I. What is electromagnetic interference:
1. Common sources of interference in
power systems may include high-voltage transmission lines, switching operations, and lightning. For example, when a switch is disconnected or closed, it may produce transient voltage or current changes that can cause electromagnetic interference. There are also devices like transformers and motors that generate electromagnetic fields during operation, which may interfere with surrounding electronic equipment.
2. The types of interference should then be categorized into conducted and radiated interference. Conducted interference is propagated through wires, such as power or signal lines, while radiated interference is electromagnetic waves that propagate through space. In power systems, both types of interference may exist. For example, transient voltages from switching operations can be conducted along wires and affect other equipment, while strong electromagnetic fields around high-voltage lines may interfere with nearby communications equipment in the form of radiation.
II. Sources of electromagnetic interference:
Natural factors: Lightning discharges, cosmic radiation and other natural phenomena can generate strong electromagnetic pulses.
Power equipment operation:
Switching operation: Arcs and transient voltages (e.g. surges) generated when circuit breakers, disconnect switches are opened and closed.
High-frequency equipment: high-frequency harmonics generated during the operation of frequency converters, inverters, and power electronic devices (e.g., IGBT).
Fault conditions: transient electromagnetic fields caused by short circuit and ground faults.
External environment: strong electric and magnetic fields near
high-voltage transmission lines, or wireless signals from neighboring communication equipment
III. The effects of electromagnetic interference:
For power systems, disturbances may lead to erroneous operation of relay protection devices, affecting the stable operation of the power system. For example, erroneous signals may lead to unnecessary tripping of circuit breakers, resulting in power outages. In addition, there are more and more electronic devices in the smart grid, such as smart meters and sensors, etc. These devices are more sensitive to electromagnetic interference, and once disturbed, data acquisition and transmission may be wrong, affecting the monitoring and management of the entire system.
IV. Protective measures:
How to deal with electromagnetic interference, common approaches include shielding, filtering, grounding, isolation and so on. For example, use metal shielding to wrap cables and reduce radiated interference; install filters at the power inlet to suppress conducted interference; a good grounding system can channel interference currents to avoid buildup; and isolation cuts off conduction paths through transformers or optocoupler isolators. In addition, it is also important to follow electromagnetic compatibility (EMC) standards when designing equipment to ensure that the equipment itself is highly resistant to interference without generating too much interference.
The following are now the mainstream pit interference filters EMI:
1. Product Appearance
2. EMI wiring diagram
V. Practical application scenarios:
Smart Grid: A large number of electronic devices (e.g. PMUs, smart meters) require high immunity to interference.
High-voltage direct current transmission (HVDC): converter stations need to suppress harmonics and electromagnetic radiation.
New energy grid connection: photovoltaic inverters and wind turbines need to avoid harmonic injection into the grid.
