How to match the braking resistance when the crane lowers the heavy objects?

How to match the braking resistance when the crane lowers the heavy objects?

When the crane lowers the heavy object, the motor is in the power generation state, and the regenerated energy is injected back into the DC bus, and the bus voltage rises, so the braking resistor is needed to convert the energy into heat energy and release it. The key to type selection is to account for two different working conditions: lifting and walking.

Working condition difference determines duty cycle.

The hoisting mechanism (up and down the hook) continuously generates electricity during the whole lowering process, and the braking duty ratio is generally 40%~50%; The traveling mechanism (big car, small car) only generates regenerative energy when it slows down, and the duty ratio can be 10%~20%. The demand difference between the two is several times, so it is a common selection mistake to configure the lifting resistor with walking standard.

The resistance is determined first, and the power is calculated later.

The resistance value should meet the allowable current constraint of the braking unit. If the resistance value is too small, it will exceed the bearing capacity of the braking unit; if it is too large, the braking torque will be insufficient. It should not be amplified after the resistance value is determined. The power is calculated by multiplying the peak braking power of a single lowering by the duty ratio, with a margin of 10%~20%.

What does Jianhong Jitai Technology's braking resistor rely on to carry heavy loads?

Holding down the heavy load depends on three parameterizable factors:

• The material is temperature resistant.The resistance of porcelain tube is based on mullite ceramic, which has stable temperature resistance; The resistance wire is wound with Fe-Cr-Al/Ni-Cr/Kang-Cu alloy, which allows long-term high-temperature operation. The material grade determines the stability of the resistor under the condition of continuous heating.
• Heat dissipation structure.Corrugated winding structure increases heat dissipation surface area, and aluminum alloy shell directly participates in heat conduction. Under the same power, different heat dissipation design, the actual continuous load duty ratio is different.
• Protection level.In outdoor or dusty environment, protective products should be selected according to IP grade to avoid moisture and dust affecting insulation performance.

Parameters to be reported to the manufacturer for selection.

Motor power, rated load, lowering speed, braking times per hour, engine room ambient temperature, installation space size. All the above parameters can be reported, and the selection accounting according to working conditions can be completed.