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Rules for installation and safety

EMC MEASURES FOR DESIGN AND INSTALLATION.

10 RULES FOR DESIGN OF INSTALLATION WITH DRIVE CONTROLLERS IN COMPLIANCE WITH EMC
(Download brochure, PDF file, 0.3 MB)

The following rules are the basics for designing and installing drives in compliance with EMC:

  • All metal parts of the cabinet have to be connected with one another over the largest possible surface area to establish a good electrical connection. This, too, applies to the mounting of the EMC filter. If required, use serrated washers which cut through the paint surface. The cabinet door should be connected to the cabinet using the shortest possible grounding straps;
  • Ensure a spacing of at least 100 mm between power cables and control or signal cables (e.g. encoder cables), or Partition cable ducts metallically. Route signal lines separately from load lines to avoid interference;
  • Contactors, relays, solenoid valves, electromechanical operating hour counters etc. in the control cabinet must be provided with interference suppression combinations. These combinations must be connected directly at each coil;
  • Non-shielded cables belonging to the same circuit (feeder and return cable) have to be twisted or the surface between feeder and return cable has to be kept as small as possible;
  • Generally, interference injection are reduced by routing cables close to grounded sheet steel panels. For this reason, cables and wires should not be routed freely in the cabinet, but close to the cabinet housing or mounting panels;
  • Lines of measuring systems have to be shielded. The shield has to be connected to ground at both ends and over the largest possible surface area. The shield may not be interrupted, e.g. using intermediate terminals;
  • The shields of digital signal lines have to be grounded at both ends (transmitter and receiver) over the largest possible surface area and with low impedance. Bad ground connection between transmitter and receiver requires additional routing of a bonding conductor (min. 10 mm2). Braided shields are to be preferred to foil shields. The shields of analog signal lines generally have to be grounded at one end (transmitter or receiver) over the largest possible surface area and with low impedance, in order to avoid low-frequency interference current (in the mains frequency range) on the shield;
  • Correctly use a mains filter recommended by producer for radio interference suppression in the supply feeder of the AC drive system. The incoming and outgoing cables of the radio interference suppression filter have to be separated;
  • Preferably use the motor power cables with shield. Keep length of motor power cable as short as possible. Ground shield of motor cable at both ends over the largest possible surface area to establish a good electrical connection;
  • The shield of the motor cable mustn't be interrupted by mounted components, such as output chokes, sine filters, motor filters.

PROTECTION OF SERVO INVERTER SYSTEMS WITH FAST SEMICONDUCTOR FUSES
To ensure adequate protection, servo inverter systems must be installed so that they are connected via fast semiconductor fuses as specified in the Technical Manuals. Slow-blow fuses are by no means permissible for inverter systems. If such fuses are nevertheless used, a short-circuit in the dc-link of a power module might result in the destruction of the power supply unit. The use of fast semiconductor fuses prevents the destruction of the power supply unit. If a short-circuit in the power modules causes damage to power supply units which were not protected as required by HEIDENHAIN, Rexroth, Siemens etc. it is the customer's fault.
For example, the following fuses must be used:

  • SIBA, typ gRL or
  • SIEMENS, typ Sitor gR.

LIGHTNING PROTECTION ZONES CONCEPT AND SURGE PROTECTIVE DEVICES FOR POWER SUPPLY SYSTEMS AND EQUIPMENT (CNC AND SERVO SYSTEMS)
(Download brochure, PDF file, 2.7 MB)

Lightning Protection Zones Concept
 Failures of technical systems and installations are very unpleasant for the operators. These require faultless operation from the equipment both under “normal“ conditions and in case of thunderstorms. Loss reports of insurance companies show clearly that there is a backlog demand both in the private and the commercial sector. A comprehensive protection concept would help to compensate it. The Lightning Protection Zones Concept enables designers, constructors and operators to plan, perform and control protection measures. Thus, all relevant devices, installations and systems are protected reliably and furthermore with economically acceptable efforts.

Sources of interferences
Surges arising due to thunderstorms, are caused by direct / close lightning strokes or distant lightning strokes. Direct or close lightning strokes are strokes into the lightning protection system of a structure, into its immediate surroundings or into the conductive systems entering the structure (e.g. low voltage power supply, telecommunication and control lines...). Due to their amplitudes and energy loads, the arising impulse currents and impulse voltages represent a special risk for the system to be protected.

At a close or direct lightning stroke, the surges are caused by a voltage drop at the impulse earthing resistance and the resulting potential rise of the structure towards the distant surroundings. This is the max. load on electrical installations in structures.

The characteristic parameters of flowing impulse currents (peak value, rate of current rise, load, specific energy) can be described with the impulse-current wave form 10/350 µs and are defined in international, European and national standards as test currents for components and devices for the protection against direct lightning strokes.

In addition to the voltage drop at the impulse earthing resistance, surges arise in the electrical structure and the connected systems and equipment due to the induction effect of the electromagnetic lightning field. The power of these induced surges and the resulting impulse currents is considerably lower than the power of a direct lightning impulse current and is therefore only described with the impulse current wave 8/20 µs. Components and equipment, which do not have to conduct currents out of direct lightning strokes, are therefore tested with impulse currents of 8/20 µs.

Protection philosophy
Distant strokes are lightning strokes from a distance to the object to be protected, lightning strokes into the medium voltage overhead line network or into its immediate surroundings, or lightning discharges from cloud to cloud. In analogy to induced surges, the effects of distant lightning strokes on the electrical system of a structure are controlled by devices and components, which are designed accordingly for impulse current wave 8/20 µs. Surges due to switching operations (SEMP) are caused by e.g.:
 – switching off inductive loads (e.g. transformers, coils, motors)
 – ignition and interruption of electric arcs (e.g. arc welding device)
 – tripping of fuses.
The effects of switching operations in electrical installations of structures are also emulated for test engineering with impulse currents of wave form 8/20 µs.
For ensuring a continuous availability of complex electrical and IT systems, even in case of a direct lightning effect, further measures for the surge protection of electrical and electronic installations are necessary, based on a building lightning protection system. Taking all causes of surges into consideration is very important. For this purpose, the Lightning Protection Zones Concept described in IEC 62305-4 is applied. A structure is subdivided in different risk zones. With these zones the necessary devices and components can be defined for lightning and surge protection. Part of an EMC-conform lightning protection zones concept is an external lightning protection system (including air-termination system, down-conductor system, earthing), equipotential bonding, spatial shielding and the surge protection for the power supply and IT systems.

In correspondence with the requirements and loads on surge protective devices regarding their installation site, these are classified as lightning current arresters, surge arresters and combined lightning current and surge arresters. The highest requirements regarding the discharge capacity are made on lightning current and combined lightning current and surge arresters, which realise the transition from Lightning Protection Zone 0A to 1 or 0A to 2

These arresters must be able to conduct partial lightning currents, wave form 10/350 µs, several times without destruction in order to prevent the penetration of destructive partial lightning currents into the electrical installation of a building. At the boundary from LPZ 0B to 1 or downstream of the lightning current arrester at the boundary from LPZ 1 to 2 and higher, surge arresters are used for protection against surges. Their function is to further reduce both the residual load of the upstream protection levels and limit the induced or own surges.

The aforementioned lightning and surge protective measures at the boundaries of the lightning protection zones apply to both power supplies and IT systems to the same extent. Due to the entirety of the measures described in the EMC-conform Lightning Protection Zones Concept, a permanent system availability of a modern infrastructure can be achieved.

Surge Protective Devices
Surge protective devices are items of equipment whose basic components are voltage-controlled resistors (varistors, suppressor diodes) and/or spark gaps (discharge paths). The function of surge protective devices is to protect other electrical equipment and installations against impermissibly high surges and/or to establish the equipotential bonding.

Surge protective devices are classified:
a) upon their application in
 – Surge protective devices for power supply systems and equipment for nominal voltage ranges of up to 1000 V
 • according to E DIN VDE 0675 Part 6:1989-11 in Ableiter (new: Ьberspannungs-Schutzeinrichtung) der Anforderungsklassen A, B, C, D – replaced by DIN EN 61643-11 from October 2004
 • according to EN 61643-1:1998-02 in SPD Type 1/2/3
 • according to IEC 61643-1:1998-02 in SPD class I / II / III
 – Surge protective devices for IT systems and equipment for protection of modern electronic systems in telecommunications and signal-processing networks with nominal voltages of up to 1000 V ac (root-mean-square value (rms)) and 1500 V dc against indirect and direct effects of lightning strokes and other transient surges.
 • according to IEC 61643-21:2000 + Corrigendum:2001, EN 61643-21:2001 and DIN VDE 0845 Part 3-1.
 – Isolating spark gaps for earth-termination systems or for equipotential bonding.
b) upon their impulse current discharge capacity and their protective effect in
 – Lightning Current Arresters for interferences due to direct or close lightning strokes for protection of installations and equipment (for use at the boundaries of Lightning Protection Zones (LPZ) 0A and 1).
 – Surge Arresters for distant lightning strokes, switching overvoltages as well as electrostatic discharges for protection of installations, equipment and terminal devices (for use at the boundaries downstream of LPZ 0B).
 – Combined Lightning Current and Surge Arresters for interferences due to direct or close lightning strokes for protection of installations, equipment and terminal devices (for use at the boundaries between LPZ 0A and 1 as well as 0A and 2).

Technical data of surge protective devices
The technical data of surge protective devices comprise information defining the application conditions upon:
– application (e.g. installation, mains conditions, temperature)
– performance on interferences (e.g. impulse current discharge capacity, follow current extinguishing capability, voltage protection level, response time)
– performance during operation (e.g. nominal current, attenuation, insulation resistance)
– performance on failure (e.g. backup fuse, disconnection device, failsafe function).

MORE INFO
For complete products information, Please, visit producers' web sites or contact directly our CNC Department by e-mail cnc@esd.bg.

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