The relay protection soft pressure plate can only be used as a

The relay protection soft pressure plate (sudden pressure relay) can only be used on transformers that have a gas space above the windings inside the tank.

Key Application Details

The soft pressure plate, also known as a sudden pressure relay, is designed to detect sudden increases in internal transformer pressure caused by faults such as arcing or insulation breakdown . It operates mechanically, using a bellows and microswitch system, and is not responsive to steady-state or slow pressure changes, ensuring it only trips during genuine internal faults .

Transformer Requirements

• Gas Space Requirement: The relay can only be applied to liquid-filled transformers that have a gas space above the windings. This gas space forms due to the decomposition of insulating oil under high temperatures, electrical discharges, or contamination, producing gases like hydrogen, methane, and ethylene .
• Mounting Location: It must be mounted above the maximum oil level in the gas space to accurately detect pressure surges .
• Transformer Type: Transformers without a gas space, such as dry-type transformers or sealed tank transformers that prevent gas accumulation, are not suitable for this relay .

Operational Principle

When an internal fault occurs, the pressure in the gas space rises suddenly, causing the bellows in the relay to expand and operate the microswitch. This triggers the relay to trip the circuit breaker or activate an alarm, isolating the faulty transformer section . The relay includes a seal-in mechanism to maintain the trip until manually reset, ensuring reliable fault response .

Summary

The soft pressure plate relay is specifically intended for transformers with a gas space, typically oil-filled types, and cannot be used on transformers lacking this feature. Its design ensures rapid detection of internal faults that may not be visible to current-based relays, providing an essential layer of protection for high-voltage transformers .