The selection of braking resistor is not only limited by the maximum allowable current of the energy consumption braking unit dedicated to the frequency converter, but also has no clear corresponding relationship with the braking unit. Its resistance value is mainly selected based on the required braking torque, and the power is determined based on the resistance value and utilization rate of the resistor.

The selection of braking resistance value has an undeniable principle: it should be ensured that the current IC flowing through the braking resistor is less than the maximum allowable current output capacity of the braking unit, i.e. R>800/IC.

Among them: 800- The maximum DC voltage that may occur on the DC side of the frequency converter. Ic - maximum allowable current of the braking unit

After selecting the resistance value of the braking resistor, the power value of the braking resistor should be determined. The selection of the braking resistor power is relatively cumbersome and is related to many factors.

The instantaneous power consumed by the braking resistor is calculated using the following formula: P instantaneous=7002/R

The power value of the braking resistor calculated according to the above formula is the power value that the braking resistor can work continuously for a long time and dissipate. However, the braking resistor is not an uninterrupted work, and this selection has a great waste. In this product, the usage rate of the braking resistor can be selected, which specifies the short-term working ratio of the braking resistor. The actual power consumption of the braking resistor is calculated using the following formula:

P amount=7002/R × RB%

RB%: braking resistor utilization rate.

In practical use, the power of the braking resistor can be selected according to the above formula, or the power that the braking resistor can withstand can be calculated based on the selected braking resistor value and power, in order to set it correctly and avoid damage caused by overheating of the braking resistor. To fully utilize the capacity of the selected frequency converter specific braking unit, the selection of braking resistance value is usually close to the minimum value calculated in the above equation as the most economical and can also obtain the maximum braking torque. However, this requires a larger braking resistance power. In some cases, a large braking torque is not required, and the more economical approach is to choose a larger braking resistor value, which can also reduce the power of the braking resistor, thereby reducing the cost of purchasing the braking resistor. This cost is that the capacity of the braking unit is not fully utilized.

Precautions for installing brake resistors

The two main factors that need to be considered in the selection process of braking resistors are power and resistance value. However, for temperature considerations, there is no regulation on braking resistor temperature in the current national standards, and the provisions on the limit temperature rise of resistors in the current "Basic Technical Conditions for Resistors" only consider the operating conditions of resistors and personal safety. However, in the braking system, in addition to considering the operation of resistors, it is also necessary to measure the entire braking system. For example, in the elevator system, if the temperature in the machine room is too high, it will have an impact on the heat dissipation of various electronic devices such as the frequency converter in the control cabinet. We all know that braking resistors mainly convert regenerative electrical energy into thermal energy and dissipate it into the air, directly affecting the working environment temperature of the entire braking system.

The following issues need to be noted during the installation operation of braking resistors:

1. Avoid installing the braking resistor and frequency converter too close together.

2. It is necessary to ensure that the braking resistor has sufficient heat dissipation space, and if necessary, install a heat dissipation device.

3. The joint of the resistor must be installed firmly to avoid cable damage due to prolonged high temperature.

4.The length of the connecting cable should not be too long to avoid wave interference.