The protection device for drytype transformers is a set of electrical components and systems designed to monitor its operating status in real time and trigger protective actions when faults (such as overheating, overcurrent) occur, thereby preventing equipment damage and expanding accident scope.

　　Core Protection Types and Their Functions

　　Drytype transformer protection devices mainly target common fault risks, and each type has a clear protection focus.

　　1. OverTemperature Protection

　　This is the most critical protection for drytype transformers, as their solid insulation (e.g., epoxy resin) is highly sensitive to high temperatures.

　　Working Principle: Temperature sensors (such as Pt100 platinum resistors or thermocouples) are embedded in the transformer windings or installed on the core surface to continuously collect temperature data.

　　Protection Actions:

　　1. Alarm: When the temperature reaches a preset warning value (e.g., 100°C for Class H insulation), the device issues an audible/visual alarm to remind operators to check the load or environment.

　　2. Trip: When the temperature exceeds the critical limit (e.g., 130°C for Class H insulation), the device immediately cuts off the transformer’s power supply to avoid insulation breakdown and burnout.

　　2. Overcurrent and ShortCircuit Protection

　　This protects against damage caused by excessive current due to load overload or internal/external short circuits.

　　Common Components: Mainly uses current transformers (CT) and overcurrent relays (or integrated protection devices).

　　Protection Logic:

　　Overload Protection: When the load current exceeds the rated value for a certain period (e.g., 1.2 times rated current for 2 hours), the device first alarms; if the overload persists, it trips.

　　ShortCircuit Protection: When a short circuit occurs (current suddenly surges to 5–10 times the rated value), the device acts instantly (within 0.1 seconds) to trip the circuit breaker, minimizing impact on the transformer and power grid.

　　3. Leakage Current Protection

　　This is especially important for drytype transformers used in humid or dusty environments (e.g., mines, basements) to prevent electric shock and insulation deterioration.

　　Implementation Method: A zerosequence current transformer is installed on the transformer’s incoming/outgoing lines to detect unbalanced current (leakage current) between the live wire and neutral wire.

　　Protection Action: When the leakage current exceeds the safe threshold (e.g., 30mA for lowvoltage systems), the device trips quickly to cut off the power supply.

　　4. OverVoltage/UnderVoltage Protection

　　This prevents insulation damage or abnormal operation caused by unstable grid voltage.

　　Working Principle: Voltage sensors monitor the transformer’s input/output voltage in real time.

　　Protection Actions:

　　When the voltage exceeds 1.1 times the rated value (overvoltage) or drops below 0.85 times the rated value (undervoltage) for a set time, the device alarms first.

　　If the voltage remains abnormal, it trips to disconnect the transformer from the grid.

　　Key Selection Criteria

　　When choosing a protection device, it needs to match the transformer’s parameters and application environment to ensure effectiveness.

　　1. Match Insulation Class: The overtemperature protection’s temperature thresholds must align with the transformer’s insulation class (e.g., lower thresholds for Class F insulation than Class H).

　　2. Adapt to Application Scenarios: For mining or explosive environments, select protection devices with explosionproof certifications (e.g., ExdI) to avoid triggering explosions.

　　3. Consider Monitoring Functions: Prioritize devices with digital displays and remote communication interfaces (e.g., RS485), which enable realtime status viewing and remote control, reducing onsite inspection workload.

　　Do you need me to sort out a drytype transformer protection device selection checklist? It will include core parameters (such as rated current, temperature range) and inspection items (such as certification, communication functions) to help you quickly verify whether a device meets your needs.