Application Scenarios, Configuration Modes and Precautions of Box-type Substation

Application Scenarios, Configuration Modes and Precautions of Box-type Substation

Box-type substation is a factory prefabricated indoor and outdoor compact power distribution equipment, which integrates high-voltage switchgear, distribution transformers and low-voltage distribution devices in accordance with a specific wiring scheme. It organically combines the functions of high-voltage power reception, transformer step-down and low-voltage power distribution, and is installed in a fully enclosed, movable steel structure box with moisture-proof, rust-proof, dust-proof, rat-proof, fire-proof, anti-theft and heat-insulating performances. Operating in a fully enclosed state, it is especially suitable for the construction and renovation of urban power grids, and is a new type of substation developed after civil-engineered substations.

Box-type substations are applicable to mines, industrial and mining enterprises, oil and gas fields, and wind power stations. They replace the traditional civil-engineered power distribution rooms and substations, and have become a new complete power transformation and distribution device. They are also widely used in residential communities, urban public transformers, bustling downtown areas, construction power supply scenarios, etc.

01 Application Scenarios of Box-type Substation

1.Street lighting box-type substation

Jinneng electric European-style box-type substations and American-style box-type substations have advantages over traditional civil power distribution rooms in small-load power consumption systems. The manufacturing cost of box-type substations is much lower than that of ordinary power distribution rooms, and they feature attractive appearances. European-style box-type substations can even adopt landscape shells, forming a beautiful scenery.

2.Power supply for parks and residential communities

Box-type substations are commonly adopted for power supply in parks and residential communities. These scenarios have high requirements for appearance and land occupation, and box-type substations perfectly solve these two problems with elegant appearance and small floor area.

3.Power supply for industrial and mining areas

Industrial plants, mines and other areas feature complex terrain and high time cost, hence putting forward high requirements for power supply equipment. Box-type substations are easy to install with less on-site construction work, and reach IP33 protection grade, which can greatly reduce construction workload and period, and are suitable for installation in complex terrain areas.

4.Temporary power supply

Construction units often change power consumption locations along with the migration of construction sites, so movable power distribution equipment is required. Box-type substations boast good mobility and sufficient load capacity, which can fully meet the temporary power demand of construction sites.

02 Classification, Advantages and Disadvantages of Box-type Substation

03 Configuration of Box-type Substation

I. Configuration of High-voltage Side of Box-type Substation

1.According to the primary wiring mode on the high-voltage side, box-type substations are divided into terminal type and loop network type.The terminal type box-type substation requires no additional wiring. If the high-voltage side adopts one-in multiple-out or multiple-in one-out configuration (mostly one-in two-out, one-in three-out, two-in one-out or two-in two-out), it can be regarded as a loop network type box-type substation.

2.European-style box-type substations can be equipped with circuit breakers on the high-voltage side, or adopt load switch-fuse combined protection. Considering the cost of box-type substations, the latter is mostly adopted for substations with a capacity not exceeding 800 kV·A and low requirements for high-voltage side protection configuration.

3.Most high-voltage load switches configured in European-style box-type substations are FLN-12 sulfur hexafluoride load switches.

4.The rated current of the high-voltage fuse link for protection is selected according to the following formula:

Irr​=KIgmax​

Where:

Irr​ – Rated current of the fuse link, A;

K – Coefficient, generally 1.3;

Igmax​ – Rated current of the transformer high-voltage side.

5.For safety in operation and maintenance, the high-voltage side configuration of European-style box-type substations shall meet the following requirements:① The load switch shall be equipped with a grounding device in the open state to ensure maintenance safety.② The load switch and isolating switch shall be interlocked with each other to ensure operation safety.

6.For American-style box-type substations, the high-voltage load switch-fuse combination unit is integrated with the transformer and assembled in the same oil-immersed tank, including position load switch, backup fuse, plug-in fuse and transformer. Its loop network mode is realized by converting the internal connection terminals of the position load switch.

 

Ⅱ.Configuration of Low-Voltage Main Distribution Cabinet for Box-type Substation

The low-voltage main distribution cabinet of a box-type substation is generally equipped with an incoming low-voltage isolating switch, a main low-voltage circuit breaker, and a main low-voltage metering device. The low-voltage isolating switch is mandatory to meet the needs of daily inspection and maintenance.The main low-voltage circuit breaker is selected based on the transformer capacity and the short-circuit current at the installation location of the circuit breaker.The main low-voltage circuit breaker of a transformer is usually a frame-type intelligent circuit breaker, and its selection and setting requirements are as follows:

1.Rated current of the circuit breaker

It is generally selected as 2.0 to 2.5 times the transformer capacity. The corresponding rated breaking current is greater than the short-circuit current on the low-voltage side of the transformer, so verification is rarely required.

2.Setting current Iset1​ of long-time-delay (inverse-time overcurrent) release

It shall satisfy:In​≤Iset1​≤Iz​Where:

In​ = rated current on the low-voltage side of the transformer

Iz​ = current-carrying capacity of the low-voltage busbar

To fully utilize the transformer capacity without affecting its service life, Iset1​ should be equal to or close to In​.

3.Setting current Iset2​ of short-time-delay (definite-time overcurrent) release

It shall satisfy:1.2Ifj​≤Iset2​≤Id​/1.3Where:

Ifj​ = short-time peak load current of the transformer

Id​ = single-phase earth fault current of the transformer

This requirement is easily satisfied for D,yn11 connected transformers, but difficult for Y,yn0 connected transformers, which is why box-type substations mostly adopt D,yn11 transformers.The short-time-delay setting time of the main low-voltage circuit breaker is generally 0.6 s, ensuring a time grading of not less than 0.2 s with the downstream circuit breakers.

4.Setting current Iset3​ of instantaneous overcurrent release

Due to the existence of short-time-delay overcurrent protection, Iset3​ can be set higher for better selectivity, usually 12 to 15 times the value of Iset1​.

 

III. Automatic Reactive Power Compensation Device of Box-type Substation

According to current national standards, the reactive power compensation capacity is generally required to be configured as 30% of the transformer capacity, which can meet the requirements under operating conditions with a high natural power factor.However, with the rapid popularization of inductive household appliances such as air conditioners, washing machines, refrigerators, and energy-saving lamps, configuring 30% of the transformer capacity sometimes fails to achieve the expected effect.It is advisable to set the compensation capacity at 40% to 60% of the transformer capacity, with automatic compensation divided into 10 control loops. Although the cost increases slightly, it is negligible compared with the total cost of the box-type substation, and the compensation effect is excellent.Jinneng electric TBBZ high voltage reactive power automatic compensation cabinet, GGJ low voltage reactive power compensation device,and new generation SVG cabinet.Our SVG Cabinet is a flexible AC transmission system device based on fully controlled power electronic components (IGBT). It utilizes voltage source converter (VSC) technology and achieves dynamic reactive power compensation through PWM control.

Compared to traditional SVCs, SVG offers faster response, higher precision, and a more compact design, making it a core component in smart grids and modern industrial power quality management.

 

IV. Configuration of Low-Voltage Outlet Cabinet

The number of circuits in the low-voltage outlet cabinet of a box-type substation is generally determined according to the load distribution in the power supply area, with 1 to 3 spare circuits reserved appropriately.The specification and model of the circuit breaker for each circuit are selected based on the corresponding calculated load.The selection and setting requirements of low-voltage feeder circuit breakers are similar to those of the main transformer circuit breaker, on the premise that the calculated load current of each feeder must be known for reasonable configuration.

 

04 Notes on Outdoor Installation of Box-type Substation

1.The grounding conductor of the box-type substation must be copper, with a cross-sectional area of not less than 30 mm². Equipment that intentionally reduces the grounding wire specification is vulnerable to lightning damage.

2.The grounding grid of the box-type substation shall ensure sufficient coverage area and depth. It is recommended to bury the grounding grid more than 1 meter underground. Vertical grounding electrodes should be added to reduce grounding resistance.

3.The box-type substation shall be installed in an area free from strong vibration and impact, with no strong electromagnetic interference nearby. Cable incoming and outgoing lines shall meet the safe construction clearance.

4.The installation site shall be dry and well-ventilated, with horizontal installation and an inclination angle of no more than 5 degrees.

5.No explosive hazardous materials, corrosive gases or liquids shall be present at the installation site.

6.Outdoor box-type substations require no on-duty operation, featuring a small footprint and low operating cost.

 

05 Treatment Measures for Common Electrical Faults of Box-type Substation

1.Overheating treatment

Overheating of electrical equipment may cause insulation aging and loose connections. Internal short circuits can raise temperatures and even cause fires. Transformer winding overheating may damage the unit.Countermeasures: timely clean dust and residues inside the substation; strengthen temperature monitoring of all equipment and issue high-temperature alarms promptly.

2.On-load tap-changer faults

On-load tap-changer faults are mostly caused by:

Long service life and deformed frame, leading to looseness or detachment;

Insufficient component strength, causing damage during switching;

Poor quality, resulting in main shaft fracture etc.Measures: strictly select qualified on-load tap-changers and ensure quality installation.

3.Low-voltage switch tripping

Main causes: busbar faults or switch maloperation.Upon tripping, inspect the substation carefully. When overcurrent protection acts on the low-voltage side of the main transformer, check and protect related equipment immediately.Distinguish between busbar and line faults, verify protection pressure plate status, and use professional instruments for testing if necessary.

 

05 Troubleshooting for Tripping Faults of Box-type Substation

1.Tripping faults during operation mainly include main transformer switch tripping and line switch tripping. Main transformer tripping is subdivided into tripping on three sides and low-voltage side tripping. Fault causes are determined by monitoring data analysis.

2.Upon outdoor tripping, maintenance personnel shall arrive on site promptly to restore power supply. Check for severe equipment damage, then inspect the tripping switch and arc-suppression coil.For spring energy-storage switches, check spring energy storage; for electromagnetic switches, inspect the power fuse.

3.For main transformer low-voltage side tripping, inspect line protection and main transformer protection.If only low-voltage overcurrent protection operates, line faults can be excluded; check output terminals and substation equipment.If both overcurrent and line protection operate, judge line faults according to line disconnection. Inspect both line outlets and the whole line before handling the tripping fault.

 

06 Notes on Fire and Explosion Prevention of Box-type Substation

1.Do not operate the box-type substation under long-term overload, especially aged equipment. Pay attention to coil and insulation aging to prevent short circuits.

2.For oil-immersed transformers, regularly check the insulation performance of transformer oil and replace substandard oil in time.

3.Monitor transformer operation in real time to avoid core overheating and insulation aging. Avoid damaging insulation layers during maintenance.

4.Pay attention to poor wire connections during routine maintenance and handle them promptly.

5.Surge arresters are installed in high-voltage cabinets, transformers and low-voltage cabinets to prevent lightning damage.

6.Ensure reasonable ventilation and heat dissipation in design, with sufficient vents and exhaust fans. Automatic temperature monitoring systems in transformer rooms effectively control internal temperature.