The solution to the problem of leakage of Nidec inverters

First, the cause of the leakage problem

According to the functional block diagram of the inverter controlling the operation of the motor (Fig. 1), the three-phase power supply is rectified by the inverter rectifier bridge, and then sent to the inverter bridge (IGBT) through capacitor filtering, and then the three-phase alternating current with adjustable output frequency and voltage of the inverter bridge is used to control the operation of the motor. The alternating current with a difference of 120 degrees flows through the three-phase stator coil winding of the motor, and produces a rotating magnetic field, so that the rotor of the motor rotates automatically under the action of the rotating magnetic field of the stator winding.

Second, the solution to the problem of leakage

In order to avoid the occurrence of this problem, when the inverter hardware is designed, the induced surge filter circuit (its equivalent circuit is shown in Figure 1), and the grounding terminal of the inductive surge filter is connected with the shell of the inverter, and in the wiring description of the inverter, the grounding terminal of the motor is required to be connected with the grounding terminal B of the inverter, and the ground (i.e. the earth) of the input power supply is connected with the grounding terminal A of the inverter.

Thereby make the induced current that motor operation produces can form a loop through the grounding wire of motor and inverter, the grounding wire between inverter and power supply, make the ground of motor, the ground of inverter and the ground of power supply (i.e. earth) are all in the same potential, and the potential difference between them is 0 volt voltage. In this way, the human body standing on the ground (also the ground of the power supply) touches the rotating electric shell, the rack of mechanical equipment (the frame of the general equipment is connected with the earth), and the shell of the inverter will not have the feeling of being electrified, because the potential difference (voltage difference) between them is 0 volts, and the human body can not feel whether there is electricity.

When the ground wire of the motor fails to be connected with the ground terminal of the inverter, and the ground wire of the power supply is not connected with the ground of the inverter, the shell of the mechanical equipment or the ground end of the electricity, the shell of the motor, the outer shell of the inverter, the ground (i.e. the earth) of the power supply is not at the same potential. If in this case, the induced voltage generated by the operation of the motor is 100V, and the motor is together with a certain part of the rack of mechanical equipment, because the ground wire of the power supply is not pulled over in the distribution room, and the electrical equivalent model of the human body can theoretically be equivalent to a resistance of about 2K ohms (if the resistance value is smaller when the human body is sweating and wet, sometimes even only tens of ohms), when the human body stands on the ground and touches the metal of the equipment connected to the motor, The induction electricity of the motor (such as 100V) can pass through the human body to discharge to the earth, then the human body will have an electric current flowing through, and there will be a feeling of being electrified. Although, theoretically, the motor shell is connected with the rack of the mechanical equipment, and the rack of the equipment is installed on the earth, it stands to reason that people standing on the ground and touching the equipment rack should not be induced electric shock, but, don't forget that although the earth also belongs to the conductor, the earth has a resistance value after all, and according to the soil composition of different lands, the resistance value is also different. Otherwise, why would the power supply bureau require the grounding wire of each substation transformer and the grounding resistance of each company's distribution room to be less than 4 ohms? Why is it not allowed to use electricity if the grounding resistance of the substation or high-voltage distribution room is not less than 4 ohms? Actually, that's the truth. There will be induced voltage when people are separated from the equipment, and when the human body touches the equipment, there will be an electric current flowing through the human body, and there will be a feeling of being electrified.

Scheme 1: Connect the grounding end of the motor shell, the frame of the mechanical equipment and the grounding terminal of the inverter together

After the ground wire of motor, inverter and frame three are connected together, they are at the same potential, and through the induction surge filter circuit inside the inverter to absorb and discharge, the induced voltage is greatly reduced, so that the voltage of the induced electricity generated by the rotation of the motor is also greatly reduced relative to the ground (i.e. the earth) of the power supply, so that people will not feel electrocuted after touching. That is to say, it doesn't matter if there is no power ground, as long as the ground of the motor, the ground of the inverter and the frame are connected together, so that the inductive surge filter inside the inverter will play a real role.

Scheme 2: Under normal circumstances, after the first scheme is processed, the induced voltage generated by the rotation of the motor is already very small, and it will not leak electricity, but due to some special reasons (such as: the motor insulation is not good, the electrical cabinet is not grounded when installing electrical appliances, etc.), the induced voltage is still high, and there will be a feeling of leakage electricity, and scheme 2 is proposed.

The solution to the problem of leakage of Nidec inverters

The solution to the problem of leakage of Nidec inverters

Sections viewed

Contact

working hours