What is a transformer protective device?

1. What is a transformer protective device?

• Transformer protection device is an integrated automation system, designed to continuously monitor the operating status of the transformer, and in the detection of internal faults or external anomalies (such as short-circuit, overload, overheating), can quickly and accurately send out alarm signals or automatically cut off the power supply of the transformer, so as to prevent damage to the equipment, to protect the stability of the power grid and the safety of personnel. It is equivalent to the transformer "nerve center" and "guardian", is to ensure the reliable operation of the power system is indispensable to the key links.

2. Components of transformer protection devices

• sensor element: Equipment used to collect transformer operating data.

  • Current Transformer (CT): Measurement of the current flowing through the transformer windings.

  • Voltage transformers (PT): Measure the voltage across the transformer.

  • Gas Relay: Detection of gas and abnormal oil flow in the tank due to malfunction.

  • temperature sensor: Monitoring of winding and transformer oil temperatures.

  • Pressure sensors/release valves:: Monitor internal tank pressure.

• Core actuators (protection relays):: The "brain" of the system, used to analyze sensed data and make decisions.

  • microcomputer protection device (MPPD): A digital unit that integrates multiple protection functions and is the core of a modern protection system.

• actuator: A device that receives commands from a protective relay and performs physical operations.

  • Circuit Breaker:: Execute the final "trip" command to break the circuit.

• subsystem:

  • DC power supply: Provides reliable power for the operation of protective devices and circuit breakers.

  • Control and signaling circuits: A cable network that transmits data, alarms and trip commands.

3. Characteristics of transformer protection devices

• selectiveness: Responds only to faults within the protection area and does not affect other normally operating equipment.

• rapidity:: Remove faults as quickly as possible to minimize equipment damage and shock to the system.

• sensitivity: Reacts reliably to even the smallest faults within the protection range.

• dependability: It must operate reliably when it is required to do so, and must not be inadvertently activated when it is not required to do so.

4. Principles of operation of core protection devices

• differential protection: Determine whether there is an internal short-circuit fault by accurately comparing the magnitude and phase of the currents on the primary and secondary sides of the transformer. When an internal fault occurs, the currents on both sides lose balance, generating a differential current, and when this current exceeds the set value, the protection immediately operates and trips.

• gas protection: Utilizes the principle that internal transformer faults cause insulating oil to decompose and produce gas. A small amount of gas gathered slowly will trigger a light gas alarm; while a serious fault produces a large amount of instantaneous gas and oil flow impact will trigger a heavy gas trip.

• Overcurrent/overload protection: Monitor the current flowing through the transformer. When the current exceeds the normal load but does not reach the short-circuit level and continues for a period of time (overload), an alarm or delayed trip is given. Instantaneous tripping when the current increases dramatically due to an external short circuit.

• temperature protection: Real-time monitoring of winding and top oil temperatures through built-in temperature sensors. When the temperature exceeds the alarm setting value, the cooling system is activated or an alarm is issued; if the temperature continues to rise to the trip setting value, the power supply to the transformer is cut off, preventing the insulation from being permanently damaged due to overheating.

5. Use of transformer protection devices

• main application: Used to protect all types of power transformers (both oil-immersed and dry-type) in the power system from damage due to electrical or mechanical faults and to minimize the impact of faults on the entire power grid.

• application scenario: Widely used in power plants, substations at all levels, industrial enterprises, data centers, rail transportation and all other places where large and medium-sized power transformers are used.

6. Role of transformer protection devices

• Isolation of faults: Isolate the faulty transformer from the grid in the shortest possible time to prevent the fault from spreading.

• Protection equipment: Avoid or mitigate damage to the transformer itself, reducing maintenance costs and downtime.

• Maintaining system stability:: Prevent transformer failure from triggering a chain reaction that could lead to widespread power outages.

• Security of personnel:: Preventing injuries to site personnel due to catastrophic accidents such as transformer explosions and fires.

7. Functions of transformer protection devices

• Main protection function: Fast and sensitive response to serious faults within the transformer (e.g. differential protection, heavy gas protection).

• Backup protection function: Acts as a second line of defense when the main protection or the protection of adjacent equipment fails (e.g., overcurrent protection).

• Monitoring and Alarm Functions: Warning signals for non-emergency anomalies (e.g., overload, slight over-temperature, light gas) to prompt the operator to check.

• Event logging function: Automatically record current, voltage and other data before and after a fault occurs (fault recording) to provide a basis for accident analysis.

8. Types of transformer protection devices

• By Protection Principle:

  • Electrical quantity protection: Protection based on changes in electrical parameters such as current and voltage (e.g. differential protection, overcurrent protection, overexcitation protection).

  • Non-electrical quantity protection: Protection based on changes in non-electrical parameters such as temperature, pressure, gas, etc. (e.g. gas protection, temperature protection, pressure relief protection).

• By Role:

  • primary protection: Primary protection that responds to faults in the zone, such as differential protection.

  • backup protection: Supplementary to the main protection in case of failure, e.g. overcurrent protection.

9. Safety levels and standards for transformer protection devices

• The design, manufacture and application of transformer protection devices need to follow strict international and national standards to ensure their performance and reliability.

  • international standard: as IEC 60255 Series (General Requirements for Measuring Relays and Protective Devices).

  • industry standard: as IEEE C37.91(Power Transformer Protection Relay Application Guide).

  • These standards make clear provisions for the accuracy, action time, resistance to electromagnetic interference, and environmental adaptability of protection devices.

10. How to choose the best transformer protection scheme

• Evaluation of transformer parameters: Consider first the transformer capacity, voltage level, wiring and type (oil-immersed/dry). The larger the capacity and the higher the voltage of the transformer, the more comprehensive and reliable the protection needs to be.

• Analyzing the operating environment:: Assess the importance of transformers in the grid. For transformers in hub substations or important users, redundant (dual) primary protection should be provided.

• Consider the balance between economy and reliability: Select the most cost-effective protection configuration scheme while meeting the basic requirements for safe operation.

• Consulting Professional Engineer: Work with a professional relay protection engineer to design the most reasonable protection scheme for the specific situation.

11. Conclusion

• A set of properly configured, high-performance transformer protection devices is a necessary investment in the transformer, an expensive and critical asset. Not only does it effectively extend the life of the transformer, it is the cornerstone of ensuring the safe, reliable and efficient operation of the entire power system. Choosing the right protection scheme is choosing to be responsible for the asset, for the grid and for safety.