In a recent meeting with electric utility professionals, a question arose about the advantages of electric powerways compared to transmission lines equipped with phase angle regulators. In particular, the inquirer wanted to know if the primary benefit of electric powerways is flow control. This week, I’ve decided the share my response, as other electric utility professionals may be wondering the same question after reading some of my ideas about the next generation electric power grid.
The following is a technical explanation of the advantages of electric powerways. To learn more about electric powerways from a more general perspective, check out my prior blog Preparing the Grid for Renewables: Electric Powerways.
Advantages of Electric Powerways
Question: What are the advantages of electric powerways compared to transmission lines equipped with Phase Angle Regulators? Is the primary benefit flow control?
Figures 1, 2 and 3 show three possible connections between two locations. Figures 1 and 2 show existing designs. Figure 3 shows next generation concepts.
Answer: There are two benefits:
Improved Flow Control
Rapid Voltage Recovery
The impedance of an overhead 2000 amp transmission line, an overhead 2000 amp electric powerway, and an overhead 2000 amp transmission line with a phase angle regulator for normal operating conditions, close in line faults and line end fault are shown in Tables 1, 2 and 3. Within each figure:
Line resistance was calculated for bundled conductors with three 1527 ACAR conductors per phase.
Line reactance was calculated for horizontal construction with 20 foot spacing.
Powerway compensators are designed for -j10 ohms per phase per compensator.
Phase angle regulator impedance is based on test reports for high voltage phase angle regulators.
1. Improved Flow Control
The equations for flow control can be simplified to the following:
Table 1 shows impedance for system normal conditions. In Table 1:
The impedance of a 50 mile, overhead 2000 amp transmission line is 40 ohms.
The impedance of a 50 mile, overhead 2000 amp electric powerway is between 12 ohms and 42 ohms.
The impedance of a 50 mile, overhead 2000 amp transmission line with a phase angle regulator is between 50 and 60 ohms.
Our experience is that a phase angle shift of 15 degrees will increase power flow approximately 20%. That is about the maximum change in power flow that can be achieved with a phase angle regulator.
Our calculations indicate that electric powerways can increase power flow 30%.
During normal operating conditions, the transmission line component of the transfer impedance can be reduced from 40 ohms to 12 ohms when transmission lines are converted to electric powerways.
2. Rapid Voltage Recovery
When faults occur, fan and pump motors slow down, compressor motors stall and Fault Induced Delayed Voltage Recovery (FIDVR) becomes an operational consideration. The factors that exacerbate FIDVR are:
Network configuration – More, higher voltage lines in a geographic area increase risk.
Fault type – Three phase faults have the greatest impact.
Fault duration – Compressors stall when voltage is less than 70% for more than 100 milliseconds.
Time of year – Air conditioners are equipped with compressors.
Load mix – Whenever and wherever 40% or more of the loads connected to the power grid are compressor type loads, the stage is set for FIDVR events.
The trigger for an FIDVR event is a three phase fault on a 230 KV, 345 KV or 500 KV component. Clearing faults in less than 100 milliseconds does not guarantee that recovery will occur. The September 8, 2011 Southwest Blackout began with a three phase fault that was cleared in 67 milliseconds.
With today’s electric power grid, if a three phase fault were to occur on any 230 KV, 345 KV or 500 KV component, near any metropolitan area in July or August, and a circuit breaker failed to open and interrupt, a multi-state, wide area blackout would follow.
Table 2 shows impedance for line end fault conditions.
Converting transmission lines to electric powerways equipped with solenoid series reactors (SSRx) will enable voltage recovery within 8 milliseconds after a fault occurs. This is 60 to 70 milliseconds before circuit breakers open.
Table 3 shows impedance for close in fault conditions when electric powerways are equipped with solenoid series reactors (SSRX).
Electric Powerways are the Solution
Electric powerways are the solution to flow path concerns, FIDVR concerns and wide area blackout concerns. Electric powerways will also help prepare the grid for distributed renewable energy sources by allowing for an easier transfer of power from location to location. It’s time to invest in research and development funding for the next generation electric power grid.
Visionaries in Electric Power
Thomas Edison and Nikola Tesla are the first visionaries that come to mind when we think of electric power systems. Michael Faraday, Joseph Henry, Werner von Siemens, Charles Wheatstone, Frank Sprague, and Samuel Insull may also be considered visionaries in this industry. When considering recent visionaries, Joseph Paquette, Louis Blackburn, Roy Billinton, and Ken Priest come to mind.
We need visionaries like these to focus our efforts on building the next generation power system. If you have ideas to improve any part of the electric power grid, please reach out.
Do you have a question about next generation electric power grid infrastructure and development? Contact us with your questions; the more technical the better! I am always excited to share my insights. Check out my other articles on Prescient’s blog to learn more.