By Carl R. Goeckeler, P.E., KCP&L
In 2003 and 2004, Kansas City Power & Light’s (KCP&L’s) network customers experienced several outages, jeopardizing the utility’s goal to maintain great customer relations and a high quality of service. In addition, concern arose when three KCP&L underground network crew members narrowly escaped injury when a network protector faulted while the workers were inside the vault. KCP&L executives tasked the company’s distribution automation engineers to provide a solution to these issues as soon as possible.
The project-driven by safety concerns, escalating costs and increasing performance issues with the utility’s aging underground network systems-developed products to reduce costs and improve efficiencies for electric utilities that use network protectors. KCP&L worked with Telemetric and Richards/ETI to develop an economical solution for network automation using commercial cellular networks along with cost-effective hardware and software. This project proved that digital GPRS (general packet radio service) could be used as a reliable and secure way to enable distribution automation in underground vault installations-a solution previously thought to be too difficult or costly to implement using private spread-spectrum radios.
KCP&L’s network systems consist of three grids with numerous transformers connected in parallel through an extensive 120/208-volt secondary grid system. Customers are connected at various parts of this network to serve high-rise office buildings and critical load centers. KCP&L also has approximately 24 concentrated networks (spot-networks) which operate at 120/208 volts or 277/480 volts.
For the project, a cross-functional team was established to study various communications options including fiber optics, one-way power line carriers, hard-wired solutions, various wireless solutions and relay control solutions. Historically, some utilities have used fiber optic systems for this application. After a detailed study, the group chose the Telemetric Corp. wireless solution.
Telemetric was already using the digital control channel of cellular telephony to achieve both low-cost and wide communications coverage. This two-way communications solution uses existing cellular towers and radio systems, thus reducing utility infrastructure investment and maintenance costs. The two-way provision was essential to KCP&L to enable control and setpoint changes.
Extensive tests and a radio survey showed that KCP&L could achieve highly reliable radio coverage using low-cost standard antennae and the Telemetric Remote Telemetry Module (RTM). The team also selected the Microprocessor Network Protector Relay (MNPR) manufactured by Richards/ETI because it supported the DNP protocol and was already in use on the system.
KCP&L worked with ETI/Richards in November 2004 to provide a way to install the radio in a concentrator box that could be mounted high inside the vault, near street level. ETI provided a submersible wiring harness. All protectors were wired with a digital contact to monitor when the protector opened or closed based on circuitry within the protector. In addition, KCP&L worked with ETI to provide a means to sense the position of the network protector handle (in the automatic position or a position other than automatic). KCP&L continues to work with ETI to enable additional DNP monitoring points and to improve the performance of this interface. The KCP&L/Telemetric contract provided for the integration of the Telemetric RTM radio with the ETI relay. This enabled the following DNP features: 22 digital points, 34 analog points, seven control points and 21 alarm points. KCP&L provided technical and financial resources to assist in the development of various Telemetric products to reduce costs and improve efficiencies.
Out with the old network protector (left) and in with the new (right).
The project specified the initial use of analog cellular radios with a migration to GPRS-based digital radios. This GPRS radio was integrated into the Telemetric RTM and shipped to KCP&L for successful bench testing in October 2005. This radio provides significantly more bandwidth and enables powerful distribution automation features such as data logging.
The project also provided for the development of some useful web-based features. (See Website Features, page 58.) As underground network crew members became more confident with the Telemetric website, they realized the need to integrate this new technology into the way they perform their work. They began carrying text-messaging pagers that immediately notified them of network system disturbances. As their understanding of the Telemetric applications grew, they saw the need to acquire and use more and more real-time data while in the field.
KCP&L’s underground network crew can connect their laptops directly to the Telemetric RTM and initiate secure automatic block and unblock commands to the ETI relay without having to be in the manhole vault.
Recently, various departments within KCP&L worked together to provide the underground network crew with a secure and progressive solution to satisfy their growing interest to perform trouble-shooting and network system analysis while in the field. They are now equipped with wireless laptops that can access the Telemetric website from the field. They can obtain a host of operating information, including relay settings, network protector switch positions, transformer loading and alarms while at the job site. They can even initiate control commands and setpoint changes from their laptops while in the truck.
KCP&L worked with ETI to apply sensors to monitor network transformer oil temperature, water in the vault and moisture inside the network protector case. These sensors have proved their value on various occasions. For example, distribution automation engineers reluctantly asked a crew to visit a network vault when they received a high water level alarm. They were suspicious of this alarm because it had not rained within the past two weeks. However, the crew verified there was a problem at this site. Water had entered the vault due to a water main break. Because they were equipped with a pump, they were able to drain the water out of the vault shortly after their arrival.
In another instance, a high oil temperature alarm was received in a vault that requires a ventilating fan to cool down the air in the vault. The crew found that the control power to the fan had been accidentally shut off during routine maintenance of other vault equipment. The fan’s electrical source was restored and the network transformer cooled back to normal temperatures.
The most important feature to the underground network crew is the ability for KCP&L to remotely control the automatic or manual (block) function of the ETI relay. KCP&L worked with Telemetric to enable the underground network crew to connect their laptops directly to the Telemetric RTM and initiate secure automatic block and unblock commands to the ETI relay without having to be in the manhole vault. For example, when a protector is taken out of service for maintenance, the crew connects a laptop to the Telemetric RTM and issues a block and open command while staying at street level and outside the vault. Similar precautions are performed when a protector is placed in service by issuing an “Automatic” command from street level. These commands can also be issued through the Telemetric secure web application to the Telemetric RTM.
KCP&L’s technology implementation should result in far fewer trips into underground vaults and a safer working environment for crew members.
KCP&L has also worked with Telemetric to implement a Telemetric TVM-3 power quality monitor with wireless reporting capabilities. KCP&L encouraged Telemetric to develop the first 277/480-volt rated TVM-3 devices to supplement the existing 120 volt-rated TVM-3 devices already available. These devices automatically report power outages plus over and under voltage events. This power quality monitoring device is installed on each spot network and at strategic locations on each of the grid networks.
The underground network crew encouraged the distribution automation engineers to automate the Country Club Plaza network as the first part of the project. (The Country Club Plaza is a 15-block shopping and entertainment area of Spanish motif with over 150 shops and dozens of restaurants.) The underground network crew was concerned about the historically high operating and maintenance costs on this network due to the high number of network protector operations previously experienced on this grid. However, they did not know the root cause of these excessive operations.
Concentrator box and TVM power quality monitor inside a KCP&L vault.
This Plaza grid was completely automated by the fall of 2005. During the summer of 2005, the Plaza network system was very stable and the protectors operated typically in the normal (closed) position. However, during the fall of 2005, distribution automation engineers noticed a significant number of switching events. Further investigation showed this switching occurred during routine substation maintenance when the network was served from an alternate (non-standard) substation transformer within the same substation.
The alternate transformer had a different per-unit impedance that caused the load to be served through the network system in a disproportionate manner. This also caused the current to circulate between the circuits in an undesirable manner. During certain load flow conditions, the network protector relays would turn on and off as designed as a result of this intermittent reverse current flow through the network protectors.
The underground network crew, distribution system operations (DSO) center and distribution automation engineers worked together to perform switching on the distribution system to mitigate this problem. Further operating experience showed this phenomena occurs when the DSO performed alternate switching of distribution systems during times when two overhead distribution circuits were paralleled for planned switching due to planned maintenance or system reconfiguration.
Thus, KCP&L discovered the cause of excessive switching of the Plaza network protectors. KCP&L is reviewing various alternatives to further mitigate this problem including: circuit reconfigurations, different relay settings and other technical solutions. Continuing network training is being provided to the underground network personnel, dispatchers and engineers so everyone will have a better understanding of this dynamic system.
The KCP&L/Telemetric contract also provided for the development of two powerful website features. The first feature provides radio performance monitoring. This allows users to monitor recent and historical radio performance at specific vaults or in geographic areas to analyze radio signal strength and performance.
The second website development included a powerful and flexible “Customized Device Report” an online query that allows users to select DNP points and simultaneously display the DNP values for various radio-controlled devices. The query feature allows the underground network crew to monitor setpoints of the ETI MNPR relay. In addition, the website automatically sends an e-mail and/or pager alarm when a setpoint changes. This feature proved invaluable when KCP&L discovered various relay setpoints were reverting to factory default settings due to a communication software anomaly that ETI has since resolved.
KCP&L also uses the website tools to build practical and smart algorithms to report nonstandard conditions based on multiple DNP points. For example, one network protector was continually calling for a close, but remained in the open position. When this condition persisted for several minutes, a pre-configured rule-based alarm was sent to the underground network crew leader. He immediately dispatched a crew to this network protector and replaced a failed motor that wasn’t allowing the network protector to close.
Overall, the project brings KCP&L numerous benefits including improved safety, reduced operating and maintenance costs, extended equipment life, and a way to proactively manage its complex underground network systems.
Carl R. Goeckeler is the distribution automation project leader for Kansas City Power & Light, where he has worked for the past 31 years. He received a BSEE degree from the University of Missouri at Rolla in May 1975 and is a registered professional engineer in Missouri. In recent years, KCP&L distribution automation projects have received three national awards, including the “T&D Automation Project of the Year Award” at DistribuTECH 2004.