How to Handle Harmonics in Electrical Power Systems

How to Handle Harmonics in Electrical Power Systems

While musical harmonics can be pleasing to the ear, electrical current harmonics are an increasing problem in power systems. Equipment and cables can overheat, motors can be damaged, and your electric bill could be a lot higher than it needs to be.

Without going into Fourier equations or requiring an electrical engineering level of knowledge, let’s look at the cause of harmonics in today’s power systems, and how a power engineering review of your facilities can help solve the problem.

Harmonic waves compared to normal alternating current and voltage waves

The dictionary definition of “harmonics” is: A wave whose frequency is a whole-number multiple of another wave.

The usual waveform of alternating current in most electric power circuits is a sine wave that changes directions at a specific frequency, usually 50 or 60 hertz. A linear electrical load draws current at the same frequency and sinusoidal wave shape as the voltage frequency and wave shape, although the timing or phase between current and voltage may change.

Examples of linear loads include incandescent lighting and electric heaters. The load for constant-speed AC motors is almost linear, and the load current is a sine wave with very little distortion because linear loads are relatively steady and don’t produce any new frequencies (harmonics).

Non-linear loads, however, cause harmonics because they draw current at frequencies other than 60 Hz, in abrupt and uneven pulses.  These non-sinusoidal distortions in the current and voltage waveforms then layer themselves as multiple frequencies upon the fundamental frequency. These multiple frequencies are called harmonics.

Offices have many sources of nonlinear loads that are harmonic generators, such as computers, printers, copiers, and LED drivers for fluorescent lighting.  Industrial sources of nonlinear loads include uninterruptible power supplies, rectifiers, variable frequency/speed drives for motors, programmable controllers, and fluorescent lighting.

AC three phase wave – add third harmonic

Harmonics can creep into your power system

The percent of non-linear loads in office buildings and industrial facilities has increased over the last decade as incandescent lighting is replaced by fluorescent lighting, as more computers and programmable controllers are connected to the electrical system, and as more electric motors use variable frequency drives (VFDs). Harmonic disturbances can also be transmitted from the network if you have an unfiltered power factor correction capacitor on your incoming power.

Third harmonics are caused by power supplies in computers and electronic ballasts, and can result in a neutral current greater than the phase currents.

The fifth and seventh harmonics produced by the three phase bridge rectifiers in the power supplies of six-pulse VFDs create pulsating torques that can cause shaft vibrations, and damage motor bearings and couplings.

Higher harmonic distortions can also lead to the nuisance tripping of circuit breakers, the overheating of cables and equipment, and the premature failure of electrical equipment.  Transformers can quickly overheat and fail after load changes due to replacing or adding electrical equipment, installing VFDs, and upgrading electronic ballasts. Plant manufacturing safety may be at risk.

How bad are your harmonics?

IEEE standard 519 provides guidelines for acceptable values of total harmonic distortion (THD).  Its focus is on the point of common coupling.  The standard also seeks to limit damage to power factor correction (PFC) capacitors and harmonic filter systems from excessive harmonics, and to prevent series or parallel resonance in the electrical system.

The goal is to limit the THD to less than 5% where an industrial power system is connected to the utility network. If your THD values exceed the IEEE 519 values, it’s important to determine whether harmonics are causing problems.

Harmonics and a poor power factor could be costing you money

Harmonics and power factor are not directly related but taking action to cure power factor could enhance the problem of harmonics. The power factor is the ratio (from -1 to +1) of the actual power used by the load compared to the apparent power available in the circuit. A change from unity or power factor of 1 to some other number leading or lagging means that current is shifted relative to the voltage applied.

A power factor of 1 means that no current is lost or distorted. A power factor of 1 says that all of the current is going into doing useful work.  Any number less than 1 indicates that some of the applied voltage goes into magnetic or other forms of energy that are not lost but when it is given back it shifts the current. A low power factor means that you are not fully using the electric power you are buying when your local utility charges a “power factor penalty” or bills you for your kVA usage instead of your KW demand.  This current is increased and causes system losses and this is what the utility is trying to cover these losses with higher demand charges or power factor penalties.

To understand the power factor, let’s look at a glass of beer. The glass represents the apparent power, or kVA.  The actual beer in your glass is the actual power or kW.  Any foam at the top of your glass is the reactive power, or kVAR.  It doesn’t perform useful work, but is used to maintain a magnetic flux in motors, for example.

The more foam you have, the less beer you have, but you still paid for a full glass. Similarly, your utility company will charge you for the apparent power, which is the sum of the actual power plus the reactive power.

Reducing harmonics and raising your power factor

A thorough energy audit by an electrical engineer can yield impressive paybacks on power factor improvements.  But without expert guidance, attempts to improve your power factor may make your harmonics worse.  Installing components like capacitors for power factor correction may actually amplify the harmonic resonance voltage distortion.  This can cause high spikes of voltage at capacitor terminals and lead to their premature failure.  The very item installed to reduce power factor penalties (the capacitor) could self-destruct because the harmonic currents are amplified by just the right system electrical conditions.

If you do not have more than 20% of your electrical load from harmonic generators and there are no power factor correction capacitors, you should not have significant harmonic issues.

However, if non filtered power factor correction capacitors are installed on a system with significant harmonic generators, Matrix can analyze the susceptibility of your facility’s electrical power system to total harmonic distortion.  We can also review the myriad utility rates and determine if your costs are significantly impacted by a poor power factor.

Matrix Technologies is one of the largest independent process design, power systems engineering, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our electrical power system capabilities and manufacturing process control solutions, contact Vince Trejchel, PE.

© Matrix Technologies, Inc.

Mobile Technology: Is Your Plant Millennial-Friendly?

Mobile Technology: Is Your Plant Millennial-Friendly?

The Millennial generation – generally considered to be people who reached adulthood around the beginning of the 21st century – has grown up in a world filled with electronics and increasingly online and socially-networked. They are the first conscious participants in an era when everyone has access to everything, everywhere, at any time. This is the generation of mobile technology, wireless communications, and clouds of continuous content.

Millennials grew up with computers, the Internet, and the graphical user interface (GUI). This familiarity makes them adept at understanding interfaces and visual languages. They tend to adjust readily to new programs, operating systems (OS), and devices and to perform computer-based tasks more quickly than older generations. Although it’s been proven that multitasking is not usually an effective way to work, Millennials may be the employees most likely to pull it off.

As Millennials have moved into the workforce, employers – including industrial manufacturers – have made major shifts and adaptations in their approaches to technology and computing.

Technology-oriented Millennials are also impacting the computing environment and contributing to the increasing stress being placed on enterprise networks. What was once only an asset used to share corporate resources on corporate computers across an organization is today evolving into the means by which qualified employees and customers access needed company information from any place at any time from any device.

To manage the growing need to disseminate information to end users and customers on an on-demand basis, corporate IT organizations are increasingly turning to cloud computing and virtualization. The traditional corporate network is fading as the network of choice; today, employees and customers alike choose to connect to corporate resources through their own personal devices, not only in the office, but remotely over the Internet as well.

As a result, IT departments find themselves creating networks that provide access to all users – on demand – regardless of where they are located or the means they use to access information.

Network Security in an Age of Mobility and Ubiquitous Access

Keeping the network secure and setting priorities on the use of personal hardware is becoming an even more difficult issue for IT departments. The trend toward the increasing accommodation of all types of mobile device access, the use of cloud computing, and the use of virtualization has a momentum of its own. More and more companies find they need to flex and adjust to incorporate these capabilities into their networking business models or else fall behind competitively.

Enter the world of mobility and ubiquitous network access. Imagine a network that can manage input and interfaces from a variety of end users and customers regardless of the type of access.

Imagine also developing an application within the network, which simultaneously acts as a friendly front end while it manages access points and devices. Such an intelligent network will distribute information and applications to the right user at the right time – on demand. It is a sophisticated response mechanism that is always ready, and one that can expand as future requirements demand.

Today’s modern knowledge workers and consumers demand it. It will manage input from a variety of devices and users and do it on demand.

How Industrial Manufacturers Can Meet these Challenges

Though technology changes are creating new challenges for industrial manufacturers, the answer can be found in the development of the mobile solutions.

Mobility can be transformative. It brings more actionable data to the right individuals, provides a clear visibility into operation along with analytics, and provides an effective communication method for user interaction. It can also assist in maintenance rounds, data collection, and commissioning.

As production workflows are automated and the factory is digitized, mobile solutions can help enforce required actions are performed in the correct sequence and data logged and tracked in near real time.

Manufacturers need an experienced partner to help them navigate all of the considerations for mobile applications. Matrix Technologies can provide you the support you need.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, contact John Lee, Strategic Manager of Manufacturing Intelligence.

© Matrix Technologies, Inc.

Choosing an Automation Platform: Compliance with IEC 61131

Choosing an Automation Platform: Compliance with IEC 61131

IEC 61131 was published in 1993 after over 10 years of development by IEC (the International Electrotechnical Commission). The 10-part standard is an attempt to standardize programmable controllers.

Each of the 10 parts addresses a different part of the programmable controller. Parts are identified by the number following the standard, such as “IEC 61131-1.”

Here are all 10 parts of the standard:

  • Part 1: General Information;
  • Part 2: Equipment requirements and tests;
  • Part 3: Programming languages;
  • Part 4: User guidelines;
  • Part 5: Communications;
  • Part 6: Functional safety;
  • Part 7: Fuzzy control programming;
  • Part 8: Guidelines for the application and implementation of programming languages;
  • Part 9: Single-drop digital communication interface (SDCI);
  • Part 10 (Under development): XML exchange formats for programs according to IEC 61131-3.

Standards are platform independent, which means that ideally, automation systems following the standard can be ported from one platform to another. However, this is not always the case in practice because each automation vendor has special functions and tools that apply only to their hardware. At a basic level, though, a code base developed in one platform will work on another platform as long as both conform to this standard.

Key Programming Parts of the Standard

Two of the most commonly known parts of this standard are part 3 and part 9. Part 3 deals with programming languages and part 9 is known as Single-drop Digital Communication Interface, SDCI, or more commonly “IO-Link.”

Part 3 defines modern PLC programming languages: Structured Text (ST), Instruction List (IL), Ladder Diagram (LD), Function Block Diagram (FBD), and Sequential Function Charts (SFC).

This part of standard details the elementary data types and the way that user data types are defined. Compliance with this standard means that data types are consistent across platforms. It means that an integer on platform A is the same size as an Integer on platform B.

It also describes the types and scope of variables in a PLC (Global, Local, I/O, External, and Temporary) and it defines the program configuration details, like Tasks and Programs. It also defines Program Organization Units (POU). These include Functions and Function Blocks. In the Rockwell world, these are called Add-on Instructions (AOIs), while most other platforms call them Functions or Function Blocks (not to be confused with Function Block Diagram programming language).

Part 8 of the standard is a technical report on how to put all the parts from Part 3 together. This part is a software development guide using the standards from Part 3

Part 10 of the standard is still under development, but it describes an XML schema for exchanging programs according to Part 3, which would enable you to take your program from one platform to another without a problem.

Whatever automation platform you choose, it is important that it meets IEC 61131. Nearly all modern platforms conform to this standard in some way. Using a system integrator company that knows this standard means that you will not be limited to any specific industrial automation platform and opens the possibilities of options.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our industrial automation services, or selecting a platform that follows the IEC standard contact Terry DuMoulin.

© Matrix Technologies, Inc.