1.Overview
This device is suitable for small current grounding systems with ungrounded neutral points or those grounded via resistors or arc suppression coils,operating at voltages from 0.4kV to 66kV.It can be widely used in power plants,substations,hydropower stations within the power system,as well as in the power supply systems of large industrial and mining enterprises such as chemical,metallurgical,coal,and railway sectors.
In power systems,a system where the neutral point is ungrounded or grounded via an arc suppression coil or resistor is called a small-current grounding system.The most common fault in such systems is a single-phase grounding fault.When a single-phase grounding fault occurs in a small-current grounding system,all lines with capacitance to ground will carry zero-sequence current.However,due to the small magnitude and significant dispersion of zero-sequence currents,identifying the faulty line is challenging,especially if the system includes an arc suppression coil,which further complicates the task.
The grounding current during a single-phase fault is relatively small.According to power system safety regulations,the system can continue operating for 1 to 2 hours after a single-phase grounding fault occurs.However,during this time,the voltage of the non-fault phases rises to the line voltage.If not addressed promptly,it can easily escalate into a two-phase short circuit,worsening the fault.Additionally,arcing grounds can trigger overvoltage across the entire system.
2.Model Description
III.Product Features:
1.The product utilizes an 80C196 16-bit microcontroller chip as its core processor,ensuring fast computation speed and high data processing capability.
2.Wide applicability:suitable for neutral point ungrounded systems,arc suppression coil grounded systems,and high-resistance grounded systems;applicable to both overhead lines and cable systems without limitation on line length.
3.The software design and programming take into account most domestic field conditions,incorporate the advantages of similar domestic products,and fully consider the requirements for convenient and quick on-site debugging and operation.
4.Three hardware interface options for data exchange:3-wire RS-232 port,2-wire RS-485 port,and 4-wire RS-422 port.Suitable for unattended substations or integrated automation equipment.
5.No fixed value setting is adopted;the residual current increment method is used to make the device unaffected by operation modes and grounding transition resistance.
6.The line alarm code output and one-to-one line alarm output are independent export modules.
7.Self-check function:Continuously monitors the core hardware circuits and software execution of the device.
8.Self-recovery function:After power-on,regardless of the current operation interface,the device automatically returns to the running interface if no operation is detected within 2 minutes(except when the device itself is in fault alarm).
9.The entire unit features a plug-in structure,making maintenance and component replacement extremely convenient.
10.Chinese character menu,simple operation,easy to understand,and straightforward debugging.
11.After being put into operation,this machine basically requires no maintenance.
IV.Main Functions and Technical Parameters
1.Applicable Scope:Small current grounding systems with ungrounded neutral points,grounded through high resistance,or grounded via arc suppression coils;
2.Number of Bus Sections:1 to 4 sections;
3.Line Selection Circuits:12,24,or 36 circuits(if a different number of circuits is required,please specify when placing the order);
4.Starting Voltage(V):30V is the default empirical value,no user adjustment needed;
5.Input rating:Zero-sequence voltage less than 100V,zero-sequence current greater than 20mA and less than 500mA(when zero-sequence voltage and zero-sequence current signals are connected to the device,the polarities must be consistent).To ensure the accuracy of the device's line selection,when a single-phase grounding fault occurs on a line,the secondary side of the zero-sequence current transformer for that line should provide a zero-sequence current greater than 20mA and less than 500mA.
6.Remote Alarm Function:Power failure alarm,local fault alarm,grounding bus alarm,grounding line alarm,coded output,and one-to-one output for grounding line alarm.This series of alarms provides a pair of passive contacts(contact capacity of 8A/250VAC,8A/30VDC)that can be connected to a central signal indicator light.
7.Communication Function:RS485.
8.Printing Function:Fully Chinese-printed local parameter settings and fault information.
9.Power Supply:AC/DC220V,AC/DC110V(select one for use).
10.Operating Environment:Temperature-30℃to 55℃,humidity≤90%,atmospheric pressure 80～110KPa.
5.Device Working Principle
When the small current system is operating normally,the open-delta voltage of the voltage transformer(PT)is very small,generally not exceeding 10V.When a single-phase ground fault occurs in the system,the ground-phase voltage drops to zero,the normal-phase voltage rises to the line voltage,and the zero-sequence voltage increases.The capacitive current of the grounded line equals the sum of the capacitive currents of the normal lines,and the direction of the capacitive current in the grounded line flows from the line to the busbar,while the direction of the capacitive current in the normal lines flows from the busbar to the line—meaning the two directions are opposite.
The device continuously monitors the open-delta voltage of the PT.When the open-delta voltage exceeds the activation threshold,the device performs multiple synchronized samplings of the zero-sequence current for all lines on the busbar.It conducts a comprehensive analysis of the reliability of the sampled data and applies optimized processing based on the group amplitude-phase comparison principle and multiple criteria.This approach fully accounts for factors such as phase and amplitude variations,PT disconnection,and changes in transition resistance that may affect the zero-sequence current.As a result,it accurately identifies the grounded line or busbar.Additionally,the introduction of relative measurement concepts and adaptive tracking technology significantly enhances the sensitivity of fault current detection,enabling strict differentiation between actual grounding and false grounding.This reduces the probability of misjudgment and missed detection,thereby improving the accuracy of line selection.
VI.Ordering Instructions
When placing an order,please specify:1.Power supply of the device(AC/DC220 or AC/DC110);
2.Communication interface(default RS485);
3.Number of line selection circuits;
4.Whether remote output functionality is required.
