Each component of an electrical installation is designed for use at a particular rated current. When the component is used within the designed current limit it will have a specific service life expectancy, which is the length of time for which the insulation will remain operationally safe.
When a component is overloaded, the temperature in the insulation exceeds the design limit, the insulation begins to deteriorate and the service life will be reduced. Quantitatively, this deterioration depends on both the temperature rise and time for which the insulation is exposed to the overload. Precautions should be taken to avoid, or at least reduce to a minimum, overloading of electrical components. An overload condition can be detected by monitoring the current flowing into an item of equipment and the time for which it flows.
The method of overload sensing incorporated into circuit breakers is usually achieved through one of three different technologies:
* Solid-state electronic sensing.
* Thermal-magnetic sensing.
* Hydraulic-magnetic sensing.
Hydraulic-magnetic mechanism as current increases
Solid state electronic sensing
This technology is often combined with microprocessor controllers and is generally restricted to larger frame circuit breakers due to cost considerations.
Hydraulic-magnetic mechanism showing trip bar activated
Thermal sensing
This is the oldest technology and has been used since the first appearance of miniature and moulded case circuit breakers. Thermal sensing components such as bimetals, are supported by instantaneously operated magnetic trips for short circuit protection.
Hydraulic-magnetic mechanism remains latched after trip
Hydraulic-magnetic sensing
This technology is widely used in South Africa and eliminates the inconvenience of early tripping of thermally operated circuit breakers at elevated ambient temperatures. Hydraulic-magnetic circuit breakers have the advantage of more accurate calibration of tripping curves and make possible a variety of tripping curves to suit application-specific requirements including fractional ampere ratings.
Hydraulic-magnetic circuit breakers operate on the principle of the opposing forces of a spring and a viscous fluid controlling the magnetic attraction on a ferrous piston inside a non-magnetic cylinder. The design has both a time delay operation (overload trip) and an instantaneous operation in the case of a short circuit.
Hydraulic-magnetic mechanism at low current
When an overcurrent occurs, the magnetic force produced in the coil overcomes the core spring and the core moves towards the pole piece. The closer the core gets to the pole piece, the more magnetised the pole piece becomes. This attracts the armature, which in turn actuates the trip bar. The viscosity of the fluid and the characteristics of the spring govern the time delay. If the overcurrent is excessive, the magnetic field is such that the armature is immediately attracted to the pole piece without the influence of the core.
Navigating solar energy adoption
Electrical Power & Protection
Although South Africa’s enhanced solar tax rebate has ended, solar and energy storage solutions remain accessible and achievable. By taking a proactive and strategic approach, businesses can successfully lower their operational costs, mitigate power outages, and secure long-term energy independence.
Read more...Portable appliance tester Vepac Electronics
Electrical Power & Protection
The new appliance tester from Vepac is the ideal tool for testing the safety of electrical appliances in accordance with DGUV regulation 3 and BetrSichV. It enables the precise measurement of protective conductor or touch current using the equivalent leakage current method.
Read more...Is sustainability enough any more?
Electrical Power & Protection
With the planet’s resources stretched to the brink and no signs of improvement, it is time we look beyond sustainability and explore regenerative thinking and design.
Read more...A simple guide to understanding the importance of IP ratings
Electrical Power & Protection
When selecting electrical products for industrial, commercial or even domestic use, it is crucial to consider how well they can withstand environmental factors like dust and water. This is where ingress protection (IP) ratings come into play.
Read more...A milestone in electrical safety ABB South Africa
Electrical Power & Protection
Celebrating a milestone in electrical safety, ABB proudly marks the 100-year anniversary of its revolutionary Miniature Circuit Breaker.
Read more...The power of water
Editor's Choice Electrical Power & Protection
The Alpenglow Hy4 is the world’s first water-based hydrogen combustion engine, offering a convincing alternative to traditional battery-electric vehicles and established hydrogen fuel cell designs.
Read more...Optimising purification for green hydrogen production Parker Hannifin - Sales Company South Africa
Editor's Choice Electrical Power & Protection
Parker Hannifin delivers advanced purification and thermal management components that enhance green hydrogen production.
Read more...A new chapter in geothermal engineering
Editor's Choice Electrical Power & Protection
The town of Geretsried in southern Germany has become a focal point in the global shift toward renewable energy. While the world’s attention often turns to wind turbines and solar panels, a quieter but no less powerful force is at work deep beneath the surface, geothermal energy.
Read more...Harnessing the ocean with wave energy
Editor's Choice Electrical Power & Protection
Wave energy is emerging as one of the most promising yet underutilised renewable sources. Tapping into the rhythmic, predictable power of ocean waves, this technology offers a clean, reliable alternative to fossil fuels and a valuable complement to wind and solar energy.
While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.
printer friendly version