Breaker Failure Relay :Back-up Protection

The relay operates based on various techniques and inputs, including monitoring the status of breaker control circuits, measuring breaker coil current, or analyzing voltage and current waveforms. It continuously evaluates the breaker’s performance and compares it to predefined criteria or expected operating sequences.

Breaker Failure Relays are commonly used in high-voltage transmission and distribution networks, where the failure of a circuit breaker can have severe consequences. They provide an additional layer of protection, acting as a fail-safe mechanism to ensure the integrity and reliability of the power system.

Breaker Failure Relays for Relay Backup

Breaker failure relays are referred to as backup protection devices, applied as stoppage protection relays for most relays. As a case in point Breaker failure relay is employed as a backup device for the differential relay of an influence Power Transformer and additionally for the distance relay of a conductor.

Why is Breaker Failure Relay required?

In the fault condition of any equipment, it’s expected that the fuse of this instrumentality will be tripped by main protection relays of such instrumentality if there’s a failure within the tripping circuit of the fuse or within the fuse itself. During this case, the fuse won’t be tripped. Then. To isolate this fault, the bus bar to which this equipment is connected should be fully isolated by tripping all the equipment connected to it at a delayed time. Then, the solely related gear to the current bus bar is the faulted one. During this case, the faulted equipment has no current transient; thus, it’s often disconnected mainly by isolates.

Principle of Buchholz Relays

The Buchholz Relay is a specialized protective device oil-filled power transformers use to detect and respond to internal faults and abnormalities. It operates based on the gas and oil flow detection principle within the transformer’s oil-filled tank and conservator.

The primary purpose of the Buchholz Relay is to provide early warning and protection against faults within the transformer’s active parts, such as the windings and core. It is particularly effective in detecting and responding to faults like internal short circuits, partial discharges, and excessive heating.

The Buchholz Relay is typically installed in the pipe connecting the transformer’s main tank and the conservator. It consists of a gas chamber, an oil flow chamber, and a float assembly. The gas chamber is connected to the upper part of the transformer tank, while the oil flow chamber is connected to the pipe between the tank and the conservator.

During normal operation, the oil in the transformer circulates between the main tank and the conservator, maintaining a balanced oil level in both chambers of the Buchholz Relay. However, when a fault occurs within the transformer, certain conditions can cause changes in the oil and gas flow patterns, triggering the Buchholz Relay’s protective action.

The importance of having multiple conditions for the operation of a Breaker Failure Relay lies in enhancing the reliability and accuracy of the protection scheme. The conditions mentioned typically include:

Tripping signal from any main protection relay

The BFR relies on receiving a trip signal from the primary protection relay of the condemned equipment. This ensures a fault condition has been detected and confirms the need for backup protection.

The fuse of the condemned equipment remains connected.

The fuse and the associated normally open (N.O.) auxiliary contact confirm that the faulted equipment is still connected to the system. If the fuse blows or the extra touch opens, it indicates a disconnection, and the BFR may not be required to operate.

Presence of current, even at a very low level

The BFR may also consider the presence of current flowing through the faulted equipment, regardless of its magnitude. This condition further validates the need for backup protection as it signifies that the faulted section is still connected to the power system.

Operation of the Buchholz Relay

The operation of the Buchholz Relay can be understood in two stages:

Gas Accumulation

When a fault occurs within the transformer, such as developing a short circuit, the resulting electrical discharge generates hydrogen and methane gases. These gases rise and accumulate in the upper part of the transformer tank. As the gas gets, it enters the gas chamber of the Buchholz Relay.

Oil Flow Disruption

The gas accumulation in the gas chamber causes a decrease in the oil level. This reduction in oil level triggers the float assembly within the oil flow chamber. The float assembly is equipped with mechanical contacts sensitive to oil level changes. When the oil level drops below a certain threshold, the float assembly activates the connections, initiating a protective action.

 

The protective actions initiated by the Buchholz Relay can vary depending on the configuration and requirements of the transformer system. Common responses include generating alarms, creating transformer trip signals, or activating mechanical locks to isolate the transformer from the electrical system.

The Buchholz Relay operates on the principle of gas accumulation and oil flow disruption within the transformer’s oil-filled tank and conservator. Detecting changes in gas and oil flow patterns provides early warning and protection against internal faults in power transformers, helping to prevent severe damage and ensuring the safety and reliability of the transformer system.

Conditions and Importance for Breaker Failure Relay

To operate the breaker failure relay, it should satisfy three conditions. They are:

• I am tripping signal from any main protection relay of the condemned equipment which exists.
• The fThe condemned equipment’s fuse continues to connect (n.o. auxiliary contact from the fuse is used).
• There’s currently passing through this equipment, notwithstanding. It’s an incredibly tiny value.

Although one of the second and third conditions is spare for the healthy operation of breaker failure relay, it’s desirable to use each for a lot of security.

The schematic arrangement shows the breaker failure relay circuit. The tripping course of the breaker failure relay is analogous to the tripping circuit of the bus bar protection relay. Generally breaker failure relay could use an equivalent tripping circuit of the bus bar protection relay