D R Meek, Product Manager, ABB South Africa (Pty) Ltd, P. O. Box 11494, Randhart, 1457, South Africa; e-mail:
dave.meek@za.abb.com
Abstract
This paper introduces the concept of intelligent switchgear and further discusses the differences between conventional control systems and intelligent control systems. Concerns with intelligent switchgear are discussed and the economic factors which influence decisions between conventional systems and intelligent systems are highlighted.
Introduction
Process industries have recently observed dynamic and unprecedented innovations to harvest the latest industrial information technological advancements. A lot has been done in the areas of process control, optimization and management information but very little is said about the plant electrical system, in particular the low voltage motor protection and control system, although the plant productivity directly relates to the smooth and efficient running of motors. Low voltage switchgear still references the conventional systems whereby, although it serves a purpose, it is unable to keep pace with other sophisticated systems in the plant.
The intelligent era
The concept of intelligent switchgear was introduced to the market over a decade ago but initially did not gain momentum, as the end user remained apprehensive on reliability and response time issues. Today this scenario is changing fast for a number of reasons, including the following:
The emergence of enabling open field bus technology is adding new dimensions to communication reliability. In response time critical control applications, field bus networks are providing a highly reliable platform for data transfer between microprocessor devices and plant process control system.
In today’s highly demanding and dynamic environment, new plant projects and the refurbishment of old projects have become highly time critical. To remain competitive, the focus is now on highly flexible solutions that can adapt process design modifications easily and quickly. The solution is found in the microprocessor devices that provide the required flexibility and reliability.
The increased intelligence of microprocessor devices is bringing an unprecedented flow of information, which was unthinkable in the past, allowing effective control of the plant process.
What is intelligent switchgear?
Conventional versus intelligent:
Conventional switchgear: In conventional switchgear the primary component for motor protection is the thermal overload relay, which uses a bi- metal strip to trip the motor under overload conditions. Depending on the application, different motor starting and control circuits have been developed using a multitude of different components. Typical control components are; relays, timers, pushbuttons, selector switches, current transformers, meters, counters, etc. While these conventional systems are still well entrenched in the industry they have a number of drawbacks, most notably the inability to preempt a trip condition. If the motor does trip, then this inevitably results in a process stoppage with enormous costs consequences, which may well have been avoidable if the operator had the ability to be proactive rather than reactive.
Intelligent switchgear: In intelligent switchgear the thermal overload relay and the control components that is required for a conventional starter is replaced with one microprocessor based protection and control unit. This microprocessor unit is able to provide electronic overload protection for the motor using a mathematical model, which is able to accurately calculate the heating effect on the motor and thus protect the motor from damage due to thermal overload. In addition to the thermal protection function the microprocessor unit is able to provide different control, measuring, monitoring and protection functions, which in the conventional system is only achievable with numerous other control components. Furthermore, using a bus system, it is possible to integrate the microprocessor unit into a higher-level system, which allows control from this higher-level system and provides status information and measured values to the system.
Multifunctional and programmable

A key requirement for any microprocessor based protection and control unit is that it must be multifunctional and programmable to meet most, if not all, the applications in the industry.
Starter types
Typical starter types supported are as follows:
Direct on line, reversing and non-reversing
Start delta
Softstarters
Two speed
Actuators
Autotransformers
Overload protection function
The overload protection function is arguably the most important function of any motor control and protection application and therefore requires comprehensive functionality. The protection function allows the configuration of preset alarm levels, trip levels and trip delays. If the thermal load of the motor increases above the preset alarm level an alarm is issued without tripping of the motor. If the thermal load increases further and the trip level is reached the motor will trip but only if the thermal load remains above the trip level for the trip delay time. Detailed information of the alarms and trips are sent via the bus to the higher-level system, providing the operator with information enabling preventative actions and educated decisions to be made before the plant status becomes critical. This empowers the operator to act proactively rather than reactively, which is normally the case with conventional switchgear.
Other important functions are the ability to determine the time that it will take for the motor to trip after the alarm is issued and how long it will take for the motor to cool down after a trip has occurred, before it can be restarted. These are important parameters for optimised process control. It may be a requirement to automatically restart the motor once it has cooled down or to bypass the tripping of the motor under overload conditions for plant critical equipment.
Motor protection functions
Other protection functions included in microprocessor based protection devices are as follows:
Phase loss protection
Phase current unbalance protection
Stall protection
Undervoltage protection with automatic restart
Rotation monitoring
Motor temperature monitoring
Earth fault protection
Limitation on the number of starts per hour
Limitation on the time between successive starts
Underload and noload protection
In general, it is possible to enable or disable each protection function, set and alarm level, trip level and trip delay time.
Reporting and supervision functions
The essence of intelligent switchgear is the ability to provide more information to the operators than is possible with conventional systems as this facilitates more optimised process control.
Typical reporting and supervision functions are as follows:
Motor status (running, ready, alarm or tripped)

Phase currents (actual, percentage, 4-20mA analogue output)
Calculated thermal load of the motor in percentage
Time to trip and time to reset.
Phase voltages
Power factor
Active power and reactive power
Earth fault current
Frequency
Networkable – connectivity and communication
Thirty years ago “automation” meant pneumatics and large panels full of interconnected contactors. Fifteen years ago,
“automation” meant programmable logic controllers, hydraulics and panels full of contactors.
Today everyone is attacking the cost of automation and supervision and the consequence is that every phase of the system is being examined with respect to cost reduction.
Today the market demands:
Connectivity: The trend is moving away from discrete cabling towards fieldbus technology where the more common fieldbusses are: Modbus, Profibus, Fieldbus Foundation, CAN, DeviceNet, Ethernet, LON, …………
Intelligence: Increasing the intelligence of the devices results in enhanced functionality, flexibility through application programming and the possibility of combining simple devices into multifunctional ones.
Interoperability: It should be possible for the user to mix and match components as required by the application.
Scalable: The system should be scalable which allows configuration in accordance with the application needs.
It should be possible to have two or more simultaneous connections to higher-level control systems, making dual redundant configurations and multi-master communications an integral part of the system design.
Concerning the implementation of fieldbus technologies, there exists two different field bus philosophies. One philosophy
(of which PROFIBUS is the main example) implements the master/slave concept, where the master devices are responsible collecting information (from the slaves), making decisions and implementing those decisions (by sending commands to the slaves). The other philosophy (of which LON is the main example) distributes intelligence and responsibility among the participating devices. In this philosophy, every device is responsible for making information available to others and collecting information from others.
LON stands for Local Operating Network, and is an atypical example of a field bus system. It is atypical in the sense that the whole concept is built around a communication engine, comprising both hardware and software. The net result is that in building a distributed system, no one has to think consciously about sending and receiving messages. A global variable is automatically available across the bus to anyone who needs it, the communication engine takes care of all the details involved.
LON is developed and marketed by Echelon, a US company that was founded for the express purpose of integrating communication and automation. This concept had its first successes in building automation, an area where the integrated communication was a critical success factor. The ability to handle automation and supervision tasks that are physically distributed over large areas remains one of the most important aspects of LON.
The peer-to-peer or master-to-master communications philosophy supported by LON allows the exchange of data between devices on an equal rights basis. Microprocessor devices and process control systems communicate on an event driven basis, which leads to shorter response times. A collision avoidance method named Carrier Sense Multiple Access (CSMA) is used to minimize the possibility of collisions on the bus.
In event driven communication data is transmitted only if it has changed state, which results in less bus communication and bus load. Heartbeats are used to control the integrity of data links between the devices and the process control system and allow the use of the failsafe functionality to switch the motor to a predefined state in the event of a loss of communications.

The architecture of Intelligent Switchgear normally provides devices at three levels in order to provide the complete switchgear management system.
The field device level: At the field device level, the microprocessor based motor control unit protects, controls, and supervises one or three phase fixed speed AC motors. The device can compute and process the information on the connected communication media.
The monitoring device level: The devices at monitoring level are capable of displaying all the diagnostics and status information. They also support complete configuration, operation, and supervision of the field devices.
The external interface device level: At the external interface device level, the intelligent switchgear provides direct interface to the plant process control system, or depending upon the supported communication protocol in the process control system, the communication interface can be achieved via the appropriate gateways. The desired information needed on every motor can be configured and displayed in the plant process control station.
Concerns in the industry
Break in communication
The break in communication between the intelligent switchgear and the process control system is one of the major concerns that need to be addressed.
Of course, redundancy is an alternative but most of intelligent switchgear goes a step further and provides the fail-safe functionality during the loss of communication. This way the planned shutdown of the plant is assured rather than a catastrophic one.
However, one can argue that the occurrence of such a possibility is rare as the communication cables are normally laid with caution. Take the case of a conventional solution where a cut cable or a loose connection may trip the plant. The probability of this happening is more probable in the case of the large number of cables and multiple connection points. The failure in
DCS I/Os can also increase the probability of a break in communication.
Response times
Indeed, there is no match to the response time of a conventional system with parallel wiring. The recommendation is that the response time needs to be evaluated in terms of the process requirement specifically in the trip situations of the drive or during the start-up of a backup motor. The criteria for measurement should be adequate response time with respect to the process tolerance limit rather than matching the fast response time of a point-to-point hardwired system.
The intelligent solutions are addressing this issue by utilizing more reliable and high-speed field buses to manage the internal data traffic effectively. Also note that response time should not only be judged by the communication speed of the interface but also by the technique adopted by media access control sub layer of the communication protocol for handling message collisions and their early detection. The solution can also be achieved with the appropriate engineering during the configuration of the system.
The complex solution
It is incorrect to assume that the sophistication adds to the complexity although it certainly calls for careful handling. The technically advanced solutions are developed to ensure the end user benefits from the technology and enable him/her to handle their day-to-day job effectively and with ease. Intelligent switchgear does not require technical experts to handle and maintain the system. Most systems are user friendly and guide the user through every aspect. References show that the reluctant purchasers are becoming repeat customers and are building confidence in the new solutions.
The utilization of information
Intelligent switchgear provides detailed information on every starter despite the fact many plant process operators argue this is unnecessary. However, properly engineered information provided by intelligent switchgear can help operators handle the process more effectively. The ability to flexibly configure alarm and trip information is a great advantage. Every protection function can be configured as desired by the process specific needs and the availability of the process can be maximized in the most optimal way. For example, the underload protection can be configured only for alarm reporting and no trip. The underload alarm information can thus be utilized to increase the process feed or the appropriate process action. Similarly in some critical process situations the overload trip of the motor that can cause catastrophic process shutdown can be bypassed temporarily.
The economics of intelligent switchgear

Engineering costs
It’s quite common to have design and process changes during the project phase. The impact of these changes is twofold.
Firstly, they reinitiate commercial and administrative formalities and secondly, they need to be co-ordinated among different departments. Both these activities are time consuming and impact the project time schedule.
The benefit when using an intelligent solution is that often these changes normally entail a few soft-parameter changes, which only take a matter of minutes. The hidden benefit is that those involved on the project can better utilise their time elsewhere on more meaningful project engineering activities.
Optimisation of electrical components
A single device replaces all protection relays (eg. TOL, Earth Fault, Phase unbalance, underload, etc), timers (eg. star-delta, autorestart timers) and metering (eg. Ammeter, Voltmeter, Pf, kW etc). Complex protection circuitry and interposing relays for external contact wiring are also eliminated.
Installation and commissioning costs
The main activities during installation and commissioning of conventional switchgear are checking the protection schemes for the individual starter modules, incorporation of commissioning changes and connecting cables to the plant’s process control system. The former needs troubleshooting in case of problems, which is a tedious procedure as no direct diagnostics are available. The latter part needs comprehensive preparation of a cable schedule and termination diagrams, the installation of cable trays, cable laying, the termination and testing of cables to DCS I/Os via a marshalling panel, etc. The intelligent switchgear simplifies the former with the standardised module wiring and generation of accurate diagnostics on the monitoring devices. The latter part needs single wire communication to the plant process control system, which eliminates complete cable trays and related cable engineering. This means reduced installation time, which helps to enhance the project start up schedule.
Compact and space efficiency
The size of the starter modules in conventional switchgear depends upon the motor rating; drive types, complexities of control schemes, protections and metering requirements. The microprocessor-based devices in intelligent switchgear are compact and do not require extra hardware and cabling. This obviously leads to less space and less civil, ventilation and lighting costs.
Accuracy
The intelligent solution allows motor configuration parameters to be set to the precise level and promotes detailed engineering. For example, setting of t6 time for thermal overload protection from five to 40 seconds. This allows optimal usage of the motor without the fear of causing any damage to it.
Inventory and storage costs
The reductions in drive specific components and elimination of different drive types, switchgear starter modules and DCS
I/O cards results in less spare parts. This reduces inventory and storage costs.
Conclusion
Intelligent switchgear is a concept that can propel low voltage systems to network based systems adding unprecedented flexibility and ease of operation. This is a result of Industrial IT , which is driving the hard solutions to soft, and facilitating the electrical move to digital. Intelligent switchgear is simplifying installation and commissioning procedures for the plant electrical system and proving to be a contributing factor in meeting the highly compressed duration of plant electrical projects without compromising the quality of engineering. The carefully selected hardware components benefited by the microprocessor technology offers precision and reliability for numerous repetitive functions with no mechanical wear and tear of components. The flexibility of fine-tuning the parameters helps to utilise the motors in the most optimal way without the fear of tripping or damaging the motor. A pre-trip warning on the developing problem enables proactive decisions to be made rather than the reactive ones. The accuracy in the fault diagnosis helps in fault finding and reducing downtime.
The field bus techniques employed by intelligent switchgear is addressing concerns on the response time. The fail-safe techniques employed during the communication failures and reliable bus redundancy to the process control station is taking away the fear of the loss of the communication.
The end users are increasingly realizing the usefulness of the concept and are becoming more adaptive to the intelligent solution and this will drive the growth of Intelligent Switchgear further in the industry.