Siemens sitrans User manual

SITRANS
Variable Frequency Drives and
Instrumentation
Using Variable Frequency Drives and
Instrumentation Without Interference
Application examples
09/2020
AG080819
Introduction
1
Overview
2
Variable Frequency Drive
3
Procedure
4

Siemens AG
Digital Industries
Postfach 48 48
90026 NÜRNBERG
GERMANY
Document order number: AG080819
Ⓟ09/2020 Subject to change
Copyright © Siemens AG 2020.
All rights reserved
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editions.

Using Variable Frequency Drives and Instrumentation Without Interference
Application examples, 09/2020, AG080819 3
Table of contents
1 Introduction ........................................................................................................................................... 4
1.1 Objective ............................................................................................................................. 4
1.2 Equipment........................................................................................................................... 4
1.3 Disclaimer............................................................................................................................ 4
2 Overview................................................................................................................................................ 5
3 Variable Frequency Drive ...................................................................................................................... 6
3.1 What is a Variable Frequency Drive? ..................................................................................... 6
3.2 How does a VFD Work? ........................................................................................................ 6
4 Procedure............................................................................................................................................... 7
4.1 What are the steps to minimize EMC issues from VFDs? ........................................................ 7
4.2 Standards Governing Electromagnetic Compatibility (EMC) of VFDs ...................................... 8

Using Variable Frequency Drives and Instrumentation Without Interference
4Application examples, 09/2020, AG080819
1Introduction
1
1.1 Objective
The objective of this application guide is to help the user become familiar with the steps
required to prevent EMC interference between VFDs and instrumentation.
1.2 Equipment
Equipment Description
MLFB/A5E Number
VFD drive and Process Instrumentation
1.3 Disclaimer
Note
While every effort is made to verify the following information, no warranty of accuracy or
usability is expressed or implied.

Using Variable Frequency Drives and Instrumentation Without Interference
5Application examples, 09/2020, AG080819
2Overview
2
This application guide describes the function of Variable Frequency Drive (VFD) and provides
tips on how to prevent interference issues when VFDs are used with process instrumentation.

Using Variable Frequency Drives and Instrumentation Without Interference
6Application examples, 09/2020, AG080819
3Variable Frequency Drive
3
3.1 What is a Variable Frequency Drive?
A Variable Frequency Drive or VFD controls the rotation of an alternating current motor by
varying the frequency of the electrical power supplied to the motor.
These flexible systems provide accurate speed control and minimize energy usage by
matching motor output to a required load. For example, rather than using a fixed speed
motor for a fan or pump and inefficiently controlling flow output through a damper or valve,
the motor speed can be varied to directly control the rate of flow. VFDs also have soft start
capabilities that reduce peak current draws and wear on electrical and mechanical parts.
These devices are also known as Variable Speed Drives, Adjustable Frequency Drives, or
Inverter Drives.
3.2 How does a VFD Work?
A ‘drive’ refers specifically to the voltage and frequency converter that controls the output to
the motor. A complete system generally includes a drive converter, an AC motor, and a
configuration and control interface.
The drive converter takes an Alternating Current (AC) input and rectifies it to Direct Current
(DC). This intermediate DC voltage is changed again to AC at a desired frequency and
amplitude using a switching inverter stage. This voltage is output to a motor and the
frequency and amplitude varied by a microcontroller to control speed.
The motor is typically a three-phase induction motor, although other configurations are
possible.
The configuration and control interface for the VFD system can be a Human Machine
Interface (HMI), a setpoint input or a module for interfacing to a communications bus, such
as PROFIBUS DP.

Using Variable Frequency Drives and Instrumentation Without Interference
7Application examples, 09/2020, AG080819
4Procedure
4
4.1 What are the steps to minimize EMC issues from VFDs?
The operating function of VFDs causes electromagnetic noise. The high-speed switching of
the inverter stage can emit significant radio frequency energy. Without mitigation, this
energy can interfere with other nearby electrical equipment.
Process control and sensor instrumentation is often found in the same area of a factory or
process as VFDs. Some of this equipment can be sensitive to interference from
electromagnetic sources and this can cause performance degradation ranging from incorrect
measurements to disabled instruments. Precise and reliable measurements require careful
installation and configuration.
Some general installation recommendations will apply in all cases where instrumentation and
VFDs are mounted near each other.
•Install Electromagnetic Compatibility (EMC) filters on the line side of the drive converter.
This will prevent noise from traveling back through the mains and affecting other
equipment.
•Use shielded motor feed cables as recommended by the VFD manufacturer.
The manufacturer will know the characteristics of the energy from the drive and will know
the optimum cable specifications to keep this energy contained.
•The length of feed cables between the drive and the motor should be as short as possible.
This will reduce line losses and will also reduce cost.
•Instrumentation cables and drive components should be as far apart as possible.
Doubling the separation distance will reduce power of the radiated energy to one quarter
of its previous value.
•Avoid parallel runs of drive cables and instrumentation cables.
Cables run in parallel can allow radio frequency energy from one to be induced in the
other.
•If an instrumentation cable must cross a drive cable, it must do so at a 90ºangle.
This will provide a minimum area of coupling between the cables.
•Use shielded and/or twisted pairs for instrumentation cables.
These types of cables are designed to both contain and resist Radio Frequency (RF)
emissions.
•Install cables close to metal surfaces to avoid creating an antenna effect.
Cables raised off metal surfaces can increase the amount of electromagnetic energy
transmitted or received by the cable.

Procedure
4.2 Standards Governing Electromagnetic Compatibility (EMC) of VFDs
Using Variable Frequency Drives and Instrumentation Without Interference
8Application examples, 09/2020, AG080819
•Keep signal cables away from motors and transformers, as they can generate large
magnetic fields.
Magnetic fields can induce currents into nearby cables.
•Follow all grounding recommendations from the VFD and instrumentation supplier.
Grounding is important for both safety and noise suppression.
•Follow all guidelines for installing wireless communication products and antennas.
Incorrect grounding or orientation of antennas can severely reduce their effectiveness and
noise immunity.
•Use quality instrumentation that has the CE or FCC mark.
Equipment with this designation has been designed, tested and certified to withstand
normal levels of electromagnetic interference.
4.2 Standards Governing Electromagnetic Compatibility (EMC) of
VFDs
The specifics of electromagnetic compatibility and standards are beyond the scope of this
document, but an overview is provided. Contact the drive manufacturer for specific details
and regional requirements.
In Europe, VFDs are covered under EMC product standard EN or IEC 61800-3 for Power Drive
Systems. This standard covers the complete system including drive, interface, motor, and
cables.
In the United States, VFD systems are covered in a general manner by FCC CFR Title 47, Part
15, but there are no specific product requirements or test procedures.
The manufacturer of the drive is not responsible for guaranteeing the EMC performance of
the fully installed drive and motor, but they will provide information on the EMC
characteristics, use, and installation of the device as part of a drive system.
Generally, the manufacturer can also supply optional filters and other equipment that will
improve EMC performance.