Frequency drives

Industrial applications

Notice if the drive is negatively influencing your engine, or if this drive is the best option

Variable frequency drives are industrial control equipment that allow the speed and torque of an associated rotating machine to be controlled. This is achieved by modulating the motor power signal. They receive the sine wave from the mains and rectify and attenuate it until a direct current signal is achieved. This direct current is then modulated through an inverter to achieve a square signal or a pulse train that excites the motor. 

The modulated signal can vary in both voltage and frequency. Therefore, it is possible to control the speed and torque of the motor precisely. By adjusting to the actual load of the motor, in case of continuous torque applications, or by being able to control the speed of the motor in detail, drives have a significant advantage in controlling motors, but also in reducing electricity consumption. However, they are power-sensitive equipment. Furthermore, they can introduce harmonic distortions, or even deteriorate the insulation and/or performance of the associated motors if they are not correctly configured and/or selected.

It is possible to find associated to all types of rotary machines, from pumps, compressors or fans to engines in transport applications of materials.

Major failures

01.

Electrical quality Power

In the case of very low voltages, they can work erratically. In the case of overvoltages, they can be destroyed by voltage peaks. In operations where the motor torque must be kept constant and at low speed, the drive can significantly reduce the motor excitation voltage. This leads to the motor working at low voltage with the corresponding problems of overheating and deterioration of the motor insulators.

02.

Presence of harmonics in the network

Mainly, they are high frequency harmonic generators. They also work to impoverish the overall electrical quality of the facility. When working by generating high-frequency pulse trains, they can cause voltage spikes in high-frequency switching operations. These peaks can be aggravated in the motor junction box due to wave reflection. For this reason, the manufacturer usually limits the maximum cable length between the variator and the motor. These surges can reach peaks up to 2.5 times the variator's continuous voltage (used to modulate the output), putting the motor at risk, deteriorating its insulation and reducing its useful life.

03.

Bad braking distensioning

The variators can receive reflux voltages from the motor in the braking operations. In the case of an improper sizing of the braking of the engine, if it is affected by a braking too fast, the motor can act as an electric generator for a short period of time, due to its inertia. The wave generated by the motor is directed towards the variator and can collide with the wave generated by the variator to control the motor. This can generate very important voltage spikes that can burn the control equipment.

Analysis

Continuous analysis of a frequency inverter allows us to assess its quality and working efficiency. In addition, we can measure its performance and know when it needs maintenance.

Evaluation

The harmonics analysis allows us to evaluate their contribution to the deterioration of the power supply network and, if necessary, to propose corrective actions .

Influence

It should be noted that an inverter is always linked to an electric motor. An analysis of the inverter, as well as allowing us to evaluate it, allows us to see if the inverter is having a negative influence on its associated motor or if this motor needs to be replaced by another one that is better suited to the output of the inverter.

Frequency drives

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