing
Common Causes of a phase failure:
In the case of an induction motor, single phasing is an electrical failure caused by the power supply. When one of a three-phase motor's three phase circuits is opened, the remaining circuits carry surplus current. Single phasing is most commonly induced by the following circumstances:-
At least one of the three backup fuses blows (or fuse wire melts if the fuse is of wire type)
The current is supplied by contactors in the motor circuit. One of the contactors is broken and has to be replaced.
Single phasing can also be caused by incorrect or incorrect settings of any of the motor's protection systems.
 If contactor routines are not followed on a regular basis, they may become covered or coated in an oxidation layer, resulting in single phasing.
The motor relay contacts are damaged or broken.
One of the motor circuit's wires is broken.
Due to a failure of the supply system's equipment
Feeder or transformer fuse blow-up due to a short circuit in one phase of a star-connected or delta-connected motor
Effects of a phase failure
A three-phase motor, as previously stated, is an AC motor designed to work on a three-phase power source. Both types of motors include a stator and rotator, therefore their construction is identical. The field of the single phase motor does not rotate, but rather reverses 180 degrees. Single phase motors are not usually self-starting. Additional provisions, such as switching out the start winding or a capacitor, are used to do this.
On a three-phase induction motor, a single phasing error will have the following consequences:
If the motor is stopped, it may not be able to start depending on the load because a single phase motor is not a self-starter (as mentioned above) and because a three phase motor includes a safety system to protect it from overheating.
 If a single phasing failure occurs while the motor is running, it will continue to operate (unless a safety cut-out mechanism is installed) due to the torque created by the remaining two phases, which is produced according to the load's requirement.
Because the remaining two phases are doing more work than the default phase, they will become overheated, potentially damaging the windings.
In the next two phases, the single phasing will result in a current flow increase of 2.4 times the average current value.
Single phasing reduces the motor's speed and causes its rpm to fluctuate.
The motor will produce strange noise and vibration. The remaining two steps produce inconsistent torque, which causes this.
The motor systems almost all include a standby configuration. If the motor is set to standby and has a single phasing problem, it will not start, causing the system to fail.
 If the problem is not resolved and the motor is operated, the windings will melt due to overheating, which could result in short-circuiting or earthing.
How Prevent motor from phase failure or Single Phasing
In this case, the motor must be protected by a device that will separate it from the system before it is permanently damaged.
To prevent damage from single phasing, all motors over 500 KW must be equipped with protective mechanisms or equipment.
The restriction indicated above does not apply to motors mounted on the ship's steering gear system. An alarm will sound only if a single phasing is detected
All three phases of the motor are equipped with overload relays in this device. This relay engages automatically as the current value rises, and the motor trips.
The electromagnetic effect created by the current is the basis for this device's operation.
The electromagnet in the coil increases as the current value increases, pulling the relay and activating the trip relay, stopping the motor.
The time delay is used in this system because the motor draws a lot of current when it first starts up, which can cause the motor to trip
Thermistors are small thermal devices that are used in conjunction with an electromagnetic overload relay to protect against overheating. The thermistors are installed in the motor's three windings. Any increase in current causes the windings to heat up, which the thermistors detect and provide signals to the amplifier.
The electromagnetic relay is connected to the amplifier. This amplifier increases the current value in the coil of an electromagnetic relay, which triggers the trip, and the motor stops or trips as soon as a signal from the thermistor regarding overheating is received.
- Bi-metal strip                      Â
The bimetallic strip is positioned in this approach in such a way that it detects circuit overheating. Due to the two different metals employed and their varying coefficients of expansion, this bimetallic strip strives to expand as soon as overheating is detected. The strip bends towards a metal with a high coefficient of expansion, completing the trip circuit and causing the motor to trip.
- Standard motor starter overload protection
It is included in a three-phase motor to handle single-phasing situations. All phases have overload heaters, which detect any overload in the phase and, if the load exceeds the motor's rated load, the heaters trip the starter off before the motor windings are destroyed.
In summary, phase failure is never a desirable condition for an induction motor's performance, and proper precautions should always be taken to prevent it.