Batteries are indeed, a waste of money. This means to say that if the power grid was 100% reliable, batteries would not be necessary!

The many worldwide power outages over the past several years make batteries essential as a backup source. Who actually gives batteries a second thought? We simply expect them to work when called upon. Experience has shown that this expectation is pure fiction.

Megger 246002B – Megger 246002B Battery Impedance Tester The instrument measures internal cell impedance and DC terminal voltage

Batteries are extremely important to provide electricity to support many assets and revenue streams during outages. For example, in a generating station, if the turbine suffers an outage, without the back-up battery the turbine lube oil priming pumps would not continuously keep the bearings lubricated causing major damage and lengthy outages. In hospitals, who wants to be in the middle of an operation when an AC outage occurs without proper battery back-up? The applications for batteries are innumerable and frequently unseen. In this world of dependency upon electricity, it is impossible to survive without battery back-up.

Battery Basics

So what makes a battery tick? All batteries, whether rechargeable (secondary) or disposable (primary), use chemical reactions to make electricity. It is necessary to have two dissimilar metallic materials in a current-carrying medium. In lead-acid batteries, the two dissimilar metallic materials are lead and lead oxide in a sulphuric acid medium. Nickel Cadmium batteries use nickel and cadmium compounds in a potassium hydroxide electrolyte medium. Nickel metal hydride batteries (NiMH) are comprised of the same nickel compound as in NiCd cells but the cadmium compound is replaced with a metallic hydride and the liquid electrolyte is replaced with a paste to carry the current. The two types of nickel cells are virtually identical in performance. Even their voltages are the same! Lithium batteries use a lithium-containing oxide or phosphate and carbon. For the purposes of stationary battery testing, this article focuses mainly on lead-acid batteries.

Megger BITE 3 – The Megger BITE3 Battery Impedance Test Equipment determines the health of lead-acid cells up to 2000 Ah

With the importance of batteries established let us consider their chemistry and ways of assessing their health. The age-old habit of testing only the voltage and specific gravity doesn’t work – it never has and never will. The reason for this is that the sum of all of the cells’ voltages must equal the charger output. Voltage (and specific gravity) of lead- acid batteries basically follows the sulphate. If a battery is fully charged, the sulphate will be in the acid and its voltage and specific gravity will be normal (with few exceptions.) If it is in a discharged state, the voltage will be low and since there is at least some sulphate on the plates, the specific gravity will also be low. These tests will therefore reveal the state of charge of the battery, but not its state of health. If the battery has a normal voltage, there is no indication of the health of the battery. When the voltage is abnormal, it may be an indication of a potential problem, but may also be that the battery is merely to some extent discharged.

Nickel cadmium batteries behave somewhat differently than lead-acid batteries. In lead-acid batteries the acid is actually part of the electrochemical process; it reacts with the lead and lead oxide to make electricity. The KOH electrolyte in NiCd batteries is simply a carrier for the current and does not enter the chemical reaction. Therefore, measuring specific gravity of NiCd batteries in service doesn’t indicate anything about the condition of the battery. The one exception is carbonation of the electrolyte. This is caused, over time, by the absorption of carbon dioxide from the air into the KOH and reduces the specific gravity of the electrolyte. If this happens, check with the battery manufacturer. It may simply be a matter of replacing the electrolyte.

Battery Tests

The range of possible tests on a battery ranges from doing nothing (not a good idea) to doing every test possible (still not a good idea). The possible tests include voltage, specific gravity, float current, ripple current, cell temperature, ambient temperature, discharge current and time, intercell connection resistance, capacity (load test), impedance (an internal ohmic test), among others.

Float Voltage

Taking them one at a time, voltage can be one of those misleading tests. Voltage is important, absolutely, and if it is abnormal, then it indicates something about the condition of the battery. If it is normal, it indicates nothing at all about a battery’s condition. This is because voltage is more of an indicator that the charger is functioning properly. The sum of the voltages of all of the batteries in the bank must equal the charger output voltage, resistive losses excluded. A normal voltage is not an indicator of battery capacity, but an abnormal voltage needs further investigation.

Specific Gravity

Specific gravity is similar to voltage as an indicator of battery health. The sulphate is part of the electrochemical reaction. If the battery is discharged, some of the sulphate migrates to the plates and the acid is reduced in specific gravity. If the battery is fully charged, all of the sulphate is in the acid and the specific gravity is normal, say 1,215. There aren’t any studies to validate any correlation between specific gravity and battery capacity. In fact, IEEE 450 has de-emphasised specific gravity to the point of checking only 10% of the batteries each quarter and the full bank annually.

Float Current

In order to keep a battery charged, there is a battle of sorts going on in the battery between its self-discharge and the charger. The battery is always in a state of self-discharge which creates a differential in potential between the battery bank and the charger. This differential in potential causes a small current to flow to keep the battery fully charged. This DC current is called float current.

In flooded lead-acid batteries there is no possibility of thermal runaway because the liquid acid cools the battery through the process of evaporative cooling. However, VRLA batteries do not have extra acid, nor is it in a free liquid form. If the float current increases due to some impending failure or overcharging condition, the temperature increases . The increased temperature allows for more current to flow and further increases the temperature of the battery. A runaway chemical reaction ensues, which can lead to the melting of the battery causing an open circuit. The time from when the float current starts to increase and when thermal runaway might occur is between one and four months. Float current is an important parameter to measure in VRLA batteries.

Ripple Current

Ripple current is a product of the charger which converts AC into DC. No charger has a 100% ripple-free conversion process, which is why filters are frequently added in certain applications. Ripple current generally increases slowly over time as electronic components degrade. If, however, a diode in the rectifier blows, the ripple current can double. As with float current, an increase in ripple current to a point greater than about 5 amps rms for every 100Ah of battery capacity (5%), leads to increased temperature and shortened battery life. Ripple current is another parameter that should be measured periodically.

Temperature

Battery and ambient temperature, although they don’t dictate immediate doom for a battery, can lead to premature failure. For every increase of 10°C in battery temperature above 20°C, the battery life is halved. This means, for example, that a 20 year battery maintained at 35°C instead of the specified 25°C will only last about ten years. In Europe the standard temperature is 20°C and 15 year design life for flooded batteries.

Discharge Current and Time

Discharge current and time is now used more frequently in on-line monitors to aid in determining amp-hours removed and replaced. The value of measuring current and time and calculating Ah removed and replaced is that battery capacity can presumably be calculated. This author believes that there is value in this calculation. The caveat is discussed below under capacity (load) tests.

Intercell Connection Resistance

Intercell connection resistance is one of the tests that needs to be performed, especially if frequent outages occur. It has been said that more than 50% of battery bank failures are due to loose intercell connectors. This is a straightforward test to perform and it can be done in conjunction with impedance testing (discussed below) or as a stand-alone test using a low resistance ohmmeter. Intercell connections come loose due to heating and cooling cycles caused by discharging and recharging as a result of outages. The posts expand and contract and because lead is very malleable will cold flow with each cycle. This is one of the reasons that battery manufacturers tend to recommend tightening bolts to the low end of the torque range so as not to add further stress during cycling.

Capacity

Capacity tests are a necessary evil. If performed properly, they are expensive, time-consuming and have limited predictive value depending upon their frequency. Consider a battery bank that is designed to provide eight hours of back up time. A proper capacity test incorporates a second battery in case of a power outage during the discharge test. This second battery must be at least the same size or bigger than the main battery being tested. The resistive load bank must be connected to the main battery bank and voltage leads are connected to each battery in the bank. This usually takes a full day.

On day 2 the eight hour test begins. A test for intercell connection resistance is often performed before the start of the capacity test. There are two schools of thought about performing the intercell connection resistance test:

1) It is not representative of a true “as found” autonomy test.

2) Certain precautions need to be taken to ensure that no major malfunctions occur that could have been avoided.

If there are major malfunctions, then the bank or at least some of the batteries will need to be replaced in an emergency situation. This decision is for those at each company who write procedures and maintain batteries.

Day 3 is the continuation of the recharge of the main bank. The voltage leads are removed and the resistive load bank is disconnected. The main battery recharge may continue on day 4 if the battery is not yet fully charged and ready for service. A properly run capacity test is the only true method of determining the bank’s actual capacity.

Impedance and Resistance

Impedance, an internal ohmic test, indicates the capability of a cell to deliver current. It is correlated to capacity. Although correlation to capacity is not 100%, it is an excellent way of finding weak batteries in the bank. The EPRI study reveals how well impedance and other internal ohmic tests work in finding weak cells. The impedance test applies and measures an AC current signal and measures simultaneously the AC voltage drop across a battery caused by the AC current signal. Following Ohm’s law, Z = E/i, impedance is calculated. Impedance is inversely proportional to capacity in that as capacity decreases, impedance increases. This test is fast (about 30 minutes for a 60-cell substation battery bank) and is non-invasive.

Data Analysis

What is done with the data collected? How is the data interpreted to ensure that the battery bank will meet the required duty cycle? With the advent of better testing methods such as impedance, more useful data (rather than only voltage and specific gravity) can now be obtained. With such data come the data-handling problems and the analysis to paralysis problems. The recommended method is to use a database to track and trend all battery data over time and dispense with paper forms that cannot compare today’s data with yesterdays. A specialized database, one with space for all measured parameters, is important to aid in determining the condition of batteries and banks.

Entering limits, with which the user is comfortable, in order to gain the most life from a battery without increasing risk, aids tremendously in extracting the most from a battery. The limits should be set for each parameter measured. For example, float voltage limits should follow manufacturers’ guidelines. Internal ohmic test limits are more debatable. In some cases, users will set a “failure limit” of 50% impedance increase for VRLA batteries from a predetermined baseline value. Float current limits tend to be less precise depending upon the size, age and alloy of the battery.

Conclusion

There are many failure modes for batteries. With care and measurement these can be dramatically reduced, especially if little to no testing is presently being performed. The battery is installed, not to add to work load, but to support critical electrical equipment or revenue streams. Proper testing and data analysis can help determine when a battery should be replaced. Testing also helps reduce emergency battery replacements and assists in budgetary planning, thus reducing cost. A properly implemented battery testing regime does not necessarily reduce the work load but it will, most likely, increase reliability of the entire DC network. (Marius Pitzer, Megger)

Megger Phasing Detectors

For use on any grounded electrical system, DETEX Voltage Detectors are available in seven models that cover a range from distribution class to transmission line voltages up to 550 kV. Biddle offers six electronic “beeper” models and one model with LED indication for greater visibility when testing indoors.

The beeper-style electronic detectors provide audible and visual indication of the presence of phase-to-ground ac voltages, in accordance with ANSI C84.1-1982 standards.

The 6.9-kV model is equipped with a telescopic pole. All other models are fitted for universal spline mounting on a hot line pole rated for the voltage of the system being tested.

Electronic voltage detectors for use on distribution line voltages (Cat. No. 514360 series) provide a single red LED.

Detectors rated for transmission line voltages (Cat. No. 514242 series) provide four LEDs for improved visibility at greater distances.

The LED-indicating voltage detector is designed for indoor testing of grounded ac systems. A bright LED indicator provides easy visibility in poor lighting conditions. During testing, the presence of voltages within the detector’s operating range will illuminate the bright LED lamp.

A built-in piezoelectric voltage source provides a test feature to ensure that the detector is operative before use. The self-test is activated by a pushbutton.

The LED detector is equipped with a 48-in. (1219-mm) telescopic pole calibrated and marked for voltages within the ratings of the detector. These demarcations assist the user in adjusting the pole to the length required for safe operation. The pole retracts to 34 in. (864 mm) for convenient storage in a vinyl carrying case when not in use.

Megger 514500-4 Phasing Detector Product Page

Testing Composite Materials

Composite materials, which are essentially high strength engineering plastics, are being used more and more widely, especially in the construction of aircraft bodies.

One of the world’s largest manufacturers of commercial jetliners and military aircraft combined has, for example, announced that as much as 50 percent of the primary structure – including the fuselage and wing – on a new passenger aircraft will be made of composite materials.

MEGGER DLRO10
Megger DLRO10 Digital Low Resistance Ohmmeter – The MEGGER DUCTER DLRO-10 and DUCTER DLRO-10X bring new standards to low resistance measurement.

Clearly there is a need for effective testing techniques for assemblies made from these novel materials. Since composite materials are inherently non-conductive, however, it is initially difficult to see what role electrical test methods can play in meeting this requirement.

The key to the answer is that electrically conductivity is, for many reasons, an essential requirement in airframes. For example, conductive airframes play an important role in dissipating the energy from lightning strikes and in preventing the build up of static charges. They also provide essential electromagnetic shielding, and allow the correct operation of many types of circuit protective device.

MEGGER DLRO200-EN

For these reasons, the composites used in airframe construction, at least for civil aircraft, invariably include a thin metal mesh specifically to provide electrical conductivity.

During the construction of the airframe, great care is taken to ensure that the meshes in individual components are electrically bonded together, since faulty bonding would not only compromise the effectiveness of the shielding provided by the mesh, but could also lead to sparking, especially during electrical storms. Such sparking, especially if it occurred in the proximity of the aircraft’s fuel systems, could have serious consequences.

Megger DLRO10HD
Low Resistance Ohmmeter – Megger Model# 1000-348 Catalog# DLRO10HDDual power 10 A low resistance ohmmeter High or low output power selection for condition diagnosis Rechargeable battery or line power supply

It’s easy to see that a reliable method of testing the bonding and the overall integrity of the mesh is essential. For this purpose, low resistance testing, which is easy to carry out with moderately priced test equipment, has much to recommend it.

The principle of low resistance testing is straightforward – a known current is injected into the item under test, and the voltage that results from this current flow is measured. Knowing the voltage and the current, the test set can easily calculate the resistance of the test object using Ohm’s law.

In practice, for dependable low resistance testing, a few refinements are necessary. Most importantly, the resistance of the test leads and the test connections will often be comparable to, and even sometimes greater than the resistance of the item under test, so accurate results will be impossible to obtain unless due allowance is made.

The best solution is to use a test set that supports four-terminal testing. With this arrangement, the current is applied through two test leads, and two entirely separate leads are used for the voltage measurement. This means that, provided the instrument measures both the current and voltage, the resistance of the test leads and connections has a negligible effect on results.

The next issues that must be carefully considered are test current and power. Low currents of up to 10 A from a source that is power limited to around 0.25 W are good for revealing contaminated connections in electrical equipment. Similar currents from power source capable of supplying, say, 25 W are better for detecting weaknesses in bonding, but some types of test objects can be damaged by the higher power available.

High current tests, which typically cover the range 10 A to 600 A, are most appropriate for measuring the current-carrying capacity of electrical equipment such as busbars and circuit breakers.

Megger’s experience with its popular DLRO family of digital low-resistance ohmmeters has shown that test currents between 2 A and 10 A are the most suitable for evaluating the capability of the conductive mesh associated with composite materials to control static build up. Testing at these currents can also reveal the type of damage to the mesh that may result from material fatigue, especially if historical reference data or data from a similar airframe know to be in good condition is available for comparison.

However, one major aircraft manufacturer determined that testing at 30 A is needed to test a large airframe’s lightning protection to provide stable, repeatable measurements in noisy hanger environments. Note that only a minority of currently available test sets, including some models in the DLRO family, are capable of working continuously with such high test currents, in combination with such high test lead resistance. Remember the instrument has to maintain the required test current through the resistance of the long test leads used as well as the resistance of the airframe being measured.

Therefore for this application we need to keep the current loop resistance to a minimum. The current leads need to be of substantial cross section and to be available with a range of test clips to suit different connection requirements. They will also need to be available in lengths from short to, for large structures, very long.

Though they have been used in small-scale applications for many years, the adoption of composite materials for large structures such as passenger jet airframes is a recent development. For this reason, the challenges of testing such structures are only now being fully addressed but, as we have seen, for airframes at least, low-resistance testing is a convenient, cost-effective and versatile option.

Believed to be the first commercially available products of their type that have been specifically designed for wind turbine applications, Megger’s new test leads eliminate the need for engineers and technicians involved in wind turbine testing to fabricate their own test leads.

Megger’s new KC series of test leads, which were developed in conjunction with leading manufacturers of wind turbines, provide a complete and convenient solution to the problem of finding reliable test leads that are long enough to be used for testing the continuity of lightning protection conductors in wind turbine blades.

Megger 1000-809
DH2 leads with duplex hand spikes and hook end Specially designed for measuring resistance of lightning protection circuit between wind turbine blade tip to ground.

Believed to be the first commercially available products of their type that have been specifically designed for wind turbine applications, Megger’s new test leads eliminate the need for engineers and technicians involved in wind turbine testing to fabricate their own test leads – a time consuming and inconvenient process – or to resort to makeshift arrangements that may deliver uncertain results.

KC-series wind turbine test leads are available 100 m, 50 m and 30 m versions, and are equally suitable for use on site or in the manufacturing plant. For convenience and ease of handling, they are supplied as standard on a heavy-duty cable reel that is fitted with a friction brake to avoid tangles when paying out the cable.

The leads are terminated with large robust Kelvin clips that have been specially designed to offer ease of use while providing the consistently reliable connections needed to ensure accurate and repeatable test results. Included with each lead set is a 5 m cable fitted with a duplex handspike for probing the lightning receptors on the tips of the turbine blades.

KC-series leads are ideally suited for use with Megger DLRO10HD low-resistance digital ohmmeters, which combine robust construction with a high test current capability. They also have an IP65 protection rating with the lid closed, and an IP54 rating when the lid is open and tests are being performed, which means that they can be safely used outdoors even when it is raining.

Megger DLRO10HD
Low Resistance Ohmmeter – Megger Model# 1000-348 Catalog# DLRO10HDDual power 10 A low resistance ohmmeter High or low output power selection for condition diagnosis

While these features make DLRO10HD ohmmeters an excellent choice for wind turbine applications, KC-series leads can also be used successfully with most modern types of low-resistance ohmmeter.

Insulation Resistance Testing

The measurement of insulation resistance provides a reliable and convenient means of monitoring the condition and state of readiness of high-capital electrical equipment. All common electrical circuitry…whether wiring, cabling, control devices, motors, transformers, generators and the like…is surrounded by some type of insulating material.

At time of manufacture, this material typically has enormous resistance, typically too high to even measure except with the highest quality testers. But when put into service, insulation begins to degrade from a variety of factors, and the decline in resistance values provides a reliable indication of the extent of this degradation, and by extension, of the expected life of the equipment.

Megger MIT520-2
Megger Model# 1000-376 Catalog # MIT520/2 – 5 and 10-kV Insulation Resistance Testers Line supply or battery operated Digital/analog backlit display

Measuring the decline and rate of change of insulation values forms the basis for “preventive/predictive maintenance”, by which the equipment is periodically monitored. Items with sufficiently high resistance are not likely to fail in the near future, and so repeat testing can be delayed appropriately to save man-hours. Conversely, items exhibiting lower resistances can be trended by their rate of decline to indicate an optimum time to take out of service for restorative maintenance, in order that they not fail in service.

Failures can also occur catastrophically, as by flooding, lightning, and extreme voltage surges. These cannot be anticipated, but insulation testing is the first step in troubleshooting and repair, and can be used to monitor the restoration of failed equipment through drying and cleaning processes.

Megger MIT510-2
Megger Model# 1000-372 Catalog # MIT510/2 – 5 and 10-kV Insulation Resistance Testers Line supply or battery operated Digital/analog backlit display

Insulation testers require a special knowledge, of greater depth than most common electrical testers. Because they are applied to insulation, a non-conductor, readings are not as self-evident as with common measurements of circuitry and components. Rather, the test item charges during the course of an insulation measurement, causing readings to change constantly over the time of the test. If this is not fully understood, the test can be rendered completely ineffective. In addition, while insulation testers themselves, despite their high voltage outputs, are not inherently dangerous, a highly charged test item can be lethal. Therefore, the operation of the tester and the nature of the charging currents must be fully understood in order for insulation testing to be both effective and safe.

Standard test methods have been widely adopted in order to expedite test time, effectively deal with the changing readings over time, and specifically identify different problems. An understanding of these methods is indispensable to effective use of an insulation tester.

Megger BM15
INSULATION RESISTANCE TESTER The BM15 and MJ15 are compact 5-kV insulation testers that are simple to use

Insulation responses to both testing and operational demands are influenced by extraneous factors such as temperature and humidity. Without proper understanding, these factors can cause misinterpretation of otherwise coherent results. Standing alone, an insulation reading of “x” Megohms can be meaningless or even misleading. When backed by proper knowledge, it is one of the most effective tools of electrical maintenance.

Is Your Resistance Low or Are You Getting Hot?

Low resistance measurement is a well-established technique that can be used almost anywhere electrical conductivity is important – its applications range from checking the quality of earth bonds to verifying the density of graphite electrodes in aluminum refineries. Recently, however, thermal imaging has been proposed as a simple and effective solution in many of the same applications. But is it?

The real answer is that both low resistance testing and thermal imaging have their place so, in order to decide which to use where, let’s take a look at the strengths and weaknesses of each.

A big benefit of low resistance testing is that it can detect problems even when there is no current (other than the test current) flowing in the object under test. This makes it very suitable for applications such as checking weld quality, verifying the performance of lightning protection bonds, confirming the integrity of aircraft structures and testing earth systems.

Low-resistance testing is also invaluable in manufacturing applications, particularly where it is necessary to test subassemblies rather than complete systems, and for checking new or modified electrical installations prior to energisation. Thermal imaging is unlikely to be suitable for any of these applications.

A further benefit of low-resistance testing is that it provides straightforward numerical results, which can easily be recorded and, even more useful, trended as part of a predictive maintenance programme.

Having said that, low-resistance testing does, of course, have its limitations. It can’t, for example, be used on live equipment. For equipment that’s in service, therefore, it’s necessary to arrange for the supply to be isolated before carrying out the test, which is not always convenient. In addition, if there are many connections to test, low-resistance testing can be time consuming.

Turning now to thermal imaging, it’s a good way of checking for overloads and unbalanced loads, which can’t be done with a low-resistance tester. Thermal imagers also have non-electrical applications, such as finding the locations of heat loss from buildings, and detecting mechanical faults such as worn bearings in a motor, which heat up because of excessive friction.

Thermal imaging also has the reputation of being easy to use, but that’s not always the case – the operator needs to understand what they are seeing and to be able to interpret the results. For example, is a transformer overheating, or is it at its normal operating temperature? What is the load on the equipment while the test is being carried out? At what point does the temperature rise become a problem?

In high-voltage environments, such as an electrical substation, a further complication is that is often not safe to get close enough to the equipment to image it clearly. In addition, items such as fuses and circuit breakers are usually mounted in metal enclosures, and thermal imaging will not work through metal.

It is often unsafe to remove covers or open doors with the supply switched on but, by the time the supply is isolated and the covers removed, the equipment will have cooled significantly, making the thermal imaging data of dubious value.

It can also be difficult to accurately relate the thermal image to the equipment being evaluated, and it is sometimes necessary to take a normal digital photograph and then use a PC to overlay this with the thermal data. Finally, trending thermal images to identify changes over time is not particularly straightforward.

Thermal imaging is, as we have seen, a very useful technique but it complements rather than replaces low-resistance testing. And there are many applications where nothing but a low-resistance test will do. It does, however, pay to take a little care in selecting a low-resistance test set if it is to offer maximum versatility and convenience.

For example, it is all too easy to make an accidental connection to a live supply when attempting to carry out low-resistance tests, particularly when testing busbar bonds and battery straps in UPS installations. It is important, therefore, that the instrument is suitably protected.

In many test sets, this protection is provided by a fuse, but this is not particularly convenient as, if a suitable replacement is not to hand, the instrument is not useable until a replacement can be obtained. Better low-resistance testers, such as those in the Megger DLRO10 family, are intrinsically protected against connection to live supplies. With these instruments, it’s possible to carry on testing normally as soon as the errant supply has been properly isolated.

It is also important to select an instrument that can supply a test current appropriate to the application – ideally, it should offer a choice of test currents covering a wide range. This is because high test currents can, in some cases, cause unwanted heating of the test piece, while in other cases the heating caused by high currents is actually desirable, as it can help to reveal weaknesses such as broken strands in a multi-core cable.

Similarly, the usefulness of low test currents is also dependent on the application. Low currents may be a problem in some circumstances, as they make not break through the contamination in bonds. In other circumstances, however, this may be a benefit, because the same situation can provide a useful indication that contamination is present!

In addition, a low test current combined with test current reversal may eliminate the need for temperature compensation of the results, and it also has the benefit of extending battery life in portable instruments.

Finally, ease of use is a crucial factor. For maximum convenience in day-to-day use, the test set should have an intuitive user interface, and it should perform tests quickly and efficiently, otherwise it will rapidly become a constant source of irritation rather than a useful tool.

In conclusion, it’s clear that both thermal imaging and low-resistance testing are invaluable techniques and the ideal situation is to have access to test equipment for both. Only then can you be absolutely certain of providing a definitive answer to the question that we’ve all, at one time or another, asked – is your resistance low, or are you getting hot?

New Megger DLRO10HD

Megger DLRO10HD Low Resistance Ohmmeter – Megger Model# 1000-348 Catalog# DLRO10HD

Dual power 10 A low resistance ohmmeter

• High or low output power selection for condition diagnosis
• Rechargeable battery or line power supply, continuous operation, even with dead battery
• 10 A for 60 seconds, less time waiting to cool, great for charging inductance
• High input protection to 600 V, inadvertent connection to line or UPS voltage will not blow a fuse
• Heavy duty case: IP 65 lid closed, IP54 operational (battery operation only)
• Rotary switch selects one of five test modes, including auto start on connection, giving ease of use

Equally at home in the laboratory, the workshop or in the field, on the bench or on the ground, the new heavy duty Megger DLRO10HD low resistance ohmmeter combines rugged construction with accuracy and ease of use. It features an internal rechargeable battery and can also operate from a mains supply, even if the battery is completely flat.

• Model: DLRO10HD
• Manufactured by: Megger
• Megger Test Equipment Page

Somewhere in the fine print of most product bulletins, you’ll find an IP rating. Is this just “boilerplate”? No! It gives vital information that could be critical to your application.

Megger products are typically rated to IP54. (If you want to sound thoroughly knowledgeable, that’s IP five-four, not fifty-four. Each digit relates to a separate rating, not to each other.) “IP” stands for “ingress protection”, the degree to which the instrument can withstand invasion by foreign matter. This has been established by the IEC (International Electrotechnical Commission), in their Standard 529. The higher the number, the better the protection. The first digit refers to particulate ingress. This reflects the degree to which solid objects can penetrate the enclosure. The typical Megger rating of 5 indicates “dust protected”, as well as protected from access with a wire down to 1.0 mm. There is only one higher category: “dust tight”.

The second digit refers to moisture ingress. A rating of 4 indicates “splashing water, any direction”. The higher ratings of 6 through 8 indicate “powerful jetting water” and “temporary” or “continuous” immersion. Not too many electricians need to work under water!

So what? Well, suppose an instrument under consideration was rated only to IP43. What would that tell you about its usability? Could it be thoroughly utilized in a quarry or cement plant? Hardly! The particulate rating 4 indicates “objects equal or greater than 1 mm”. That’s a boulder in comparison to particles typically produced by industrial processes. Flying dust could put the unit out of commission before the purchasing agent is done stalling payment. What about a paper mill? Wrong application again! The moisture rating 3 covers “spraying water, up to 60° angle from vertical.” This is adequate protection for occasional incidental encounters, but still leaves a wide margin for invasion where water is a common hazard. Moisture could penetrate the unit, corrode and short out the board, and produce nagging repair delays that could critically disrupt a time-focused preventive maintenance program.

By contrast, a typical Megger model rated to IP 54 will perform up to and beyond expectations in all of these environments. Protected against dust and moisture under all but the harshest of conditions, the instrument will meet the test for a full life expectancy. Avoid the embarrassment of having to tell the “boss” or purchasing agent that a unit has failed when they still think of it as “brand new”. Make a mental review of the types of environment in which the instrument will possibly be used, the nature of foreign materials to be encountered, and what that will demand in terms of IP rating. Then purchase a unit that matches or exceeds that requirement, and don’t be caught red-faced with a “brand new” instrument that is literally “choked with dust” or “dead in the water”.

Check out the New Megger SCT+MMA+SMA

Megger SCT+MMA+SMA. Megger (1001-711) SCT2000 + Multimode + Singlemode Kits

SCT-MMA/SMA
Fiber Optic Adapters

- Certify singlemode and multimode fiber optic links at 850, 1300, 1310 and 1550 nm wavelengths
- Provide fully compliant Tier 1 Certification
- Capabilities include length, loss and power measurements, power meter and light source
- Perform bi-directional testing without swapping primary and secondary units
- Integrated VFL for diagnosing link problems
- Most intuitive and easy to operate fiber optic certification tester on the market

As the number of fiber optic links in the network increases it s essential that your certification tester seamlessly certifies both copper and fiber, efficiently combining all media results together for analysis and reporting. The SCT-MMA and SCT-SMA fiber optic adapters fulfill this need by converting the SCT into a fully compliant Tier 1 multimode and singlemode fiber optic certification tester. Now you can confidently certify all of your copper and fiber optic links with the snap of an adapter.

The SCT fiber optic solution offers powerful capability and features including length measurement, two-fiber, dual-wavelength loss measurements, single and bi-directional fiber measurements, power meter mode, light source mode, Fiber-Map and visual fault locator (VFL) capability. The SCT Autotest differs from other units by returning a length measurement and four loss measurements when testing dual fibers.

Fully Compliant Tier 1 Certification

The SCT fiber optic adapters create a fully Tier 1 compliant testing solution measuring length, loss, and polarity.

The SCT also differs from some units by performing bi-directional testing on two fibers at two wavelengths without exchanging the Primary and Secondary units.

Testing Fiber and Copper is a Snap

Fiber optic and copper certification is a snap with the SCT. Switching between copper and fiber certification is faster and more reliable than any other solution, simply snap in an adapter. Only the SCT allows the user to create dual media projects that store all necessary copper and fiber optic certification parameters in one project. With dual media projects and the ability to automatically recognize copper and fiber optic adapters the SCT can seamlessly switch between copper and fiber optic testing and project parameters with the snap of an adapter.

Visual Fault Locator

The SCT fiber optic adapters include a visual fault locator (VFL) as an easy to use troubleshooting tool. The VFL can locate and visibly identify faults on fiber optic cables. The VFL features a 635-nm visible red laser source. The presence of the VFL s red light indicates a trouble spot in the fiber such as a break or sharp bend. The VFL can be used with either multimode or singlemode fiber. The VFL creates a continuous or modulated light source powerful enough to escape from sharp bends and breaks in jacketed or bare fiber as well as poorly mated connectors, making it ideal for locating trouble spots in jumper cables, distribution frames, splice strays, patch panels, cable splice points and for tracing fiber runs.

The MIT300 Series Insulation Testers are rated for use on CATIV 300V applications as well as the existing CATIII 600V applications.

Why is the CAT rating important?

The CAT (Category) rating of a test instrument defines where in the electrical supply chain the instrument can be safely used. This is usually printed on the instrument across the test connections and appears as CATII, CATIII or CATIV. CATI is generally no longer used as it has no practical application.

Check Out the New Megger Insulation Testers Here

What is a CAT rating?

The CAT rating defines the level of transient (spike or surge) the instrument has been designed to withstand. These transients vary in size and duration depending on the source of the transient. The transient riding on a high-energy supply is more dangerous than a transient on an isolated cable as it can deliver larger currents when a fault occurs (a spike on steroids if you like).

A transient may be several kV in amplitude but its duration is typically very short, maybe only 50 microseconds. On its own the transient will cause little damage. However, when it occurs on top of the normal mains sinusoidal supply voltage it can start an arc, which continues until the end of the cycle. In the case of a CAT IV system the available short circuit current can be in excess of 1000 amps. This generates hundreds of kilowatts of heat in a small space for a few milliseconds, creating a big bang, possibly causing burns, fire or explosion.

Instruments designed with the correct category rating have sufficient clearance between critical parts to prevent an arc from creating the initial breakdown when a transient occurs.

IEC61010 defines the design requirements for instruments that declare a specific category rating and specifies both the electrical and physical requirements.

Recently companies such as EDF (France) have stipulated all electrical test instrumentation to be rated CATIV. This is a result of injuries sustained by engineers using inappropriately rated instruments on the supply. This is being applied to insulation testers as well as Loop testers.

Where are CATIV applications found?

The electrical supply can be broken down into categories from CATI to CATIV as shown below:

The picture shows the transmission lines (overhead or underground) as Category IV because the energy available from the supply is much higher near to the transformer. Test equipment suitable for use in this environment need to be rated to CATIV.

By the time the voltage goes through the fuse panel into the house, the circuit impedance is higher and transients are damped, reducing the available energy in the transient. The ability of the test instrument to withstand this surge is less stringent, hence a Category III rating.

The further down the supply you progress the lower the protection a test instrument has to provide. At the socket or lighting outlet the circuit is rated CATII and items such as photocopiers, televisions etc can be considered as CATI environments.

Most electricians’ testers will be rated to CATII, or the better ones to CATIII. These instruments are not designed to be used on the higher energy CATIV circuits. However in reality this does occur.

Arguably an RCD tester would never need to be CATIV due to its location in the supply chain.

Why 300V?

To achieve the same impulse withstand voltage (6kV) the working or steady state supply voltage has been reduced to 300V RMS Phase to neutral. This requires no change in the physical or electrical design of the instrument.

The 300V working (or steady state) voltage implies the instrument can be connected to a 300V single phase or 415V 3-phase supply without risk to the instrument or operator.

But an insulation tester is for dead system testing?

Absolutely, but the MIT300 can be used for voltage measurement and as such could be used for verification of supply voltage. In this application it is no different to a multimeter

Who will want CATIV?

This applies to insulation testers as well as LIVE testers, as the capability to measure supply voltage exists on a voltage measurement range, as well as accidental connection to live circuits whilst in other test modes.

Small transients (a few hundred volts) occur on supply systems most days of the year. Large transients (5 to 10 kV) do not occur very often. However, they are unpredictable, mostly caused by lightening strikes on overhead lines. Using a correctly rated instrument the chances of a dangerous breakdown are something like one in a million for every hour connected to the supply. Using one category less increases the chances of an accident by a factor of about 30. This means that if 100 engineers are using instruments with wrong category ratings and they connect to live systems for one hour every day, 200 days a year, a dangerous situation is likely to occur once every 18 months!

Railroad Insulation Testing Applications

Railroads rely heavily on cable maintenance to keep the trains running. Signal cables, as well as other types in critical functions, are subjected to considerably more stress than are cables in more tranquil environments. Heavy-duty rail yards, highway crossings, public access areas, industrial feeder lines, and so on, make up a patchwork of varied environments that contribute heavily to wear and tear. Accordingly, railroads have commonly learned the value of the preventive maintenance concept. With schedules to be met and traffic crossings to be kept clear and safe, reactive maintenance after a breakdown is virtually out of the question in critical functions. Cables are tested on a regular maintenance schedule that includes insulation testing.

Commonly employed acceptance values for signal cables are 200,000 and 500,000 Ohms. If the cable tests above 500,000 W (0.5 MW), it is passed. If between 500,000 and 200,000 W (0.2 MW), it is earmarked for a more dedicated test schedule (typically, every 12 months). If below 200,000 W, it is pulled and replaced immediately.

Obviously, Megger Insulation Testers are the instrument of choice for this application. The wide variety of models that will meet this fairly general requirement enable the prospective customer to satisfy both budget restraints and personal preferences on a number of additional functions. The cables involved are generally 600 V, so that the operator can readily choose between a 500 V “operational” type of test or a 1000 V “stress” test. Since most models offer both of these test voltages, this is an easy match. The pass / fail range is also readily met, but just be careful to keep the customer apprised of the units of measurement in which they will be working: one half, and two tenths, of a MegOhm. On Major Meggers, the analog scale shows divisions at the required values: 0.5 is marked as such, and 0.2, while not specifically noted, is the next “tick” mark above 0.1. These are both readily distinguishable in terms of pointer travel. The digital model (210600) will display the desired values as 0.20 and 0.50. Hand-held models also provide the correct divisions, essentially the same as do the Majors, whether digital or analog. And while 5 kV models may represent overkill in terms of test voltage, the MJ15 & BM15 models do offer the plastic overlay accessory that can be conveniently marked with the desired pass/fail values to help reduce the possibility of operator error in interpreting and recording results. It should be noted, however, that with these models, the amount of pointer travel in the desired range is reduced compared to that of Majors, because of their overall greater measuring range.

And remember, the general testing concepts adopted by the railroads apply just as well to all cable applications, with modifications to the particular industry. If you have railroads among your customer base, talk to the cable maintenance foreman or supervisor, and indicate the value of a Megger Insulation Tester in keeping the railroads chugging. (Jeff Jowett; Senior Applications Engineer)

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Free Megger Best Practices Battery Maintenance and Substation Seminars

Megger Best Practices Battery Maintenance and Substation Seminars now in Atlanta, Georgia and Orlando, Florida

Secondary batteries play an essential role in many areas of business and commerce, but to be sure that they deliver their full performance when called upon to do so, regular testing is needed.

To learn more Megger is presenting FREE one-day seminars across the United States and recently we have added events in Georgia and Florida. The seminars address some of the most important and costly issues relating to battery and substation maintenance, and include extensive practical
presentations.

Megger’s Best Practices Battery and Substation Seminars are being held at the following locations:

October 26th
Holiday Inn Atlanta/Roswell
909 Holcomb Bridge Rd.
Roswell, Georgia 30076
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October 28th 2010
Holiday Inn Main Gate
5711 West U.S. Hwy 192
Kissimmee, FL 34746
click here to register

Focus
The key focus of the Best Practices Battery and Substation Seminar is condition analysis, and the assessment of power transformers. All sessions include show-and-tell demonstrations of practical techniques for maximizing reliability, including the most commonly used methods and practices.

Among the topics covered in detail for circuit breakers are basic testing techniques, first trip testing, static and dynamic resistance measurements, vibration analysis, the formulation of test plans and reporting.

For power transformers, recent advances in condition analysis and assessment are presented, complemented by discussion and demonstration of the most useful and convenient test techniques. These include power factor testing, sweep frequency response analysis (SFRA) and insulation diagnostic analyzer (IDAX) applications.

Invaluable information is also provided on Battery Performance Testing and Reporting data collection, trending and analysis via PowerDB software, as well as insights into how companies are coping with the North American Electric Reliability Corporation (NERC) and Federal Energy Regulatory Commission (FERC) data collection and management requirements.

Participants of this training seminar will improve business skills, share insights, and learn from Megger’s technology specialists as they share their expertise by addressing many of the challenges seen in the electric power industry today. Topics will highlight HV Circuit Breaker Testing and Condition Analysis, and Assessment of Power Transformers. Each session will include show and tell demonstrations on the practical aspects of ensuring reliability including common methods and practices.

Sign up early as spaces are limited. Please contact Nicole Stokes at 214 330 3245 or email nicole.stokes@megger.com to register.

(source  www.megger.com)

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