For power systems of different voltage levels, the grounding method for the neutral point varies. According to China’s national conditions, small-current grounding operation is predominantly adopted in China’s 6–66 kV distribution systems. To prevent arc-grounding faults and eliminate ground faults, in accordance with the new regulations stipulated by the national standards for overvoltage protection design, when the capacitive current of the power grid exceeds 10 A, an arc-suppression coil device must be installed. Since the power system with a neutral point grounded via an arc-suppression coil has a small grounding current, its minimal interference with nearby communications is also an advantage of this grounding method.

Our company has developed and manufactured the DT-XHKII-K phase-controlled arc-suppression coil device. This complete set of equipment features a standard industrial-grade computer system, a large-screen touch LCD display, and fully Chinese-character-based display. It boasts characteristics such as stable operation, intuitive display, convenient operation, and strong anti-interference capability. Moreover, the system is equipped with comprehensive parameter-setting and information-query functions. This system overcomes the previous limitation of narrow adjustment ranges found in earlier arc-suppression coil devices and enables precise adjustment.

    Phase-controlled arc-suppression coil This device is used for line selection in high-voltage grounded systems, offering highly accurate line-selection capabilities. It is suitable for substations in large-scale industrial and mining enterprises—including power supply companies, power plants, metallurgical plants, mines, coal mines, paper mills, and petrochemical facilities—and is applicable to voltage levels ranging from 6 to 66 kV. It represents an ideal replacement and upgrade for older arc-suppression coils, and also serves as a complementary component for grounding compensation and line-selection systems in newly constructed substations.

Product features:

(1) The controller uses an industrial-grade computer platform for stable operation.

(2) It features a large-screen, touch-sensitive LCD display with full Chinese text, making parameter display, setting, and inquiry convenient and intuitive.

(3) Accurate and fast adjustment with a wide adjustment range, capable of operating from 0. ~100% The rated current can be adjusted over its entire range, and a follow-up control method is employed, eliminating the need for damping resistors.

(4) The short-circuit impedance, rather than the excitation impedance, is used as the operating impedance; therefore, its volt-ampere characteristic can be 0. ~110% Linearity maintained within the rated voltage range;

(5) The control system and primary equipment have a simple structure. Low noise, no rotating or transmission mechanisms, and no on-load tap changers or contactors.

(6) An embedded high-voltage grounding fault location module ensures accurate fault location.

(7) Equipped with RS232 RS485 And with the IEC61850 communication interface, communication with the host computer can be realized, enabling long-distance transmission of signals.

(8) It can realize an audible and visual alarm function for single-phase ground fault detection.

(9) Equipped with a standard printer capable of printing data and grounding information.

(10) Equipped with a one-to-two control function, allowing one controller to manage two sets of arc-suppression coil complete units.

Performance metrics:

(1) Voltage rating: 6 kV ~ 66 kV 。

(2) Number of busbar sections: Two sections.

(3) Current adjustment range: 0~100% Rated current

(4) Current regulation mode: Stepless continuous adjustment

(5) Capacitance current measurement error: less than 2% 。

(6) Settling time: Less than 5 ms 。

(7) Grounding residual current: Less than 2A 。

(8) Controller power supply: AC 220V Rated frequency: 50 Hz; DC 220 V/110 V, rated frequency: 50 Hz.

(9) Controller operating environment: Temperature: -10 ℃~+45℃; Humidity: less than 95%.

(10) Number of selectable lines: 8–42 Road.

(11) Communication interfaces: RS232/RS485/IEC61850 。

Working principle:

The phase-controlled arc-suppression coil system employs a controllable arc-suppression coil based on a high-short-circuit-impedance transformer. The structural schematic diagram and equivalent circuit diagram are shown below:

The structure of a phase-controlled arc-suppression coil is similar to that of a conventional transformer, featuring both primary and secondary windings. Its primary winding, serving as the working winding (Nw), is connected to the neutral point of the distribution network. The secondary winding, acting as the control winding (Cw), is short-circuited by two anti-parallel thyristors (SCRs). The firing angle of the thyristors is controlled by a trigger controller. By adjusting the firing angle of the thyristors from 0 to 180 degrees, the equivalent impedance Zeq across the Nw terminals varies continuously from infinity down to the transformer’s short-circuit impedance ZSC. Consequently, the output compensation current can be smoothly and continuously adjusted between zero and its rated value.

When a single-phase ground fault occurs in the power grid, the control device calculates the required inductive current compensation based on the measured capacitance value. It then adjusts the firing angle of the thyristors to output the inductive current and employs closed-loop feedback control for precise regulation. The filtering devices designed in the system suppress the harmonics generated during thyristor conduction, ensuring that the output current remains at the power-frequency level. The thyristors operate in a series-connected inductive circuit without any capacitors; thus, their operating conditions are free from both the threat of reverse peak voltages and the impact of sudden current changes, thereby guaranteeing their safe operation.

Overall device configuration:

The phase-controlled arc-suppression coil consists of a grounding transformer, a phase-controlled arc-suppression coil, a local control cabinet, a microcomputer controller, and other components. The overall block diagram is shown below: