Those who have experience with motors will tell us that the motor will burn if it is out of phase.
There will also be experience in the motor, which will tell us that the motor will not rotate if it is out of phase.
There are two types of phase loss:
1. When I was using it, I suddenly lost a phase.
2. A phase is missing when starting.
This corresponds to the two situations mentioned by the experiencer, burning and not turning.
f you take it more seriously, you can still score points when you use it, whether it's when you're accelerating, when you're decelerating, or when you're running at a steady speed.
When it was running stably, there was a sudden loss of phase.
Stable operation indicates that the torque provided by the motor is exactly equal to the load torque, if it is greater than it, it will accelerate, if it is less, it will decelerate.
Intuitive analysis, if the other two phases remain unchanged, there must be a lack of output of one phase, breaking the balance, and the speed is bound to decrease. When the rotational speed decreases, the other two phases will also change.
There is a lack of phase when starting, and if there is no starting torque, it will definitely not be able to get up. The starting torque is less than the load torque, and it can't get up.
All of the above is a sensory analysis.
Quantitative analysis relies on the symmetrical component analysis method of "positive order, negative order, and zero order".
What is the Positive Order, Negative Order, Zero Order, Symmetric Component Method?
The engineering has not been used for a long time, and was invented in 1918 by Canadian electrician Charles Legeyt Fortescue. But the math comes from linear algebra. I have to say more here that linear algebra is too awesome, and the familiar but unfamiliar Clark transform, Park transform, etc., are all linear algebra at work, and look at the world from a different angle (change coordinates).
The symmetrical component method means that if the frequency is the same, the phase angle difference is 120, if their amplitudes are unequal, they can be expressed by adding up the other three groups, one group is in normal order, and the amplitude of the three quantities in the normal order is equal and the difference is 120 degrees; A set of negative sequences, the three quantities of the negative sequence are also equal in amplitude, with a difference of 120 degrees;
There is also a set of zeros but only one quantity, which is also a phasor, with amplitude and phase.
The positive order is because the three are combined to form a positive rotational quantity, the negative order forms a negative directional rotation quantity, and the zero order does not rotate.
If they can represent each other, then they have to be one-to-one correspondence, that is, there is a unique solution. This can be rigorously proven mathematically.
If you don't believe it, you study mathematics and use it after you believe it, and if you believe it, then use it directly. Why be so tired, just use it.
It can be decomposed by the symmetrical component method, but there must be a condition for the decomposed quantities to work together on the system to ensure that the output result is the same as before decomposition, that is, the system must be linear.
As an inappropriate example, I can push a car with a force of 100 kilograms, but I can't use a force of 100 kilograms to push a car separately.
Decomposition may seem like a hassle, but it actually simplifies the problem.
1. How do you represent the absence of a phase?
2. The voltage and current are expressed as symmetrical components
The voltage of the motor leads with a lack of phase is not known, so the component voltage cannot be obtained by the symmetrical component method. What we are looking for is the case of torque and current, and we can find the voltage and component voltage there without it. After a period of tossing, it can be concluded that:
From the relationship between positive and negative sequence currents, it can be concluded that the positive and negative sequence equivalent circuits should be connected in reverse series, and the voltage after series connection is jUbc divided by the root number 3.
3. Equivalent circuit
When the rotor is relative to the positive sequence and negative sequence components.
because the slip difference is different, the impedance in the equivalent circuit is different, and it can be seen from the above figure that the difference is in the denominator of the equivalent resistance, one is s, and the other is 2-s.
4. Torque comparison
Expression of moment in the absence of phase and under normal conditions:
As can be seen from the formula:
If there is a lack of phase at start-up, S is equal to 1, the starting torque is zero, and it will not start. The stalled current is very large, and it will burn after a long time.
If there is a sudden lack of phase during stable operation, simply let Rm and Xm open the circuit, I2 + and I2 - are approximately equal, the torque will drop sharply, the speed will decrease, the current will increase, if the load does not decrease with the decrease in speed, the motor will eventually burn out.
The load of water pump and fan will generally decrease as the speed decreases, in this case, the motor may hold on for a period of time without being burned out.
About Dongchun Motor
Dongchun Motor is a renowned manufacturer specializing in electric motors, including IEC standard three-phase motors (IE1, IE2, IE3, IE4, IE5), single-phase motors, brake motors, and VFD frequency variable motors.
With over 20 years of experience, Dongchun Motor is committed to delivering high-quality, efficient, and reliable products that undergo rigorous testing. They provide OEM/ODM support and offer a two-year warranty on their products, ensuring excellent performance and customer satisfaction worldwide.
For more details, visit Dongchun Motor's official website.
