The arc suppression coil (ASC) was invented by Petersen in 1916, and consequently, it is called Petersen coil. Our ASC, with Chinese National Patent, is divided into two types which are turn-adjusting type (MRD-XHZ) and biasing magnetic type (MRD-XHP), and it also passes type test. This neutral earthing reactor is able to serve for as long as 15 years, and it has already been utilized in 35kV substation in Georgia. In addition, you should choose a proper product according to the electrical system design, while on-site installation guide and factory acceptance test are both available.

Brief Introduction
For electric power systems with different voltages, various neutral grounding methods shall be applied, and 6-66kV power distribution systems mainly adopt small current neutral grounding. In order to prevent arc grounding and improve power supply quality, an arc suppression coil shall be installed if the capacitive current is over 10A. This method results in a small grounding current, which has little interference on the communication system nearby.

Our earthfault compensation system makes use of advanced algorithms (remnant current increment method, active power method, etc.) to select fault line in a prompt and accurate way, and it adopts industrial computer system with bus-organization, multi-layer circuit board and full-color large LCD screen, so it features reliable running, direct data display, good anti-interference capacity and so on. On the other hand, our product also realizes parameter setting and information inquiry functions, and its adjustment range is very wide which is very different from conventional products.

Application
The arc suppression coil is extremely suitable for substations and power distribution stations in many large factories of metallurgy, mining, coal, paper making, power supplying, power generating, petrochemical engineering and other industries. This earth fault protection system fits for system voltage of 6-110kV, and it is a perfect choice to replace old-generation coils, or work with newly-built substations to offer grounding compensation and fault-line selection functions.

System Composition
The neutral grounding system is primarily composed of grounding transformer, arc suppression coil, on-load adjustment switch and earthfault compensation controller, while damping resistor is only necessary for turn-adjusting coil.

1. The grounding transformer adopts zigzag connection at the high voltage side, namely ZN, yn11. Based on this structure, each phase winding is composed of two sections of windings which are located on two iron core posts for different phases and are connected in opposite polarity. Thus, the zero sequence magnetic flow generated by the two phase windings is neutralized mutually, leading to low zero sequence impedance and no-load loss. In this way, the capacity of our grounding transformer is completely used.

On the other hand, a zigzag transformer allows the arc suppression coil to have a very high capacity, technically speaking, 90%-100% of that of the grounding transformer. However, for a common transformer, 20% is the upper limit. In this regard, a lot of money will be saved if a zigzag transformer is adopted.

2. The turn-adjusting arc suppression coil has several taps, and an on-load tap changer is utilized to regulate the value of inductance. When the power grid is under normal operation, a microcontroller inside our multi-tap arc suppression coil real-time detects the amplitude and phase changes of electrical current that flows through our product, and calculates the capacitive current of power grid under such circumstances. Then, based on the preset minimum residual current or tuning-off degree, it adjusts the tap changer to a desired position, thus limiting residual current at fault point within the preset range when earthing fault takes place.

3. The microcontroller is a core part for neutral grounding, and it is responsible for control, display, calculation and communication. The following paragraphs give brief introduction on its major functions.
a. It automatically measures capacitive current and carries out regulation control.
b. It reveals system voltage, displacement voltage, coil current, frequency, residual current, tune-off degree, time and other parameters. It also records the number of ground connection and corresponding system parameters.
c. It allows fault inquiry and printing at any time.
d. It could communicate with upper computer via RS232 or RS485 interface.

In addition, one microcontroller control one arc suppression coil and two microcntrollers can be installed in one panel and be able to operate in parallel.

4. The abovementioned microcontroller is installed on a control panel whose standard size is 800×600×2260mm, and two microcontrollers can be installed on one control panel at the same time. Aside from microcontrollers, this control panel is also fitted with other low-voltage apparatus, such as ampere meter, voltmeter, printer and various kinds of relays.

5. The damping resistor for MRD-XHZ turn-adjusting type arc suppression coil is manufactured from high-quality stainless steel alloy, and this material also exhibits excellent resistance to high temperature. When single phase ground fault occurs, our damping resistor will be short circuited by the system to protect itself from damage, and it will be reconnected to the arc suppression coil in series after power system recovers, otherwise resonance overvoltage may take place.