How does a mercury wetted relay work?
Mercury relays consist of a vertical (usually glass) tube containing liquid mercury. They have isolated contacts at the bottom of the tube and partway up, usually in a side arm of the glass. The relay works by displacement. When energised, this coil attracts the slug, lifting it upwards and out of the mercury pool.
How long do mercury relays last?
Because of this, mercury contacts cannot switch currents of more than a few amperes. The electrical life expectancy of general purpose and power relays is generally rated to be 100,000 operations minimum, while mechanical life expectancy may be one million, 10, or even 100 million operations.
Why is mercury switch used in Buchholz relay?
Gas produced by abnormal conditions in the transformer, collects in the Buchholz relay which lowers the oil level so that the top float gradually comes down and ultimately operates the mercury switch when it reaches a certain level. This surge displaces the lower float operation the mercury switch associated with it.
Why is mercury used in switches?
A mercury switch is an electrical switch that opens and closes a circuit when a small amount of the liquid metal mercury connects metal electrodes to close the circuit. This design is used in relays in industrial applications that need to switch high current loads frequently.
What is the working principle of relay?
Relay works on the principle of electromagnetic induction. When the electromagnet is applied with some current it induces a magnetic field around it.
What is a mercury wetted contactor?
A mercury contactor uses a pool of mercury, inside a glass sealed tube, to electrically connect two contacts. Basically, a mercury wetted contact relay consists of one or more glass switch capsules surrounded by a coil. Thus, in effect, the mercury wetted contact relay provides a new contact surface for each closure.
What is Buchholz relay and its significance in Transformers?
Buchholz relay is a security device which is normally used in large oil absorbed transformers. The Buchholz relay purpose is to give the protection to a transformer from the different faults happening in the transformer like the Short circuit, inter-turn, core, incipient, etc.
What is working principle of Buchholz relay?
Working principle of buchholz relay Whenever a fault occurs inside the transformer, such as insulation failure of turns, breakdown of core or excess core heating, the fault is accompanied by production of excess heat. This excess heat decomposes the transformer insulating oil which results in production of gas.
What is another name of mercury switch?
principles of operation The so-called mercury, or “silent,” switch is used extensively for controlling home lighting circuits.
Who invented the mercury switch?
In the 1910s Phelan invented and developed various forms of the mercury switch, on which he obtained 52 patents.
What is relay explain the operation and application of relays?
A relay is an electrically controlled switching device. It consists of an electromagnet and a set of contacts that open or close when voltage is applied to the electromagnet. In the beginning, electromechanical relays were used to transfer the Morse-code signal to long-distance through a wire.
What kind of relay is mercury wetted with Mercury?
Mercury-wetted relay • A mercury-wetted relay is a form of reed relay in which the contacts are wetted with mercury.
How does a mercury relay bridge the contacts?
A pool of mercury fills the lower portion of the tube, but is insufficient to bridge the contacts. A magnetic slug of iron or steel is placed in the tube, where it sinks by gravity so as to displace the mercury. The displaced mercury rises in the tube, sufficiently to bridge the contacts and complete the circuit between them.
What kind of relay is used for high speed?
For high-speed use, the mercury-wetted relay is used instead. This combines the speed of a low-mass relay, together with the fast wetting of mercury contacts. A relay, usually a reed relay, has its contacts coated with a small quantity of mercury.
What do you need to know about reed relays?
Reed relay • Reed relays can switch. A reed relay is a reed switch enclosed in a solenoid. • The switch has a set of contacts inside an faster than larger relays and require very little power from the control circuit. However, they have relatively low switching current and voltage ratings.