370 KVA Earthing Transformer-22/0.11 KV | South Africa 2024

Reliable grounding, stable power supply-choose exceptional earthing transformers!

01 General

1.1 Project Description

This 370kVA earthing transformer is exported to South Africa in August, 2024. The primary voltage is 22 kV, the secondary voltage is 0.11 kV, the special transformer is equipped with no load tap changer, the tapping range is ±2*2.5% at primary side, the cooling is ONAN.

In the power system, grounding a transformer is a special transformer, it bears the important responsibility of protecting equipment, personal safety and improving the reliability of power supply. The grounding transformer realizes the effective grounding of the neutral point through the ingenious working principle, and then eliminates the influence of the unbalanced current on the system.

The purpose of the grounding a transformer is to provide an artificial neutral point for the system where the neutral point is not grounded, and to facilitate the use of arc suppression coils or small resistance grounding methods. Its working principle is mainly to ground the neutral point in the system and introduce the unbalanced current to the ground, so as to achieve the protection and safe operation of the system. Under normal circumstances, the neutral point of the ground transformer is not grounded, but when a fault in the system causes the neutral point voltage to rise, the ground transformer will play a role. When the neutral voltage rises to a certain extent, the grounding transformer will automatically turn on and ground the neutral point, thereby introducing the unbalanced current to the ground, preventing the voltage from continuing to rise, and protecting the system equipment and personal safety.

1.2 Technical Specification

370 kVA grounding a transformer specifications type and data sheet

1.3 Drawings

370 kVA grounding a transformer diagram drawing and size.

02 Manufacturing

2.1 Core

The core of the grounding a transformer is made of silicon steel sheet, which has low hysteresis loss and eddy current loss, which helps to improve the energy efficiency of the transformer. In design, the shape of the core is generally closed loop in order to form a stable magnetic flux and reduce magnetic leakage.

In a grounding a transformer, the main function of the core is to provide a good flux path, so that the transformer can effectively isolate and convert voltage. At the same time, the core also helps to direct the leakage current in the transformer to the grounding system, thus improving the safety of the system. Through reasonable core design, the noise and vibration can be effectively reduced, and the operation stability of the equipment can be improved.

In order to enhance the anti-interference ability and electromagnetic compatibility of the ground transformer, the core surface is usually treated to reduce eddy current losses and improve aging resistance. In addition, measures are taken during the manufacturing process to reduce the air gap in the core to optimize its magnetic properties and achieve higher work efficiency. In general, the iron core of the grounding transformer is not only the guarantee of electrical performance, but also an important part of ensuring the safe and reliable operation of the equipment.

2.2 Winding

Coil winding of transformer is the core link in its construction, which directly affects the electrical performance and efficiency of transformer. Coils are usually made of highly conductive copper or aluminum wire to ensure excellent current conductivity and low energy loss. The winding method of the coil is generally layer winding or concentrated winding, which can effectively reduce the resistance and inductive reactance of the coil and increase the power density of the transformer. In the winding process, the number of turns and the arrangement of the coil have an important effect on the voltage ratio, power conversion efficiency and flux distribution of the transformer. In order to optimize coil performance, the designer will accurately calculate the number of turns of each set of coils according to the application requirements of the transformer to ensure that it can achieve the required voltage conversion. In addition, the insulation of the coil is also very critical, and the commonly used insulation materials include epoxy resin, paper and polyester film to prevent short circuit and leakage phenomenon.

2.3 Tank

Oil tanks feature a sealed structure to prevent external air and impurities from entering, maintaining the purity of the transformer oil. The tank body is assembled with welded or bolted connections to ensure high strength and tight sealing. The exterior is treated with special coatings to adapt to various climates and installation environments, such as high humidity, salty air, or industrial pollution.

2.4 Final Assembly

03 Testing

1. Type Tests

● Temperature Rise Test: Verifies that the temperature rise is within permissible limits.

● Short-Circuit Impedance and Load Loss Test: Measures short-circuit impedance and load losses.

● No-Load Loss and Current Test: Checks the efficiency during no-load operation.

● Insulation Performance Test: Tests the electrical strength of the insulation system.

2. Routine Tests

● DC Resistance Measurement: Checks winding connections and material quality.

● Turns Ratio and Polarity Test: Confirms the correct ratio and polarity.

● Power Frequency Withstand Voltage Test: Verifies the insulation system’s voltage resistance capability.

● Grounding Resistance Test: Ensures stable grounding performance.

3. Special Tests

● Lightning Impulse Test: Simulates lightning strikes to verify insulation resistance to surges.

● Partial Discharge Test: Detects internal discharge within the insulation system.

● Noise Test: Measures operational noise to ensure it meets standards.

● Short-Circuit Test: Examines mechanical strength and thermal stability.

04 Packing and Shipping

05 Site And Summary

Earthing transformers are classified as standard reactors. An earthing transformer (neutral coupler) is a three-phase transformer connected to a power system to provide a neutral ground connection, which can be achieved either directly or through impedance. Earthing transformers can also provide additional local auxiliary loads.

During a single-phase fault, the reactor limits the fault current at the neutral point and improves the recovery of the power line. According to IEC 60076-6, a ground reactor is connected between the neutral point of a power system and the ground in order to limit the current of the line to the ground to a desired value in the event of a ground fault in the system.

An earthing transformer can provide a neutral point to the power grid. Usually ZN connection is used. The Z-connection provides a linear and specific zero-sequence impedance. The earthing transformer can also be connected in YN+d mode.