What are the main transformer protection devices

Transformer protection device is an important equipment to ensure the safe operation of the transformer, the following are some common protection devices:

gas protection

Principle and function: Gas protection is the utilization ofGas RelayTo achieve this, when a fault occurs inside the transformer, gas or oil flow will be generated, and the gas relay detects these changes and sends out an alarm signal or trip command. Gas protection can be divided into light gas and heavy gas two kinds of action. Light gas action generally only sends out an alarm signal, while heavy gas action will be directly tripped to cut off the transformer and the power supply connection, to prevent further expansion of the fault.
Scope of protection: mainly for transformer internal phase short circuit, turn-to-turn short circuit, core failure, etc..

overcurrent protection

Principle and function: realized by overcurrent relay, when the current flowing through the transformer exceeds the set value, the overcurrent relay will act and send out a trip signal to cut off the circuit after a certain delay. This protection device is mainly used to protect the transformer from overcurrent caused by external short-circuit, and as a backup protection in case of internal failure.
Action characteristics: usually with a certain delay characteristics, in order to avoid the load inrush current in a short period of time caused by false action.

differential protection

Principle and function: Differential protection is to compare the size and phase of the current on the inlet and outlet side of the transformer to determine the fault. During normal operation, the currents on both sides are equal, and the differential relay will not act; when a fault occurs inside the transformer, there is a difference in the currents between the two sides, and the differential relay will act quickly to cut off the connection between the transformer and the power supply when it detects this difference. Differential protection is characterized by high sensitivity and fast action.
Scope of protection: It is mainly used to protect the transformer windings and lead wires from phase-to-phase short circuit and other faults.

Overexcitation protection

Principle and function: When the voltage of the transformer increases or the frequency decreases, it will lead to an increase in the magnetic flux density of the transformer, causing the phenomenon of overexcitation. The overexcitation protection device judges whether overexcitation occurs by monitoring the change of voltage and frequency, and sends out alarm or trip signal when the degree of overexcitation exceeds the set value, so as to prevent the transformer from being damaged due to overexcitation.
Role: To protect the core and other insulating parts of the transformer from overheating and insulation aging due to overexcitation.

distance protection

Principle and function: Distance protection is a protection that judges the fault location and acts by measuring the electrical distance from the fault point to the protection installation. For transformers, distance protection is mainly used to protect faults on their lead wires. When a fault occurs, the distance protection device will judge the fault distance according to the measured impedance change and act when the impedance value is less than the set value.
Scope of protection: mainly for short circuit faults on transformer lead wires and adjacent lines.

temperature protection

Principle and function: The temperature protection device monitors the oil and winding temperatures by means of a temperature sensor installed in the transformer tank. When the temperature exceeds the permissible range, the temperature protection device will issue an alarm signal and take measures when the temperature is too high, such as starting the cooling system or cutting off the power supply, in order to prevent the transformer from being damaged due to overheating.
Importance: High temperatures accelerate the aging of transformer insulation materials, affecting their service life and operational safety.

Insulation supervision and protection

Principle and function: The insulation supervision device is used to monitor parameters such as zero sequence current or voltage to ground in the neutral grounding circuit of the transformer, in order to determine whether there is a fault in the internal insulation of the transformer. When the zero sequence current or voltage changes due to insulation damage, the insulation supervision device will issue an alarm or trip signal.
Application Scenario: For transformers with neutral grounding for early detection of insulation faults.

backup protection

Principle and Function: Backup protection is a protective device that functions when the main protective device (e.g. differential protection, gas protection, etc.) fails. It usually has a long action delay to ensure that the fault can be cut off if the main protective device fails. Backup protection may include overcurrent protection, distance protection, etc.
Importance: Improves the reliability of the transformer protection system and ensures effective protection of the transformer in all fault conditions.