Pictures of the Future    Spring 2006

The Toughest of Tests

Whether destined for use in locomotives, ships or conveyor belts, all of Siemens' large electrical drives are extensively tested by experts at the system test center in Nuremberg before shipping. Even the motors for Bill Gates' yacht were subjected to their first challenging workout in this unique lab.

Red warning lights flash and blue barriers block access to forbidden areas. Protective screens surround the test stand with all of its instrumentation and display screens. Such precautions are justified, because hazardous electrical voltages lurk beyond these obstacles.

The venue is the Siemens Automation and Drives (A&D) test center for large electrical drives in Nuremberg, Germany. On the stand is a frequency converter destined for use in a freight double locomotive in China. "This particular test takes three days," explains manager Robert Aust. The drive unit involved has a rated output of 4.8 MW, roughly the power of 80 mid-size passenger cars.

Both in terms of size and equipment, the A&D system test center is unrivaled. It opened for business in January 2003 and cost 17 mill. €. At present, some 30 people work there. "Our team includes engineers and technicians as well as electricians and metalworkers," Aust reports. Its two large departments—Rail Systems Testing and Systems & Machines Testing—include five test bays and occupy an area of 4,000 m². Up to six tests can be set up concurrently in Rail Systems Testing. "But then we'd be running two shifts," says Aust.

Alongside the converter, Aust's employees are also testing the motor for one of the Chinese locomotives in one of the test bays. These tests simulate actual trips down to the last detail: A virtual train travels along uphill and downhill grades, and negotiates tight turns. A load machine simulates the weight the drive must propel at a specified speed. The test system also factors in the train's aerodynamic characteristics and the resulting drag.

Set up in an adjacent wet cell is a subway drive unit that will soon transport people beneath the busy streets and avenues of Manhattan. This drive unit is being sprayed with water from all sides repeatedly, ten minutes at a time. In this way, it is possible to simulate the sort of wind-driven water that will strike the train's underbelly when it rains heavily.

At the system test center, specialists extensively test all kinds of large electric drives under conditions that are as realistic as possible. Here, experts focus their attention not only on motors and frequency converters for locomotives, trains and trams, but also on electric motors for use in chemical and steel plants, in oil or gas production, or aboard ships. They also test prototypes from Siemens' research and development departments, such as the world's first superconductive generator for marine use.

In many cases, the intended users visit the center to watch tests in person. As far as ship propulsion systems are concerned, it is actually common practice to have an inspector from the ship's owner attend the test. Even Microsoft's Bill Gates sent an emissary to the acceptance-test for the two Siemens motors Gates had ordered for his yacht. Customers are especially amazed by the way test results are recorded and displayed. "I'm really impressed by the quality of the documentation," says Jeff Saldivar, an engineer at Dow Chemical, who attended the acceptance test of an extruder drive.

Some of the tests are conducted to meet legal requirements. Electric motors must comply with regulatory limits concerning maximum temperatures, noise levels or vibrations—and these limits vary, depending on the location. What's more, many users want the drive systems they have ordered to be tested to the fullest extent. "Especially in critical applications, customers really want to play it safe," explains Aust. Systems tests here also include the software. That's especially important for converters and control systems for train motors, because every rail project differs in some essential details from its predecessor when it comes to software.

A total of 32 transformers, stacked two stories high along one of the sides of the building—plus even more transformers in the basement—provide the test center with electric power at any required voltage. In Rail Systems Testing, individual machines can be operated under load at levels of up to 1.6 MW. The maximum speed is 6,000 rpm, and available voltages range from 400 V to 30 kV a.c. In the adjacent department for industrial drives, the maximum power level is as high as five megawatts, the equivalent of 6,800 hp.

The machine in Test Bay 2 is emitting a piercing whine. But this noise level doesn't seem to bother the young technician who is watching the monitors and the instrument panel. In fact, he is taking off his orange-colored ear protectors. He can read all the essential data on his control console: power level, voltage, torque and revolutions, as well as oscillatory behavior, temperature and noise level. That's a very adequate range of parameters in most cases for testing the operational readiness of a drive—at least for temperate zones and interior industrial facilities.

The Arctic or Tropics. The test center also has a climate chamber for testing drives under more extreme conditions. Here, test objects can be subjected to temperatures ranging from -55 °C to +85 °C and to humidity levels as high as 98 %—in other words, from bitter arctic cold to the sweltering heat of the tropics.

In many cases, the harsh operating conditions under which Siemens drives have to operate can be very accurately mimicked in computer models. As a result, there are few surprises in actual endurance tests. "Deviations from the computed data are very small," notes Aust. But once in a while, a motor may exceed a specified noise, heat or vibration level, in which case it is returned to the plant for reworking. In addition, experts from R&D and design engineering use the measurements to adapt their computer models.

Aust's group tests about 600 industrial drives in projects covered by customer contracts. That's slightly over five percent of the production volume of the Siemens plant for large drives in Nuremberg.

Of course, in addition to these special tests, every product that leaves the plant undergoes routine final testing right after final assembly. In addition to development projects and around 600 machines that undergo special testing annually, the system test center also tests seven or eight complex drive systems for railroad customers based around the globe.

In the case of industrial motors, a simple product test may take half a day, whereas a systems test under load might require four weeks, depending on customer requirements. But a test of a train drive system may go on for several months, sometimes even for a whole year, because software development for a rail vehicle is very time-consuming. And so is test setup. To ensure that the test closely simulates reality, the drive unit must be installed in such a way that it experiences the conditions it will later encounter in real operation. As Aust explains, "We fully commission the drive system here, just as the customer does later on."

Thoroughness and attention to detail are of the essence, because electric drive systems have to withstand especially demanding operating conditions. "An automobile operates, on average, perhaps 250 hours per year, while an electric motor often has to run for more than 8,000 hours," says Aust. "And in many industries our machines run 24 hours a day, seven days a week, and 52 weeks a year."
                                                                                                          Günter Heismann