1.Overview

When a single-phase grounding occurs in the generator circuit of a power plant, and the fault current reaches a certain value, it may make the occurrence of "intermittent" arc grounding overvoltage have a specific "critical" condition, resulting in the generation of arc grounding overvoltage; The withstand voltage level of the machine is weak, and its insulation is easily damaged. If the ground fault current is too large, it will cause the iron core of the generator to burn, and accompanied by a higher than normal mechanical pressure acting on the generator and its circuit. Therefore, high-resistance grounding is usually used at the neutral point of the generator. When a single-phase grounding occurs in its circuit, it can limit the arc grounding overvoltage, reduce the burn to the iron core, and reduce the mechanical pressure on the generator and its circuit.

The HYGFN type intelligent generator neutral point grounding resistance cabinet is a complete set of equipment dedicated to high resistance grounding of the neutral point of the generator in the power plant.

2.Product model description

3. Equipment principle

Since the generator has a usable star point, a single-phase transformer associated with the load resistance can be used to form a high-resistance grounding method. The principle wiring is shown in the figure。

The primary side of the transformer is connected to the neutral point of the system and the earth, and the load resistance is connected in parallel to the secondary side of the transformer. When a single-phase ground fault occurs, the load resistance limits the current passing through the secondary side of the single-phase transformer, and in turn limits the ground fault current returning to the system through the primary side of the ground transformer. Generally speaking, the resistance unit is usually designed to follow a fault current of 2-12A at this time. The rated time is 10 seconds or 1 minute. The transformer size is designed according to the same situation. The voltage rating of the transformer primary side is the same as the system line voltage. Its nominal voltage is the system single-phase acid ground line voltage divided by √3. The secondary side voltage is usually 220V or 110V. In view of the internal fault of the transformer, an overcurrent relay can be used to protect it. Transformers, resistance units and connected terminal blocks are installed in an independent cabinet.

4. Product features

1. The material of the resistance cabinet is made of stainless steel or cold-rolled steel plate, with beautiful appearance and strong corrosion resistance;

2. The neutral point resistor of the HYGFN generator is made of high-quality nickel-chromium alloy, which is installed on the secondary side of the grounding transformer, with stable performance, high temperature resistance and strong flow capacity;

3. Intelligent control part: The traditional grounding resistance cabinet is only a pure hardware protection device. The resistance cabinet developed by our company has added the intelligent control part. The hardware of the controller is based on an industrial-grade single-chip computer, and the software adopts C and assembly language mixed programming, and the display part is a large-screen LCD Chinese characters. When the intelligent controller is normal, it can monitor the temperature of the neutral point unbalanced current, resistor slices, transformers, and resistance cabinets. When a single-phase ground fault occurs, it can record the magnitude of the grounding current, grounding time, temperature changes and grounding of the resistors, transformers and resistance cabinets. The number of actions and the reserved communication interface can transmit the detected and recorded information to the main control room, so that the operating personnel can get complete relevant information in the first time.

5. Conditions of Use

1. Altitude: not more than 5000m, ambient temperature: -40℃~+60℃, relative humidity: not more than 95% (25℃);

2. Grid frequency: 58~68Hz (60Hz system), 48~(52Hz system);

3. The air in the site should not contain chemically corrosive gas and steam, and no explosive dust. For special conditions of use, please specify when ordering.

6. Common specifications, models, technical parameters

7. Appearance and installation

1. Equipment installation as shown

Figure 2 The structure of a secondary parallel resistor connected to a single-phase grounding                    Figure 3 Directly grounded structure via high resistance

8. Ordering instructions

Please inform the following parameters when ordering

1. The rated voltage of the system, the capacity and transformation ratio of the transformer, the way of entering and exiting lines;

2. The material, IP protection level, color and installation location of the resistance cabinet;

3. Resistance value, tap position, flow time, current transformer ratio;

4. If the cabinet needs to install an intelligent control system, our company will provide specific principles and wiring drawings.

9. Product acceptance

1. Check that the components of the resistor are intact and the accessories are complete, and disconnect the connecting copper bars between the electrical components in the resistance cabinet;

2. Measure the resistance of the resistance unit at room temperature. The change range should be within ±5% of the rated resistance. After the test is completed, restore the original wiring in the cabinet;

      10. Transportation and storage

        1. HYGFN type intelligent generator neutral grounding resistance cabinet is packed and transported. During transportation, it should be rainproof, put lightly, and stand upright to prevent collision;

2. Ensure that it is placed upright during storage. The ambient temperature of the storage place should generally be between 40°C and +60°C. The air should not contain chemically corrosive gases and vapors, and no explosive dust.