Pick up nearly any power industry magazine and you'll find a feature about cutting costs in the utility market place. As deregulation introduces competition between power utilities, each utility is faced with the challenge of finding competitive advantages.
Optimizing utility operations to provide the most efficient and economical power delivery is more important than ever - and is part of an overall trend to control costs.
With a new dedication to efficiency, many utilities are discovering significant economic benefits through the use of microprocessor-based relays. Larry Gross, Protection Services Manager at Schweitzer Engineering Laboratories (SEL), a leading designer and manufacturer of digital relays for over 16 years, offers the following tips for cost savings through intelligent microprocessor-based relays.
Tip #1
Use Advanced Technology to Reduce Outage Time
Use microprocessor-based protective relays with fault locating and automated/remote control capabilities. Fault-location capabilities assist crews in finding trouble areas much more quickly than by random line patrol - an extremely valuable asset when costly helicopter fly-overs are required to find the trouble spot. In addition, programmable automatic reclosing (fuse-saving or trip-saving methods) provides the ability to restore the line automatically. In addition, the remote capability allows SCADA or other master device commands to restore the line.
"On long transmission lines, it's extremely critical to find the point of failure on the line quickly,Ó Gross pointed out. "In the past, someone would just drive down the line until the fault was found. For critical lines, a helicopter might be used-but that still consumes a lot of expensive time."
Tip #2
Use Advanced Relaying Technology to Maximize Flexibility
Microprocessor-based relays are feature-rich, programmable devices with configurable I/O that provides for flexible designs. Relay settings can be downloaded locally by means of a laptop computer, or remotely through a modem connected to one of the relay serial ports. Multiple settings groups give the user the flexibility to select the appropriate settings for system conditions via a selector switch, serial port command, or from the relay Human Machine Interface (HMI).
"Microprocessor relays can be programmed to support PLC type functions, so that engineers can create a logic scheme within the relay. That helps eliminate auxiliary devices and gives you a lot of flexibility," commented Gross. "That way, you can ensure that if your scheme needs to change six months from now, you don't have a lot of wiring changes. Instead of replacing the relay, you can simply change the logic settings to take care of the new scheme you want to implement."
Tip #3
Take Advantage of System Analysis Tools
Microprocessor-based relays can be used to provide system analysis by means of full-length event reports and programmable Sequence of Events Recorder (SER) reports.
Microprocessor relays can also provide some power system measurements for both power providers and users. Breaker wear and DC battery monitoring are other features that allow analysis of the integrity of the breaker or battery bank in question.
Tip #4
Consider System Reliability
High quality components and a proven, robust relay design lead to a highly reliable product which in turn leads to increased system reliability. The combination of a high mean time between failure (MTBF), relay self test diagnostics, and alarm capability helps to ensure that the relay will provide proper, reliable protection.
Also, since microprocessor-based relays are less expensive than the many devices they replace, it is more economically feasible to provide redundant backup protection and further improve system reliability.
Tip #5
Maximize System Protection Availability
According to Gross, protection availability is improved through high product reliability, reduced maintenance intervals, self test diagnostics and relay trouble alarming that microprocessor relays offer. Should the relay become disabled, it is easily identified and can be quickly repaired or replaced. This provides minimal downtime and maximum system protection availability that is unmatched by electromechanical or solid state devices.
Self-tests offer a major advantage over electromechanical relays, which are equipped with no self-checking facility, and are only tested at scheduled maintenance intervals. "With electromechanical relays, if you have a failure, the best case scenario is that you'd find out at the next test," Gross noted. "In the worst case, you find out when your entire system fails because of an undiscovered electromechanical relay failure."
"With microprocessor relays, most problems will cause the alarm function to activate. Operators are notified within a few seconds and a technician can be sent to the station. This keeps unavailability times to a minimum."
Tip #6
Reduce Commissioning Time
Commissioning is the process of verifying the entire scheme before it is put into operation.
"When you install a system, you want to make sure that it will provide reliable service. Microprocessor-based relays have a lot of metering features and remote capabilities that allow you to provide quicker, simpler commissioning," Gross explained. "With microprocessor-based relays, the time required for commissioning is easily reduced by 50 per cent."
Tip #7
Reduce Space Requirements
Save panel space by using feature-rich microprocessor-based relays where one device may replace multiple relays, meters, control switches, indicators, and quite often, communications gear and RTUs. Create more room in the control house by replacing complete panels of equipment with just a few microprocessor-based devices.
Complicated dual panel layouts per terminal for protection and control are easily reduced to a clean, single panel or rack that includes all of the protection, monitoring, and control - with space to spare.
Tip #8
Reduce Wiring Requirements
In addition to requiring less panel space, the use of multifunction microprocessor-based relays reduces the amount of panel wiring required in a design. Control wiring is minimized, and specific functions such as reclosing, torque control, and trip coil monitoring are performed by the single relay unit instead of several devices. "Complete use of microprocessor relays can reduce panel wiring by 70 per cent," Gross advised.
"In any project, one of the biggest costs is the labor required for installation and testing," Gross pointed out. "But with microprocessor relays, several efficiencies can be realized. First, there are fewer relays, so you don't have to wire as many of them. Second, microprocessor relays can provide a lot of the logic functions that used to be implemented in wiring, so you don't have extraneous wires serving as logic systems.
Third, some of the communication schemes that once required auxiliary equipment now can be connected relay-to-relay through the serial port. The best part about it is that, with less wiring and auxiliary equipment, there are fewer potential points of failure."
Tip #9
Take Advantage of System Self-Diagnostics
Save money by changing maintenance procedures to take advantage of microprocessor relay capabilities. Microprocessor-based relays do not require the same periodic maintenance associated with electromechanical devices and are equipped with self-test diagnostics that continuously monitor the health of the device.
A relay that is malfunctioning or has failed closes a dedicated "alarm" output contact to signal that assistance is required. This signal can also be used to activate special back up protection, or modify protection schemes when the primary protective relay has detected a problem and taken itself out of service. The periodic tests required to detect failures that the self-tests do not detect are reduced to a minimum.
In addition, users can analyze data from relay event reports to detect unusual conditions earlier than the next periodic test.
Tip #10
Simplify Design
Replacing multiple relays, meters, switches, indicators, and communications gear with a single microprocessor-based protective relay leads to simplified designs. Substation/system schematics and wiring diagrams are much easier to generate and reproduce due to the reduced number of devices and related wiring.
"A simplified design saves both time and money," Gross stated. In some cases, the same relay may be used across the power system from distribution to sub-transmission or from network distribution to Extra High Voltage (EHV). Utilizing a similar design for all voltages reduces design time, installation time, and operation review."
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