1 Introduction to the device

Single phase grounding is the most common fault in medium voltage distribution networks. Although the system can continue to operate with the fault after grounding, if not handled in a timely manner, it may develop into a threat of non fault phase insulation damage and subsequent phase to phase short circuit due to the increase in relative ground voltage. Timely and accurate determination of the grounding circuit is the basis for quickly eliminating single-phase grounding faults. The protective device for determining the grounding fault circuit is usually referred to as a small current grounding line selection device. However, early line selection devices often had errors and omissions, and the effect was not satisfactory.

The small current grounding line selection device is a supporting product of the new generation substation automation system independently developed by Hunan Liling Huayi Electronic Technology Co., Ltd. This product adopts a comprehensive line selection theory based on the comparison of transient zero sequence current amplitudes. Through high-speed sampling, it extracts and analyzes the various harmonic components of transient zero sequence current at the moment of grounding occurrence, and uses the unique properties of characteristic frequency bands to identify faulty lines. The line selection theory requires strong hardware platform support, so this device adoptsMCU+ARMStructure,ARMResponsible for human-machine and communication management,MCUComplete the route selection task.

II Device features

3.1Powerful and stable hardware platform

a) ARMThe system, protection, and monitoring are relatively independent, more stable, and reliable;

b) Samsungmain stream32A microprocessor with powerful data processing and logical operation capabilities;

c) 12a flat16positionAD, every cycle512Simultaneous sampling of points;

d) powerfulFPGA, ControlADSampling and Implementing Logic Programming Outlets

e) Ethernet+RS485Communication mode, each communication channel is completely independent;

f) Equipped with printing function, it can achieve on-site printing (this function is optional)

g) Full touch screen design, no need for buttons on the panel, more reliable.

3.2 Embedded real-time multitasking operating system

a) Adopting embedded real-time multitasking operating system LinuxManage hardware resources most effectively;

b) Fully meet the real-time requirements of the power system.

3.3Humanized design concept

a) Fully localized touch color LCD screen display, easy and convenient to operate, providing full online help menu and graphical and tabular output interface;

b) Multiple sets of protection settings can be independently set, and the settings can be adjusted and switched online, which is completely convenient;

c) Plug and play design concept;

d) The application of process holographic reconstruction technology;

e) Real time voltage and current waveform display

f) Suitable for industrial aesthetic appearance design.

3.4Conceptual design with no adjustment and easy maintenance

a) The whole machine has no adjustable components, and high-precision and highly stable industrial grade components are selected to ensure high precision during normal operation and avoid increased sampling errors caused by environmental changes or long-term operation;

b) Equipped with comprehensive self checking function, device abnormalities can be located on the chip;

3.5Specialized structural design

a) The device adopts a full panel back plug-in structure design, completely separating strong and weak electricity, and has excellent electromagnetic compatibility performance;

b) The whole machine has good sealing performance, carefully designed for dust and earthquake resistance, and can achieve fully decentralized installation without the need for any external anti-interference devices;

c) The modular design of functions allows for the addition, removal, and movement of functions through plug and play of plugins, making it plug and play.

3.6Wide applicability

Suitable for neutral point ungrounded/Grounding through arc suppression coil/Grounding system with high resistance; Suitable for overhead lines/Cable system; There is no limit to the number of long and short lines, and there is no limit to the number of parallel output lines;Distinguishable between line and bus grounding.

3、 Technical indicators

1Power supply voltage:AC/DC 110V~220V

2Power consumption of the whole machine: ≤20W；

3Environmental temperature:-10℃～+55℃； Relative humidity of the air: not greater than90%；

4Environmental requirements: The surrounding medium should be free of conductive dust or corrosive gases, molds, etc. that may damage the insulation. The installation site should have wind, rain, sand, and dust prevention facilities;

5Rated parameters:

Number of bus segments:1～4Paragraph;

Number of selected lines:1-60road,

zero sequence voltage(1PT～4PT)：100VZero sequence current（CT1～CT60）：1Aor5A

6Alarm output: The contact capacity of the alarm relay is:AC220V,5A；

7Communication interface: RS485、CANOptional; Communication ProtocolMOUDBUS，TCP/IPoptional；

4、 Installation and usage instructions

5.1 Installation instructions for the device

The device adopts4UHigh height chassis, with embedded screen installation and rear wiring. In addition to meeting the requirements for mechanical structure, the installation should also ensure the electrical related installation requirements. Users are advised to read this section carefully.

Most users of cable outgoing lines use zero sequence current transformersCTTo obtain zero sequence current, the installation of the transformer should ensure that the zero sequence current signal is not short circuited, as shown in the figure. The fixing bolts on the insulation board in the figure should ensure that the clip (i.e. cable sheath) is insulated from the ground. The grounding wire of the busbar side cable casing should pass through the zero sequenceCTGrounding again.

Ø For installed three-phase systemsCTThe user can obtain zero sequence current by connecting them into a zero sequence current filter. Due to the extremely low input impedance of the device's current input circuit, it does not affect the user's ability to connect other current measurement components in series in the zero sequence current filter circuit.

Ø Yes, onlyA、Ctwo-phaseCTThe user must installBeach otherCTAnd it is required that its accuracy ratio and other characteristics be consistent withA、COnly when they are the same can they be connected to form a zero sequence filter and use this device.

5.1.3Same name end (polarity) requirement

Ø The device has no requirement for consistent zero sequence voltage signal access at the same end (except for versions containing power direction and comprehensive criterion algorithms).

Ø The device requires that the same terminal (also known as polarity) of the zero sequence current transformer be connected to the machine uniformly.

Ø three-phaseCTThe same terminal of the zero sequence current filter also requires consistent connection to the local machine.

Ø Regarding the existing zero sequenceCTThere are also systems with three-phase filters that require identical terminals to be connected to this device.

5.2 Device usage instructions

The device adopts a full touch screen design, as it utilizesReal time multitasking operating system Linux, So the startup time is relatively long. After the device is started, it enters the main menu and the display interface shows no operation5After minutes, it will automatically turn off and display when lightly touched on the screen.