Substation Transformer Solutions

The main transformer of a substation is the core equipment of the power grid, responsible for the key tasks of energy transmission, voltage conversion, and power distribution. Its application scenarios mainly include the following aspects: energy transmission and voltage conversion. The main transformer increases the output voltage of the power plant to 66kV, 110kV, 132kV, 220kV, 232kV, 330kV or higher, achieving long-distance low loss transmission; At the same time, high-voltage (66kV, 110kV, 132kV, 220kV, 232kV, 330kV) electricity is stepped down to 6-35kV in the substation. For example, the 500kV main transformer is used for power exchange in the regional power grid, while the 33kV/20kV/11kV transformer serves the urban distribution network.

 

II、Classification of Substation Transformers

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1. Classified by the purpose of substation transformers

*Step up transformer: used in power plants to increase the output voltage of the generator (such as 10.5kV) to the transmission voltage (such as 110kV or 500kV).

*Contact Transformer: Connect power grids of different voltage levels (such as 222kV/110kV) to achieve energy dispatch and balance.

*Step down transformer: used in distribution networks to step down high voltage electricity to the user side voltage (such as 10kV/0.4kV).

2. Classification by Transformer Structure of Substation

*Double winding transformer: the most common type, suitable for single voltage conversion scenarios.

*Three winding transformer: equipped with three independent windings (such as 220kV/110kV/35kV), used for multi voltage level interconnection, and the capacity allocation needs to meet the requirements of high voltage side ≥ medium voltage side ≥ low voltage side.

*Autotransformer: Shared winding, low loss, small size, suitable for ultra-high voltage power grids or small safety lighting equipment.

3. Classified by insulation and cooling methods of substation transformers:

Natural cooling (ONAN), natural cooling+forced air cooling (ONAF), forced oil circulation water cooling (OFWF), forced oil circulation air cooling (OFAF).

Oil immersed self cooling (ONAN) achieves cooling through natural convection of oil and heat exchange between the radiator surface and air.

Oil immersed air-cooled (ONAF) adds a fan for forced heat dissipation on the basis of oil immersed self cooling.

Forced oil circulation air cooling (OFAF): using a fan to cool the oil in the cooler

Forced Oil Circulating Water Cooling (OFWF): The oil is cooled through a water cooling system.

 

 

III、Advantages of Substation Transformers

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1. Efficient and energy-saving

*Low loss design: Using high magnetic conductivity silicon steel sheets and optimized core structure, the no-load loss is reduced by more than 15%. For example, Hengfengyou Electric's S20 power transformer achieves a 20% energy saving by selecting low loss silicon steel sheets.

*Intelligent voltage regulation: Integrated on load voltage regulation function (optional MR, Huaming), real-time adjustment of output voltage, reducing energy waste, and extending the life of electrical equipment.
 

2. High reliability

*Multiple protection mechanisms: Gas protection can detect internal short circuits and abnormal oil levels; Differential protection quickly eliminates external faults to prevent accidents from escalating.

*Anti interference design: Oil immersed transformers are equipped with explosion-proof pipes and pressure relief valves to adapt to extreme outdoor weather conditions.

3. Intelligent operation and maintenance

*Real time monitoring: temperature and current data are collected through IoT terminals, combined with AI algorithms to predict faults and achieve cloud based management.

*Long life maintenance: maintenance free moisture absorber (such as MESSKO) ®） And online oil chromatography analysis (such as MSENSE) ®  DGA extends the service life of equipment.

 

IV、 How to choose a substation transformer?

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1. Capacity and quantity planning of substation transformers

*Capacity calculation: Select based on the future 5-10 year load plan and consider overload capacity. For example, when a single main transformer is shut down, the remaining transformers need to meet 70% -80% of the total load demand.

*Quantity configuration: Important load stations require 2-3 main transformers, ordinary substations usually have 2 transformers, and new energy stations can add regulating transformers to cope with fluctuations.

2. Selection of Transformer Types and Structures for Substations

*Oil immersed vs dry: Oil immersed is preferred for outdoor scenes (with good heat dissipation and overload resistance); Choose dry (flame-retardant, pollution-free) 67 for indoor or high fire protection scenarios.

*Winding form: Three winding transformers are suitable for multi voltage level interconnection, while autotransformers are suitable for large capacity transmission.

3. Requirements for voltage regulation and parallel connection of substation transformers

*Voltage regulation requirements: Load regulating transformers (such as Dyn11 type) can dynamically adapt to load changes and are recommended for use in power grids with frequent voltage fluctuations.

*Parallel conditions: It is necessary to ensure that the rated voltage, impedance voltage, and connection group are consistent, with a capacity difference of no more than 1:3, to avoid circulating current losses of 78.

4. Energy efficiency and environmental protection of substation transformers: S11, S13 or amorphous alloy transformers are preferred, which can save more than 30% energy compared to the traditional S9 series and have lower lifecycle costs.

 

 

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Ⅵ、 Substation Transformer FAQ

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1、What factors affect the lifespan of substation transformers? How to extend its service life?

*Operating temperature: Transformers generate heat during operation, and excessively high temperatures can accelerate the aging of insulation materials. Generally speaking, for every 6-8 ℃ increase in winding temperature, the insulation aging rate will accelerate by about 50%. Long term operation at high temperatures can make insulation materials brittle, lose elasticity, reduce insulation performance, and thus shorten the life of transformers.

*Insulation aging: During long-term operation, insulation materials will gradually undergo aging due to various stresses such as electricity, heat, and machinery. For example, partial discharge can corrode insulation materials, and the invasion of moisture and impurities can also reduce insulation performance, accelerate aging processes, lead to insulation breakdown, and affect the service life of transformers.

*Overload operation: When the transformer operates under overload for a long time, the current in the winding increases, which further increases the temperature of the winding, accelerates insulation aging, and mechanical component wear. At the same time, overload may also lead to an increase in electromagnetic force inside the transformer, causing winding deformation and affecting the performance and lifespan of the transformer.

*Short circuit fault: During a short circuit, the transformer will bear a huge short-circuit current and electric force, which may cause deformation, displacement, and even damage to the insulation of the winding. Even if the short-circuit fault is eliminated in a timely manner, there may still be hidden dangers inside the transformer, such as insulation damage, local overheating, etc., which will have a negative impact on the lifespan of the transformer.

*Hengfengyou Electric's production substation transformer has a design life of ≥ 30 years

 

2、What are the core functions of smart substation transformers?

*Voltage conversion: This is the main function of a transformer. Substation transformers can increase the low voltage generated by power plants to high voltage, reducing energy loss during transmission and achieving long-distance high-capacity transmission; It can also reduce high voltage to a low voltage suitable for user use, meeting the electricity needs of different users. For example, converting 110kV voltage to 10kV or 380V.

*Electricity transmission: Through the principle of electromagnetic induction, transformers can transmit electricity from the primary side to the secondary side, playing a pivotal role in the distribution and transmission of electricity in the power system, ensuring that electricity can be efficiently transmitted from the power source to various power terminals.

*Impedance matching: In the power system, transformers can be used to match the impedance of different parts, achieving optimal power transmission between the power source and the load, reducing reflected waves and power losses, and improving the stability and efficiency of the power system.

*Electrical isolation: The primary and secondary windings of a transformer are coupled by a magnetic field without direct electrical connection, thus achieving electrical isolation between the primary and secondary circuits. This can effectively prevent electrical faults on the high voltage side from being transmitted to the low voltage side, protect the safety of equipment and personnel on the low voltage side, and also reduce electromagnetic interference, improving the reliability and safety of the power system.

 

3、Why must the iron core of a substation transformer be grounded?

*Prevent floating potential discharge: During the operation of transformers, the iron core and other metal components are subjected to strong electric fields. If the iron core is not grounded, there will be a potential difference between it and the surrounding conductors. When this potential difference reaches a certain level, discharge will occur, which will damage the insulation of the transformer, affect its normal operation, and even cause safety accidents.

*Ensure the equipotential of the iron core: Grounding the iron core can keep it at the zero potential of the ground, thereby avoiding the accumulation of charges caused by induction, ensuring that the potential difference between the iron core and other metal components is zero, and preventing problems such as local overheating. Because when there is a potential difference in the iron core, a circulating current will be formed, causing the iron core to heat up. Prolonged heating will cause the insulation material to age and reduce the service life of the transformer.

*Provide fault current path: When insulation breakdown or other faults occur inside the transformer, the grounding of the iron core can provide a return power path for the fault current, so that the protection device can detect the fault current in a timely manner and act to cut off the power supply, thereby protecting the transformer and other equipment from damage and ensuring the safety of personnel and equipment.

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4、What faults can be detected by gas protection of substation transformers?

*Internal short circuit, inter turn fault

*Abnormal oil level (such as oil leakage causing a decrease in oil level)

*Poor contact or overheating of the tap changer

 

5、How to choose the brand of on load tap changer for substation transformers (based on Shanghai Huaming and Germany MR)?

Market share: MR: The global market share is about 60%, especially dominant in the high-end markets of Europe and America. Huaming: With a market share of over 90% in China and a global market share of about 30%, its price is only 1/3 to 1/4 of MR, and its cost-effectiveness advantage is significant.

From the perspective of maintenance costs: MR products have a short maintenance cycle and high costs, requiring reliance on professional agency services (such as an annual maintenance budget of nearly 100000 yuan per unit). Huaming's product design focuses on maintenance free features, such as the service life of on load tap changers for distribution transformers that are consistent with the transformer body and do not require regular maintenance.

Procurement cost: Shanghai Huaming's price is only 1/4 of MR's

 

High end technology and reliability priority: MR is recommended for ultra-high voltage engineering, large-scale industrial projects, or scenarios with extremely high stability requirements (such as electrolytic aluminum rectifier), where MR's long-term verification experience is more advantageous.  

6、What are the precautions for operating on load tap changers in substation transformers?

a. Pre operation inspection

*Check whether the oil level and color of the on load pressure regulating switch are normal, and whether there is any oil leakage. If the oil level is too low or the oil color is abnormal, it may affect the insulation and heat dissipation performance of the switch, and it needs to be dealt with in a timely manner.

*Check if the control power supply of the on load voltage regulating device is normal, and if all indicator lights and signal devices are working properly. Ensure stable control power supply to ensure accuracy and reliability of operation.

*Check if the counter of the on load tap changer indicates correctly and record the current tap position. This helps to understand the number of operations and current status of the switch, providing reference for subsequent operations.

*Check the operating status of the transformer, including whether the load, oil temperature, winding temperature, etc. are normal. If the transformer is in an overloaded or abnormally hot state, caution should be taken when adjusting the voltage to avoid increasing the burden on the transformer.

b. Attention during the operation process

*The operation of the on load tap changer should be carried out under no-load or light load conditions of the transformer. This can reduce the impact on transformers and power systems during voltage regulation, and avoid excessive voltage fluctuations caused by load changes.

*Strictly follow the operating procedures during operation, adjust step by step, and do not continuously and quickly adjust multiple tap positions. Continuous rapid adjustment may cause damage to the internal mechanism of the switch or cause voltage fluctuations, affecting the stable operation of the power system.

*After each operation, observe the changes in transformer voltage and current, as well as whether the on load tap changer operates normally. If abnormal fluctuations in voltage or current are found, or if the switch action is not smooth or there are abnormal sounds, the operation should be stopped immediately and checked and dealt with.

*During the operation, it is necessary to closely monitor the indication signals of the on load voltage regulating device, such as tap position indication, motor operation indication, etc. Ensure that the indication signal matches the actual operation. If there are any indication errors or inconsistencies, the cause should be promptly identified.

*When a short circuit fault occurs in the system or there is an abnormal situation inside the transformer, it is prohibited to operate the on load tap changer. Performing operations at this time may exacerbate the malfunction and even lead to more serious accidents.

c. Check after operation

*After the operation is completed, check again whether the voltage and current of the transformer are stable within the normal range to ensure that the voltage regulation effect meets the requirements. If the voltage adjustment is not in place or there are abnormal fluctuations, the cause should be analyzed and corresponding measures should be taken.

*Check if the tap position of the on load tap changer is correct and if the counter is counting correctly. Ensure that the actual position of the switch is consistent with the indicated position, and the counter accurately records the number of operations.

*Check if all components of the on load voltage regulating device are functioning properly, and if there are any abnormal phenomena such as heating or discharging. If heating or discharge signs are found in the components, it may be due to poor contact or insulation damage inside the switch, and timely maintenance is required.

 

*Keep operation records, including operation time, operation reason, changes in tap position, voltage and current changes, and other information. Detailed operation records help to track and analyze the operation of transformers, providing a basis for subsequent maintenance and repair.

7、What are the conditions for parallel operation of substation transformers?

The parallel operation of transformers requires the following conditions to be met: the winding wiring group is the same; The voltage ratio is equal, and the allowable difference is not more than ± 0.5%; The short-circuit impedance is equal, and the allowable difference is not more than ± 10%. Only by meeting these conditions can we ensure that the load distribution is reasonable and there will be no circulating current when the transformer operates in parallel, thereby ensuring the safe and stable operation of the transformer.

How to reduce the operational losses of substation transformers?

*Choose S11/S13 or amorphous alloy energy-saving models.

*The load rate should be controlled between 60% and 80% (either too low or too high will increase losses).

 

*Regularly clean the radiator dust and optimize ventilation conditions.

How to deal with cracks in the bushing of a substation transformer?

 

Cracks in the casing can reduce insulation strength and may cause short circuits when exposed to rain or snow. Immediate shutdown and replacement of the casing are required, while checking the oil spectrum data to confirm if there is any internal damage.

What are the reasons for the high temperature rise of substation transformers?

*Overloading: Reduce the load or increase capacity.

*Poor heat dissipation: Clean up oil stains and check if the cooling fan is working properly.