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One of the significant challenges that substation engineers face is justifying substation automation investments. The positive impacts that automation has on operating costs, increased power quality, and reduced outage response are well known. But little attention is paid to how the use of a communication standard impacts the cost to build and operate the substation. Legacy communication protocols were typically developed with the dual objective of providing the necessary functions required by electric power systems while minimizing the number of bytes that were used by the protocol because of severe bandwidth limitations that were typical of the serial link technology available 10-15 years ago when many of these protocols were initially developed. Later, as Ethernet and modern networking protocols like TCP/IP became widespread, these legacy protocols were adapted to run over TCP/IP-Ethernet.
This approach provided the same basic electric power system capabilities as the serial link version while bringing the advantages of modern networking technologies to the substation. But this approach has a fundamental flaw: the protocols being used were still designed to minimize the bytes on the wire and do not take advantage of the vast increase in bandwidth that modern networking technologies deliver by providing a higher level of functionality that can significantly reduce the implementation and operational costs of substation automation.
IEC 61850 is unique. IEC 61850 is not a former serial link protocol recast onto TCP/IP-Ethernet. IEC 61850 was designed from the ground up to operate over modern networking technologies and delivers an unprecedented amount of functionality that is simply not available from legacy communications protocols. These unique characteristics of IEC 61850 have a direct and positive impact on the cost to design, build, install, commission, and operate power systems. While legacy protocols on Ethernet enable the substation engineer to do exactly the same thing that was done 10-15 years ago using Ethernet, IEC 61850 enables fundamental improvements in the substation automation process that is simply not possible with a legacy approach, with or without TCP/IP-Ethernet. To better understand the specific benefits we will first examine some of the key features and capabilities of IEC 61850 and then explain how these result in significant benefits that cannot be achieved with the legacy approach
Key Features
The features and characteristics of IEC 61850 that enable unique advantages are so numerous that they cannot practically be listed here. Some of these characteristics are seemingly small but yet can have a tremendous impact on substation automation systems.
For instance, the use of VLANs and priority flags for GOOSE and SMV enable much more intelligent use of Ethernet switches that in and of itself can deliver significant benefits to users that aren’t available with other approaches. For the sake of brevity, we will list here some of the more key features that provide significant benefits to users:
- Use of a Virtualized Model. The virtualized model of logical devices, logical nodes, ACSI, and CDCs enables definition of the data, services, and behavior of devices to be defined in addition to the protocols that are used to define how the data is transmitted over the network.
- Use of Names for All Data. Every element of IEC 61850 data is named using descriptive strings to describe the data. Legacy protocols, on the other hand, tend to identify data by storage location and use index numbers, register numbers and the like to describe data.
- All Object Names are Standardized and Defined in a Power System Context. The names of the data in the IEC 61850 device are not dictated by the device vendor or configured by the user. All names are defined in the standard and provided in a power system context that enables the engineer to immediately identify the meaning of data without having to define mappings that relate index numbers and register numbers to power system data like voltage and current.
- Devices are Self-Describing. Client applications that communicate with IEC 61850 devices are able to download the description of all the data supported by the device from the device without any manual configuration of data objects or names.
- High-Level Services. ACSI supports a wide variety of services that far exceeds what is available in the typical legacy protocol. GOOSE, GSSE, SMV, and logs are just a few of the unique capabilities of IEC 61850.
- Standardized Configuration Language. SCL enables the configuration of a device and its role in the power system to be precisely defined using XML files.
Major Benefits
The features described above for IEC 61850 deliver substantial benefits to users that understand and take advantage of them. Rather than simply approaching an IEC 61850 based system in the same way as any other system, a user that understands and takes advantage of the unique capabilities will realize significant benefits that are not available using legacy approaches.
- Eliminate Procurement Ambiguity. Not only can SCL be used to configure devices and power systems, SCL can also be used to precisely define user requirement for substations and devices. Using SCL a user can specify exactly and unambiguously what is expected to be provided in each device that is not subject to misinterpretation by suppliers.
- Lower Installation Cost. IEC 61850 enables devices to quickly exchange data and status using GOOSE and GSSE over the station LAN without having to wire separate links for each relay. This significantly reduces wiring costs by more fully utilizing the station LAN bandwidth for these signals and construction costs by reducing the need for trenching, ducts, conduit, etc.
- Lower Transducer Costs. Rather than requiring separate transducers for each device needing a particular signal, a single merging unit supporting SMV can deliver these signals to many devices using a single transducer lowering transducer, wiring, calibration, and maintenance costs.
- Lower Commissioning Costs. The cost to configure and commission devices is drastically reduced because IEC 61850 devices don’t require as much manual configuration as legacy devices. Client applications no longer need to manually configured for each point they need to access because they can retrieve the points list directly from the device or import it via an SCL file. Many applications require nothing more than setting up a network address in order to establish communications. Most manual configuration is eliminated drastically reducing errors and rework.
- Lower Equipment Migration Costs. Because IEC 61850 defines more of the externally visible aspects of the devices besides just the encoding of data on the wire, the cost for equipment migrations is minimized. Behavioral differences from one brand of device to another is minimized and, in some cases, completely eliminated. All devices share the same naming conventions minimizing the reconfiguration of client applications when those devices are changed.
- Lower Extension Costs. Because IEC 61850 devices don’t have to be configured to expose data, new extensions are easily added into the substation without having to reconfigure devices to expose data that was previously not accessed. Adding devices and applications into an existing IEC 61850 system can be done with only a minimal impact, if any, on any of the existing equipment.
- Lower Integration Costs. By utilizing the same networking technology that is being widely used across the utility enterprise the cost to integrate substation data into the enterprise is substantially reduced. Rather than installing costly RTUs that have to be manually configured and maintained for each point of data needed in control center and engineering office application, IEC 61850 networks are capable of delivering data without separate communications front-ends or reconfiguring devices.
- Implement New Capabilities. The advanced services and unique features of IEC 61850 enables new capabilities that are simply not possible with most legacy protocols. Wide area protection schemes that would normally be cost prohibitive become much more feasible. Because devices are already connected to the substation LAN, the incremental cost for accessing or sharing more device data becomes insignificant enabling new and innovative applications that would be too costly to produce otherwise.
Conclusions
IEC 61850 is now released to the industry. Ten parts of the standard are now International Standards (part 10 is a draft international standard). This standard addresses most of the issues that migration to the digital world entails, especially, standardization of data names, creation of a comprehensive set of services, implementation over standard protocols and hardware, and definition of a process bus.
Multi-vendor interoperability has been demonstrated and compliance certification processes are being established. Discussions are underway to utilize IEC 61850 as the substation to control center communication protocol. IEC 61850 will become the protocol of choice as utilities migrate to network solutions for the substations and beyond.
SOURCE: Ralph Mackiewicz SISCO, Inc. Sterling Heights, MI USA
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Cost benefits of AC drives
In addition to their technical advantages, AC drives also provide many cost benefits. In this chapter, these benefits are reviewed, with the costs divided into investment, installation and opera- tional costs.
At the moment there are still plenty of motors sold without variable speed AC drives. This pie chart shows how many motors below 2.2 kW are sold with frequency converters, and how many without. Only 3% of motors in this power range are sold each year with a frequency converter; 97% are sold without an AC drive.
This is astonishing considering what we have seen so far in this guide. Even more so after closer study of the costs of an AC drive compared to conventional control methods. But first let’s review AC drive technology compared to other control methods.
How many motors below 2.2 kW are sold with and without frequency converters
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Technical differences between other systems and AC drives
AC drive technology is completely different from other, simpler control methods. It can be compared, for example, to the dif- ference between a zeppelin and a modern airplane.
We could also compare AC drive technology to the develop- ment from a floppy disk to a CD-ROM. Although it is a simpler information storage method, a floppy disk can only handle a small fraction of the information that a CD-ROM can.
The benefits of both these innovations are generally well known. Similarly, AC drive technology is based on a totally different technology to earlier control methods. In this guide, we have presented the benefits of the AC drive compared to simpler control methods.
Technical differences between other systems and AC drives
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No mechanical control parts needed
To make a proper cost comparison, we need to study the configurations of different control methods. Here we have used pumping as an example. In traditional methods, there is always a mechanical part and an electrical part.
In throttling you need fuses, contactors and reactors on the electrical side and valves on the mechanical side. In On/Off control, the same electrical components are needed, as well as a pressure tank on the mechanical side. The AC drive provides a new solution. No mechanics are needed, because all control is already on the electrical side.
Another benefit, when thinking about cost, is that with an AC drive we can use a regular 3-phase motor, which is much cheaper than the single phase motors used in other control methods. We can still use 220 V single phase supply, when speaking of power below 2.2 kW.
| Conventional methods: | AC drive: |
| • Both electrical and mechanical parts | • All in one |
| • Many electrical parts | • Only one electrical component |
| • Mechanical parts need regular maintenance | • No mechanical parts, no wear and tear |
| • Mechanical control is energy consuming | • Saves energy |
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Factors affecting cost
This list compares the features of conventional control methods with those of the AC drive, as well as their effect on costs. In conventional methods there are both electrical and mechanical components, which usually have to be purchased separately. The costs are usually higher than if everything could be pur- chased at once. Furthermore, mechanical parts wear out quickly. This directly affects maintenance costs and in the long run, maintenance is a very important cost item. In conventional methods there are also many electrical components. The installation cost is at least doubled when there are several different types of components rather than only one.
And last but not least, mechanical control is very energy con- suming, while AC drives practically save energy. This not only helps reduce costs, but also helps minimise environmental impact by reducing emissions from power plants.
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Investment costs: Mechanical and electrical components
Price Comparison For Pumps
In this graph, the investment structure as well as the total price of each pump control method is presented. Only the pump itself is not added to the costs because its price is the same regardless of whether it’s used with an AC drive or valves. In throttling, there are two possibilities depending on whether the pump is used in industrial or domestic use. In an industrial environment there are stricter requirements for valves and this increases costs.
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The motor
As can be seen, the motor is much more expensive for traditional control methods than for the AC drive. This is due to the 3-phase motor used with the AC drive and the single phase motor used in other control methods.
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The AC drive
The AC drive does not need any mechanical parts, which reduc- es costs dramatically. Mechanical parts themselves are almost always less costly than a frequency converter, but electrical parts also need to be added to the total investment cost.
After taking all costs into account, an AC drive is almost always the most economical investment, when compared to differ- ent control methods. Only throttling in domestic use is as low cost as the AC drive. These are not the total costs, however. Together with investment costs we need to look at installation and operational costs.
| Throttling | AC drive | |
| Installation material | 20 USD | 10 USD |
| Installation work | 5h x 65 USD = 325 USD | 1h x 65 USD = 65 USD |
| Commissioning work | 1h x 65 USD = 65 USD | 1h x 65 USD = 65 USD |
| TOTAL: | 410 USD | 140 USD |
| Savings in installation: 270 USD! | ||
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Installation costs: Throttling compared to AC drive
Because throttling is the second lowest investment after the AC drive, we will compare its installation and operating costs to the cost of the AC drive. As mentioned earlier, in throttling there are both electrical and mechanical components. This means twice the amount of installation material is needed.
Installation work is also at least doubled in throttling compared to the AC drive. To install a mechanical valve into a pipe is not that simple and this increases installation time. To have a mechanical valve ready for use usually requires five hours compared to one hour for the AC drive. Multiply this by the hourly rate charged by a skilled installer to get the total installation cost.
The commissioning of a throttling-based system does not usu- ally require more time than commissioning an AC drive based system. One hour is usually the time required in both cases. So now we can summarise the total installation costs. As you can see, the AC drive saves up to USD 270 per installation. So even if the throttling investment costs were lower than the price of a single phase motor (approximately USD 200), the AC drive would pay for itself before it has even worked a second.
| Throttling | AC drive | |
| Power required | 0.75 kW | 0.37 kW |
| Annual energy 4000 hours/year | 3000 kWh | 1500 kWh |
| Annual energy cost with 0.1 USD/kWh | 300 USD | 150 USD |
| Maintenance/year | 40 USD | 5 USD |
| TOTAL COST/YEAR: | 340 USD | 155 USD |
| Savings in installation: 185 USD! | ||
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Operational costs: Maintenance and drive energy
In many surveys and experiments it has been proved that a 50% energy saving is easily achieved with an AC drive. This means that where power requirements with throttling would be 0.75 kW, with the AC drive it would be 0.37 kW. If a pump is used 4000 hours per year, throttling would need 3000 kWh and the AC drive 1500 kWh of energy per year.
To calculate the savings, we need to multiply the energy con- sumption by the energy price, which varies depending on the country. Here USD 0.1 per kWh has been used.
As mentioned earlier, mechanical parts wear a lot and this is why they need regular maintenance. It has been estimated that whereas throttling requires USD 40 per year for service, maintenance costs for an AC drive would be USD 5. In many cases however, there is no maintenance required for a frequency converter.
Therefore, the total savings in operating costs would be USD 185, which is approximately half of the frequency convert- er’s price for this power range. This means that the payback time of the frequency converter is two years. So it is worth considering that instead of yearly service for an old valve it might be more profitable to change the whole system to an AC drive based control. To retrofit an existing throttling system the pay-back time is two years.
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Total cost comparison
Total Savings Over 10 Year - USD 1562
In the above figure, all the costs have been summarised. The usual time for an operational cost calculation for this kind of investment is 10 years. Here the operational costs are rated to the present value with a 10% interest rate.
In the long run, the conventional method will be more than twice as expensive as a frequency converter. Most of the savings with the AC drive come from the operational costs, and especially from the energy savings. It is in the installation that the high- est individual savings can be achieved, and these savings are realised as soon as the drive is installed.
Taking the total cost figure into account, it is very difficult to understand why only 3% of motors sold have a frequency con- verter. In this guide we have tried to present the benefits of the AC drive and why we at ABB think that it is absolutely the best possible way to control your process.
SOURCE: ABB Drives
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