Transformer accessories play an essential role in improving transformer safety, monitoring performance, and extending service life. A power transformer is not only composed of the core, devanados, and insulation system; reliable operation also depends on the correct selection and performance of transformer accessories such as Buchholz relays, casquillos, silica gel breathers, and oil level indicators.A power transformer is not only composed of the core, devanados, and insulation system. The reliability of a transformer also depends heavily on the performance of its accessories.

Transformer accessories are responsible for:

• Monitoring transformer operating conditions;
• Protecting against abnormal operation;
• Maintaining insulation performance;
• Providing early warnings before serious failures occur.

Sin embargo, selecting the correct transformer accessories is not always straightforward.

Many problems in transformer installation and maintenance are caused by incorrect accessory selection, such as:

• Wrong voltage rating;
• Incorrect mounting dimensions;
• Unsuitable material selection;
• Missing communication requirements;
• Poor compatibility with the transformer design.

For engineers, understanding the key selection parameters of transformer accessories can significantly improve transformer reliability and reduce maintenance costs.

1. Transformer Accessories Selection Starts with Transformer Design

Before selecting any accessory, engineers should first understand the transformer basic parameters.

The following information is normally required:

Accessories are not independent components. They must match the transformer design.

Por ejemplo:

A Buchholz relay installed on a 33kV power transformer requires different specifications compared with one used on a small distribution transformer.

2. How to Select a Buchholz Relay?

A Buchholz relay is one of the most important protection devices for oil immersed transformers equipped with a conservator tank.

It detects:

• Gas accumulation;
• Oil flow caused by internal faults;
• Serious insulation problems.

Key Selection Parameters

2.1 Pipe Diameter

The relay size must match the connection pipe between:

Transformer tank → Conservator tank

Common sizes include:

• DN25
• DN50
• DN80

Incorrect pipe size may affect oil flow detection accuracy.

2.2 Transformer Capacity

Large transformers generally require higher sensitivity and stronger mechanical design.

Selection depends on:

• Transformer rating;
• Oil volume;
• Internal fault protection requirements.

2.3 Alarm and Trip Contacts

Engineers should confirm:

• Number of contacts;
• Contact rating;
• Signal type.

Typical requirements:

• Alarm contact;
• Trip contact.

For modern substations, remote monitoring capability is increasingly required.

3. Transformer Bushing Selection Parameters

Transformer bushings provide electrical connection between internal windings and external circuits.

Incorrect bushing selection may cause:

• Insulation failure;
• Overheating;
• Descarga parcial.

Important Parameters

Tensión nominal

The bushing voltage class must match the transformer system voltage.

Example:

Corriente nominal

The current rating must be higher than the transformer operating current.

Insufficient current capacity may cause overheating.

Creepage Distance

For outdoor transformers, creepage distance is critical.

Higher pollution areas require longer creepage distance.

Environmental factors include:

• Coastal salt;
• Industrial pollution;
• Desert dust.

4. Selecting the Right Silica Gel Breather

A silica gel breather protects transformer insulation by preventing moisture from entering through the conservator tank.

Key Parameters

4.1 Transformer Oil Volume

The breather size should match the transformer oil expansion volume.

Small breathers may not provide sufficient breathing capacity.

4.2 Silica Gel Capacity

Common considerations:

• Amount of silica gel;
• Moisture absorption capacity;
• Easy replacement design.

4.3 Maintenance Requirements

A good breather design should allow:

• Easy silica gel replacement;
• Visual moisture inspection;
• Reliable sealing.

5. Oil Level Indicator Selection

Oil level indicators monitor transformer oil level changes caused by temperature variation.

Selection Factors:

Display Type

Las opciones incluyen:

• Mechanical indicator;
• Magnetic oil level gauge;
• Remote signal type.

Alarm Function

For critical transformers, engineers may require:

• Low oil level alarm;
• Remote monitoring output.

Installation Position

Before ordering, confirm:

• Mounting flange;
• Connection size;
• Indicator direction.

6. Pressure Relief Device Selection

A pressure relief device protects transformers from dangerous internal pressure increases.

When an internal fault occurs, gas generation can rapidly increase pressure inside the tank.

The relief device releases pressure to prevent tank deformation or explosion.

Important Parameters:

7. Consider International Standards

For export transformer projects, standards are extremely important.

Common standards include:

IEC Standards

• CEI 60076 — Power transformers
• CEI 60137 — Insulated bushings
• CEI 60214 — Tap changers

IEEE Standards

Commonly required in North American projects.

Before quotation, engineers should confirm:

• Required standard;
• Testing requirements;
• Certification documents.

8. Common Mistakes When Selecting Transformer Accessories

Mistake 1: Selecting Only Based on Price

Low-cost accessories may lead to:

• Shorter service life;
• Higher maintenance cost;
• Unexpected failures.

Mistake 2: Ignoring Installation Dimensions

Electrical parameters may be correct, but mechanical dimensions may not match.

Always confirm:

• Drawings;
• Mounting holes;
• Connection dimensions.

Mistake 3: Not Considering Future Maintenance

A transformer may operate for 25–40 years.

Accessories should be selected considering:

• Replacement availability;
• Spare parts;
• Maintenance convenience.

9. Engineer Checklist Before Ordering Transformer Accessories

Before purchasing, confirm:

☑ Transformer rated voltage

☑ Transformer capacity

☑ Accessory model

☑ Installation drawing

☑ Applicable IEC/IEEE standard

☑ Required testing report

☑ Alarm and communication requirements

☑ Environmental conditions

Manufacturer Insight

As a transformer manufacturer and transformer accessories supplier, PDDN recommends that customers provide complete technical information before selecting accessories.

For OEM and replacement projects, the following documents are helpful:

• Transformer nameplate;
• Existing accessory model;
• Installation drawing;
• Technical specification;
• Required standard.

Proper selection during the engineering stage can prevent installation problems and improve transformer operating reliability.

Acerca de PDDN

PDDN is the online platform ofTecnología de energía Co. de Luoyang Datang., Limitado., a trusted manufacturer and global supplier oftransformadores de potencia, accesorios para transformadores, switchgear components, sistemas de almacenamiento de energía en baterías (BESS), and EV charging solutions. Since 2015, we have supported utility companies, EPC contractors, and industrial customers worldwide with reliable products, OEM/ODM services, and technical expertise.