Transformer Auxiliary Protection Devices, Part 3: Sudden Pressure Relays (63)

Auxiliary Protection:

1. Oil Level Indicators (71)

2. Thermal Protection (26, 49)

3. Sudden Pressure Relays (63)

4. Gas Accumulators and Buchholz Relays (80)

5. Dissolved Gas and Moisture Monitors

6. Bushing Monitors

In this article we will review and read about Sudden Pressure Relay (63) device.

Sudden pressure relays possess a distinctive characteristic in their utilization of mechanical quantities, specifically sudden changes in internal transformer pressure, to detect low-level internal faults that are often not able to be identified by other relays relying on electrical quantities. The design of sudden pressure relays ensures that they do not activate in response to steady state or non-fault changes in these quantities. Instead, they are engineered to promptly activate with an inverse time characteristic when such changes occur as a result of internal faults.

Sudden Pressure Relay is mounted above the maximum oil level in the gas space when applied on transformers.

Sudden pressure relays are employed to detect faults that are not normally seen by current based (overcurrent or differential) relays. They are applicable to just about any size and type of liquid filled transformer.

Sudden Pressure Relay can only be applied to transformers with a gas space.

The Sudden Pressure Relay can only be used on transformers that have a gas space. A gas space in a transformer refers to a cavity or area within the transformer where gas can accumulate, typically due to the decomposition of insulating materials or the presence of combustible gases. Transformers that utilize insulating oil as the cooling and insulating medium typically have a gas space.

Typically, transformers that use insulating oil as the cooling and insulating medium have a gas space.

Typically, transformers that use insulating oil as the cooling and insulating medium have a gas space because the oil can degrade over time, resulting in the formation of gases. This degradation can occur due to factors such as high temperatures, electrical discharges, or the presence of moisture or contaminants. As the oil degrades, gases such as hydrogen, methane, and ethylene can be generated, leading to an increase in pressure within the transformer.

The Sudden Pressure Relay is designed to detect the sudden increase in pressure and initiate protective actions.

However, it is worth noting that not all transformers with insulating oil will have a gas space. Some transformers are designed with a sealed tank that prevents the accumulation of gases. Additionally, transformers that use alternative cooling and insulating mediums, such as dry-type transformers or transformers filled with non-flammable gases, may not have a gas space.

One advantage of sealed tank transformers is their ability to prevent the accumulation of gases inside the transformer.

The decision to use a sudden pressure relay may be based on the following factors:

1. Cost: The more expensive the transformer, the more protection that can be justified. The decision to use the protection on less expensive transformers is another matter. The true cost may not be just that of the transformer directly, but that of the labor, the downtime for replacement, and the loss of revenue from the customers fed by the transformer.

2. Transformer MVA size: The larger the transformer, the more protection that can be justified as the larger size implies a more expensive transformer, higher levels of load and often more customers.

3. Location within the power system: If the transformer is in a location where it is critical to maintaining service to customers, i.e. a radial system; then perhaps the expense of incorporating a sudden pressure relay is justified. Small transformers that are in a substation with several others may not have the sudden pressure relay since the loads can be switched to alternative sources. Transformers feeding high impact customers, i.e. hospitals, may warrant the installation of sudden pressure relays at any cost.

4. Past operating experience: Many utilities have incorporated sudden pressure relaying for tripping, but later removed or converted the relay to alarm only due to misoperations of the scheme. Such changes more commonly occurred on older, less secure schemes. Newer relays and designs have reduced misoperations and may warrant reconsideration for those utilities that changed their designs to alarm only or removed the trip.

The decision to use the sudden pressure relay is often based on the transformer size, location within the power system, cost, and past operating experience.?

Some utilities have elected to alarm only for fear of a possible false operation. Older circuit designs seemed to have more issues and more modern designs appear to have reduced problems.