Design

What is EMC

EMC stands for “electromagnetic compatibility”; it describes the capability of a device to operate satisfactorily in the electromagnetic environment, without causing electromagnetic interference which is unacceptable for other devices in this environment. In other words, the different devices must not interfere with each other.

Emitted interference and interference immunity

EMC depends on two characteristics of the devices involved: emitted interference and interference immunity. Electrical devices can be interference sources (transmitters) and/or interference sinks (receivers).

Electromagnetic compatibility exists when the interference sources do not affect functioning of the interference sinks.

A device can be simultaneously an interference source and sink. For example, the power section of a converter can be considered as an interference source and the control section as an interference sink.

Limit values

Product standard EN 61800-3 (IEC 1800-3, DIN VDE 160 Part 100) covers electrical drives. According to this product standard, not all EMC measures are essential for industrial supply systems; a solution must be defined which is adapted to the actual environment. This it may be economically more advantageous to increase the interference immunity of a sensitive device rather than implement interference suppression on the converter. The choice of solution, therefore, also depends on economic factors.

To some extent, adherence to EN 55011 is required. This defines the limit values for emitted interference in industry and in residential buildings. Conducted interference at the supply connection is measured under standardized conditions as a radio interference voltage and electromagnetically emitted interference is measured as interference emission The standard defines limit values “A1” and “B1” which apply to radio interference voltage over the range 150 kHz and 30 MHz and to interference emission over the range 30 MHz to 2 GHz. Since the SIMOREG K converters are used in industry, limit value “A1” applies. To achieve limit value “A1”, the SIMOREG K units must be provided with external RFI filters.

Interference immunity describes the behavior of a device under the influence of electromagnetic interference. Standard EN 50082-2 governs the requirements and assessment criteria for the behavior of the devices in industry. This standard is met by the converters listed in the following Section.

Ungrounded supply systems

In some branches of industry, ungrounded supply systems (IT systems) are used to increase availability of the plant. In the event of a ground fault, there is no ground current and the plant can continue with production. In conjunction with radio interference suppression filters, however, there is a fault current in the event of a ground fault which can result in a shutdown of the drives or even the destruction of the filter. The product standard therefore does not specify limit values for these systems. For economic reasons, interference suppression, if required, should be implemented on the grounded primary side of the supply transformer.

EMC planning

If two devices are electromagnetically incompatible, you can reduce the emitted interference of the source or increase the interference immunity of the sink.

Interference sources are usually power electronics devices with a high current consumption. To reduce their emitted interference, elaborate filters are required. Interference sinks are, in particular, control units and sensors including their evaluation circuits. Enhancing the interference immunity of low-power devices is less involved. For economical reasons in industry, therefore, it is often more favorable to increase the interference immunity than to reduce emitted interference. To satisfy limit value class A1 of EN 55011, for example, the radio interference voltage at the supply terminals must not exceed 79 dB (µV) between 150 and 500 kHz, and 73 dB (µV) (9 mV or 4.5 mV) between 500 kHz and 30 MHz.

In industry, the EMC of equipment should be based on a judicious balance between emitted interference and interference immunity.

The least expensive suppression method is to separate the interference sources and sinks, provided that this is taken into account during the planning of a machine/plant. For each device used, the first question is whether it is a potential interference source or sink. Examples of interference sources in this context are converters and contactors. Examples of interference sinks are programmable controllers, encoders and sensors.

The components in the cabinet (interference sources and sinks) should be separated, if necessary with partition plates or by installing them in metal housings. Fig. 5/35 shows a possible arrangement of components in the cabinet.