S1-568, S1-1068, and S1-1568 insulation resistance testers
High noise immunity
Noise rejection of 8 mA - twice that of most comparable instruments – with four user-selectable software filters
Resistance range up to 35 TΩ
Insulation resistance up to 35 TΩ at 15 kV and 10 kV, and 15 TΩ at 5 kV
Safety rated up to CAT IV
Up to 1000 V at altitudes up to 4000 m for the S1-1568, and CAT IV 600 V to 3000 m for the S1-568 and S1-1068 test instruments
Battery and AC operation
Operate with rapid charge Li-ion battery that meets IEC 62133, or AC source when the battery is flat
New PI PredictorTM
Obtain 10 minute PI values in typically half the time with the new patented PI predictor
About the product
The S1-568, S1-1068, and S1-1568 insulation resistance testers from Megger come with class-leading noise rejection of 8 mA – twice that of most comparable instruments – and enhanced software filtering that has four user-selectable options. These DC insulation resistance testers come in 5 kV, 10 kV, and 15 kV and deliver dependable results in even the most severe of electrical environments, including high voltage transmission and distribution substations.
The performance of these groundbreaking instruments has been exhaustively proven in the laboratory and, more importantly, has been convincingly demonstrated in the field. Accurate and consistent results were, for example, obtained in a working 765 kV substation where no other insulation tester had been able to operate successfully.
Megger’s S1 series of insulation testers are available in three models:
- The S1-568 tests at up to 5 kV and can measure insulation resistance up to 15 TΩ
- The S1-1068 operates at up to 10 kV and measures up to 35 TΩ
- The S1-1568 has 15 kV capability and measures up to 35 TΩ
All models have a high short-circuit current of 6 mA to ensure rapid charging of items under test. The S1-568 and S1-1068 have a CAT IV 600 V safety rating, at altitudes up to 3,000 m, with the S1-1568 having CAT IV 1000 V to 4,000 m, in line with IEC 61010.
Other innovative features include the provision for remote control via a fully isolated USB port, which makes the instruments ideally suited for use in production environments, and internal storage for date- and time-stamped results. Stored results can be recalled to the display, downloaded via a Bluetooth wireless link, or accessed via the USB port.
To ensure that testing is never delayed through lack of power, these S1 insulation testers incorporate rapid-charge Li-ion batteries that give up to 6 hours of testing on a full charge for the 5 kV model and 4.5 hours for the 10 kV and 15 kV models. With just 30 minutes of charging from flat, the batteries give around one hour of testing time, and it’s also possible to operate the instrument from an AC power supply even if the battery is completely flat.
Compact and lightweight, the S1 insulation resistance testers feature a rugged dual-case design and, with the lid closed, they have an IP65 ingress protection rating. They offer timed insulation resistance (IR), dielectric absorption ratio (DAR), polarisation index (PI), dielectric discharge (DD), step voltage (SV) and ramp diagnostic tests, as well as a dedicated voltmeter function.
The patented PI predictor enables you to obtain 10 minute PI values in as little as 3 minutes! The new method starts to predict the final IR curve from 3 minutes into the test and as soon as the predictor is confident with the prediction, the test is stopped and the predicted value of the PI displayed. In most cases, this happens within 5 minutes, meaning the test time is typically halved!
Product documentsAdditional documentation can be found on the support tab
FAQ / Frequently Asked Questions
There are several reasons to select a test set with a high output current. Possibly the most important is that a high output current means that the item under test will be charged more quickly, which means that the test can be completed in a shorter time and also that there’s less risk that the readings will be taken before the test voltage has had time to stabilise properly. And, if you’re using the instrument’s guard terminal, don’t forget that a lot of output current may well be diverted via the surface leakage of the item under test. Unless the instrument has a high output current capability, this could mean that the output voltage will collapse, and the test results will not be valid.
That depends upon the size, complexity, and criticality of your equipment. Even identical units can differ in the required check periods; experience is your best guide. In general, however, working apparatus – such as motors and generators – are more likely to develop insulation weaknesses than wiring, insulators, and the like. A test schedule for working equipment should be established, varying from every 6 to 12 months, depending on the size of the equipment and the severity of the surrounding atmospheric conditions. For wiring and the like, tests once a year are generally sufficient unless the installation conditions are unusually severe.
These facilities are useful in a wide range of applications. For example, when testing a large item such as a power transformer, the instrument can be positioned on top of the asset near its terminals so that the test leads are kept short and operated from a much more convenient – and much safer – location, using the remote control option. Additionally, it’s sometimes necessary to carry out tests in hazardous areas, such as inside an energised substation. In these cases, once it has been connected, you can operate the test set and access your results outside the hazardous area, significantly increasing the operator’s safety. Finally, in production line test applications, it’s often desirable to control the test unit and retrieve the test results automatically. The remote control and remote downloading facilities offer a convenient way of achieving this and providing any safety interlocks that may be needed.
The electrical insulation should be top-notch when your plant’s electrical system and equipment are new. Furthermore, manufacturers of wire, cable, motors and other electrical equipment have continually improved their insulations for services in industry. Nevertheless, even today, insulation is subject to many effects which can cause it to fail – mechanical damage, vibration, excessive heat or cold, dirt, oil, corrosive vapours, moisture from processes, or just the humidity on a muggy day.
To various degrees, these enemies of insulation are at work as time goes on – combined with the electrical stresses that exist. As pin holes or cracks develop, moisture and foreign matter penetrate the insulation surfaces, providing a low resistance path for leakage current.
Once started, these attack agents often aid each other, permitting excessive current through the insulation.
Sometimes the drop in insulation resistance is sudden, as when equipment is flooded. Usually, however, it drops gradually, giving plenty of warning if checked periodically. Such checks permit planned reconditioning before service failure. If there are no checks, a motor with poor insulation, for example, may be dangerous to touch when voltage is applied and subject to burnout. Over time, what was good insulation has become a partial conductor.
In cases of this type, the source of trouble is almost always induced noise in the measuring circuit. You can reduce noise pick-up on the test leads by keeping them as short as possible and using screened test leads. With screened leads, the screen is connected to the insulation test set guard terminal to divert the noise currents from the measuring circuits. However, if the noise is being picked up by the item under test rather than the test leads, these measures can’t help. In such cases, the only effective solution is to use an insulation test set with high noise immunity and effective filtering. The S1 has noise immunity of 8 mA, which ensures reliable operation in the harshest conditions, such as EHV substations. They also have adjustable long time constant filtering, which allows users to choose between faster operation when noise levels are only moderate, and slower operation but with enhanced noise rejection when working in the most challenging environments.
Further reading and webinars
Unfortunately, lithium-ion batteries eventually wear out and can no longer accommodate a charge. This event is a common and, sooner or later, inevitable issue, but fortunately it is easily corrected. Replacement batteries are available from Megger, and you can quickly change one following the instructions in the User Guide.
Do a visual inspection of the unit, and don’t overlook the lead set. It is understandable to focus on the instrument and take the lead set for granted, but the leads are commonly knocked about from handling more than the instrument. In particular, the strain relief at the end of the lead becomes damaged - its absence is a strong indication that the lead set soon needs to be replaced. Damaged leads tend to affect the most negligible leakage currents first, so the instrument may not be able to indicate measurement into the tera-ohm (TΩ) range. This symptom means that the lead set should be repaired or replaced.
These are control and measurement boards post error codes. These appear on the display as “E” followed by a 1- or 2-digit number. The User Guide gives brief definitions. These are not user-adjustable. They indicate component failures or calibration resets that a Megger repair technician or authorised repair centre must perform.
This symptom indicates that the power supply transformer has broken off the power supply board, usually due to rough handling and/or dropping. The transformer, being relatively heavy, will come loose from its mountings. This breakage interrupts or terminates power to the circuitry, resulting in a ‘dead’ instrument. Contact your local Megger repair technician or authorised repair centre.
Yes - remove the S1 from the AC source. Press both the “OK” and backlight buttons while switching the main rotary switch from the “OFF” position to the “settings” icon.
Insulation tests are automatically stopped in breakdown mode, and “brd” is displayed when a fault causes the applied voltage to drop rapidly. Burn mode IR tests ignore breakdown and continue to test the insulation and are, therefore, destructive tests. Burn mode is used to purposely create a carbon track in insulation to facilitate fault location.
Interpreting test results
Insulation resistance readings should be considered relative. They can be quite different for one motor or machine tested three days in a row, yet it does not mean bad insulation. What matters is the trend in readings over a longer period, showing lessening resistance and warning of coming problems. Periodic testing is, therefore, your best approach to preventive maintenance of electrical equipment, using record cards or SW to trend the results over time.
Whether you test monthly, twice a year, or annually depends upon the equipment's type, location, and importance. For example, a small pump motor or a short control cable may be vital to a process in your plant. Experience is the best teacher in setting up the scheduled periods for your equipment.
We recommend making these periodic tests in the same way each time. That is, with the same test connections and test voltage applied for the same length of time. Additionally, we recommend performing tests at about the same temperature or correcting them to the same reference temperature. A record of the relative humidity near the equipment during the test is also helpful in evaluating the reading and trend.
In summary, here are some general observations about how you can interpret periodic insulation resistance tests and what you should do with the result:
|What to do
|Fair to high values and well maintained
|No cause for concern
|Fair to high values but showing a constant tendency towards lower values
|Locate and remedy the cause and check the downward trend
|Low but well-maintained values
|Condition is probably acceptable, but you should investigate the cause of low values
|So low as to be unsafe
|Clean, dry out, or otherwise recondition the insulation to acceptable values before placing equipment back in service (test wet equipment after drying out)
|Fair or high values, previously well-maintained but showing a sudden decrease
|Make tests at frequent intervals until you locate and remedy the cause of low values; or until the values have become steady at a lower level but safe for operation
The resistance of insulating materials decreases markedly with an increase in temperature. However, we’ve seen that tests by the time-resistance and step-voltage methods are relatively independent of temperature effects, giving relative values.
To make reliable comparisons between readings, you should correct the measurements to a base temperature, such as 20 °C, or take all your readings at approximately the same temperature.
A good rule of thumb is to halve the resistance for every 10 °C increase in temperature or, for every 10 °C decrease, double the resistance.
Each type of insulating material will have a distinct degree of resistance change with temperature. Factors have been developed, however, to simplify the correction of resistance values. Please refer to the document "Stitch In Time" to find such factors for rotating equipment, transformers, and cables (Section: Effect of Temperature on Insulation Resistance).
User guides and documents
FAQ / Frequently Asked Questions
The S1-568 and S1-1068 can record insulation temperature and humidity measured by independent sensors.
The filter has four settings: 10 s, 30 s, 100 s, and 200 s. It is also possible to turn off the hardware filter to speed up the response when no noise is present. If a one-minute spot test is to be performed, a suitable filter would be 10 s, or possibly 30 s activated towards the end of the test. Setting a longer filter would be meaningless because the test only lasts 60 s. The S1 range memorises all results in the current test to give an instantaneous meaningful filtered reading of results as long as the test duration is longer than the filter length.
You can select a downloading data function by switching to the ‘download via USB’ icon on the central rotary switch. Before starting a download, you must connect a USB cable between a PC and the USB port on the instrument or a Bluetooth connection setup to a suitably enabled PC or similar device.
PowerDB Pro, Advanced, and Lite are Megger’s asset and data management software packages with integrated forms for the S1 range of instruments. Ensure that the applicable version of PowerDB is loaded and running on the PC, then select the appropriate S1 by model number.
During insulation testing, we are often so preoccupied with the resistance of the actual insulator that we forget the resistance path on the outer surface of the insulation material. However, this resistance path is a part of our measurement and can dramatically affect our measurements. For example, when dirt or some other contaminant is present on a bushing's outer surface, the surface leakage current can be up to ten times that flowing through the insulation.
The surface leakage presents as a resistance in parallel with the material's insulation resistance that we wish to isolate and measure. The instrument's measurement circuit can separate and ignore the surface leakage current when we use its guard terminal, performing a so-called three-terminal test. Surface leakage mitigation is often necessary when high resistance values are expected, such as when testing high voltage components like insulators, bushings, and cables. These tend to have large surface areas exposed to contamination resulting in high surface leakage currents across them.