Network Controls For Electrical Systems
Networking Of Electrical Systems Has A Number Of Aspects That Should Be Considered.
- A single operator can control the flow of energy into and out of his network.
- The operator can, at a glance, determine the system status and make system adjustments to maintain the stability of his network.
- Operators can use predictive software to determine whether there might be future system capacity or overloads that should be addressed immediately. The operator can shed generating capacity, bring additional generating capacity online to increase his spinning reserves, or shed selective loads.
- Networked SPS systems can have an inherit increase in reliability.
- If the system data are accurate and properly used, the network can be quite useful.
- Inaccurate data or a failure of the operator to properly use the data can precipitate a system-wide failure. Data collection can range from $500 to $5000 per point, so an extensive data collection network can be very expensive. If data are only collected and not used in the network operation, the expense is difficult to justify.
- Strong ties between systems can be disastrous when system B fails and system A does not have the capacity or stability to assume the load. When this happens and the operator for system A does not sever his connection to system B, then both systems A and B can fail.
- Multiple systems, all connected with strong ties, can result in a widespread failure that can ripple across multiple counties or states. Under worst-case conditions, major sectors of a country or adjacent countries can be affected.
- The beginnings of one of the largest power outages in U.S. history was a computer software bug in an energy management system that caused incorrect telemetry data to be reported to a power flow monitoring system. At 12:15 p.m., this problem was discovered and corrected by a system operator who failed to restart the power monitoring system.
- Following this minor monitoring failure, a generating station was taken offline by its operating personnel due to extensive maintenance problems.
- A 345 kV transmission line in northeast Ohio made contact with a tree and tripped out of service.
- The alarm system at the local utility control room failed and was not repaired.
- One transmission line after another tripped offline as they were sequentially overloaded by the failing network. More than 20 major transmission lines ranging from 138 to 345 kV were taken offline due to undervoltage and overcurrent. At this time, the shedding of 1.5 GW in the Cleveland region could have averted subsequent failures. However, the network operational data was inaccurate, unavailable, or not acted upon by the network control personnel in a timely fashion (4:05:57 p.m.).
- Between 4:06 and 4:10 p.m., multiple transmission lines experienced undervoltage and overcurrent conditions and were tripped offline. Seconds later, multiple power generating stations along the East Coast were overloaded and tripped offline to protect themselves. At this point, the blackout was in full swing.
- At 4:10:37, the Michigan power grids isolated themselves.
- At 4:10:38, the Cleveland power grid isolated itself from Pennsylvania.
- At 4:10:39, 3.7 GW of power flowed west along the Lake Erie shoreline toward southern Michigan and northern Ohio. A surge that was 10 times the power flow only 30 seconds earlier caused a major voltage drop across the network.
- At 4:10:40, the power flow flipped to a surge of 2 GW eastward, a net of 5.7 GW, and then reversed again to the west, all in the span of 0.5 seconds.
- Within 3 seconds of this event, many of the international connections failed. This resulted in one of the Ontario power stations tripping offline due to the unstable network conditions.
- By 4:12:58, multiple areas on both sides on the United States-Canada border disconnected from the grid and New Jersey separated itself from the New York and Philadelphia power grids. This caused a cascade of generator station failures as the network conditions continued to deteriorate, both in New Jersey and westward.
- At 4:13 p.m., 256 power stations were offline with 85% of them failing after the grid separations occurred. Most of these were caused by automatic protective controls in the power network or the individual power station.