When designing a plant or system, the EMC concept is an important component and is essential when it comes to achieving a high plant availability. When developing our cabinets, a lot of emphasis was placed on an EMC-compliant design. The cabinets are designed based on an EMC zone concept, and cables are routed so that there is a clean demarcation. In addition, the customer interfaces – that are easy to access – provide sufficient space to connect cable shields. Noise emission can be additionally reduced by selecting the radio interference suppression filter option (L00).

Basic information about EMC

What is EMC?

EMC stands for "ElectroMagnetic Compatibility" and describes "the capability of a device to function satisfactorily in an electromagnetic environment without itself causing interference unacceptable for other devices in the environment". Therefore, the various units should not mutually interfere with one another.

Interference emission and interference immunity

EMC is dependent upon two properties of the units involved in the system: interference emission and interference immunity. Electrical units can be sources of interference (senders) and/or potentially susceptible equipment (receivers).

Electromagnetic compatibility is ensured when the existing sources of interference do not impair the function of potentially susceptible equipment.

A unit may even be a source of interference and potentially susceptible equipment at the same time. For example, the power section of a converter unit should be viewed as a source of interference and the control unit as potentially susceptible equipment.

Product standard EN 61800-3

The EMC requirements for "Variable-speed drive systems" are described in the product standard EN 61800-3. A variable-speed drive system (or Power Drive System PDS) consists of the drive converter and the electric motor including cables. The driven machine is not part of the drive system. EN 61800?3 defines different limits depending on the location of the drive system, referred to as the first and second environments.

Residential buildings or locations at which the drive system is directly connected to a public low-voltage supply without intermediate transformer are defined as the first environment.

The term second environment refers to all locations outside residential areas. These are basically industrial areas which are supplied from the medium-voltage line supply via their own transformers.

Definition of the first and second environments

Four different categories are defined in EN 61800-3 Ed.2 depending on the location and the power of the drive:

Category C1: Drive systems for rated voltages < 1 000 V for unlimited use in the first environment.

Category C2: Stationary drive systems for rated voltages < 1 000 V for use in the second environment. Use in the first environment is possible if the drive system is marketed and installed by qualified personnel. The warning information and installation instructions supplied by the manufacturer must be observed.

Category C3: Drive systems for rated voltages < 1 000 V for exclusive use in the second environment.

Category C4: Drive systems for rated voltages ? 1 000 V or for rated currents ? 400 A for use in complex systems in the second environment.

The following diagram shows how the four categories are assigned to the first and second environments:

Definition of categories C1 to C4

SINAMICS DC MASTER is almost exclusively used in the second environment (categories C3 and C4).

Radio interference suppression filters are always required for use in Category C2 (option L00); further, the commutating reactor cannot be deselected.

SINAMICS DC MASTER conforms to the interference immunity requirements defined in EN 61800-3 for the second environment, and thus also with the lower requirements in the first environment.

Standard EN 55011

Some situations require compliance with standard EN 55011. This defines limit values for interference emissions in industrial and residential environments. The values that are measured are conducted interference at the line supply connection as interference voltage, and electromagnetically radiated interference as radio interference, under standardized conditions.

The standard defines limit values "A1" and "B1" which, for interference voltage, apply to the 150 kHz – 30 MHz range and, for radio interference, the 30 MHz – 2 GHz range. Since SINAMICS DC MASTER converter units are used in industrial applications, they are subject to the limit value "A1". To achieve limited value "A1", radio interference suppression filters (option L00) are always necessary; further, the commutating reactor must not be deselected.

SINAMICS DC MASTER, industrial applications

Industrial applications demand that units demonstrate an extremely high level of interference immunity, but by contrast place very low requirements on them in terms of interference emission levels. The limit values for interference emission "A1" of EN 55011 are maintained when using the additional radio interference suppression filter (option L00) and EMC-compliant connection of the cabinets. If the drive cabinet forms part of a plant or system, it does not initially need to fulfill any interference emission requirements. However, EMC legislation does stipulate that the plant or system as a whole must be electromagnetically compatible with its environment.

Non-grounded line supplies

Non-grounded line supplies (IT line supplies) are used in some branches of industry in order to increase the availability of the plant. In the event of a ground fault, no fault current flows and the plant can continue with production. However, in conjunction with radio interference suppression filters, in the case of a fault, a fault current flows, which can cause the drives to shut down or possibly even destroy the radio interference suppression filter. This is the reason that the product standard does not define any limit values for these types of line supplies. From an economic perspective, any necessary EMC conformance measures should be taken on the grounded primary side of the supply transformer.

EMC planning

If two units are not electromagnetically compatible, you can reduce the interference emission level of the source of interference or increase the interference immunity of the potentially susceptible equipment.

Sources of interference are generally power electronics units with high power consumption. Reducing their interference emission levels requires complex filters. Potentially susceptible equipment usually refers to controlgear and sensors, including their evaluation circuit. Lower costs are involved with increasing the interference immunity of units with lower power ratings. This means, that from an economic perspective, increasing the interference immunity is generally a more favorable option for industrial applications than reducing the interference emission level. For example, to maintain limit value class A1 of EN 55011, the radio interference voltage at the line supply connection point between 150 and 500 kHz can be a max. of 79 dB (?V) and between 500 kHz and 30 MHz, a max. of 73 dB (?V) (9 or 4.5 mV).

In industrial applications, EMC between units should be based on a carefully-balanced combination of the interference emission and interference immunity levels.

The most cost-effective measure that can be put in place to achieve EMC conformance is to physically separate sources of interference and potentially susceptible equipment - provided that you have taken this option into account during the planning stage of your machine/plant. In the first instance, it is necessary to determine whether each unit used is a potential source of interference or potentially susceptible equipment. Within this context, converter units and contactors, for example, can be counted as sources of interference. While examples of potentially susceptible equipment include PLCs, encoders and sensors.

The components in the drive cabinet (sources of interference and potentially susceptible equipment) must be physically separated, by means of partition plates if necessary, or by installing them in metal enclosures.

EMC-compliant drive installation (installation instructions)

General information

Not only are drives operated in a wide variety of environments, but the electrical components used (controls and switched mode power supplies, and so on) can also differ widely with respect to interference immunity and interference emission levels, meaning that all installation guidelines of any kind can offer is a practical compromise. For this reason, EMC rules do not need to be always precisely implemented, provided that measures are tested on a case-by-case basis.

In order to ensure electromagnetic compatibility (EMC) in your control cabinets in rugged electrical environments and adhere to the standards required by the relevant legislating body, the EMC rules listed below should be followed during the construction and design stages.

Rules 1 to 8 are generally valid. Rules 9 to 11 must be followed in order to fulfill interference emission standards.

Rules for EMC-compliant installation

Rule 1
Signal cables ¹⁾ if at all possible, should only be routed at just one level in the cabinet.

Rule 2
Unshielded cables in the same circuit (outgoing/incoming conductors) must be twisted wherever possible, or the area between them minimized, to prevent the unnecessary formation of frame antennae.

Rule 3
Connect spare wires at both ends to the cabinet ground (ground ²⁾). This provides an additional shielding effect.

Rule 4
Avoid unnecessary cable lengths. This keeps coupling capacitances and inductances low.

Rule 5
Crosstalk is generally reduced, if cables are routed close to the control cabinet ground. Therefore, do not route cables freely around the cabinet, but route them as close as possible to the cabinet enclosure or to the mounting plates. This also applies to spare cables.

Rule 6
Signal and power cables must be physically separated (to prevent coupling paths). A minimum distance of 20 cm must be observed.

If it is not possible to physically separate the encoder and motor cables, the encoder cable must be decoupled either using a partition or by routing it in a metal conduit. The partition or metal conduit must be grounded at several points.

Rule 7
Ground the shields of digital signal cables at both ends (source and destination), ensuring maximum contact area and good conductivity. In the event of poor equipotential bonding between the shield connections, run an additional equipotential bonding conductor with a cross-section of at least 10 mm² parallel to the shield for the purpose of reducing the shield current. Generally speaking, the shields may also be connected to the cabinet enclosure (ground) at several points. The shields can be connected several times even outside the drive cabinet.

Foil-type shields should be avoided, as they are at least 5 times less effective than braided shields.

Rule 8
Shields for analog signal cables may be connected to ground at both ends if the equipotential bonding is good (this must be done through a large surface area with good conductivity). It can be assumed that equipotential bonding is good if all of the metal parts are interconnected with one another through a good electrical connection and the electronics components are supplied from a single source.

Connecting shields at one end prevents low-frequency, capacitive interference from being coupled in (e.g. 50 Hz hum). In this case, the shield should be connected in the drive cabinet; whereby the shield can also be connected using a separate wire.

Rule 9
A line reactor must be included in the field circuit for controlled field power supplies.

Rule 10
A commutating reactor must be included in the armature circuit of the converter.

Rule 11
The motor cables do not have to be shielded. There must be a clearance of at least 20 cm between the line supply feeder cable and the motor cables (field, armature). If necessary, a separating metal partition should be used.

Additional diagrams show details that are not immediately clear in the overview diagram and which may also have an effect on the resistance to interference/interference emission levels of the drive cabinet as well as different shield connection techniques.

Shielding at the cable entry to the cabinet

Shielding in the cabinet

Shield connection

Shield connection

(1) Connecting terminal on a copper bar, max. cable diameter 15 mm

(2) Bar-mounting terminal on a copper bar, max. cable diameter 10 mm

(3) Metal tube or cable tie on a bare-metal comb-type/toothed bar

(4) Clamp with metal backing plate on a cable support rail

¹⁾ Signal cables are defined as:
Digital signal cable:
Cables for pulse encoders,
Serial interfaces, e.g. PROFIBUS?DP or
analog signal cable, e.g. ± 10 V setpoint cable.

²⁾ Generally speaking, "ground" refers to all metallic conductive parts that can be connected to a protective conductor, such as the cabinet enclosure, motor enclosure, or foundation ground etc.