【Daily Question】Question from Issue 20151120
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Participation reward: 2 Wealth. Reward for correct answer: 9 wealth. When oscillations occur in the power system, （ ） may malfunction. A. Current differential protection B. Out-of-sequence current quick-break protection C. Current quick-break protection 【Production and Management Division】Seeking moderators and technical discussants to join
When oscillations occur in the power system, (A. current differential protection) may malfunction.
When oscillations occur in the power system, （ ） may malfunction. C, Current quick-break protection
When oscillations occur in the power system, (C) may malfunction. A. Current differential protection B. Out-of-sequence current quick-break protection C. Current quick-break protection
Answer: A (In option B, “alternative sequence current” should be replaced with “zero-sequence current”). (1) During oscillation, the voltage and current values at various points in the system fluctuate back and forth, whereas in the case of a short circuit, the current and voltage values change suddenly. Furthermore, during oscillation, the rate of change of current and voltage values is slow, whereas in a short circuit, the changes in current and voltage values are sudden and significant. Since the operating current value of the current quick-break protection is very high, and the current during power system oscillations is much lower than this value, the current quick-break protection will not operate. (2) During oscillation, the phase angle between current and voltage at any point in the system changes as the power angle changes ； During a short circuit, the angle between current and voltage remains essentially constant. (3) During oscillation, the three phases of the system are symmetric (i.e., the zero-sequence current quick-break protection will not operate) ； During a short circuit, the system may experience three-phase asymmetry. Power oscillations are generally divided into local oscillations and wide-area oscillations. The causes of such oscillations include generator out-of-step operation, asynchronous paralleling, and local faults that lead to a loss of dynamic stability. Oscillations generally last from a few seconds to a few minutes, and within the area where oscillations occur, voltage, current, and other parameters fluctuate.
When oscillations occur in the power system, (c) may malfunction. A. Current differential protection B. Out-of-sequence current quick-break protection C. Current quick-break protection
When oscillations occur in the power system, (C) may malfunction.
When oscillations occur in the power system, (C) may malfunction.
C. Current quick-break protection. ------------------
When oscillations occur in the power system, (C) may malfunction. A. Current differential protection B. Out-of-sequence current quick-break protection C. Current quick-break protection