SHORT-CIRCUITING THE CIRCUIT BREAKER
by Mike Raynor

Mike Raynor, Product & National Sales Manager at LPA Channel Electric, tries to short-circuit the research process for circuit breakers, and explains why his company is concentrating on hydraulic-magnetic circuit breaker technology under the brand name of HY-MAG. This technology is ideal for “modern” military installations in equipment and telecommunications systems that today can find itself in the freezing wastes of Antarctica and tomorrow in the baking sun of desert combat situations.

Need to do a bit of research on circuit breakers suitable for your application? You could start on the Internet. The Google Search Engine will provide you with a fast access to over 146,000 “circuit breaker” sites.  You can, of course, refine and simplify your search by adding parameters such as “manufacturers”, “thermal-magnetic circuit breakers”, hydraulic-magnetic circuit breakers” or “IEC Standards.”

Along the way you’ll discover a host of interesting facts:  the new test methods for electronic circuit breakers with arc fault detection capability, what the 2,210 circuit breaker sites listed for the UK have to offer, and that the Italian for circuit breakers is interruttori di circuito. You can even establish that South Africa was the first country in the world to mandate by law in 1954, the use of 30mA earth leakage devices for people protection. 

The choice and thus confusion in the virtual world about who to buy from, specific applications, appropriate solutions, the different technologies available, conformity to standards, which standards apply, product reliability and technological performance are mirrored in the real world. That’s why, if you’ll excuse the pun, I’d like to short-circuit your entire research process.  LPA Channel Electric, you see, has already done the homework for you.

For a number of reasons, not least safety, performance and efficiency, the major technology focus at LPA is increasingly on the hydraulic-magnetic circuit breaker side of their business.

HY-MAG D Frame Range of CBE Circuit Breakers with rating from 20mA to 100 Amps in a single frame. Available in any number of pole and different Ampere configurations.

HYDRAULIC-MAGNETIC TECHNOLOGY

As stated above the HY-MAG range of circuit breakers operate on the Hydraulic-Magnetic technology, which is extremely precise, making it invaluable for “modern” installations in telecommunications, power generation, data processing, theatres, the marine environment, broadcasting equipment, military, hospital applications and transportation.

A HY-MAG circuit breaker consists of a magnetic frame comprising a series-connected solenoid coil wound around a hermetically sealed tube containing an iron core, a spring and hydraulic fluid. Mounted onto this magnetic frame is an armature, which when activated unlatches the trip latch of the circuit breaker. As the electrical current passing through the coil increases, the strength of the magnetic field around the magnetic frame also increases. As the current approaches the circuit breaker’s rating, the magnetic flux in the coil produces sufficient pull on the core to overcome the spring tension and start it moving towards the pole piece.

If the overload is of short duration, the core returns to its rest position once the overload disappears.  However, if the overload persists, the core reaches the pole piece. The armature is now attracted to the pole piece; this in turn unlatches the trip latch causing the circuit breaker to trip, thereby opening the electrical contacts and stopping the flow of current. As there is now no current flowing in the circuit the core returns to its rest position.

Should the fault current not be overload but a short circuit then the coil produces such a strong magnetic field that it will attract the armature to the pole piece without the core moving at all.
This type of circuit breaker is so sensitive it can measure and trip at current values as low as 20mA. This is because it only reacts to the magnetism that the current creates in passing through the coil. 

Hydraulic-Magnetic Principle

THERMAL MAGNETIC TECHNOLOGY

Its main rival is the thermal-magnetic circuit breaker.

This type of circuit breaker uses a Bi-Metal strip made up of 2 dissimilar metals that are welded together. Because the expansion coefficients of these 2 metals are different, when this strip is heated it will bend. This mechanical bending action is used to operate a tripping mechanism causing the circuit breaker to trip. Any current flowing though this Bi-Metal strip will heat the strip up causing it to bend. There are several disadvantages of the latter principal that can well be imagined. 

Ambient Temperatures

The first being the fact that because the thermal- magnetic products rely on heat as its tripping reference points then the ambient temperature as well as the current flow will affect it. Therefore in hot environments, thermal breakers can trip well below their designated current rating, producing unpredictable and unwanted equipment shut downs. In a cold environment, they will trip at a higher current level with adverse implications for the safety of personnel and equipment.
In the past Electrical Engineers have got around this disadvantage by derating the thermal breakers by up to 20% to allow for these temperature fluctuations unfortunately this cannot always be calculated accurately. But even this crude method is only good if the ambient temperature can always be guaranteed. Moreover, in an outdoor environment, there may be wide fluctuations in temperature due to seasonal changers with consequent variations in the trip point of the thermal magnetic circuit breakers.

Depending upon the standards applied, the thermal circuit breakers will be calibrated at 30°C or 40°C and therefore it is only at these temperatures that their tripping points are stable in relationship to their rated current. If the equipment is moved from one temperature zone to another then the circuit breakers should be replaced with new circuit breakers that are calibrated for these new temperatures.

Because HY-MAG circuit breakers rely solely on the magnetism produced by the current flowing though them the Ambient Temperatures do not affect their tripping point.

Parasite Heating

The problem caused by ambient temperature is compounded even more if you mount two or more thermal products side by side. This produces a condition known "Parasite Heating". Whereby the heat from one of the thermal circuit breakers heats up the one next to it. So now the circuit breaker is influenced 1) by the ambient temperature, 2) the current which is passing though it and 3) the heat from it's neighbour. To allow for this situation the manufacturers of thermal products recommend that a further group-derating factor of another 20% be applied.

Because the HY-MAG circuit breaker registers only magnetism produced by the current, it is unaffected by parasite heating associated with side-by-side mounting.

Thermal Memory

Because the thermal product relies on heat as its reference point for tripping and so if the Bi-Metal strip is cold then before it can start to work it must be warmed up, slowing down it's response time. The amount of deviation that the Bi-Metal strip moves is directly proportional to the % of heat (over current, ambient temperature and parasite heating) it is measuring. The hotter it gets the more the deviation. Now should the thermal circuit breaker trip due to a large over current situation, before it can be re-set time must be allowed for the Bi-Metal strip to cool down permitting the tripping mechanism re-engage so the circuit breaker can now be re-energised. This is just the situation you don't want in a field combat scenario when your communications equipment trips out.

Unlike the thermal-magnetic circuit breaker the HY-MAG circuit beaker has no warm up period to slow down its response to overload and no cool down (thermal memory) period after overload event, allowing it to be reset immediately.  It is, simply put, much more reliable and much more efficient!

Thermal Fatigue

Because the Bi-Metal strip is constantly flexing during its lifetime in response to heat it can develop a condition known as Thermal Fatigue, This is a condition whereby the Bi-Metal strip becomes softer and bends more easily. This can be imagined as what would happen if you would constantly bend a plastic spoon backwards and forwards until it breaks. This Bi-Metal fatigue can cause the circuit breaker to trip prematurely below its rated current value.

Because the HY-MAG principal has less moving parts and they are not affected by Bi-Metal fatigue they carry a 10-year warranty on their circuit breakers and 3-warranty on their RCD's.

Size is everything

Some specifiers, faced with the problem of nuisance tripping due to higher than foreseen ambient temperature, tend to assume that a bigger circuit breaker designed for heavier overloads should be used to compensate in such situations. That is not so. It’s the technology, not the size of the thing, that’s responsible here. And, as everyone knows, the space available for enclosures containing circuit breakers, in, for example modern military equipment, is getting smaller by the day. As a result, it is not possible nowadays to install traditional ‘jumbo size’ circuit breakers in a large enclosure.

A top seller in LPA Channel Electric’s circuit breaker portfolio is the newly launched Q Frame series, a range of miniature circuit breakers (MCB’s) using hydraulic-magnetic technology, which provide a 25% space saving over conventional MCB designs. They are available in widths of just 13mm with current ratings from 0.5 to 60A.

13mm Q Frame HYMAG Circuit Breaker and Internal View of a HY-MAG Circuit Breaker

Hydraulic-magnetic technology also scores on their flexibility in regards to technical issues such as the required trip point, time delay curves and inrush current handling capacity, and also on their ability to be tailored to suit a customer’s particular application requirements. Such flexibility makes HY-MAG products a very responsive solution to any design problems or harsh environmental criteria.

Standards

Circuit breaker product standards include various test requirements to verify that the circuit breaker is not only suitable for its intended application but that, under abnormal operating conditions, the product will not be hazardous to human life and health. It is not surprising that specifiers, users, manufacturers and test laboratories are often confused by the myriad of both national and International Standards all claiming to be applicable to Low Voltage circuit breakers. South Africa, the home of Circuit Breaker Industries Ltd. (CBI) and the Q Frame circuit breaker, is in the unique position of being one of the longest-term users of MCBs and MCCBs, having had an indigenous manufacturing and usage base in place since the early 1950s.

Decades of experience

Several decades of South African application experience in diverse and harsh environments have resulted in the evolution of meaningful and appropriate national standards for circuit breakers, which are, in some instances, more stringent than their international counterparts. While CBI breakers conform fully to the relevant international standards, such as Mil, IEC, JIT and UL, it is perhaps more significant that they conform to those set out by the eminently tougher South African Bureau of Standards (SABS).

Meanwhile, CBI continues to represent the SABS on the technical committees of the International Electrotechnical Commission (IEC), and is thus instrumental in the development of international electrical safety standards.

I hope I’ve managed to convince you about the advantages of HY-MAG in general and LPA Channel Electric products and technical back up in particular. If you need more information, you can always go back to Google and search on the Internet. This time, however, key in www.lpa-channel.com and also www.cbibreakers.com.  In the 146,000 strong databases, they’re the only circuit breaker websites you’ll ever need.

Mike Raynor
LPA-Channel Electric
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