May 31, 2021 
Vacuum Contactors
A vacuum contactor is a device that contains electrical contacts inside a sealed “vacuum interrupter” called a vacuum bottle. This sealed environment in which the switching takes place allows for a fast, clean “make/break” action of the contacts in harsh, dirty environments. The vacuum bottle prevents the external environment from affecting its operation.
When closed contacts carrying current are separated, the current continues to flow through space, which is observed by the eye as an arc. Any contactor must address the issue of energy dissipation. In the case of harsh, dirty environments the vacuum contactor’s sealed vacuum bottle can provide a better environment than free air for breaking the arc. Within the sealed vacuum bottle, the arc burns in the metal vapour of the contact material. Without air to ionize, the arc extinguishes more quickly.
Since the arc burns on the contact, it is important that the material and construction for a set of vacuum contacts is designed to address the arc quenching. Contacts in a vacuum bottle are
typically made with a harder material than with “air break” contacts. For low-voltage vacuum
contactors (under 1500V) a dual material alloy is often used, such as WCu (Tungsten Copper) or WAg (Tungsten Silver). This material helps to reduce the possibility of welding. Additionally, the contacts are larger allowing heat to dissipate more quickly. The reduced arc time reduces contact erosion. With minimal erosion and the avoidance of contaminants, the contacts remain clean and dependable.
The speed of the contact separation can affect the contact performance. Contaminated contacts due to dirty, harsh environments may lead to “slow breaking” of air-break contacts after a number of operations. Since the vacuum tube is sealed, the arc chamber does not become exposed to impurities from the application environment.
Vacuum Contactors is available through Quick Time Engineering Inc.
Current Limiting Fuse
A current-limiting fuse is a fuse that, when its fusible element is melted by a current within the fuse’s specified current limiting range, abruptly introduces a high resistance to reduce current magnitude and duration, resulting in subsequent current interruption. For a fuse to be considered “current-limiting”, it must interrupt the circuit within 180 electrical degrees (one-half electrical cycle) after the fault occurs. This is accomplished by producing an arc voltage across the fuse greater than the system voltage. This higher arc voltage forces current to zero before the available short-circuit current reaches its first peak. In a non-current-limiting fuse, the fault current continues to flow until extinguished by the cycle of the supply system (zero-crossing).
A current-limiting fuse generally consists of two fusible parts:
- A fast blow element that operates rapidly in response to an overload.
- A high resistance element used to reduce the fault current during the remainder of the fault clearing time.
Operation of the fast element switches the high resistance element into the circuit, thus reducing the fault current. The high resistance element then continues with the arc extinction process. Arc voltages are created in the fuse by the melting of the fuse links. This produces a number of high resistance arcs (gaps) in series, and there exists a voltage drop across each gap. When the total voltage drop exceeds the system voltage, the current is interrupted. As this occurs, a transient voltage spike is generated in the system. It is important to make sure that this voltage does not exceed the system’s basic insulation level (BIL). Arc (or transient) voltage will usually not be a problem in a system if the fuse’s maximum design voltage rating does not exceed 140% of the system’s voltage.
Current Limiting Fuse is available through Quick Time Engineering Inc.
Three-phase Transformer Circuits
A three-phase transformer is made of three sets of primary and secondary windings, each set wound around one leg of an iron core assembly. Essentially it looks like three single-phase transformers sharing a joined core as in the figure.
Three-phase transformer circuits are available through Quick Time Engineering Inc.
Quick Time Engineering Inc is an international company with offices and distribution networks in the USA, Hong Kong, Europe and Malaysia.
In its 20 years of operation since 1998, Quick Time Engineering Inc had emerged from a local engineering company with a single staff that provided solutions in factory automation to become nowadays a company that serves the Oil & Gas industries, EPC contractors, System Integrators and other industrial automation and process control companies worldwide. Customers from over 50 countries worldwide trust us with their need for process control instruments and industrial automation products.
For more information about Quick Time Engineering Inc, visit www.quicktimeonline.com or email enquiry@quicktimeonline.com
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