buchholz relay

Relay - Relay is a simple electro mechanical device or switch which is use to make the circuit connect and disconnect like a switch but in normal switch operate in manually but in a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit as per the requirement. 

The relay operates on the electro-magnetic induction principle.

Relay types - Relay is classified into different part as per it's function, structure and it's use.. 

• Thermal
• Differential
• Distance
• Automotive
• Frequency
• Polarized
• Rotary
• Sequence
• Moving Coil
• Buchholz
• Electromagnetic
• Latching
• Electronic
• Non-Latching

Buchholz Relay definition-  it's an gas operated type of relay which is used in oil impressed transformers to protect transformers form internal faults.

It's placed between the main tank of the transformer and conservator tank.

It is not used in small transformer because of  its pricing issue.

 

Buchholz Relay working Principle- The temperature of the oil rises when a fault occurs inside the transformer. The main tank's oil evaporates and turns into gas. The magnitude of the fault that occurs inside the transformer determines the generation of flu gas. Internal failure occurs in the transformer due to either insulation breakdown between the winding or a weak initial contact between the winding.

 

Buchholz-relay -The arc is caused by the defect, which raises the temperature of the oil. The oil evaporates and rises in the atmosphere. Before tripping the transformer and disconnecting it from the main supply source, the Buchholz relay detects the failure and warns the staff.

  

Construction of Buchholz Relay - Buchholz relays are made out of an oil-filled chamber. In the chamber, there are two hinged floats, one at the top and one at the bottom. A mercury switch is attached to each float. The upper float's mercury switch is connected to an alarm circuit, while the lower float's mercury switch is connected to an external trip breaker to cut the supply source.

1) Two hinged floats

2) Two mercury switches 

3) Release cock

4) Test cock

5) outer enclosure 

Construction of Buchholz Relay

# The minimum operating time of the relay is very minimum  (0.1 seconds).

 

Limitations of Buchholz Relay- There are some limitations of the buchholz relay.

1) the relay is only used in oil-immersed transformers.

2) it's work only for internal faults.

3) Relay response time is very high.

Testing and Maintenance of buchholz Relay

By forcing air into the float chamber to remove the liquid and make the floats fall, it is typically able to test the float operators. By turning a rod, or portable lever, attached on the relay's housing, the baffle plate can be inspected. By measuring the resistance with a typical multi meter, the condition of the electrical switches themselves can be determined.

Advantages of Buchholz Relay -

1) Operation is reliable. 

2) Simple in construction

Disadvantages of Buchholz Relay

1) only used for oil immersed transformers. 

2) only used for internal faults.