In power engineering, there is a common misunderstanding: since the transformer core is conductive, more grounding points should be safer. However, all industrial specifications and practical operation experience clearly point out that the transformer core must be reliably grounded, and only one point grounding is allowed. This rule is especially important for 250 kVA power transformer and 250 kVA 3 phase transformer widely used in industrial and commercial power distribution, which are core products of JINSHANMEN TECHNOLOGY CO., LTD.
I. Why Must the Core Be Grounded?
During operation, the transformer core is in a strong alternating electromagnetic field generated by the winding. Without grounding, static potential will be induced on the core surface due to the distributed capacitance between the winding and the core, forming a floating voltage of tens of volts or even higher. This floating voltage not only poses a serious electric shock risk to maintenance personnel but also may cause partial discharge between the core and the winding, accelerating the aging of insulation materials. For 250 kVA 3 phase transformer used in high-frequency operation scenarios, the risk of floating voltage is more prominent. Therefore, grounding the core is to clamp its potential to zero, eliminate floating charge, and lay a foundation for safe and stable operation.
II. Why Is Multi-Point Grounding Dangerous?
Many on-site operators think that "more grounding points mean more protection", but this is completely wrong for transformer cores. The core is not a single solid metal block, but a laminated structure composed of multiple silicon steel sheets. Once multi-point grounding is adopted, it will artificially form a closed loop between the core and the ground grid.
2.1 Multi-Point Grounding Forms Core Circulating Current
When the transformer is in operation, there is alternating magnetic flux in the core. There is a tiny potential difference between different grounding points on the core. Under the action of this potential difference, a closed loop will be formed through "core → grounding wire → ground grid → another grounding point". At this time, the core becomes a low-impedance short-circuit loop. Even for a 250 kVA power transformer with small capacity, the circulating current generated by this loop will continuously generate heat, which is difficult to be detected by the protection device.
2.2 Hidden Hazards Caused by Core Circulating Current
The core circulating current has the characteristics of "small current but long-term existence". It does not pass through the main protection loop of the transformer, so it is difficult to be found in daily inspection. However, long-term circulating current will lead to local overheating of the core, accelerate the aging of transformer oil and insulation paper, and even cause local carbonization of the core in severe cases. For JINSHANMEN TECHNOLOGY CO., LTD's 250 kVA power transformer and 250 kVA 3 phase transformer, which are designed with high insulation standards, multi-point grounding will directly damage the product service life and operational reliability.
III. Why Is Single-Point Grounding the Safest Choice?
The core purpose of single-point grounding is "fixing potential without forming a loop". By grounding the core at one point, its potential to the ground is clamped at zero, which fundamentally eliminates the floating voltage. At the same time, since there is no second grounding point, there is no potential difference, and naturally, no closed loop or core circulating current will be formed. This is the key to ensuring the safe operation of the core.
Therefore, JINSHANMEN TECHNOLOGY CO., LTD strictly implements the single-point grounding standard in the production of 250 kVA power transformer, 250 kVA 3 phase transformer and other products. The core grounding wire is independently led out, the grounding point is fixed and easy to inspect, and it is strictly prohibited to add additional grounding points without authorization during operation, so as to maximize the safety of the product.
IV. Relevant Industry Standards
The requirement of "only one point grounding for transformer core" is not an empirical conclusion, but a mandatory regulation clearly stipulated in multiple national and industry standards:
GB 50150 《Code for Acceptance Test of Electrical Installation Engineering of Electrical Equipment》
DL/T 596 《Code for Precautionary Test of Power Equipment》
DL/T 572 《Operating Code for Transformers》
All the above standards emphasize that the transformer core shall be reliably grounded and only one point grounding is allowed. A large number of accident cases also prove that multi-point grounding of the core is one of the main causes of transformer overheating, insulation damage and even equipment failure.
V. About JINSHANMEN TECHNOLOGY CO., LTD
JINSHANMEN TECHNOLOGY CO., LTD is a professional manufacturer integrating R&D, production and sales of power transmission and distribution equipment. The company mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment.
With strict quality control and mature production technology, the company's 250 kVA power transformer and 250 kVA 3 phase transformer have the advantages of stable performance, low loss and high safety, and are widely used in industrial and mining enterprises, urban power distribution, new energy power generation and other fields. Adhering to the concept of "precision manufacturing and safe power supply", JINSHANMEN TECHNOLOGY CO., LTD provides reliable power transmission and distribution solutions for global customers.