In the power transmission and distribution system, the grounding specification of the transformer iron core is the core premise to ensure the long-term stable operation of the equipment. Especially for widely used equipment such as oil filled distribution transformers and 800kva transformer, strictly following the principle of "reliable grounding at one point" is even more crucial. This article will detailedly analyze the core reasons and specification requirements for transformer iron core grounding, and combine the product advantages of JINSHANMEN TECHNOLOGY CO., LTD to provide professional reference for industry practitioners. 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.
I. Why Must the Iron Core Be Grounded?
Core Purpose: To prevent floating potential from being generated in the iron core and metal components, thereby avoiding ground discharge (sparks/breakdown) and ensuring the safe and stable operation of the equipment. This requirement is fully applicable to oil filled distribution transformers, 800kva transformer and all types of transformers, and is also one of the key quality points strictly controlled by JINSHANMEN TECHNOLOGY CO., LTD in the production process.
1. The Iron Core Is in a Strong Electric Field
When the transformer is in operation, its windings are connected with high voltage and large current, and this powerful alternating current will generate a strongly changing magnetic field. According to the principle of electromagnetic induction, this changing magnetic field will induce an electric potential (voltage) on the iron core itself and all surrounding metal components (such as clamps, fasteners, oil tank walls, etc.). Whether it is an 800kva transformer or a large-capacity oil filled distribution transformer, its iron core is in such a strong electric field environment for a long time, and the generation of induced potential is inevitable.
2. Hazards of Floating Potential
If the iron core is not grounded, it is insulated from the earth (ground potential) and is in a "floating" state. The induced potential has no release path and will continue to accumulate and change, forming a "floating potential". There is an insulating medium (transformer oil, insulating cardboard) between the iron core and surrounding grounded metal components (such as oil tanks). When the potential difference between them rises enough to break down these insulating media, intermittent spark discharge will occur. For oil filled distribution transformers, this discharge will directly affect the insulating performance of transformer oil, and since 800kva transformer is often used in industrial power distribution scenarios, discharge faults may also affect the normal operation of surrounding electrical equipment.
3. Severe Consequences of Discharge
1) Insulation damage: Continuous spark discharge will gradually carbonize and erode solid insulation (such as cardboard, wood blocks), reduce its insulation strength, and eventually may lead to serious inter-turn short circuit or main insulation breakdown, which is fatal to the service life of oil filled distribution transformers and 800kva transformer. 2) Generation of fault gases: Discharge energy will decompose transformer oil, producing characteristic gases such as hydrogen (H₂) and acetylene (C₂H₂). These gases will dissolve in the oil and deteriorate the oil quality, especially affecting the oil-immersed insulation effect of oil filled distribution transformers. 3) Interference with gas relay (buchholz relay): The generated gas may accumulate in the gas relay, causing the relay to send false signals (light gas alarm) or even trip incorrectly in severe cases, affecting the continuity of power supply. 4) Increased no-load loss: The discharge itself consumes energy, leading to increased no-load loss of the transformer and decreased operating efficiency, which will increase electricity costs for 800kva transformer users who focus on energy conservation. 5) Generation of local overheating: High temperature will be generated at the discharge point, forming local overheating points and accelerating equipment aging.
Therefore, grounding the iron core is to provide a discharge channel for these induced charges, force the iron core to be fixed at (ground) zero potential, thereby eliminating the potential difference between it and the grounded components, and completely avoiding the above-mentioned discharge phenomenon. When producing 800kva transformer and oil filled distribution transformers, JINSHANMEN TECHNOLOGY CO., LTD will strictly implement the iron core grounding process to avoid discharge risks from the source.
II. Why Must It Be "Grounded at One Point"?
This is the key and delicate part of the problem. The iron core grounding is not arbitrary, but requires only one point and a reliable connection. This principle is crucial for all transformers, especially oil filled distribution transformers and 800kva transformer. Once violated, it is easy to cause equipment failures and even safety accidents.
Core Purpose
To avoid the formation of a closed loop by "multi-point grounding", thereby preventing the generation of circulating current (eddy current) in the loop from causing local overheating and ensuring the safe operation of the transformer. For oil filled distribution transformers, local overheating will also accelerate the aging and deterioration of transformer oil, while local overheating of 800kva transformer may affect its load capacity and lead to unstable power supply.
1. Hazards of Multi-Point Grounding
The iron core of a transformer is formed by laminating many layers of silicon steel sheets, and insulating paint is applied between the sheets to block the "eddy current" path generated when the magnetic flux passes through the steel sheets, thereby reducing "eddy current loss", which is the basic principle of transformers. Both 800kva transformer and oil filled distribution transformers follow this design logic in their iron core structure. If the iron core is grounded at two or more points such as point A and point B at the same time, a closed conductive loop will be formed between the iron core, the grounding wire and the grounding point.
2. Circulating Current and Overheating
A part of the main magnetic flux of the transformer will pass through this closed loop. According to Faraday's law of electromagnetic induction, the alternating magnetic flux will induce an electromotive force in the loop, thereby generating a considerable circulating current. When this circulating current flows through the contact points of the iron core laminations with high resistance, it will generate a lot of heat, leading to severe local overheating of the iron core. This situation is particularly prominent in oil filled distribution transformers and 800kva transformer, because the iron core volume and load demand of such equipment will make the heat accumulation caused by circulating current faster.
3. Consequences of Multi-Point Grounding Faults
1) Local high temperature: The temperature of the overheating point may reach several hundred or even thousands of degrees Celsius, which is enough to burn nearby insulation parts and accelerate the aging of transformer oil, which has a more direct impact on oil filled distribution transformers. 2) Generation of characteristic gases: High temperature will decompose the oil, producing a large amount of characteristic gases such as methane (CH₄) and ethylene (C₂H₄). These gases can be detected by dissolved gas analysis (DGA), which is an important basis for diagnosing iron core multi-point grounding faults and a common method used by JINSHANMEN TECHNOLOGY CO., LTD in equipment inspection. 3) Catastrophic faults: If not handled in time, local overheating will develop into iron core melting and large-area insulation carbonization, eventually leading to catastrophic accidents such as winding short circuits and transformer burnout. Such faults will cause huge economic losses and power outages, whether it is 800kva transformer or oil filled distribution transformers.
III. Summary
1. Why grounding? To prevent the iron core from generating floating potential and ground discharge, protect the insulation, and ensure the safe operation of the equipment. This is a basic requirement that 800kva transformer, oil filled distribution transformers and all transformers must comply with, and also the product quality bottom line adhered to by JINSHANMEN TECHNOLOGY CO., LTD. 2. Why only one point grounding? To avoid the formation of a closed loop, prevent circulating current from causing local overheating of the iron core, burn out the equipment, and ensure the long-term stable operation of the transformer.
You can understand it vividly like this: No grounding: It is like walking on a dry carpet with rubber soles. The body will be charged, and touching the doorknob will cause a "pop" discharge. If the transformer iron core is not grounded, this kind of "small spark" will occur continuously, causing continuous loss to the insulation system of oil filled distribution transformers and 800kva transformer. Multi-point grounding: It is like putting a copper ring in a changing magnetic field, and the copper ring will heat up quickly and even melt. Multi-point grounding of the iron core is equivalent to forming this "heating ring" by itself, which eventually leads to equipment failure.
Therefore, "reliable grounding at one point" is the only correct and must be strictly followed principle for transformer iron core grounding. For transformers in operation, the grounding state (whether connected) of the iron core is an important indicator that needs regular monitoring. As a professional transformer manufacturer, JINSHANMEN TECHNOLOGY CO., LTD strictly implements the iron core grounding process in accordance with international standards when producing 800kva transformer, oil filled distribution transformers and various other transmission and distribution equipment. At the same time, it provides users with professional equipment operation and maintenance suggestions to help users avoid grounding fault risks and ensure the safe and stable operation of the power system.