Monitoring of events in the power system provides a great deal of insight into the behavior of the system. Events with impact on the entire power system typically occur in or near the transmission network and are therefore best monitored at transmission system substations. This puts great demands on the equipment and in general restricts the use of the data since it becomes property of the transmission system operator. An alternative is to measure at lower voltage levels. This paper documents the close agreement between voltage and frequency at low and high voltage levels during a remote and a nearby fault in the transmission network. The very high quality of the data suggests that valuable information about the transmission system can be obtained at lower voltages.Index Terms-Power system dynamic stability, power system faults, power system monitoring.

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This paper reports on the black start test of the Swedish power system, performed by Svenska Kraftnät, early October 2010. The tests, performed on a regular basis, aim at verifying the black start capability of the Swedish and Nordic system, with respect to total black start of a number of power stations, energizing of major transmission lines, synchronizing of additional power stations, energizing of more lines, and finally system loading. The test system includes three major power stations and a controllable load. The test is focused on voltage control and governor control, of the entire test system, as well as on the capability of the individual power units. During the test, synchronized phasor measurements were performed in two major power stations and in substations along the power system. The recordings show that the black start strategy applied, as well as the generating units involved, are very well suited for black start of the Nordic system. The test system was exposed to stepwise load increases of 100 MW, and responded very accurately. Minor shortcomings in the frequency control were observed. The black start test also serves as a performance quality check of the normal operation ancillary services provided by the generators involved in the test. One of the PMUs used for the recordings was perfectly synchronized with a 140 m long antenna cable.Index Terms-black start, phasor measurements, voltage control, governor control.

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