HNC Electric HV480 Series, Руководство пользователя

Страница: 144 / 179

140
55 120 0.18 112 40
75 165 0.13 150 35
93 180 0.11 176 30
110 225 0.09 210 20
132 260 0.08 253 16
160 305 0.07 304 13
185 350 0.06 340 11
200 385 0.06 380 11
220 430 0.05 426 9
250 470 0.04 465 9
280 530 0.03 520 8
315 600 0.03 600 6
355 700 0.03 700 5
400 800
0.03
800 5
450 1000 0.02 1000 4
500 1250 0.02 1000 3
560 1600 0.02 1250 3
8.2.5 Selection of energy consumption braking unit and braking resistance
When the motor is operating in the braking state, the motor will generate regenerative energy, which is
electrical energy converted by the mechanical energy released when the rotating speed of the rotating motor
changes from high to low and fed back to the main circuit being powered, which raises the voltage of the main
circuit. The amount of the energy depends on the overall system characteristics and the parameter settings of the
frequency inverter. In order to make the system work properly, this part of energy is dissipated by resistance, i.e.
DC energy consumption braking.
1) The selection of the resistance value of the braking resistor RB
It also indirectly determines the magnitude of the braking torque of the system. If the braking torque is too small,
it will not be restrained. The rise in the voltage of the main circuit will lead to over-voltage of the main circuit of the
system and trip protection. If the braking torque is too large, the stable operation of the system will be affected. In
order to stabilize the braking voltage of the system, it is generally chosen to be about 1.8 times of the rated AC input
voltage. For 380 v standard motor control system, the working point of energy consumption braking is generally
selected to be about 700 v. If this voltage is too low, braking may occur within the maximum operating range of the
power supply. If this voltage is selected too high, over voltage protection action may occur.
Assuming KB is the mechanical energy / electrical energy conversion efficiency coefficient when the motor
power is p (kw) feedback, usually kb = 0.7, then, when the brake operating point voltage u = 700 volts, according
to the energy conservation relation that the motor generates energy that is completely absorbed by the brake
resistor, the following relation exists when the motor has 100 % brake torque:
1000P*KB=U²/RB
That is,
RB= U²/1000 P*KB=700/P
Considering that KB is an empirical value and the duty cycle of the braking current, the actual maximum braking
torque occurs at the extreme limit of KB = 1, at this time: KBmin = 0.7 * 700 / P ≈ 500 / P at this time, the braking
current reaches the maximum. If this limit is exceeded, the device will be damaged.
2) The selection of braking resistor power
For the calculation of the power dissipated by the braking resistor itself is still fully absorbed by the braking
resistor according to the regenerative energy and uses thermal energy. Considering the form of release, assuming
that the resistance power is PB, the braking frequency KF, and the power margin ks, then
PB=P*KB*Kf*Ks