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

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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

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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

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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

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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.

Getting to Know the MTO210
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Top Panel Controls
Figure 1: MTO210 Front Panel
Input AC Power Module:
This module is an IEC320 interface to the mains power. The module has an
integrated switch, fuse holder and input filter module. Above the module are the
voltage, frequency and power requirements for the product. Below the module are
the fuse type and ratings based on the input voltage used. The green light on the
right side of the module illuminates when power is ON.
0, OFF position
- , ON position
Output Current Terminals
These connections are used to connect to the transformer winding(s) and pass the
DC power into the transformer winding for testing and demagnetization. The
connection is capable of supplying up to 50 volts DC and up to 10 amps current.

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Input Voltage V1
These connections are used to connect a transformer winding for input voltage
measurement. The instrument will automatically calculate the resistance of this
input in combination with the current source. The connectors are also used as a
path for current to flow during discharges. Voltage leads shall always be used in
conjunction with current leads.
Input Voltage V2
These connections are used to connect a second transformer winding for input
voltage measurement. The instrument will automatically calculate the
resistance of this input in combination with the current source. The connectors
are also used as a path for current to flow during discharges. Voltage leads
shall always be used in conjunction with current leads.
Earth/Ground Lug
This connection is used to connect a transformer under test to earth ground for
safety. The transformer and the MTO shall be at the power ground/earth
potential when being operated.
Emergency Shut Down Switch
This switch, when pushed will disable the source power supply and
automatically discharge the transformer. The instrument is continuously
monitoring this switch in the event of an emergency. If the switch is engaged,
no testing can commence.
Current Set Switch
This switch is used to control the amount of current the instrument will use to
test a transformer.
Symbol represents the maximum output level of test current.
Warning Beacon Connector
When the Warning Beacon is attached to the connector, the user will have a
more visible indication of the activation mode of the MTO.
Break Before Make INDICATOR
During testing, the unit will indicate disruptions in the current loop. During
testing of On Load tap changers, this indication will signify that a faulty break
before make condition has occurred.
USB Interface
Not accessible at this time

Getting to Know the MTO210
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Maintenance Port
This port is provided for software upgrades and diagnostics, the interface
panel can be removed and an Ethernet connection is available to attach the
instrument externally to a PC. Port is NOT network compatible. This product is
not intended for network use.
RS232 Connection
This connection is used for printing to a thermal 4” printer and/or transferring
data from MTO to a user PC.
Remote Control Switch
This connector is used to interface with a remote switch. This switch is
primarily used when the system is used for testing On Load Taps of a
transformer
The Remote Control Switch can remotely start the MTO test and store multiple
resistances reading for tap changes. The storage function in remote mode is
sequential and occurs during a continuous resistance test. The unit will also
store break before make events in local storage.
Interlock Connections
These connections are used in the event that testing requires lockout
mechanisms from the transformer. If the Interlock connection is open, the unit
will not be capable of going into Test Mode. If the interlock is broken during
test, the unit will automatically shutdown and discharge an energized
transformer. Further testing will be prohibited.
Data Output Mode Switch
MTO will Print and Save Data
MTO will Save Data
MTO will Print Data
MTO will just Display Data
Function Mode Switch
MTO is in Test Mode
MTO is in Storage Review Mode
MTO is in Set Date and Time Mode
MTO is in select Date Format Mode

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IDLE STATE - When pushed the unit will start a test
on a transformer. This will only occur if the
instrument is in Test Mode (see Function Mode
Switch above).
The TEST INDICATOR above the button will
illuminate during the test.
TEST STATE – When pushed the unit will stop a
test on a transformer, maintain the results on the
screen. It will save and/or print the results
dependent on the Data Output Mode Switch.
When pushed will stop testing and discharge the
transformer. The DISCHARGE INDICATOR to the
left will illuminate during the discharge cycle.
When pushed will perform a transformer
demagnetization. The DEMAG INDICATOR to the
right will illuminate during the demagnetization
cycle.
When pushed, the unit will acknowledge data entry,
displayed messages and during test mode, save
data presented on the display.
Symbol highlights that the button will PRINT
the test results out the RS232 port when pushed
and in Storage Review Mode.
In ready mode, button will change the
sensitivity of the current transition detection
sensitivity. Off is default.
Symbol highlights that the button will give the
user the ability to DELETE the last recorded test in
memory. If pressed a second time, the unit will give
the user the ability to delete all tests in memory. If
pressed a third time the unit will no longer be in the
delete function.
In ready mode, button turn toggle ON/OFF the
OHM2 display.

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2
Safety
Safety is theresponsibility of the user
Only qualified and trained operators should operate the MTO system. Operator
must read and understand this entire Instruction Manual prior to operating the
equipment. Operator must follow the instructions of this Instruction Manual and
attend the equipment while the equipment is in use. In the event of equipment
malfunction, the unit should immediately be de-energized and returned to
Megger for repair.
“The Safety precautions herein are not intended to replace your Company’s
Safety Procedures. Refer to e.g. IEEE 62-1995/IEEE C57.152 and IEEE 510 -
1983, IEEE Recommended Practices for Safety in High-Voltage and High-
Power Testing, for additional information.”
F
WARNING
When applying current to a transformer with very high
inductance, additional care should be taken not to remove current
or voltage leads while current is still flowing. This causes an
extremely high voltage to develop across the point where current
is broken. Under certain conditions, this voltage could prove to
be lethal.
The Megger Transformer Ohmmeter has built-in safety protection thru the
VOLTAGE POTENTIAL LEADS. Voltage leads shall always be connected in
parallel with the current leads.
Example: If a current lead is disconnected while current is flowing through the
transformer, the current will flow through the alternate path of the
potential lead without damage to instrument or electrical shock to
operator.
F WARNING
It is very important not to connect any leads on top of or too close
to one another. Take the necessary precautions to assure one
lead falling off will not take a second lead with it.

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General Safety Precautions
The MTO and the Unit Under Test (UUT) should both be considered as sources
of instantaneously lethal levels of electrical energy. Observe the following safety
precautions:
Observe all safety warnings on the equipment. They identify areas of
immediate hazard that could result in injury or death.
Use this equipment only for the purposes described in this manual. Observe
strictly the Warning and Caution information provided in this manual.
Treat all terminals of high-voltage power equipment systems as potential
electric shock hazards. Use all practical safety precautions to prevent contact
with energized parts of the equipment and related circuits.
Use suitable barriers, barricades and/or warnings to keep persons not directly
involved with the work away from test activities.
Never connect the test equipment to energized equipment.
Do not use in an explosive atmosphere.
Use the grounding and connection procedures recommended in this manual.
Always disconnect test leads from power equipment before attempting to
disconnect them at the test set. The ground connection MUST be the first
made and removed last. Any interruption of the grounding connection can
create an electrical shock hazard.
Personnel higher than 5 feet should follow proper tie off safety requirements.
Personnel should use proper safety gear to prevent bodily harm.
Personnel using heart pacemakers should obtain expert advice on the
possible risks before operating this equipment or being close to the
equipment during operation.
Fuse selection is dependent on input voltage. 230VAC uses 3.15 amp fuses
and 120VAC uses 6.3 amp fuses.
F WARNING
No user serviceable parts inside! Refer all
servicing to the factory or a qualified authorized
service company!

Safety
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G CAUTION
Use only factory supplied mains cord!
Mains cord shall not be substituted!
Input Power Precautions
This instrument operates from a single-phase, sine wave, power source. It has a
three-wire power cord and requires a two-pole, three-terminal (live, neutral, and
ground) type input source. The voltage to ground from the live pole of the
power source must be within the following rated operating voltage:
For Cat. No MTO210: 120/230 V 10%, single-phase sine, 50/60 2 Hz
The neutral pole must be at ground potential. Before making connection to the
power source, determine that the instrument rating matches the voltage of the
power source. The power input plug must be inserted only into a mating
receptacle with a ground contact.
F WARNING
Do not bypass the grounding connection. Any interruption of the
grounding connection can create an electric shock hazard.
Determine that the receptacle is properly wired before inserting
the plug.
The control circuits of the instrument are protected by two mains circuit fuses.
These fuses are located in the ON/OFF switch module and are replaceable by
the operator. To avoid electric shock and fire hazard, use only the fuse specified
in Section 8 Parts List and Optional Accessories, that is identical in respect to type,
voltage rating, and current rating. A detailed procedure for Fuse Replacement is
defined in Section 7 - Service.
F WARNING
Before replacing the fuses, disconnect the power
input plug from the live power source.

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3
Preparing for a Test
Site Preparation
Choose a location that meets the following conditions:
The location is as dry as possible.
There is no flammable material stored in the vicinity.
The test area is adequately ventilated.
Be sure all equipment is de-energized and all terminals of the Unit Under
Test (UUT) are accessible. Erect suitable safety barriers to protect the
operator from traffic hazards and to prevent intrusion by unauthorized
personnel. User provided Warning lights are recommended.
Verify that the Local station ground is intact and has impedance continuity to
earth.
Making Circuit Connections
Connections should be made in the order as listed below.
1. Ground. Use the Megger supplied Safety Ground Cable (15 ft (4.6 m)) to
connect the MTO Wing Nut Ground Terminal directly to Local Station
Earth Ground. Ensure that the Transformer chassis also has a low
impedance connection to Local Station Earth ground potential.
2. Input Power Source Ground. Input Power Source Ground Terminal
should be less than 100 milliohms of impedance to Local Station Earth
Ground.
3. Connect the Input Power Cord. Before making this connection, insure
the Input Power Source meets the requirements as listed in Section 2 Safety
and Section 9 Specifications. Also make sure that the ON/OFF switch
(Figure 1) is in the OFF position. Connect the input power cable to the
MTO first, then to the power source. At this time, leave the ON/OFF
switch in the OFF position.

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4. Connect the Serial Cable (optional). If the user chooses to use an
external printer or PC, using PowerDB Lite PC software, then connect
the serial cable between the MTO and the printer or PC at this time.
5. Connect the Remote Control cable (optional). If the user chooses to
operate the Test Button of the MTO from a remote distance then,
connect the RCC cable at this time.
6. Connect Warning Beacon (optional). If the user chooses to operate
the Warning Beacon then, connect the WBC cable at this time and place
the beacon in a conspicuous location.
7. Connect Interlock Switch. The MTO has an external interlock switch
feature. Connect the external Interlock Switch via banana jack
connection to the interlock input jacks on the front panel. The interlock
switch function is a fail open, therefore if not used, an interlock jumper
shall be placed in the jacks. If the circuit is open “IntLoc” will be
displayed at the middle LCD.
8. Connect the I and V leads (to the MTO end only at this time). With
the clamps disconnected from the UUT, connect the I and V cables to
the MTO at this time. Be sure that all plugs are fastened securely to the
MTO so they will not become loose even in the event of the operator
inadvertently tripping over the current leads.
MTO210 is programmed to read two voltage inputs at all times. If a
voltage input is not used, the high impedance input characteristics of the
input cause the unit to give readings that are not zero. If a jumper is
installed, the reading will be very low.
9. Connecting to the Transformer. When testing high-voltage
transformers, caution must be used at all times and all safety precautions
followed. Read, understand, and employ all safety precautions and circuit
connections described in Sections 2 Safety and Section 3 Preparing for Test.
F WARNING
Ensure that the transformer to be tested is completely
de-energized. Check every winding. Ensure that all
terminals of the transformer are disconnected from line
or load at the transformer. Connections to ground may
be left in place.
F WARNING
For all testing as described herein, care shall be taken
to ensure any and all unused clamps shall be isolated
from each other, from ground, and from personnel.