Problems in the use of Delta inverters and Delta motors

Delta's motors are the most frequently used rotating things so far, and with the development and spread of Delta inverters, they need to be used in conjunction with inverters.

Problems in the use of Delta inverters and Delta motors

Problems in the use of Delta inverters and Delta motors

However, in the process of combining the inverter and the motor, it is inevitable to encounter many problems. These exposed issues deserve more and more in-depth consideration and communication.

1. Can the motor soft starter save energy?

Soft start has limited energy savings, but it can reduce the impact of starting on the grid, achieve smooth starting, and maintain motor windings.

According to the theory of conservation of energy, due to the addition of a more chaotic control circuit, the soft engine not only saves energy, but also consumes a lot of energy, but reduces the starting current of the circuit and plays a maintenance role.
　　
2. What about the starting current and starting torque of the motor when the frequency conversion is working?

Frequency conversion work, according to the acceleration of the motor to increase the frequency and voltage, the starting current will be limited to less than 150% of the additional current (depending on the model, 125%-200%). When the commercial frequency power supply is directly started, the starting current is 6-7 times.

As a result, an electrical shock to the machinery occurred. The variable frequency drive can be started smoothly (the starting time is longer). The inverter with automatic torque enhancement function is 1.2-1.5 times of the additional current and the additional torque of 70%-120% of the starting torque, and the starting torque is more than 100%, and it can be started with full load.

3. Is there any relationship between motor overload and short circuit?

There are 2 types of overload of the motor: 1. Mechanical load overload: the overload of the propulsion exceeds the extra value or the transmission system is blocked, which has nothing to do with short circuit. 2. Normal load: the motor current is overloaded, which may be due to the phenomenon of local ground and inter-turn short circuit in the motor winding.

4. What is the inverter used for? What are the strengths?

It can also be applied to rotating machinery with speed regulation requirements.

Before the realization of frequency conversion speed regulation (which has been realized in theory, but in practice it is after the invention of power electronic equipment) the traditional speed regulation is DC, and the defects of DC speed regulation are as follows

(1) The structure of the DC motor is messy and the maintenance cost is high;

(2) Due to the presence of the commutator, the power of the DC motor does not rise much

The advantage of frequency conversion speed regulation is

(1) It can make the communication motor obtain the same excellent speed regulation performance as DC speed regulation.

(2) The maintenance of the communication squirrel cage asynchronous motor is simple and convenient.

(3) The power of the communication motor is not constrained by the commutator.

5. If a 100KVA transformer is used to supply electrical equipment with a total power of 100kW (up to 37kW), can it be used?

How much load can a 100KVA transformer load? Just look at the formula below

P = capacity * power factor * 80% = 100 * 0.9 * 80% = 72KW, the general overload of 20% work promised for 1 hour, so it can be used. The first thing is that the total current does not exceed, the high-voltage current of the transformer of 100KVA is 5.8A, the low-voltage current is 150A, and there is no problem to exceed it occasionally, the first thing is that the temperature rise does not exceed 55 degrees. The temperature rise is equal to the practice temperature minus the ambient temperature.

6. How to measure the insulation resistance of the motor?

If it is a three-phase communication motor, measure the insulation resistance of the three-phase winding of the motor between phases and to ground.

If it is a DC motor, measure the armature winding to the ground, the direct excitation winding to the ground, the other excitation winding to the ground, and the direct excitation winding to the other excitation winding. Select the appropriate dial according to the voltage level of the motor to be tested.

Measurement process:

--- block the power supply

--- to ground discharge

--- three-phase communication motor turns over the center point (if possible)

When --- the DC motor, lift the brushes.

--- meters detect the insulation resistance between phases and to ground, respectively

--- to ground discharge

--- rehabilitation line

--- record insulation resistance and ambient temperature

7. What is a brushless ring starter?

The brushless starter is a starting equipment that overcomes the defects of sliding, carbon brush, and messy starting equipment in the winding asynchronous motor, and retains the advantages of the winding motor, such as small starting current and large starting torque.

The JR, JZR, YR, YZR three-phase winding rotor communication asynchronous motor (excluding variable speed and camera) activated by resistance starter, reactor, frequency rheostat, liquid variable resistance starter, and soft starter can be replaced with a brushless starter.

8. How many ways to start the capacitor of the motor?

There are two launches

1. Capacitor start (refers to the capacitor disconnection after the motor starts)

2. The capacitor works after starting (the capacitor works after starting).

9. Will the transformer become the load of the inverter?

In principle, it is possible, but in practice it is not practical. Even if the inverter does not step up the transformer, there should be a type that can be used for circuits above 380V, and if a higher voltage is required, a 220V or 380V direct inverter can be used to obtain a high-voltage circuit by doubling the voltage.

It is recommended to use other inverter circuits, because the inverter is mainly used for load drive (such as electric motors), and is not used much in the power inverter, but the function of the inverter is not limited to the inverter itself, with various additional functions such as maintenance, so it is not economically ambitious to get the inverter power supply in the inverter.

10. Can the inverter be adjusted to 1Hz? What is the maximum HZ that can be adjusted?

When the inverter is used in a general communication asynchronous motor, the inverter will never be close to DC when it becomes 1Hz. The motor operates at the maximum current within the confinement of the inverter, and the motor may be burned out.

When working beyond 50Hz, the iron loss of the motor increases, which is not good for the motor, and generally does not exceed 60Hz (exceeding the allowable value in a short time) will affect the life of the motor.

11. What is the working principle of the frequency modulation resistor of the inverter? Why does conditioning resistor change frequency?

The frequency adjustment resistor of the inverter is used to divide the 10V reference voltage of the inverter and return it to the main board of the inverter. The inverter motherboard converts the voltage sent by the resistor into analog and digital, reads the data, converts it into a share value of the additional frequency, and outputs the current frequency, so that the frequency of the inverter can be adjusted by adjusting the resistance value.

12. Can the inverter decouple the motor current?

Can the inverter be decoupled? Cannot! However, as long as the output frequency f and the synchronous speed n1 keep the slip rate in the stable region or the additional slip rate Se, it is equivalent to making the motor current decoupled, the rotor power factor is 1 at the moment, and the rotor current is the torque current that we should decouple and control The inverter is the speed regulating device of the asynchronous motor, which exceeds the mechanical characteristics of the asynchronous motor

13. Why is the current high when the induction motor is started? Will the current become smaller after starting?

When the induction motor is in the abort state, from an electromagnetic point of view, like a transformer, the stator winding that receives the power supply is equivalent to the primary winding of the transformer, and the rotor winding of the closed circuit is equivalent to the secondary winding of the transformer that is short-circuited, and there is no electrical connection between the stator winding and the rotor winding, but only the magnetic connection, and the magnetic flux is equivalent to the stator, air gap and rotor

At the moment of switching, the rotor does not rotate due to inertia, and the rotating magnetic field blocks the rotor windings at the maximum interception speed - synchronously at the rotational speed, and the highest potential is induced in the rotor winding, so that a large current flows in the rotor conductor, and the current cancels out the magnetic energy of the stator magnetic field, and the secondary magnetic flux of the transformer cancels out the primary magnetic flux

The stator side automatically increases the current in order to maintain the original magnetic flux corresponding to the power supply voltage. At this time, due to the large current of the rotor, the stator current also becomes larger, and reaching 4-7 times of the additional current is the reason for the large starting current.

What is the reason why the current becomes smaller after starting: as the speed of the motor becomes higher, the speed of the stator magnetic field to intercept the rotor conductor is reduced, the induced potential in the rotor conductor is reduced, the current in the rotor conductor is also reduced, and the current in the stator current that counteracts the influence of the magnetic flux generated by the rotor current is also reduced, so the stator current becomes smaller after becoming larger, which is normal

14. What is the influence of carrier frequency on inverter and motor?

The carrier frequency affects the output current of the inverter;

(1) The higher the working frequency, the larger the duty cycle of the voltage wave, and the smaller the harmonic component of the current higher order, that is, the higher the carrier frequency, the better the smoothness of the current waveform

(2) The higher the carrier frequency, the smaller the current that the inverter promises to output

(3) The higher the carrier frequency, the smaller the capacitive impedance of the wiring capacitor (since Xc = 1/2fC), and therefore the greater the leakage current based on high-frequency pulses. Effect of carrier frequency on motor:

The higher the carrier frequency, the smaller the oscillation of the motor, the smaller the working noise, and the less heat generated by the motor. However, the higher the carrier frequency, the higher the frequency of the higher harmonic current, the greater the skin effect of the stator of the motor, the greater the motor loss, and the smaller the output.

15. Why can't the inverter be used as a variable frequency power supply?

The circuit of the inverter power supply is composed of a communication, DC, communication, and filter, etc., so the output voltage and current waveforms are pure sine waves, which are very close to the desired communication power supply. It is able to output the voltage and frequency of the power grid of which country in the world.

The inverter is composed of communication and DC communication (modulated wave) and other circuits, and the standard name of the inverter is the inverter governor. The output voltage waveform is a pulse square wave, with many harmonic components, and the voltage and frequency are changed together in shares, which cannot be adjusted separately, and does not meet the requirements of communication power supply.

Basically, the power supply cannot be used, and it can only be used for the speed regulation of three-phase asynchronous motors.

16. When using the inverter, why does the temperature rise of the motor be higher than the commercial frequency?

The output waveform of the inverter is not a sine wave, but a deformation wave, and the motor current under the extra torque is about 10% more than the commercial frequency, so the temperature rise is slightly higher than the commercial frequency.

Another point is that when the speed of the motor decreases, the speed of the motor cooling fan is insufficient, and the temperature of the motor rises.

17. What does the maintenance level of the motor mean?

For example, the so-called IP23 motor can prevent the motor from penetrating into solid objects of more than 12 mm, prevent human fingers from touching the internal parts, and prevent the incursion of foreign objects at medium scale (diameter of 12 mm or more). It prevents the intrusion of distributed water and the damage caused by the intrusion of water that is distributed from a vertical angle of less than 60 degrees.

The World Maintenance (IP) Maintenance Hierarchy is recommended by the World Telecommunication Union (IEC). Motors are classified according to their dust- and moisture-resistant properties. The foreign body mentioned here contains something, and human fingers should not touch the live part of the motor to avoid electric shock.

The IP maintenance rating consists of two numbers, the first number indicates the level of protection of the motor against dust and foreign objects, the second number indicates the tightness of the motor with moisture and waterproof intrusion, and the higher the number, the higher the maintenance level.

Problems in the use of Delta inverters and Delta motors

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