Metro’s 7000-series cars require more electricity, but the agency says there’s no systemic issue

Metro’s new 7000-series railcars are drawing more electricity from the railcar propulsion system than the old cars, causing the agency to need to set aside more money to power its trains. The agency’s newest budget proposal includes an additional $6 million budgeted for electricity on top of the previous year's request to allow continued operations.

Metro’s Fiscal Year 2019 budget notes that its energy costs are expected to increase by $5.6 million (from $87.7 million to $93.5 million), which is “primarily due to increased propulsion usage of the new 7000 series railcars.” The planned cost increase comes a year after the agency reduced the total number of trains running in the system during rush hour from 143 to 125. Trains used to run every six minutes during rush hour, but they now only come every eight.

Translating the additional cost into actual power usage, Metro’s tests showed that an 8-car 7000-series train pulling another 8-car 7000 draws a maximum of 11,208 amps from stop to full acceleration when departing a station. Metro says the rail system is designed for max train power draw of 12,960 amps, so the additional load doesn’t indicate a larger issue or require any extra changes.

Public knowledge of the 7000-series power increase first came to light in the FY2018 Q1 Vital Signs report, which noted that in mid-August 2017 Metro “put in place a 35 mile per hour speed restriction covering almost 23 miles of track…to reduce trains’ traction power while Metro completes an analysis to optimize the power system used to propel trains.”

Metro sets aside additional money to power its 7000-series railcars

Energy costs for the overall Metro system have risen from $83 million in FY2016 to $83.3 million in FY2017, then to an estimated $87.7 million in FY2018, and now to a projected $93.5 in the upcoming budget. The 7000-series railcars were first introduced in the last quarter of FY2016, and now make up approximately 40 percent of the Metrorail fleet. Metro policy limits the cars so they only run in 8-car trainsets during service. None run as 6-car trains, although they're technically capable of doing so.

The power costs just for the railcar propulsion portion of the system’s energy costs — which doesn’t include buses or other electricity needs — is forecast to increase from $47.9 million in FY2018 to $53.9 million if the Metro Board approves the FY2019 budget later this spring. That's an increase of $6 million, or about 9 percent.

The amount of power a train draws is very dependent on a number of factors, and can be constantly changing. Power draw not only goes up or down depending on number of people in a car, but how long the HVAC system is working, the grade of tracks, etc.

The increase in power consumption in the new cars was big enough, according to one source, that it triggered the General Manager’s office to order a study to determine what was causing the difference. Testing to validate how much power the new cars actually draw recently wrapped up and the results are now being analyzed.

In response to a request for information, a Metro spokesperson confirmed that the newest cars indeed draw more power than the older legacy cars, but says “it does not come close to exceeding the capacity of the system.

Metro also notes that work is already underway to upgrade the entire rail system to support 100 percent 8-car trains over time; Metro is increasing the amount of power available to pump into the third rail system at Traction Power Substations which transform electricity from Dominion and PEPCO into the power that the trains can actually use.

The power consumption issue has reportedly been handled as a “top priority” for some Metrorail senior management, and multiple department heads became involved in testing to help determine the root causes of the increase. Testing was performed not only to validate how much the railcars and each of their subsystems consume, but to compare the “real life” numbers to the technical specs provided by the manufacturer, Kawasaki, to determine where any differences may lie.

It appears that the power consumption increase is not due to the propulsion system which moves the cars — which a source described as even being slightly more efficient than the older cars — but rather the auxiliary power system, which powers things including the air conditioning and heater system.

Fine-tuning software configuration changes has been ongoing

The new cars came to Metro with brand-new management software systems which none of the older “legacy” cars use, and has been tweaked over time to find what settings are most efficient. The new cars are a lot more like computers than the older ones, so more settings can be updated easier than in the past.

One configuration change included in this is the level at which the cars send power back into the third rail power system when the train cars are braking. Metro railcars include a feature called regenerative (or “dynamic”) braking, where power generated while the railcar is slowing down can be fed back into the third rail power system. This power can then be used by other trains in the vicinity instead of “new” power from the power grid that Metro is paying for.

Metro's legacy cars are configured to feed power back into the third rail system until a lower threshold of 760 volts is reached, just above the third rail’s nominal power voltage of 750 volts. That same threshold for the 7000-series has been set to 840 volts, which would reduce the amount of power that braking Metro trains are generating and putting back into the system.

A higher cutoff for the regenerative braking system means that less power would be feeding back to the traction power system, but doesn’t necessarily indicate higher power draw. Newer, more efficient electronics on the cars — including better capacitors to store power — mean that the generated power could be used more on the railcar itself, changing how and where the power is consumed.

Railcar weight could be — but likely isn’t — part of the issue

It is unclear if further Metro tests of the various railcar systems has narrowed down the difference to any specific subsystems or parts, but one system - the Auxiliary Power Supply - is one that a source noted draws more power than old cars. This system runs things like the HVAC in the cars, and reportedly draws around 20 percent more power than the older ones. That's not a massive increase by itself, but one that adds up over time as the cars run every day during service. Each 7000-series railcar has its own components (the LVPS) which comprise the APS system; the old cars have one LVPS per pair, which could also be a contributor.

Weight is another possible factor, but not likely a large one. The 7000-series railcars do in fact weigh more than the previous cars Metro runs, but the difference in the long run ends up being relatively minor. The 1000-series each weigh 72,000 pounds when empty, while an empty 7000-series railcar weighs 85,000 pounds for a difference of 13,000 pounds (18 percent). Loaded with 120 passengers each and utilizing the average weight of an adult American person of 182.1 pounds, the weights of each resulting car ends up being 93,852 and 106,852 pounds for an 8.8 percent weight difference.

The weight difference is such that an empty 7000-series train, Metro says, requires less power to move than a crush-loaded 5000-series. The number of people on the cars and other system factors change the amount of power, but not by vast differences.

Railcar reliability numbers are still going up

While the new cars might be pulling more power than expected, they’re otherwise still on their way to achieving the reliability requirements Metro set out in its contract with Kawasaki. The contract requires the cars to meet a minimum threshold of 20,800 miles Mean Distance Between Failures (MDBF), and the latest Metro Performance Report says that the cars exceeded 21,500 MDBF in August of 2017. The average for July through December was 17,800 MDBF. This statistic includes when any component on the railcar fails, not just when an issue on a railcar causes a train to be delayed.

The same cars averaged 12,485 MDBD from January to March 2017, while the total fleet including all 2/3000, 5000, and 6000’s, averaged 7,089 MDBD.

As of this writing, Metro has received at least 488 of the new cars, with 748 total #newcars expected to be delivered within the next few years.