A protection method and system for exciting winding interphase short circuit faults of an alternating current excitation synchronous motor

A technology of excitation windings and synchronous motors, applied in the direction of automatic disconnection emergency protection devices, circuit devices, emergency protection circuit devices, etc., can solve problems such as reducing the response speed of relay protection equipment to short-circuit faults

Active Publication Date: 2018-02-02

NR ELECTRIC CO LTD +1

4 Cites 4 Cited by

AI-Extracted Technical Summary

Problems solved by technology

For example, in pumped storage units with AC excitation, the generally required excitation frequency varies within the range of -0.1fN to 0.1fN (fN is the rated frequency), and the minimum operating frequency can reach 0.1Hz. ...

Abstract

The invention provides a protection method and system for exciting winding interphase short circuit faults of an alternating current excitation synchronous motor. The method comprises the steps of: firstly collecting three-phase exciting winding currents of a motor; calculating an absolute value of current instantaneous values and a current effective value according to the collected currents; during decision making for over-current protection, setting an over-current instantaneous value criterion as the main criterion and an over-current effective value criterion as an auxiliary criterion; performing accumulative counting on moments which meet the current instantaneous value out-of-limit criterion or which do not meet the current instantaneous value out-of-limit criterion but meet the current effective value out-of-limit criterion by using a time delay counter; performing progressive subtraction on moments which do not meet the current instantaneous value out-of-limit criterion and thecurrent effective value out-of-limit criterion; further determining the over-current protection start, operation and start return time according to values of the time delay counter. The method combines the rapidness of the instantaneous value criterion and the reliability of the effective value criterion and can rapidly reflect exciting winding interphase short circuit faults of an alternating current excitation synchronous motor.

Application Domain

Emergency protective arrangements for automatic disconnection

Technology Topic

Return timeTime delays +10

Image

Examples

Experimental program(3)

Example Embodiment

[0044] Example 1

[0045] A protection method for phase-to-phase short-circuit faults of excitation windings of AC-excited synchronous motors includes:

[0046] S1: Collect the current of the three-phase excitation winding of the motor in real time; the current of the three-phase excitation winding of the motor is collected by an electronic current transformer or a Hall current transformer;

[0047] S2: Calculate the absolute value of the instantaneous value of the three-phase field winding current and the effective value of the three-phase field winding current according to the current value collected in real time;

[0048] The absolute value of the instantaneous value of the field winding current is the absolute value of the current current value collected by the current transformer; the effective value of the field winding current is calculated by using the Fourier algorithm or the root mean square algorithm according to the real-time current value of an electrical cycle before the current moment The effective value of current;

[0049] Root mean square effective value calculation formula among them T is the electrical cycle, T s Is the analog sampling period, I 1 ,I 2...I N Is the current sampling value in an electrical cycle

[0050] Fourier algorithm calculation formula among them T is the electrical cycle, T s Is the analog sampling period, I 1 ,I 2...I N It is the current sampling value in an electrical cycle.

[0051] S3, setting the overcurrent threshold of the instantaneous value of the three-phase current and the overcurrent threshold of the effective value of the three-phase current;

[0052] Define the current instantaneous value over-limit criterion as the maximum value of the absolute value of the three-phase current instantaneous value calculated by S2 exceeds the overcurrent threshold of the three-phase current instantaneous value, and the current effective value over-limit criterion is the three-phase excitation calculated by S2 The maximum value of the effective value of the winding current exceeds the overcurrent threshold of the effective value of the three-phase current;

[0053] S4, define the delay fixed value of the delay counter;

[0054] The delay counter is used to accumulate and count the time that meets the current instantaneous value over-limit criterion, or does not meet the current instantaneous value over-limit criterion, but meets the current effective value over-limit criterion; and does not meet the current instantaneous value over-limit criterion at the same time Accumulate count down according to the time when the current effective value exceeds the limit criterion;

[0055] When the delay counter value is greater than 0, the overcurrent protection starts;

[0056] When the accumulated delay counter value is greater than the delay set value, the overcurrent protection will act;

[0057] When the countdown reaches the delay counter value equal to or less than 0, the overcurrent protection starts and returns.

[0058] In S4, using the delay counter to determine the protection start, action or start return includes steps:

[0059] S41: Compare the maximum value of the absolute value of the instantaneous value of the three-phase excitation winding current obtained by S2 with the set three-phase current instantaneous value overcurrent threshold value. If the current instantaneous value over-limit criterion is met, the delay counter value is accumulated Count, and the overcurrent protection is activated at the same time, and then go to step S43, if not satisfied, go to step S42;

[0060] S42: Compare the maximum value of the effective value of the three-phase excitation winding current obtained by S2 with the set three-phase current effective value overcurrent threshold value. If the current effective value over-limit criterion is met, the delay counter value is accumulated and counted. At the same time, the over-current protection is activated, and then go to step S43, if it is not satisfied, the delay counter value will count down and go to step S44;

[0061] S43: Determine whether the delay counter value is greater than the delay fixed value, if it is, the overcurrent protection is activated, if not, go to step S41 for judgment at the next moment;

[0062] S44: It is judged whether the delay counter is less than or equal to 0. If it is, the overcurrent protection starts and returns; if not, it goes to step S41 for judgment at the next moment.

[0063] In this embodiment, the overcurrent threshold of the instantaneous current value is 1.2 to 2 times the absolute value of the instantaneous current value when the excitation winding is working normally, and the overcurrent threshold of the effective current value is 1.2~2 times the effective current when the excitation winding is working normally. 2 times. The delay time of the delay counter is set to 0.1s~10s.

Example Embodiment

[0064] Example 2

[0065] This embodiment takes AC excitation pumped storage unit as the research object, assuming normal operation ( Figure 1 ~ Figure 3 The effective value of current in the interval between t1 and t2 Amplitude is I n.amp =5000A, the current frequency is 0.5Hz. At the zero crossing point of one phase current ( Figure 1 ~ Figure 3 At time t2) a phase-to-phase metallic short-circuit fault occurs, the maximum value of the effective value of the fault current Maximum amplitude is I f.amp.max = 20000A. The technical solution of the present invention will be introduced from several different situations below.

[0066] 1. Only after the instantaneous value criterion, without the effective value criterion, the protection starts and operates.

[0067] Delay setting t zd = 0.6s, according to figure 1 The waveform analysis shows that the maximum value of the absolute value of the instantaneous value of the fault current at t3 is I f.inst.max Exceed the instantaneous value fixed value I zd.inst , The protection starts at this time, the delay counter continues to count, and the delay counter exceeds the delay set value t at tp zd , At this time protection action.

[0068] 2. Simultaneously pass the instantaneous value criterion and the effective value criterion, the protection starts and operates.

[0069] Delay setting t zd =1.2s, according to figure 2 The waveform analysis shows that the maximum value of the absolute value of the instantaneous value of the fault current at t3 is I f.inst.max Exceed the instantaneous value fixed value I zd.inst , The protection starts at this time, the delay counter starts counting, the maximum value of the fault current effective value I at t4 f.rms.max Exceed the effective value fixed value I zd.rms , The effective value auxiliary criterion is satisfied at this time, so the maximum value of the absolute value of the instantaneous current value I at t5 f.inst.max Less than the instantaneous value I zd.inst Time, the delay counter still accumulates, and the delay counter exceeds the delay fixed value t at time tp zd , At this time protection action.

[0070] 3. After passing the instantaneous value criterion and the effective value criterion at the same time, the protection will return after starting.

[0071] Delay setting t zd =1.2s, according to image 3 The waveform analysis shows that the maximum value of the absolute value of the instantaneous value of the fault current at t3 is I f.inst.max Exceed the instantaneous value I zd.inst At this time, the protection starts and the delay counter starts counting. At t4, the fault is eliminated (such as a transient fault), the current returns to normal, and the instantaneous current decreases below the overcurrent set value. According to the effective value waveform, the effective value at this moment Maximum I f.rms.max Does not exceed the effective value fixed value I zd.rms , The effective value auxiliary criterion is not satisfied, so the delay counter starts to decrease until it decreases to 0 (at t5) when the protection starts and returns.

[0072] Based on the above several situations of this embodiment, it can be seen that the relay protection method of the present invention has both the rapidity of the instantaneous value criterion and the reliability of the effective value criterion, and can quickly and reliably reflect the phase-to-phase short circuit of the excitation winding of the AC excitation motor Faults can ensure that the relay protection device can quickly detect the short-circuit faults between the excitation windings and remove them in time even under low-frequency conditions.

Example Embodiment

[0073] Example 3

[0074] A protection system for short-circuit faults between excitation windings of AC-excited synchronous motors, which includes:

[0075] Real-time current acquisition module for real-time acquisition of the current of the three-phase excitation winding of the motor;

[0076] The current instantaneous value calculation module is used to calculate the absolute value of the instantaneous value of the three-phase excitation winding current according to the current value collected in real time;

[0077] The current effective value calculation module is used to calculate the effective value of the three-phase excitation winding current according to the current value collected in real time;

[0078] The over-current threshold setting module is used to set the over-current threshold of the instantaneous current value and the over-current threshold of the current effective value;

[0079] Delay fixed value setting module, used to set the delay fixed value of the delay counter;

[0080] And the logic judgment and decision module, which is used to judge and decide whether the over-current protection needs to be started, acted, or returned according to the calculated absolute value of the instantaneous value of the three-phase excitation winding current and the effective value of the current:

[0081] Define the current instantaneous value over-limit criterion as the calculated maximum value of the absolute value of the three-phase current instantaneous value exceeds the over-current threshold value of the instantaneous current value, and the current effective value over-limit criterion is the calculated three-phase excitation winding current effective value The maximum value of exceeds the overcurrent threshold of the effective value of the current;

[0082] The delay counter is used to accumulate and count the time that meets the current instantaneous value over-limit criterion, or does not meet the current instantaneous value over-limit criterion, but meets the current effective value over-limit criterion; and does not meet the current instantaneous value over-limit criterion at the same time Accumulate count down according to the time when the current effective value exceeds the limit criterion;

[0083] When the delay counter value is greater than 0, the overcurrent protection is activated;

[0084] When the accumulated delay counter value is greater than the delay set value, the overcurrent protection will be activated;

[0085] When the countdown reaches the value of the delay counter equal to or less than 0, the overcurrent protection starts and returns.

[0086] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, this application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

PUM

Description & Claims & Application Information

We can also present the details of the Description, Claims and Application information to help users get a comprehensive understanding of the technical details of the patent, such as background art, summary of invention, brief description of drawings, description of embodiments, and other original content. On the other hand, users can also determine the specific scope of protection of the technology through the list of claims; as well as understand the changes in the life cycle of the technology with the presentation of the patent timeline. Login to view more.