A power quality detection method and system for a multi-functional instrument used in a medium voltage switch cabinet of a crane

Abstract

The application discloses a power quality detection method and system for a medium-voltage switch cabinet of a crane by using a multifunctional instrument, and the multifunctional instrument is connected to each isolated cabinet body to monitor the incoming line power quality and the operation state of a transformer; the multifunctional instrument is connected to each feeder circuit to monitor the power consumption and the operation state of each mechanism; and the multifunctional instrument is connected to a reactive power compensation device to monitor the power factor and the reactive power compensation effect. The application realizes comprehensive monitoring and analysis of the power quality under the operation state of the medium-voltage switch cabinet, and potential problems can be found and solved in time.

Description

Technical Field

[0001] This invention relates to the testing technology of port loading and unloading cranes, and more specifically, to a method and system for testing the power quality of medium-voltage switchgear in cranes using a multi-functional instrument. Background Technology

[0002] Medium-voltage switchgear, as a key electrical device in port cranes, undertakes the important tasks of power distribution, control, and protection. The voltage level of medium-voltage switchgear on port cranes is generally 3.6~15KV, and the cabinet typically adopts a metal-armored, center-mounted structure; for example... Figure 1 As shown, the switchgear is functionally divided into medium-voltage incoming cabinet A, main transformer outgoing cabinet B, and auxiliary transformer outgoing cabinet C. These cabinets are connected by a copper busbar 1. Internal electrical components include a handcart-type disconnect switch 2, a vacuum circuit breaker 3, a current transformer 4, a surge arrester 5, a live indicator 6, a fuse 7, a cable terminal 8, a grounding switch 9, and a voltage transformer 10. Traditional medium-voltage switchgear monitoring methods are often limited to simple electrical parameter measurements, which are insufficient to meet the comprehensive, accurate, and real-time monitoring needs of modern cranes. With the widespread application of power electronic equipment such as frequency converters and nonlinear loads, power quality problems in the power grid are becoming increasingly prominent, such as harmonic pollution, voltage fluctuations and flicker, and three-phase imbalance. These problems not only affect the normal operation of port cranes but may also lead to energy waste and environmental pollution. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for power quality detection of medium-voltage switchgear in cranes using a multi-functional instrument, enabling comprehensive monitoring and analysis of power quality during the operation of the medium-voltage switchgear, and timely detection and resolution of potential problems.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The first aspect of this invention provides a method for power quality detection using a multi-functional instrument in a crane medium-voltage switchgear;

[0006] The multi-functional instrument is connected to each isolation cabinet to monitor the incoming power quality and the operating status of the transformer;

[0007] The multi-functional instrument is connected to each feeder circuit to monitor the power consumption and operating status of each mechanism;

[0008] The multi-functional instrument is connected to the reactive power compensation device to monitor the power factor and the reactive power compensation effect.

[0009] Preferably, the multifunction instrument is a PowerLogic™ PM8000 multifunction instrument.

[0010] Preferably, the multi-functional instrument is connected to the isolation cabinet, specifically including:

[0011] The input terminals Ua, Ub, Uc, and Un of the multi-functional instrument are connected to the secondary terminal block of the voltage transformer in the isolation cabinet to form a voltage signal acquisition circuit. This circuit acquires the three-phase bus voltage for monitoring voltage amplitude, imbalance, and frequency parameters, and for determining power supply quality.

[0012] The input terminals Ia+, Ia-, Ib+, Ib-, Ic+, and Ic- of the multi-functional instrument are connected to the secondary terminal block of the current transformer in the isolation cabinet to form a current signal acquisition circuit. The three-phase load current is collected to calculate active / reactive power, electrical energy, harmonic parameters, and to monitor load and overload risk.

[0013] Preferably, the multi-functional instrument captures the power quality waveforms of the isolation cabinet, including harmonic distortion waveforms, voltage sag waveforms, voltage swell waveforms, and three-phase unbalanced power quality waveforms.

[0014] Preferably, optimization measures based on the monitoring data of the multi-functional instrument include:

[0015] Based on the harmonic distortion rate monitored by the multi-functional instrument, corresponding harmonic mitigation and treatment measures are taken.

[0016] Based on the power factor value monitored by the multi-functional instrument, reactive power compensation optimization measures are taken.

[0017] Based on the monitoring results from the multi-functional instrument, voltage quality improvement measures are taken to reduce the percentage of voltage fluctuations and the number of voltage sags.

[0018] Preferably, the harmonic mitigation and treatment includes:

[0019] A 12-pulse rectifier is installed in the main transformer system to reduce harmonic distortion; an active power filter is installed in the crane terminal system to control high-order harmonics; and an LC passive filter is installed in the frequency converter system to control the 5th, 7th, and 11th harmonics.

[0020] The reactive power compensation optimization measures include:

[0021] A dynamic reactive power compensation device is adopted; the capacitor switching strategy is optimized to avoid resonance.

[0022] The voltage quality improvement measures include:

[0023] Install dynamic voltage restorers; optimize transformer tap changer strategies.

[0024] A second aspect of the present invention provides a power quality detection system that implements the power quality detection method for medium-voltage switchgear in cranes using a multi-functional instrument as described in the first aspect of the present invention, comprising:

[0025] On the field level, multiple multi-functional instruments are arranged in various isolated cabinets;

[0026] In the communication layer, the multi-functional instrument is connected to the crane's PLC control system and / or the management unit of the medium-voltage switchgear via Modbus TCP / IP and fiber optic networks;

[0027] Management level, the software platform of the PLC control system installed on the crane and / or the management unit of the isolation cabinet.

[0028] Preferably, the power input terminals L+ and N- of the multi-function instrument are connected to the secondary side terminal block of the voltage transformer in the isolation cabinet to obtain power.

[0029] The communication terminal of the multi-functional instrument is connected to the communication terminal block of the isolation cabinet.

[0030] The present invention provides a method and system for power quality detection of medium-voltage switchgear in cranes using a multi-functional instrument. Based on the high-precision measurement, rich functional features and powerful communication capabilities of the multi-functional instrument, it can realize comprehensive monitoring and analysis of power quality under the operating state of medium-voltage switchgear, timely detection and resolution of potential problems. This is of vital importance for ensuring the safe and stable operation of port cranes, improving energy utilization efficiency and operational efficiency, and reducing crane failure rate. It also provides technical reference and practical experience for the intelligent transformation of medium-voltage switchgear and the efficient operation of power systems. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a single electrical line inside a medium-voltage switchgear.

[0032] Figure 2 This is a schematic diagram of capturing harmonic distortion waveforms in the power quality detection method of the present invention;

[0033] Figure 3 This is a schematic diagram of capturing voltage sag / surge waveforms in the power quality detection method of the present invention;

[0034] Figure 4 This is a schematic diagram of capturing the waveform of three-phase unbalanced current in the power quality detection method of the present invention;

[0035] Figure 5 This is an Ethernet loop topology diagram of the power quality detection system of the present invention. Detailed Implementation

[0036] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0037] Combined Figure 1 As shown, the present invention provides a method for power quality detection of medium-voltage switchgear in cranes using a multi-functional instrument;

[0038] The multi-function meter 20 is connected to each isolation cabinet (medium voltage incoming cabinet A, main transformer outgoing cabinet B, and auxiliary transformer outgoing cabinet C) to monitor the incoming power quality of 6KV, 10KV or higher voltage levels in real time, including parameters such as voltage, current, power factor, and harmonics, providing data support for power metering and quality analysis.

[0039] The multi-function instrument 20 is connected to each isolation cabinet to monitor the operating status of the transformer, including load rate, temperature rise, power loss, etc., and preventive maintenance of the transformer is realized through real-time data acquisition.

[0040] Connect the multi-functional instrument to the feeder circuit of each feeder cabinet to monitor the power consumption and operating status of various mechanisms such as hoisting, trolley, crane, and pitching, providing a basis for energy management and fault diagnosis.

[0041] By connecting a multi-functional meter to a reactive power compensation device, the power factor and reactive power compensation effect can be monitored, the reactive power compensation strategy can be optimized, and the efficiency of power utilization can be improved.

[0042] The parameters that need to be covered for the operation status monitoring of medium-voltage switchgear include: three-phase voltage, three-phase current, apparent power, active power, reactive power, power factor, frequency, and cumulative energy value. Therefore, the multi-function meter 20 in this invention adopts the PowerLogic™ PM8000 multi-function meter.

[0043] The core data acquisition process of the PowerLogic™ PM8000 multifunction meter is analog signal acquisition - signal conditioning - analog-to-digital conversion (ADC) - digital signal processing. First, medium-voltage high current is converted into a small measurable signal (e.g., 0~5A current, 0~100V voltage) by current transformers and voltage transformers. Then, the signal conditioning circuit filters and amplifies the input signal to eliminate harmonic interference and noise. Next, a high-precision ADC chip converts the analog signal into a digital signal, with a conversion accuracy typically no less than 16 bits and a sampling frequency reaching the kHz level. Finally, a digital signal processing (DSP) chip calculates the acquired data to derive derived parameters such as active power and reactive power.

[0044] In this invention, the multi-functional instrument 20 is connected to the isolation cabinet, specifically including:

[0045] The input terminals Ua, Ub, Uc, and Un of the multi-function meter 20 are connected to the secondary side terminal block of the voltage transformer 10 in the isolation cabinet to form a voltage signal acquisition circuit, which collects the three-phase bus voltage and is used to monitor the voltage amplitude, unbalance, and frequency parameters to determine the power supply quality.

[0046] The input terminals Ia+, Ia-, Ib+, Ib-, Ic+, and Ic- of the multi-function meter 20 are connected to the secondary terminal block of the current transformer 4 in the isolation cabinet to form a current signal acquisition circuit. The three-phase load current is collected to calculate active / reactive power, electrical energy, harmonic parameters, and monitor load and overload risk.

[0047] In this invention, the I / O connections (status monitoring and alarm output) of the multi-functional instrument 20 include:

[0048] (1) Digital Input (DI)

[0049] Signal source: Auxiliary contacts of vacuum circuit breaker 3 / grounding switch 9.

[0050] Connection path: Auxiliary contact terminal → Terminal block → DI input terminal of multifunction meter 20.

[0051] Function: Monitors the opening and closing status of switches, the protection status of cabinets, etc., to achieve linkage monitoring of equipment status.

[0052] (2) Digital Output (DO)

[0053] Output objects: cabinet intermediate relays, audible and visual alarms, or PLC input modules.

[0054] Connection path: DO output terminal of multifunction meter 20 → relay coil → controlled device (such as alarm light, trip circuit auxiliary contact).

[0055] Function: Trigger overcurrent / overvoltage alarms, over-limit event alarms, or link with other control loops.

[0056] In this invention, the multi-functional instrument 20 captures the power quality waveform of the isolation cabinet, including:

[0057] (1) Harmonic distortion waveform

[0058] (1.1) Harmonic Order Distribution: The multi-function instrument 20 can display the amplitude of the 1st to 63rd harmonics. By observing the amplitude of each harmonic, the main harmonic source can be identified. For example, the 5th and 7th harmonics are usually generated by frequency converters, and the 3rd harmonic is usually generated by three-phase unbalanced loads.

[0059] (1.2) Harmonic content calculation: Multifunctional instrument 20 calculates and displays the content of each harmonic (the ratio of harmonic amplitude to fundamental amplitude).

[0060] (1.3) Determination of Total Harmonic Distortion (THD): The multi-function instrument 20 calculates and determines the harmonic distortion rate, such as... Figure 2 The abnormal voltage and current waveforms after harmonic interference are shown.

[0061] (2) Voltage sag waveform

[0062] (2.1) The amplitude of the voltage waveform suddenly drops to about 70%~90%, forming a "dip".

[0063] (2.2) The voltage waveform during the sag may remain sinusoidal or may be distorted.

[0064] (2.3) After the temporary drop ends, the voltage quickly returns to the normal level.

[0065] (2.4) This may be accompanied by a phase jump, especially during fault clearing, such as Figure 3 The input / output voltage sag waveforms are shown.

[0066] (3) Voltage spurt waveform

[0067] (3.1) The amplitude of the voltage waveform suddenly increases to about 110%-130%, forming a "bulge".

[0068] (3.2) The rising edge of a temporary rise is usually very steep and may contain high-frequency oscillations.

[0069] (3.3) The amplitude of the surge may exceed 150% of the rated voltage, posing a threat to the equipment insulation.

[0070] (3.4) After the voltage rise ends, it may oscillate and decay, such as Figure 3 The voltage rise waveform shown is shown.

[0071] (4) Three-phase unbalanced power quality waveform

[0072] (4.1) Asymmetric amplitude: The amplitudes of the three-phase voltages or currents are significantly different. For example, the voltage of phase A is 10kV, phase B is 9kV, and phase C is 11kV.

[0073] (4.2) Abnormal phase relationship: The phase difference between the three phases is no longer strictly 120°. This abnormality can be more intuitively displayed through a phasor diagram.

[0074] (4.3) Prominent negative sequence component: In spectral analysis, the amplitude of the negative sequence component is significantly increased. Under normal circumstances, the negative sequence component should be less than 2% of the positive sequence component.

[0075] (4.4) Occurrence of zero-sequence component: In a neutral-point grounded system, the occurrence of zero-sequence component indicates the presence of a ground fault or severe three-phase imbalance, such as... Figure 5 The waveform of the three-phase current imbalance is shown.

[0076] In this invention, the monitoring parameters of the multi-functional instrument 20 are as follows:

[0077] (1) Basic electrical parameters: three-phase voltage, current, power, power factor, frequency.

[0078] (2) Power quality parameters: harmonics (up to 63rd order), voltage sag / surge, voltage imbalance, flicker.

[0079] (3) Event log: voltage sag / surge, harmonic overrun, overvoltage / overcurrent, switching operation.

[0080] (4) Waveform recording: voltage and current waveforms for 10 cycles before and after the fault.

[0081] In this invention, the monitoring data of the multi-functional instrument 20 is as follows:

[0082] (1) Harmonic detection:

[0083] (1.1) Main drive system: Harmonic content exceeds the standard multiple.

[0084] (1.2) Transformer system: the proportion of 3rd, 5th and 7th harmonics exceeding the standard.

[0085] (1.3) Frequency converter system: content of 5th, 7th, 11th and 13th harmonics.

[0086] (1.4) Additional losses caused by harmonics: percentage of total losses.

[0087] (2) Power factor detection: Monitor the power factor of each bus.

[0088] (3) Voltage quality monitoring:

[0089] (3.1) Voltage fluctuation: percentage of maximum fluctuation amplitude.

[0090] (3.2) Voltage sag: the average number of times it occurs per day.

[0091] (3.3) Three-phase imbalance: percentage of maximum imbalance.

[0092] (4) Equipment operating status detection:

[0093] (4.1) Transformer temperature rise: The amount by which the average temperature rise exceeds the design value.

[0094] (4.2) Motor failure: The percentage of annual failure rate that is higher than expected.

[0095] (4.3) Capacitor life: Percentage reduction in average life.

[0096] In this invention, the optimization measures taken based on the monitoring data of the multi-functional instrument 20 include:

[0097] (1) Harmonic mitigation: Based on the harmonic distortion rate monitored by the multi-functional instrument 20, corresponding measures and treatment plans are adopted:

[0098] (1.1) Install a 12-pulse rectifier in the main transformer system to reduce harmonic distortion rate.

[0099] (1.2) Install active power filters (APF) in the crane terminal system to control high-order harmonics.

[0100] (1.3) Install LC passive filters in the frequency converter system to control the 5th, 7th and 11th harmonics.

[0101] (2) Based on the monitored power factor values, adopt reactive power compensation optimization schemes to improve the power factor.

[0102] (2.1) A dynamic var compensator (SVG) is adopted.

[0103] (2.2) Optimize capacitor switching strategy to avoid resonance.

[0104] (3) Based on the monitoring results of the multi-function instrument 20, a voltage quality improvement plan is adopted to reduce the percentage of voltage fluctuations and the number of voltage sags:

[0105] (3.1) Install a dynamic voltage restorer (DVR).

[0106] (3.2) Optimize the transformer tap adjustment strategy.

[0107] (4) Based on the monitoring data and waveform analysis of the multi-functional instrument 20, and after taking the treatment measures and plans, an economic benefit analysis was obtained:

[0108] (4.1) Annual electricity cost savings: approximately 20%.

[0109] (4.2) Equipment failure rate reduced by approximately 35%.

[0110] (4.3) Equipment lifespan extended by approximately 20-30%.

[0111] (4.4) Production efficiency improvement: approximately 5%~15%.

[0112] In this invention, the multi-functional instrument 20 and the traditional instrument detection method are compared as shown in the table below.

[0113] Evaluation indicators Traditional pointer instrument Multifunctional instrument Improvement effect Measurement accuracy ±2% ±1.5% Improved by 92.5% Data real-time Manual reading, delay ≥1 hour Real-time transmission, latency ≤0.5s Significantly improved Fault early warning capability No warning function Multi-level early warning system with an accuracy rate of 99%. Add core features Number of unplanned power outages 12 times / year 2 times / year Reduced by 83.3% Annual maintenance costs Approximately 450,000 yuan Approximately 300,000 yuan Reduced by 33.3%

[0114] The present invention also provides a power quality detection system for implementing the power quality detection method of the present invention, comprising:

[0115] On the field level, multiple multi-functional instruments are arranged in various isolation cabinets.

[0116] In the communication layer, the multi-functional instrument connects to the crane's PLC control system and / or the management unit of the medium-voltage switchgear via Modbus TCP / IP and fiber optic networks.

[0117] Management level: The software platform for the management unit of the PLC control system and / or medium-voltage switchgear installed on the crane.

[0118] In this invention, the multifunction meter adopts the PowerLogic™ PM8000 multifunction meter. The PowerLogic™ PM8000 multifunction meter has two communication interfaces: a local communication interface and a remote communication interface, which are adapted to different application scenarios.

[0119] (1) Supported communication interface types: two independent Ethernet ports (dual-port Ethernet); RS-485 serial communication port, supporting half-duplex mode; Ethernet to serial gateway, supporting protocol conversion.

[0120] (2) Supported communication protocols: Modbus RTU (via RS-485); Modbus TCP / IP (via Ethernet); DNP3.0; IEC61850 (optional); ION communication protocol; SNMP (Simple Network Management Protocol); HTTPS communication protocol.

[0121] (3) Supported communication parameters: RS-485 communication rate: up to 115200bps; supports GPS time synchronization (RS-485) or IRIG-B time synchronization (DI), with a time synchronization accuracy of ±1ms.

[0122] To maximize the performance of the power management system, this invention directly connects the PowerLogic™ PM8000 meter to an Ethernet network. For example... Figure 5 The Ethernet loop topology diagram shown is as follows: 100 is an Ethernet switch; 200 is a PowerLogic™ PM8000 instrument connected via Ethernet; and 300 is a LAN / WAN.

[0123] The power input terminals L+ and N- of the multi-function instrument are connected to the secondary side terminal block (auxiliary power output terminal) of the voltage transformer in the isolation cabinet to provide continuous power and ensure the normal operation of measurement, communication and alarm functions.

[0124] The communication terminals of the multi-functional instrument (such as the A and B terminals of the RS-485 interface) are connected to the communication terminal block of the isolation cabinet to upload data such as electrical parameters, alarm events, and switch status, supporting remote monitoring and parameter configuration; the commonly used protocols are Modbus RTU / Modbus TCP.

[0125] Combined Figure 1 and Figure 5 As shown, the current transformer 4 on the busbar copper busbar 1 corresponds to the current signal source, and its secondary side is connected to the current input of the multi-function instrument; the secondary side of the voltage transformer 10 is connected to the voltage input of the multi-function instrument; the auxiliary power supply in the isolation cabinet provides working power to the multi-function instrument; the communication line is led out from the multi-function instrument and connected to the communication terminal in the cabinet, and finally connected to the crane central control system; the circuit breaker auxiliary contact can be connected to the DI terminal to monitor the switch status; the DO output can be linked to the indicator light or alarm device shown in the figure.

[0126] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for power quality detection using a multi-functional instrument for medium-voltage switchgear in cranes, characterized in that: The multi-functional instrument is connected to each isolation cabinet to monitor the incoming power quality and the operating status of the transformer; The multi-functional instrument is connected to each feeder circuit to monitor the power consumption and operating status of each mechanism; The multi-functional instrument is connected to the reactive power compensation device to monitor the power factor and the reactive power compensation effect.

2. The method for power quality detection of a crane medium-voltage switchgear using a multi-functional instrument as described in claim 1, characterized in that: The multifunction meter is a PowerLogic™ PM8000 multifunction meter.

3. The method for power quality detection of a crane medium-voltage switchgear using a multi-functional instrument as described in claim 2, characterized in that, Connecting the multi-functional instrument to the isolation cabinet specifically includes: The input terminals Ua, Ub, Uc, and Un of the multi-functional instrument are connected to the secondary terminal block of the voltage transformer in the isolation cabinet to form a voltage signal acquisition circuit. This circuit acquires the three-phase bus voltage for monitoring voltage amplitude, imbalance, and frequency parameters, and for determining power supply quality. The input terminals Ia+, Ia-, Ib+, Ib-, Ic+, and Ic- of the multi-functional instrument are connected to the secondary terminal block of the current transformer in the isolation cabinet to form a current signal acquisition circuit. The three-phase load current is collected to calculate active / reactive power, electrical energy, harmonic parameters, and to monitor load and overload risk.

4. The method for power quality detection of a crane medium-voltage switchgear using a multi-functional instrument as described in claim 3, characterized in that: The multi-functional instrument captures the power quality waveforms of the isolation cabinet, including harmonic distortion waveforms, voltage sag waveforms, voltage swell waveforms, and three-phase unbalanced power quality waveforms.

5. The method for power quality detection of a crane medium-voltage switchgear using a multi-functional instrument as described in claim 3, characterized in that, Optimization measures based on the monitoring data of the multi-functional instrument include: Based on the harmonic distortion rate monitored by the multi-functional instrument, corresponding harmonic mitigation and treatment measures are taken. Based on the power factor value monitored by the multi-functional instrument, reactive power compensation optimization measures are taken. Based on the monitoring results from the multi-functional instrument, voltage quality improvement measures are taken to reduce the percentage of voltage fluctuations and the number of voltage sags.

6. The method for power quality detection of a crane medium-voltage switchgear using a multi-functional instrument as described in claim 5, characterized in that, The harmonic mitigation and treatment include: A 12-pulse rectifier is installed in the main transformer system to reduce harmonic distortion; an active power filter is installed in the crane terminal system to control high-order harmonics; and an LC passive filter is installed in the frequency converter system to control the 5th, 7th, and 11th harmonics. The reactive power compensation optimization measures include: A dynamic reactive power compensation device is adopted; the capacitor switching strategy is optimized to avoid resonance. The voltage quality improvement measures include: Install dynamic voltage restorers; optimize transformer tap changer strategies.

7. A power quality detection system for implementing the power quality detection method using a multi-functional instrument for medium-voltage switchgear in cranes as described in any one of claims 1-6, characterized in that, include: On the field level, multiple multi-functional instruments are arranged in various isolated cabinets; In the communication layer, the multi-functional instrument is connected to the crane's PLC control system and / or the management unit of the medium-voltage switchgear via Modbus TCP / IP and fiber optic networks. Management level, the software platform of the PLC control system installed on the crane and / or the management unit of the isolation cabinet.

8. The power quality detection system according to claim 7, characterized in that: The power input terminals L+ and N- of the multi-functional instrument are connected to the secondary side terminal block of the voltage transformer in the isolation cabinet to obtain power. The communication terminal of the multi-functional instrument is connected to the communication terminal block of the isolation cabinet.

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