Baltimore oil circuit breaker tests

In view of the tremendous growth of electric power systems it has been realized for sometime by many of the larger operating companies that many of the old circuit breakers were not adequate for the increased duty. There seemed also to be considerable uncertainty as to the actual ratings of many of the more modern types. It was realized that this condition was largely due to the fact that the manufacturer was handicapped in making tests due to lack of power. These circumstances led the Consolidated Gas, Electric Light and Power Company of Baltimore and the Pennsylvania Water and Power Co. to make a series of oil switch tests on their interconnected 13, 200-volt, 25-cycle power system, cooperating with the Westinghouse Electric and Manufacturing Company and the General Electric Company. The largest generating capacity used on these tests was 170,000 kw. Currents obtained vary from 750 to 23,700 ruptured r. m. s. arc amperes. All of the tests were made by throwing three-phase metallic short circuits directly on the system which the breaker under test was called upon to clear immediately. Proper protection of the system was provided in case of failure of test breaker. Three oscillographs were utilized to record the sequence of events. A total of about 200 short circuits was made directly on the Baltimore system without any breakdown whatever of the major equipment of the two operating companies, and in practically all cases without causing more than a momentary voltage disturbance to the system. The results as described in the papers submitted by Messrs. Hilliard and MacNeill indicate that it is possible with proper design to build oil circuit breakers which can be relied upon to satisfactorily interrupt large currents on high-capacity systems many times in succession without damage to the breakers, without oil throw, and without change of oil or adjustments.