Blog Post 10: Optimize voltage profile, reduce transmission losses
As much as 6% of the electricity that runs through transmission & distribution lines simply disappears in the form of line losses. What can be done about it?
Advanced grid analytics evaluate the grid characteristics using operational data to identify transmission lines where losses can be reduced and the voltage profile improved. Grid analytics also recommend steps that help maintain optimum VAR flow, which in turn supports megawatt transfers over the lines. In addition, these analytic processes can suggest operational steps to bring greater efficiency to power transformers and capacitor banks, and recommend actions to maintain optimum power factor at delivery points. Better analytics results in more efficiency and less loss of electricity across the bulk transmission system.
Overall, reactive power management has a significant impact on the efficient utilization of the transmission grid, and therefore on power system security and economics. It has to be carefully coordinated with megawatt generation and transmission, while respecting prevalent security standards including NERC, N-1 contingency analysis, and other standards.
Advanced transmission analytics processes are routinely used to control voltages and VARs to minimize composite objectives combining factors like cost of reactive power interchanges, MW losses, MVAR losses - subject to all system constraints. This can provide major cost reductions within flexible operating margins. Analytics can be used to minimize the number of set-point changes or perform least-squares total control shift calculation, for pre- and post-contingency system operations in both normal and emergency operation.
For financial impact calculations, a cost/price curve is assigned to the MVARs of each generating unit or station, or through each defined network interface. Analytics are used to calculate, optimize, and dispatch these MVARs to minimize total cost, subject to system operating limits, providing comprehensive marginal cost analysis.
In addition, for proactive VAR management, analytics can determine the best location for installation of new or relocation of existing shunt capacitors and other devices for VAR support. The analytics process initially tries to satisfy all system pre- and post-contingency constraints using existing controls and equipment. If any constraints cannot be enforced, analytics will then determine the required reactive compensation in the optimum amounts and locations to minimize net capital installation cost.
In my next post I’ll describe how increasingly prevalent utility-scale renewables can be better integrated using advanced analytics.
Vice President Product Management at Resource Innovations/Nexant
7 年Great question Andre! First, looking globally, the losses for transmission and distribution vary considerably by country. Here's an excellent data source: https://data.worldbank.org/indicator/EG.ELC.LOSS.ZS?view=map The losses range from 72.5% in Togo to 2.0% in Singapore, with an average of 13.3% for the 2014 data. To answer your specific question, the IEC in a report entitled “Efficient Electrical Energy Transmission and Distribution” breaks losses down per the following: 1-2% – Step-up transformer from generator to Transmission line 2-4% – Transmission line 1-2% – Step-down transformer from Transmission line to Distribution network 4-6% – Distribution network transformers and cables To further break this down for distribution, Hydro One completed a study on distribution line losses, which included breakdown by urban and rural networks, with the following results: Estimated Loss as a Percentage of Energy Sold Subtransmission Lines - Urban: 0.1%, Rural: 0.7% Power Transformers - Urban: 0.1%, Rural: 0.7% Distribution Lines - Urban: 0.9%, Rural: 2.5% Distribution Transformers No Load - Urban: 1.2%, Rural: 1.7% Distribution Transformers Load - Urban: 0.8%, Rural: 0.8% Secondary Lines - Urban: 0.5%, Rural: 0.9% Total - Urban: 3.6%, Rural: 7.3% The main determinant is of course current and resistance: I^2 x R, meaning the losses increase with the square of the current (“I” or amperage) multiplied by the resistance (R) of the transformer winding or line conductor. For an excellent source on this and other topics including reducing transformer and line losses, power factor and reactive power, benefits of demand response programs on line losses, etc. see https://www.4cleanair.org/sites/default/files/Documents/Chapter_10.pdf Another good source is https://insideenergy.org/2015/11/06/lost-in-transmission-how-much-electricity-disappears-between-a-power-plant-and-your-plug/ This includes average electricity losses by US state. A few interesting statistics from this publication: generating electricity, the USA lost 22 quadrillion BTU from coal, natural gas, nuclear and petroleum power plants in 2013, which is more than the energy produced by gasoline use. Moving electricity from generation plants to end consumers via transmission and distribution, the USA lost 69 trillion BTU in 2013; about how much energy Americans use drying our clothes every year. For more details on losses I will also refer you to https://electrical-engineering-portal.com/total-losses-in-power-distribution-and-transmission-lines-1 which is another excellent resource.
CTO at BlockchainBTM
7 年Do you have breakdown on where the 6 percent loss occurs? (Transformer downlink, substation, grid distribution point, interties,...) Thanks.
Vice President Product Management at Resource Innovations/Nexant
7 年Good comment Raj. This is all part of the analytics data acquisition strategy, whether provided from AMI, PMU, SCADA, or other sensing devices.
As a standard practice , if smart meters are deployed , plan ahead and capture voltage as a channel and determine how frequently AMI data with voltage is fed to the analytics platform.