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What is the working principle of AC contactor?

The AC contactor is an electromagnetic AC contactor with a NO main contact, three poles, and air as the arc extinguishing medium. Its components include: coil, short-circuit ring, static iron core, moving iron core, moving contact, static contact, auxiliary NO contact, auxiliary NC contact, pressure spring sheet, reaction spring, buffer spring, arc extinguishing The cover is composed of original parts. The appearance structure of the common AC contactor is shown in the figure below:

Electromagnetic system: It includes coil, static iron core and moving iron core (also called armature).

Contact system: It includes main contacts and auxiliary contacts. The main contact allows a larger current to pass through and plays the role of connecting and cutting off the main circuit. Usually, the maximum current allowed by the main contact (ie, the rated current) is one of the technical parameters of the contactor. Auxiliary contacts are only allowed to pass small currents, and are generally connected to the control circuit when used.

The main contacts of AC contactors are generally NO contacts, and the auxiliary contacts are either NO or NC. A contactor with a smaller rated current has four auxiliary contacts; a contactor with a larger rated current has six auxiliary contacts.

NO and NC refer to the state of the contacts before the electromagnetic system is energized. That is, the NO contact means that when the coil is not energized, its moving and static contacts are in an open state, and the coil is closed after it is energized. NC contact means that when the coil is not energized, its moving and static contacts are closed, and when the coil is energized, it is disconnected.

The function of the arc extinguishing device is to quickly cut off the arc when the main contact is broken. If it is not cut off quickly, the main contact singeing and welding will occur. Therefore, AC contactors generally have arc extinguishing devices. For AC contactors with larger capacity, arc extinguishing grids are often used.

The working principle structure of the AC contactor is shown in the figure below. When the coil is energized, the iron core is magnetized, attracting the armature to move downward, making the normally closed contact open and the normally open contact closed. When the coil is de-energized, the magnetic force disappears. Under the action of the reaction spring, the armature returns to the original position and the contact returns to the original state.

Impact of the Circuit Breaker and Budget Measures in Response to COVID-19

The COVID-19 pandemic and consequential measures taken to contain the pandemic, including lockdowns and travel restrictions, have adversely affected economic activity globally.

In Singapore, the Circuit Breaker measures, which were necessary to stem the community spread of COVID-19 and save lives, had a negative impact on the economy. In particular, the closure of most physical workplace premises from 7 April to 1 June, which had affected businesses that could not operate remotely from home, is estimated to have reduced Singapore’s annual real GDP by 2.2 per cent.

The Government has introduced four Budgets this year to fight COVID-19, with a total commitment of $93 billion in economic and social support and public health management measures. The Budget measures are expected to cushion the fall in employment and economic output arising from COVID-19. Specifically, the four Budgets are estimated to avert a loss in real GDP of about 5.5 per cent in 2020, and reduce the rise in resident unemployment rate by 1.7 percentage-points.

Overall, the four Budgets have supported economic livelihoods and prevented an even more significant disruption to income and cash flows. They also contribute to the longer-term objective of helping viable firms stay afloat and facilitating a quicker recovery. In addition to the economic benefits, there will also be positive externalities from the public health management measures that have been put in place to safeguard Singapore from COVID-19.

How Does a Magnetic Motor Starter Work?

Magnetic starters rely on electromagnets to function. They have an electromagnetically operated set of contacts that starts and stops the attached motor load, and an overload relay. The overload relay opens the control voltage to the starter coil if it detects an overload on a motor. A control circuit with momentary contact devices that are connected to the coil executes the start and stop function.

A 3-pole full-voltage magnetic motor starter has the following workings: a set of stationary contacts, a set of movable contacts, a solenoid coil, a stationary electromagnet, pressure springs, a set of magnetic shading coils, and the moving armature. Magnetic starters use momentary-contact pilot devices (such as switches and relays) that require a restart after a power loss, or if a low voltage condition causes the contactor to drop off. They can also be wired to restart motors automatically if the application requires.

A magnetic starter contactor is similar to a relay but switches a larger amount of electrical power and handles higher voltage loads. A contactor has a contact carrier with electrical contacts to connect the incoming line power contact to the load contact. It also consists of an electromagnet that provides the force to close the contacts, and the enclosure, an insulating material that holds the parts together and protects the components. Contactors are typically made with contacts that stay open unless forced closed, meaning the power doesn’t go to the load until the coil is activated, closing the contactor.

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