Monitoring Underground Power Networks

Transcription

1 Monitoring Underground Power Networks By Mark Stiles Merve Cankaya ABSTRACT Underground electric distribution systems are common in large cities throughout the United States. Power usage for the entire system is typically monitored at the substation, but individual transformers that directly serve a customer or a smaller network are unmonitored. The first notification that a problem exists is often the customers complaint. To be immediately aware and proactive, Public Service Electric and Gas New Jersey (PSE&G) installed a Network Monitoring System (NMS) on its 26 kv underground networks to provide a higher quality power distribution system. Using technologies that were proven in the industry to provide reliability and ease of maintenance, PSE&G now has an economical method of improving the reliability, power quality, and efficiency of underground network systems. The NMS allows PSE&G to monitor the real-time status of all equipment on the network and receive alerts to all events on the network, thereby reducing the number of interruptions by intelligently and proactively managing the equipment on the network and improving response to failures by better understanding failure locations, thus minimizing the length of time to locate the failed component. 1. INTRODUCTION By installing an NMS on its 26 kv underground network, PSE&G is taking action to solve challenges commonly faced by today s distribution operations. Both regulatory bodies and consumers demand improved reliability and quality of electric service to homes business and industrial customers. Minimizing outages, maintaining acceptable voltage and reactive power profiles, reducing outage times and slowing down the growing cost of system operations, have all proven important incentives for distribution operators to look toward creative automation solutions. Disturbances in the underground system can result in extended outages. By monitoring cable failures, voltage disturbances and other power quality issues, such as from nonlinear loads and equipment problems of its 26 kv underground network system, PSE&G is able to respond quickly and ultimately reduce outages and other instances of failures. The installed network monitoring system is a highly reliable automation and monitoring system for large dedicated subtransmission (26 kv) underground secondary networks. The network monitoring system is a two-way installed communication network, providing real time

2 monitoring of network parameters and control of transformer network protector relays. The system enables remote monitoring and data collection of the electrical system s distribution transformers normally found in underground manholes or building vaults. Primary monitoring of the system is from the dispatcher s supervisory control and data acquisition (SCADA) workstations at the division headquarters. Transformer data is collected from a relay mounted in the protector, and from sensors in the protector and vault. This data is available for both alarming and historical analysis. The use of a redundant fiber optic communications ensures a fast, secure and reliable system. 2. SYSTEM ARCHITECTURE An Open Systems International (OSI) monarch SCADA system was installed at each of the PSE&G division headquarters for operations monitoring and control. The system includes a terminal server, operator interface and front-end processor. The front-end processor polls the remote terminal units (RTUs) on a periodic basis and on an exception basis to retrieve the data from the field devices. An OSIsoft PI data historian system is installed in the PSE&G corporate headquarters for data storage and analysis. The system includes the PI server and analytical software. The distribution system includes the substation and distribution transformers, located in a manhole or vault, with one to four transformers per location. The networking and communications hardware is located in the substation. Communications, data acquisition and control hardware are located in each of the transformer locations. The communications network, from the master station to the substations, is frame relay provided by a third party. The communications network from the substation to the transformer locations is a redundant fiber optic ring. For the initial installations (1 st generation) of the networks, all fiber and communications were concentrated at one substation, and a single RTU provided the interface to the transformer locations. The final installation (2 nd generation) added redundant communications to two substations and located a vault RTU at each transformer location to improve reliability. 3. COMMUNICATIONS TECHNOLOGY Fiber Optics A Singlemode optical fiber cable (1310 nm) backbone was installed for the communications from the substation to near the individual vaults. The fiber was designed for maximum throughput and redundancy. A 72 count primary fiber was installed underground in existing conduits in a ring configuration, leaving the substation through one patch panel and returning to the substation on another patch panel. A 4 count fiber was spliced into the primary fiber for communications to each individual RTU.

3 More than 50 miles of fiber, 29 miles for the main loop, and 21 miles for the drops to the individual vaults, was installed for the five networks of the NMS. Redundancy Redundancy was built into the system for the communications to the underground transformer locations. Each end of the primary fiber was connected to a switch in the substation(s), and a secondary fiber was spliced into the primary fiber at the transformer vault, connecting to a switch. All switches were programmed for Rapid Spanning Tree (RST) technology. Reference Figure 3 for a schematic lay out of the system. The 1 st generation installations provided redundancy for the communications to the transformer vaults through switch 1 and switch 2, but the communications to the master station was a single non-redundant connection to a single RTU. For the 2 nd generation installation, switch 1 was located in one substation, switch 2 was located in a second substation and all RTUs were located in the transformer vaults. This allowed for a fully redundant system from the master station to the transformer vault. Reference Figure 4 for a schematic layout of the system. 4. SCADA An OSI SCADA system is installed in the PSE&G distribution centers. The OSI system provides the following functions: Graphical User Interface Supervisory Control and Data Acquisition Communications Front-end Processing Alarm Management Data Storage For long-term historical data storage and data analysis, an OSIsoft PI Server collects the data from the SCADA system. The PI server utilizes the PI Com connector to interface to the SCADA database. PSE&G has a Computer Maintenance Management System (CMMS) that utilizes OSIsoft ProcessBook program for graphical representation of data and condition based alarming. PSE&G also utilizes the OSIsoft Coresight program for data analysis.

4 Status and Alarms In the master station, alarms are categorized as high, medium, low, and low-low. The alarm group for each status point is assigned to allow filtering of ancillary alarms during high activity events, such as storms. Algorithms have been developed in the CMMS system to provide condition based alarming. A typical condition would be an overload condition, which is based on both the KVA reading at or above 100% and the temperature of the transformer at or above 160 F. The following status and data were captured from each transformer and vault: Status points for transformer and vault Protector Open Protector Closed Transformer Relay Trouble Transformer Data Transformer Protector Relay Analog Data: A-B-C phase Current A-B-C phase Voltage A-B-C Differential A-B-C Current Angle 3 phase KW Network KW Transformer Protector Relay Control: Block Close Auto Trip Transformer Protector Relay Status Data: NWPR Status Close Blocked Relaxed Close Transformer Analog Sensors: Transformer Temperature Transformer Pressure Transformer Oil Level Fault Detector Status Vault High Liquid Level 2411 Relay Trouble 3 phase KVAR 3 phase KVA % KVA Cycles Temperature Enable Relaxed Close Disable Relaxed Close Fail To Operate (FTO) Close Fail To Operate (FTO) Open

5 5. BENEFITS PSE&G performs inspections of spot network locations prior to switching of primary feeders to avoid a customer interruption. These inspections commonly called day priors require large blocks of man-hours and divert these crews from other important work. The online monitoring system eliminates the need for these inspections, since all parameters of spot network locations are available remotely. Monitoring and automation of the underground network has been proven to improve reliability and power quality of these systems, to operate these systems in a more efficient manner, and to reduce man-hours required for inspections. Using data for analysis Operations and Engineering can use the data from the PI historian for planning. The OSIsoft PI software is typically used by PSE&G for graphic trends and spreadsheet listings. Typical uses include: Assessment of distribution network loading Monitoring customer loads Transformer overloading Load shedding Fault analysis New customer expansion Maintenance planning Using PI Data for Alarming The following conditional alarms have been programmed using the data from the PI historian. Blown Fuse Network Heartbeat Protector Operations Protector Case Pressure Transformer % KVA Loss of Transformer Pressure Transformer Temperature 6. CONCLUSION PSE&G now has an economical method of improving the reliability, power quality, and efficiency of underground network systems. In order to provide this high reliability of service, PSE&G is aware of the real-time status of all equipment on the network, and is alerted to all events on the network, thereby reducing the number of interruptions by intelligently and proactively managing the equipment on the network, improving response to failures by better understanding failure locations, and minimizing the length of time to locate the failed component.