7. EMC (Electromagnetic Compatibility)

7.1 Definition
Electromagnetic compatibility is the ability of the electric equipment to work in the electromagnetic interference environment and implement its function stably without interferences in the electromagnetic environment.

 

7.2 EMC Standard Description
In accordance with the requirements of the national standard GB/T12668.3, the inverter needs to comply with electromagnetic interference and anti-electromagnetic interference requirements.
Products apply the latest international standard—IEC/EN61800-3: 2004 (Adjustable speed electrical power drive systems part 3: EMC requirements and specific test methods), which is equivalent to the national standard GB/T12668.3.
IEC/EN61800-3 assesses the inverter in terms of electromagnetic interference and anti-electronic interference. Electromagnetic interference mainly tests the radiation interference, conduction interference and harmonics interference on the inverter (required for the inverter for civil use). Anti-electromagnetic interference mainly tests the conduction interference rejection, radiation interference rejection, surge interference rejection, fast and mutable pulse group interference rejection, ESD interference rejection and power low frequency end interference rejection (specific test items including: 1. Interference rejection tests of input voltage sag, interrupt and change; 2. Phase conversion interference rejection test; 3. Harmonic input interference rejection test; 4. Input frequency change test; 5. Input voltage unbalance test; 6. input voltage fluctuation test).
The tests should be conducted strictly in accordance with the above requirements of IEC/ EN61800-3, and the products of our company are installed and used according to Section 7.3 and have good electromagnetic compatibility in general industry environment.

 

7.3 EMC Guide
7.3.1 Harmonic effect
Higher harmonics of power supply may damage the inverter. Thus, at some places where mains quality is rather poor, it is recommended to install AC input reactor.

 

7.3.2 Electromagnetic interference and installation precautions
There are two kinds of electromagnetic interferences, one is interference of electromagnetic noise in the surrounding environment on the inverter, and the other is interference of inverter on the surrounding equipment.
Installation precautions:
1) The earth wires of the Inverter and other electric products should be well grounded;
2) The power input and output power cables of the inverter and weak current signal cables (e.g. control line) should not be arranged in parallel and vertical arrangement is preferable.
3) It is recommended that the output power cables of the inverter employ shield cables or steel pipe shielded cables and that the shielding layer be earthed reliably. The lead cables of the equipment suffering interferences are recommended to employ twisted-pair shielded control cables, and the shielding layer should be earthed reliably.
4) When the length of motor cable is longer than 100 meters, it needs to install output filter or reactor.

 

7.3.3 Handling method for the interferences of the surrounding equipment on the inverter
The electromagnetic interference on the inverter is generated because plenty of relays, contactors and electromagnetic brakes are installed near the inverter. When the inverter has error action due to the interferences, the following measures can be taken:
1) Install surge suppressor on the devices generating interference;
2) Install filter at the input end of the inverter. Refer to Section 7.3.6 for the specific operations;
3) The lead cables of the control signal cable of the inverter and the detection line employ shielded cable and the shielding layer should be earthed reliably.

 

7.3.4 Handling method for the interferences of inverter on the surrounding equipment
These interferences include two types: one is radiation interference of the inverter, and the other is conduction interference of the inverter. These two types of interferences cause the surrounding electric equipment to suffer electromagnetic or electrostatic induction. The surrounding equipment hereby produces error action. For different interferences, it can be handled by referring to the following methods:
1) For the measuring meters, receivers and sensors, their signals are generally weak. If they are placed nearby the inverter or together with the inverter in the same control cabinet, they are easy to suffer interference and thus generate error actions. It is recommended to handle with the following methods: Put in places far away from the interference source; do not arrange the signal cables with the power cables in parallel and never bind them together; both the signal cables and power cables employ shielded cables and are well earthed; install ferrite magnetic ring (with suppressing frequency of 30 to 1,000MHz) at the output side of the inverter and wind it 2 to 3 cycles; install EMC output filter in more severe conditions.
2) When the equipment suffering interferences and the inverter use the same power supply, it may cause conduction interference. If the above methods cannot remove the interference, it should install EMC filter between the inverter and the power supply (refer to Section 7.3.6 for the prototyping operation); the surrounding equipment is separately earthed, which can avoid the interference caused by the leakage current of the inverter’s earth wire when common earth mode is adopted.
3) The surrounding equipment is separately earthed, which can avoid the interference caused by the leakage current of the inverter’s earth wire when common earth mode is adopted.

 

7.3.5 Leakage current and handling
There are two forms of leakage current when using the inverter. One is leakage current to the earth, and the other is leakage current between the cables.
1) Factors influencing the leakage current to the earth and the solutions:
There are distributed capacitance between the lead cables and the earth. The larger the distributed capacitance is, the larger the leakage current will be. The distributed capacitance can be reduced by effectively reducing the distance between the inverter and the motor. The higher the carrier frequency is, the larger the leakage current will be. The leakage current can be reduced by reducing the carrier frequency. However, reducing the carrier frequency may result in addition of motor noise. Note that additional installation of reactor is also an effective method to remove the leakage current.
The leakage current may increase following the addition of circuit current. Therefore, when the motor power is high, the corresponding leakage current will be high too.
2) Factors of producing leakage current between the cables and solutions:
There is distributed capacitance between the output cables of the inverter. If the current passing the lines has higher harmonic, it may cause resonance and thus result in leakage current. If thermal relay is used, it may generate error action.
The solution is to reduce the carrier frequency or install output reactor. It is recommended that thermal relay not be installed before the motor when using the inverter, and that electronic over current protection function of the inverter be used instead.

7.3.6 Precautions for Installing EMC input filter at the input end of power supply
1) When using the inverter, please follow its rated values strictly. Since the filter belongs to Classification
I electric appliances, the metal enclosure of the filter should be large and the metal ground of the installing cabinet should be well earthed and have good conduction continuity. Otherwise there may be danger of electric shock and the EMC effect may be greatly affected.
2) Through the EMC test, it is found that the filter ground must be connected with the PE end of the inverter at the same public earth. Otherwise the EMC effect may be greatly affected.
3) The filter should be installed at a place close to the input end of the power supply as much as possible.