Buchholz relay is a specialized protective device used for transformer protection, particularly for oil-filled transformers. It provides detection and protection against internal faults, such as short circuits between windings or incipient winding faults. Below an overview of Buchholz relay transformer protection:
Principle of Operation:
The Buchholz relay is installed in the oil-filled conservator tank connected to the transformer. It operates based on the principle that internal faults in the transformer generate gas or oil surges within the tank. The relay detects these surges and initiates protective actions.
Gas and Oil Detection:
The Buchholz relay consists of two chambers within the conservator tank: the upper chamber and the lower chamber. The upper chamber filled with gas (typically nitrogen) and connected to the transformer’s main tank. The lower chamber is filled with oil and is connected to the transformer’s oil circuit.
Gas Accumulation Detection:
When a fault occurs within the transformer, such as a short circuit or an incipient fault, it generates heat, which causes the decomposition of the insulating oil, resulting in the production of gas. The gas generated in the transformer rises to the conservator tank and accumulates in the upper chamber of the Buchholz relay.
Gas Accumulation Alarm:
The accumulation of gas in the upper chamber of the Buchholz relay triggers an alarm signal. This alarm indicates the presence of a fault within the transformer and allows for early detection and investigation of the problem.
Oil Surge Detection:
In addition to detecting gas accumulation, the Buchholz relay can also sense oil surges caused by severe faults. These surges generated when a significant amount of oil displaced due to fault currents or pressure variations within the tank.
Trip Action:
The Buchholz relay equipped with contacts that can initiate a trip signal to disconnect the transformer from the power system in response to severe faults. This trip action usually reserved for major faults that pose a serious risk to the transformer’s insulation and integrity.
Fault Localization:
The Buchholz relay can provide some indication of the fault location within the transformer. The rate of gas accumulation or oil surge can give an approximate idea of whether the fault is occurring in the upper winding (near the Buchholz relay) or the lower winding (closer to the core).
The Buchholz relay provides an additional layer of protection for transformers, especially against internal faults that may lead to catastrophic failures. It acts as an early warning system, allowing for timely investigation and maintenance before the fault escalates. The gas and oil detection capabilities of the Buchholz relay make it particularly effective in detecting and protecting against faults that can occur within the transformer windings and insulation.
Buchholz Relay Working Principle
The Buchholz relay operates based on the principle of gas and oil detection within the conservator tank of an oil-filled transformer. Its primary function is to detect and provide protection against internal faults that generate gas or oil surges. Here’s a breakdown of the working principle of the Buchholz relay:
Installation and Configuration:
The Buchholz relay is typically installed between the transformer tank and the oil conservator tank. It is positioned vertically and connected to both chambers. The relay is equipped with two float-operated switches: the upper float and the lower float.
Normal Operating Condition:
Under normal operating conditions, the oil level within the transformer is at a normal level, and the upper float of the Buchholz relay remains in a lowered position. The lower float is also in a lowered position as the oil level is below it.
Gas Accumulation Detection:
When an internal fault occurs within the transformer, such as a short circuit or incipient fault, it generates heat and leads to the decomposition of insulating oil. This decomposition produces gas, mainly hydrogen, which rises to the conservator tank.
Upper Float Activation:
As gas accumulates in the conservator tank, it displaces the oil, causing the level of oil in the tank drop. This drop in oil level causes the upper float of the Buchholz relay to rise.
Alarm Signaling:
When the upper float rises, it typically triggers an alarm signal. This alarm indicates the presence of a fault within the transformer and allows for early detection and investigation. The alarm can be in the form of an audible or visual signal.
Severe Fault Detection:
In the case of severe faults, such as major short circuits or core failures, a significant amount of gas and oil surge occurs within the transformer. This surge can cause rapid displacement of oil, leading to a sudden rise of the lower float in the Buchholz relay.
Trip Action:
When the lower float rises rapidly, it activates the trip contacts of the Buchholz relay. These contacts connected to the circuit breaker or other protective devices, which initiate a trip signal to disconnect the transformer from the power system. This trip action typically reserved for severe faults that pose a serious risk to the transformer.
Fault Localization:
The Buchholz relay can provide some indication of the fault location within the transformer. Gas accumulation or rapid oil surge can give an approximate idea of whether the fault is occurring in the upper winding (closer to the Buchholz relay) or the lower winding (closer to the core).
The Buchholz relay acts as an important protective device for oil-filled transformers, providing early detection and protection against internal faults. By detecting gas accumulation and oil surges, it serves as an alarm and tripping mechanism, helping prevent further damage and allowing for timely maintenance and investigation of faults within the transformer.