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- BM21
- Simple, push-button operation is user-friendly and easy
to use.
- Analog/digital LCD enables direct reading in all ranges.
- Lock-down TEST button and integral timer are useful for
extended tests such as polarization index.
- Rechargeable, battery-powered instrument is useful
anywhere because of its portability.
- Automatic discharge of capacitive test sample charge
promotes user safety.
- Guard terminal eliminates surface leakage current from
the measurement.
- BM25
- Insulation test to >5 TΩ tracks insulation resistance on
highly specified high-voltage equipment.
- Automated testing allows diagnostic tests to be applied
to routine maintenance, saves time and avoids operator
error.
- Polarization index tests track insulation condition on
many different types of equipment with no need for
temperature correction.
- Step voltage tests detect localized insulation problems
- Dielectric discharge tests diagnose failed layers in
multilayer insulation.
- Optically isolated RS-232 interface allows download of
test results for storage on a PC.
- Integral timer eases test operation.
- Specifications are well-suited for accuracies and
environmental performance.
- Capacitance measurement at the end of a test ensures
confidence in test piece identification.
- Automatic charging control allows easy charging from 95
V to 265 V and prevents overcharging.
- Durable, field-portable, weatherproof, tester gives long
service life
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The Megger BM21 5-kV Insulation Resistance
Testers are portable, battery-powered, high-voltage
instruments that use the latest electronic design and
technology. The instruments have user-friendly keypads
with push-buttons to select test voltages of 500, 1000,
2500, and 5000 V dc. In addition to the standard test
voltages, a variable voltage feature on the BM21 selects
test voltages between 25 and 5000 V dc in 25-V steps.
An integral timer automatically controls the duration test
and stops the output voltage when the preset time has
expired.
Analog/digital displays offer practicality and precision. The
analog/digital
LCD displays readings of insulation resistance to 5 Tohms
leakage current to below 1 nA, and capacitance to 10 μF.
The analog scale rapidly identifies insulation condition and
monitors variable measurements. The digital display
complements the analog scale by simultaneously
displaying an easy-to-read, precise measurement.
As a safety feature, these testers act as an ac/dc safety
voltmeter, indicating the level of applied voltage before a
test and monitoring discharge voltage after a test. For
added safety, an alarm warns the operator if the circuit
under test has not been de-energized.
Both testers incorporate a guard terminal to eliminate the
effects of surface leakage in the item under test, thus
ensuring accurate measurements.
The Megger BM25 is a compact automated 5 kV insulation
tester. It can be used to conduct polarization index, step
voltage, dielectric discharge diagnostic and standard
insulation tests up to 5 Tohms.
Results and test options are displayed on a large, clear
analog/digital readout for both practicality and precision.
The BM25 provides an optically isolated RS-232 port for
direct download of test results. This enables the user to
conduct cost-effective predictive maintenance programs.
The instrument displays leakage current down to <1 nA
and the capacitance of the test piece up to 10 μF. A guard
terminal allows surface leakage to be removed.
Standard test voltages are preset at 500 V, 1000 V, 2500 V
and 5000 V and combined with an output voltage setting
that is variable in 25 V steps. The integral timer starts
automatically at the beginning of a test and can be used to
control test duration.
The BM25 is powered by rechargeable lead-acid batteries.
The built-in charger operates from 95 V to 265 V power
supplies without switch selection. The instrument is
supplied complete with test leads, RS-232 interface lead
and file transfer utility software. |
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- APPLICATIONS
- The BM21 series test the insulation resistance of:
- High-voltage power cables
- Large motor/generator windings
- Line and substation transformers
- High-voltage buses
- Both instruments perform spot tests, step-voltage tests, and
dielectric absorption tests for the following applications:
- Acceptance testing at installation to check conformance
to specifications.
- Routine preventative/predictive maintenance testing after
installation.
- Quality assurance testing as part of the manufacturing
process.
- Diagnostic testing to isolate faulty components for
repair.
- Detect high- or low-resistance
grounds and short circuits in apparatus, cables, wiring,
caused by moisture, oil, dirt, corrosion, damage to
insulation or natural deterioration. The units determine the
presence of moisture, solvents and semiconducting foreign
materials in wires, cables and other conductors, and in
built-up insulation systems such as those found in motor
windings.
- The BM25 is designed for testing the insulation of highvoltage
electrical equipment. Its wide voltage range also
allows applications to low-voltage equipment.
Generators, motors, transformers, cables and switchgear all
require effective maintenance. The test techniques on the
BM25 provide valuable diagnostic information.
Insulation suffers from gradual, steady decline as well as
occasional sudden damage. The effects of dirt, grease,
moisture, vibration and chemical attack can be tracked by
recording polarization index tests which are not limited by
the temperature-dependence of raw insulation resistance
measurements.
- Polarization index (PI) is a time-resistance dielectric
absorption test. PI tests are also helpful when full test
records have not been maintained.
To find more localized insulation problems, the BM25
includes both step voltage and dielectric discharge tests.
Step voltage identifies local weak spots which respond
differently as electrical stress is increased. The dielectric
discharge test can show a single bad layer in multilayer
insulation.
- The key to predictive maintenance is the trending of
diagnostic tests. The BM25 can download to a PC to store
test results.
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| Insulation Ranges |
BM21 |
BM25 |
| Test Voltages: |
500, 1000, 2500, 5000 V; plus 25 to 5000 V in 25 V steps |
500, 1000, 2500, 5000 V; plus 25 equal steps to 5000 V
in 25 V steps |
| Insulation Resistance
Range: |
Digital
10 kΩ to 500 GΩ
@ 500 V
10 kΩ to 1 TΩ
@ 1000 V
10 kΩ to 2,5 TΩ
@ 2500 V
10 kΩ to 5 TΩ
@ 5 kV
Analog
100 kΩ to 1TΩ
@ all voltages |
| Accuracy |
±5% on 100 MΩ load ±25V for test voltages <500V |
| Short Circuit
Current |
1,8 mA nominal, 2 mA max. |
| Basic Accuracy |
±5% of reading 1MΩ to 1 TΩ
@ 5 kV (0 to 30°C)
(32 to 86°F) |
| Voltage Range |
50 to 1000 V d.c. or a.c. (0 to 5000 V d.c. when testing) |
| Accuracy: |
±2% ±1 V |
| General |
BM21 |
BM25 |
| Display : |
analog/digital (3 digits) |
Interference
Rejection: |
1 mA r.m.s. per kV to a maximum 2 mA |
Capacitor
Discharge Time: |
< 2 s per μF to discharge from 5000 V to 50 V |
Leakage current
measurement |
0,01 nA to 999 μA --Accuracy ±5% ±0,2 nA |
Capacitance
measurement: |
0,01 - 10,0 μF (displayed at end of test)
Accuracy ±15% ±0,03 μF |
| Operating Temperature : |
Operating -20to +50°C (-4 to 122°F)
Storage -25°C to +65°C (-13 to 149°F) |
| Storage Temperature: |
-25°C to +65°C,
(-13 to 149°F) |
Temperature
Coeffecient: |
(Applies over range 0 to 30°C)
0,2% per °C for test currents >100 nA (0.1%/°F)
0,1% per °C for test voltage (0.05%/°F) |
| Humidity Range |
90% RH @ 40°C max. (104°F) |
| Safety |
Safety IEC348 |
IEC1010-1 (1995), EN61010 (1995) to installation
category III, 300 V, phase to earth, 500 V phase to
phase |
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