Megger MTO210 User manual

AVTMMTO210
Rev 7
Sept 2013
Instruction Manual
for
Transformer Ohmmeter
DC Winding Resistance Test Set
MTO210
Catalog Number MTO210
HIGH-VOLTAGE EQUIPMENT
Read this entire manual before operating.
M
Valley Forge Corporate Center
2621 Van Buren Avenue
Norristown, PA 19403-2329
U.S.A.
610-676-8500
www.megger.com

Transformer Ohmmeter
DC Winding Resistance Test Set
MTO210

Copyright© 2011 by Megger. All rights reserved.
The information presented in this manual is believed to be adequate for the intended use of the product.
If the product or its individual instruments are used for purposes other than those specified herein,
confirmation of their validity and suitability must be obtained from Megger. Refer to the warranty
information below. Specifications are subject to change without notice.
WARRANTY
Products supplied by Megger are warranted against defects in material and workmanship for a period of
one year following shipment. Our liability is specifically limited to replacing or repairing, at our option,
defective equipment. Equipment returned to the factory for repair must be shipped prepaid and insured.
Contact your MEGGER representative for instructions and a return authorization (RA) number. Please
indicate all pertinent information, including problem symptoms. Also specify the serial number and the
catalog number of the unit. This warranty does not include batteries, lamps or other expendable items,
where the original manufacturer’s warranty shall apply. We make no other warranty. The warranty is
void in the event of abuse (failure to follow recommended operating procedures) or failure by the
customer to perform specific maintenance as indicated in this manual.
M
Valley Forge Corporate Center
2621 Van Buren Ave
Norristown, PA 19403-2329
610-676-8500 (Telephone)
610-676-8610 (Fax)
www.megger.com

AVTMMTO210 Rev 7 Sept 2013
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Table of Contents

1 Getting to know the MTO210 ...........................................................................................................................1
Product Overview ................................................................................................................................................1
Top Panel Controls..............................................................................................................................................3
2 Safety ......................................................................................................................................................................7
Safety is the responsibility of the user...............................................................................................................7
General Safety Precautions .................................................................................................................................8
Input Power Precautions.....................................................................................................................................9
3 Preparing for a Test........................................................................................................................................... 11
Site Preparation.................................................................................................................................................. 11
Making Circuit Connections............................................................................................................................ 11
4 Operating the MTO210.................................................................................................................................... 15
Description of Test Sequence ......................................................................................................................... 15
5 Transformer Testing ......................................................................................................................................... 25
Winding Resistance Testing............................................................................................................................. 25
Testing a Single-Phase Transformer............................................................................................................... 26
Testing Delta Configured Windings............................................................................................................... 33
Testing Transformers with Tap Changers..................................................................................................... 35
Testing Voltage Regulators.............................................................................................................................. 36
Demagnetizing a Transformer......................................................................................................................... 39
6 MTO210 Series PowerDB Lite ....................................................................................................................... 41
Introduction ....................................................................................................................................................... 41
Software Installation ......................................................................................................................................... 42
Using PowerDB Lite......................................................................................................................................... 45
Frequently Asked Questions (FAQ’s)............................................................................................................ 52
7 Service ................................................................................................................................................................. 53
Maintenance ....................................................................................................................................................... 53
Fuse Replacement ............................................................................................................................................. 53
Calibration .......................................................................................................................................................... 54
Repairs................................................................................................................................................................. 55
ERROR CODES .............................................................................................................................................. 56
8 Parts List and Optional Accessories............................................................................................................... 63
9 Specifications...................................................................................................................................................... 65

AVTMMTO210 Rev 7 Sept 2013
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List of Figures
MTO210 Transformer Ohmmeter Test Set....................................................................................................iii
Figure 1: MTO210 Front Panel ........................................................................................................................3
Figure 2: Single Winding Measurement.........................................................................................................26
Figure 3: Dual-Winding Test...........................................................................................................................28
Figure 4: Reading obtained is per phase, Resistance of A-N Winding .....................................................31
Figure 5: Reading obtained is between pairs of terminals, Resistance of A and B Windings................32
Figure 6: Reading is between pairs of terminals. Resistance of A in parallel with B+C windings........32
Figure 7: Odd Position Tap.............................................................................................................................36
Figure 8: Even Position Tap............................................................................................................................36
Figure 9: Connection to a Regulator ..............................................................................................................37

AVTMTO210 Rev 7 Sept 2013
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Upon Receipt of Product
Prior to operation, check for loosened hardware or damage incurred during
transit. If these conditions are found, a safety hazard is likely, DO NOT attempt
to operate equipment. Please contact Megger as soon as possible.
MTO210 Transformer Ohmmeter Test Set

AVTMMTO210 Rev 7 Sept 2013
iv
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AVTMMTO210 Rev 7 Sept 2013
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1
Getting to know the MTO210
Product Overview
The Megger Transformer Ohmmeter is a line-operated, field-portable instrument
designed specifically to measure the DC resistance of all types of magnetic
windings safely and accurately.
Its predominant use is the measurement of the DC resistance of all types of
transformer windings within the defined ranges of current and resistance. It can
also test rotating machine windings and perform low-current resistance
measurements on connections, contacts and control circuits.
Four features are combined to make this instrument unique: dual measurement
and current injection, on-load tap-changer testing, automatic discharge and
demagnetization..
The dual set of potential inputs, simultaneously measure the resistance of the
primary and secondary windings of a single- or three-phase transformer. The
dual reading characteristic will speed up the measurement when current leads are
driving more than one winding.
The Transformer Ohmmeter is extremely useful when testing the windings and
contact resistance on tap-changers with make-before-break contacts and voltage
regulators. A warning light will flash and the internal shutdown circuit will be
triggered if the tap-changer contacts have a break before make event. This action
checks for pitted or misaligned contacts and indicates such events.
Likewise users are protected by the shutdown circuit safety feature: any
inadvertent disconnection of a test lead or loss of power to the instrument will
safely and quickly discharge the energy stored within the test sample.
The MTO210 has an added post test feature. At the end of a transformer test,
the instrument has a demagnetization function. This function will cycle thru the
transformer with alternating DC current. At the end of 8 cycles, the transformer
core is demagnetized.
The Transformer Ohmmeter's wide resistance range (1 micro-ohm to 1999
ohms) gives a high degree of resolution for even the lowest winding resistance
tested.

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Features include:
Direct digital reading saves time, no manual balancing is required.
Built-in discharge circuit safely discharges the specimen when test is
completed, if lead accidentally disconnects, or if power is lost.
Test indicator light gives a visual indication of either a charged or discharged
specimen, even if power to the instrument is lost.
Two independent measuring channels allow simultaneous testing of primary
and secondary windings or measurement of two phases at a time.
The sensitive tap-changer test circuitry monitors the contact operation of on-
load tap-changers for their correct make-before-break sequence. If an open
circuit condition exists, the instrument shuts down immediately.
Electronically generated and patented regulated current supply overcomes
high-inductance transformers quickly, allowing fast measurements to be
taken. Display of measurement occurs only after test current stabilizes.
Wide resistance range is suitable for testing a wide variety of transformers.
Current ramp-up mode continuously tests input compliance voltage and sets
the maximum current based on the specific test load.
Lightweight and portable, the MTO is ideal for use in workshop or
substation environments.
Over temperature protection provides automatic current shutdown and
indication to prevent instrument damage.
Meets the requirements of both the European EMC and Low Voltage
Directives.
It is recommended that the user becomes familiar with the MTO before making
any connection to a transformer.