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Brake resistance related calculation!

source:正阳兴 date:2020-10-26 21:39:50 author:正阳兴电子
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Brake resistance related calculation!

First, the choice of brake resistance value

The selection of brake resistance is not only limited by the maximum allowable current of energy consumption brake unit for frequency converter, but also has no clear corresponding relationship with the brake unit. The resistance value is mainly selected according to the required braking torque, and the power is determined according to the resistance value and utilization rate of the resistance. The selection of the resistance value of the brake resistance has an inviolate principle: it should be guaranteed that the current IC flowing through the brake resistance is less than the permissible maximum current output capacity of the brake unit, that is: R > 800/ IC.

Where: 800 -- the maximum possible DC voltage on the DC side of the frequency converter. Ic -- Maximum permissible current of the brake unit. In order to make full use of the capacity of the special brake unit for frequency converter, the selection of the brake resistance value is usually close to the minimum value calculated in the above formula as the most economical, and the maximum braking torque can be obtained at the same time. However, this requires a large brake resistance power. In some cases, a large brake torque is not needed, at this time the more economical way is to choose a larger brake resistance resistance value, so that the power of the brake resistance can be reduced, so as to reduce the cost of buying the brake resistance, the cost is that the capacity of the brake unit is not fully utilized.

Two, brake resistance resistance power calculation

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

The instantaneous power consumed by the brake resistance is calculated as follows: P = 7002 / R instantaneous power braking resistance is calculated according to the type value is braking resistor can be long uninterrupted work dissipation power, braking resistor is not continuous work, however, there is a big waste, the selection in this product, can choose a braking resistance of usage, it specifies the braking resistance rate of short work. The actual power consumed by the brake resistance is calculated as follows: P amount =7002 /R× Rb [%] Rb [%] : utilization rate of the brake resistance.

In actual use, the brake resistance power can be selected according to the above formula, and the brake resistance resistance value and power can also be selected to calculate the utilization rate that the brake resistance can withstand in turn, so as to set the correct setting and avoid the damage caused by overheating of the brake resistance.

Three, the determination of brake resistance utilization rate

The brake resistance utilization rate stipulates the use efficiency of the brake resistance, so as to avoid overheating and damage of the brake resistance, which will affect the braking effect of the brake unit. The lower the utilization rate of the brake resistance is, the smaller the heating degree of the resistance is, the less energy consumed on the resistance is, and the worse the braking effect is. At the same time, the capacity of the brake unit is not fully utilized. Theoretically speaking, when the brake resistance utilization rate is 100[%], the brake unit capacity can be fully utilized and the braking effect is the most obvious. However, this requires the cost of larger brake resistance power, which should be taken into comprehensive consideration by users.

Under the premise that the resistance value and power of the brake resistance have been determined, for the large inertia load with slower deceleration, the lower utilization rate of the resistance will achieve better results. For the load that needs to stop quickly, it is advisable to select a larger brake resistance utilization rate.

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