Method for measuring zero-sequence current in three-phase ungrounded system
A grounding system and zero-sequence current technology, applied in the direction of measuring electricity, measuring devices, measuring electrical variables, etc., can solve the problems of low measurement accuracy and inaccurate bus zero-sequence current measurement, achieve high measurement accuracy, reduce power outage time, The effect of increasing the resolution
Inactive Publication Date: 2014-10-22
SHAANXI ASUR ELECTRICAL
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Problems solved by technology
[0004] The technical problem to be solved by the present invention is to provide a measurement method of zero-sequence current in a three-phase ungrounded system, which solves the problem that the measurement method of traditional bus zero-sequence current adopts the small transformation ratio of current transformer for measurement, and has measurement accuracy The shortcoming of inaccurate measurement when the zero-sequence current of the busbar is small;
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Embodiment 1
[0028] For example, the zero-sequence current of the primary side line is 1A, and the current transformer with a ratio of 600:1 is used for measurement, and the secondary current is 1 / 600=1.667mA;
[0029] 5: 2.5mA for the secondary side miniature current transformer, the output current is 0.833mA;
[0030] The output of the miniature current transformer is converted to a voltage of 0.1667V by using a 200-ohm resistor in series, which is easily converted into a digital signal by an AD converter.
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The invention discloses a method for measuring zero-sequence current in a three-phase ungrounded system. The method includes the following steps: step one, using current transformers with large transformation ratios to measure primary side three-phase current; step two, using the abovementioned current transformers to perform secondary side current three-phase synthesis; step three, using a micro current transformer with a small transformation ratio to measure the synthetic secondary side current to output small current; and step four, after connecting the output small current in the step three with a resistor, converting the output small current to output voltage which is converted to digital signals through an AD converter and sent to a detection device. According to the invention, the method for measuring a primary part of zero-sequence current adopts a large transformation ratio method, production is convenient, measuring accuracy is high, and small current can be measured; the resolution ratio of zero-sequence current measurement of a bus can be improved, and when a ground fault occurs in the bus, ground current of the ground fault can be precisely judged according to the method, thereby reducing power failure time caused by ground connection of the bus.
Description
technical field [0001] The invention belongs to the field of power measurement and relates to a method for measuring zero-sequence current in a three-phase ungrounded system. Background technique [0002] When a single-phase ground short circuit occurs in a power system where the neutral point of the power transformer is not grounded, there is no short circuit circuit and no short circuit current will be generated. The relay protection of the power system does not need to trip, and the power system is allowed to continue to run for a period of time. But single-phase grounding is also harmful to the power system. Therefore, when a single-phase ground short circuit occurs in this kind of system, the relay protection must send out an alarm signal, and the operator on duty will make corresponding treatment, and finally carry out power-off maintenance on the faulty line. [0003] In order to carry out power-off maintenance on the faulty line, the relay protection should send out...
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Login to View More IPC IPC(8): G01R19/175G01R31/02
Inventor 岳夕皓
Owner SHAANXI ASUR ELECTRICAL