Raytech mini-ATOS User manual

Preliminary
INSTRUCTION MANUAL
ENGLISH
mini-ATOS
mini Automatic Transformer
Observation System
RAYTECH AG, OBEREBENESTRASSE 11, CH-5620 BREMGARTEN, SWITZERLAND

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Preliminary
Contents
1Safety Precautions.............................................................................................................. 6
1.1 Operators Qualifications .............................................................................................. 6
1.2 High Voltage Apparatus Accessibility During the Tests................................................ 6
1.3 Ground the Instrument................................................................................................. 6
1.4 Before Applying Power ................................................................................................ 7
1.5 Keep Away from Live Circuits...................................................................................... 7
1.6 Do Not Operate in An Explosive Atmosphere .............................................................. 7
1.7 Do Not Substitute Parts or Modify Instrument .............................................................. 7
1.8 Do Not Operate in A Condensing Humidity or Under Rain........................................... 7
1.9 Always Keep Distance from the Test Object During the Tests ..................................... 7
2Unpacking........................................................................................................................... 9
3Introduction........................................................................................................................10
4Calculation and Measurement Methods.............................................................................11
4.1 Turns Ratio Measurement...........................................................................................11
4.1.1 Principle...............................................................................................................11
4.1.2 Voltage Ratio and Turns Ratio.............................................................................11
4.1.3 Relative Error.......................................................................................................13
4.2 DC Resistance Test....................................................................................................14
4.2.1 Principle...............................................................................................................14
4.2.2 Temperature Correction.......................................................................................15
4.2.3 Resistance Deviation...........................................................................................16
4.3 Demagnetization.........................................................................................................17
4.3.1 Raytech SPP Demagnetization Method...............................................................18
4.3.2 Three-Phase Transformer Demagnetization........................................................18
4.4 Magnetic Balance.......................................................................................................19
4.5 Short Circuit Impedance .............................................................................................20
4.5.1 Principle...............................................................................................................20
4.5.2 Short Circuit Jumpers ..........................................................................................21
4.5.3 Temperature Correction.......................................................................................21
4.5.4 Short circuit impedance deviation........................................................................21
4.6 Dynamic Resistance Measurement (DRM).................................................................22
4.7 OLTC Motor Drive Current..........................................................................................24
5Measurement Setup...........................................................................................................25
5.1 Connecting Test Cables to Transformer Terminals.....................................................25

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Preliminary
6Operation Elements...........................................................................................................27
6.1 Mains Input, Fuse and Mains Switch...........................................................................27
6.2 Ethernet Interface.......................................................................................................27
6.3 USB Interfaces (1x Host, 2x Device)...........................................................................27
6.4 Safety Indicators.........................................................................................................27
6.5 Protective Earth Terminal ...........................................................................................28
6.6 Emergency Stop.........................................................................................................28
6.7 Display and Touch Panel............................................................................................28
6.8 Low Voltage Side Receptacles ...................................................................................28
6.9 High Voltage Side Receptacles...................................................................................28
6.10 Thermal Printer...........................................................................................................28
6.11 Tap Control.................................................................................................................28
6.12 External ......................................................................................................................28
6.13 Current Clamp Receptacle..........................................................................................28
6.14 Temperature Channels Receptacles...........................................................................29
7User Interface....................................................................................................................30
7.1 Home Screen..............................................................................................................30
7.2 Archive .......................................................................................................................32
7.3 Templates...................................................................................................................35
7.4 Settings.......................................................................................................................37
7.4.1 Date and Time.....................................................................................................37
7.4.2 Regional ..............................................................................................................37
7.4.3 Naming Scheme..................................................................................................38
7.4.4 Networking...........................................................................................................38
7.4.5 Remote Access....................................................................................................39
7.4.6 Maintenance........................................................................................................40
7.4.7 License................................................................................................................41
7.4.8 System Info..........................................................................................................41
8Test Objects.......................................................................................................................42
8.1 Power Transformer.....................................................................................................42
8.1.1 Windings..............................................................................................................43
8.1.2 Winding Configuration Autodetect........................................................................46
8.1.3 Nameplate...........................................................................................................47
8.1.4 General................................................................................................................48
8.1.5 Tap Changer........................................................................................................50
8.1.6 Electrical Values..................................................................................................52
8.2 Auto Transformer........................................................................................................56

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Preliminary
9Inspection and Test Plan....................................................................................................57
10 Measurements ...............................................................................................................60
10.1 Turns Ratio.................................................................................................................60
10.1.1 Table view modes................................................................................................62
10.1.2 Turns ratio settings..............................................................................................63
10.1.3 Turns Ratio Results View.....................................................................................64
10.2 Winding Resistance....................................................................................................66
10.2.1 Dual Supply Winding Resistance.........................................................................70
10.2.2 Winding Resistance Settings ...............................................................................71
10.2.3 Winding Resistance Result View .........................................................................74
10.2.4 Auto Transformer Winding Resistance.................................................................75
10.3 Winding Resistance Interval........................................................................................78
10.3.1 Winding Resistance Interval Settings...................................................................80
10.3.2 Winding Resistance Interval Result View.............................................................82
10.4 Demagnetization.........................................................................................................83
10.4.1 Demagnetization Settings....................................................................................85
10.5 Magnetic Balance.......................................................................................................86
10.5.1 Magnetic Balance Settings ..................................................................................88
10.5.2 Magnetic Balance Result View.............................................................................89
10.6 Short Circuit Impedance .............................................................................................90
10.6.1 Short Circuit Impedance Settings.........................................................................92
10.7 Dynamic Resistance Measurement.............................................................................94
10.7.1 Dynamic Resistance Measurement Settings........................................................99
10.8 Dynamic Resistance Measurement Result View.......................................................102
11 Go Taps.......................................................................................................................105
12 Remote Access Instruction...........................................................................................107
13 Interfaces.....................................................................................................................109
13.1 USB..........................................................................................................................109
13.2 Ethernet....................................................................................................................109
13.3 External (4pins version)............................................................................................110
13.4 External (6pins version)............................................................................................111
13.5 Tap Control...............................................................................................................112
14 Technical Specifications...............................................................................................113
14.1 General.....................................................................................................................113
14.2 Accuracies................................................................................................................114
14.2.1 Turns Ratio Measurement .................................................................................114
14.2.2 Resistance Measurements ................................................................................115

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Preliminary
14.2.3 Temperature Measurement................................................................................115
14.3 Standards and Approvals..........................................................................................116
AWarranty Conditions ........................................................................................................119
A.1 Limitation of Warranty...............................................................................................119
A.2 Arbitration.................................................................................................................120
BMaintenance....................................................................................................................121
B.1 Instrument Cleaning Instruction ................................................................................121
B.2 How to Insert Paper into Thermal Printer..................................................................121
B.3 Thermal Printer Cleaning instruction.........................................................................122
CIndex................................................................................................................................123
DContacts ..........................................................................................................................125

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Preliminary
1 Safety Precautions
The following safety precautions must be observed during all phases of operation, service and
repair of this instrument. By purchasing this equipment, the purchaser assumes all liability for
the operation and use of this equipment. The intended use of the instrument, its design and
manufacture, is to be conducted within the precautions or other specific warnings located within
this manual. Failure to comply with these precautions and other specific warnings violates the
safety standards of design, manufacture, and intended use. Raytech assumes no liability for the
operation and use of this equipment.
1.1 Operators Qualifications
Only qualified, knowledgeable persons should be permitted to or attempt to operate this test
equipment. All testing personnel should fully familiarize themselves with the correct application
and operation of this and all test equipment before operation.
The measurements should never perform by only one operator without the presence of other
personnel or supervisors. Someone else other than the main operator must be aware and easily
accessible to help in case of an emergency.
1.2 High Voltage Apparatus Accessibility During the Tests
Persons directly and indirectly engaged in the operation of this test equipment should keep
clear of all high voltage apparatus while conducting tests and measurements. A barrier band
must always use so the test object under the test is not accessible to any person during the test.
1.3 Ground the Instrument
The power cord supplied with the equipment must be connected to an electrical receptacle with
an electrically grounded terminal (earthed ground). To minimize shock hazards, the ground
terminal on the instrument must be properly connected to the earth point. In many cases, the
quality of the safety ground terminal provided by the power cord does not fulfil the safety
requirements.
Never connect the instrument to an energized transformer!
WARNING!
Non-grounded instruments are dangerous and may cause damage to
personnel and to the instrument.
WARNING!

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Preliminary
1.4 Before Applying Power
Read this manual carefully before operating the system. The instrument is line operated. The
system is designed to be used with either 110VAC or 230VAC 50/60 Hz. The system performs
a self-check each time it is powered on.
1.5 Keep Away from Live Circuits
Operating personnel must not remove instrument covers. Component replacement and internal
repairs must be made by qualified service personnel. Do not replace components or service this
instrument with the power cable connected. To avoid injuries, always discharge circuits,
disconnect power and remove external voltage sources before touching components.
1.6 Do Not Operate in An Explosive Atmosphere
Do not operate the instrument in the presence of flammable gases or fumes.
1.7 Do Not Substitute Parts or Modify Instrument
Because of the danger of introducing additional hazards, do not install substitute parts or
perform any unauthorized modification to the instrument. Return the instrument to a Raytech
service department for service to ensure proper operation and that safety features are
maintained.
Instruments, which appear damaged or defective, should be made inoperative and secured
against unintended operation until they can be repaired by qualified service personnel.
1.8 Do Not Operate in A Condensing Humidity or Under Rain
Operating the instrument in condensing humidity or under the rain can introduce an electric
shock hazard for the user and also can damage the instrument. This instrument is not supposed
to be installed permanently outdoor.
1.9 Always Keep Distance from the Test Object During the Tests
During performing the tests, there may be a hazardous voltage at the terminals of the test
object. Always keep a distance of a minimum of 1.5m from the test object. The unsafe area
must be specified and restricted with barrier tapes or ropes like Figure 1. Enter the area only
when not testing and when the instrument shows that there is no output voltage which is
specified when the green light indicator on the front panel is on.

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Preliminary
Figure 1: The unsafe area must be specified and restricted with barrier tapes or ropes
Always keep distance from the test object during the tests and the
unsafe area must be specified and restricted with barrier tapes or
ropes
WARNING!

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Preliminary
2 Unpacking
The Instrument
Cable Bags
Measuring Cables H (H0-H3)
Measuring Cables X (X0-X3)
Safety Ground Cable
Power Cord
Spare Paper rolls & Fuses
USB Memory Stick
Instruction Manual (Pre.)

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Preliminary
3 Introduction
The Raytech precision mini–Automatic Transformer Observation System (mini-ATOS) is a
professional multifunctional power transformer and substation diagnosing test instrument
developed by Raytech engineers. It is designed for a high degree of accuracy and ease of use.
This compact and intelligent instrument can perform many routines and advanced tests such as
Winding Resistance (WR), Dynamic Resistance Measurement (DRM), Turns Ratio (TR),
Frequency Response of Stray Losses (FRSL), Magnetic Balance, and other diagnostic
parameters. With the built-in fully automatic multiplexer, only a one-time connection is required for
nearly all functions which saves a considerable amount of time. The portable, rugged case is
perfect for use anywhere onsite or in a laboratory. It is specially designed for fast and easy
measurements with the well-known high precision and quality of all Raytech instruments.
The mini-ATOS field case is a waterproof design (IP67). A pressure
regulator activates when the case is opened to compensate for
atmospheric pressure changes.
INFO:

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Preliminary
4 Calculation and Measurement Methods
4.1 Turns Ratio Measurement
4.1.1 Principle
The transformer turns ratio test is used for measuring the ratio of turns of wires of the two sets of
windings e.g., the primary side and the secondary side of a transformer. The turns ratio test does
not tell exactly how many turns of wire are in each coil, but rather, it measures and displays the
ratio of the number of turns of two coils.
This is a useful test to check for shorted turns and also to find probable incorrect settings of tap
changers during manufacturing or repairing.
The mini-ATOS performs the turns ratio by applying voltage on the high voltage side of each phase
and measuring the applied voltage and transformed voltage. Figure 2 represents the very simple
schematic of the measuring circuit.
Figure 2: Very simple schematic of mini-ATOS turns ratio measuring circuit
The excitation current is also measured during the turns ratio test. The value of the excitation
current has a direct relation to the test voltages. A higher test voltage leads to a higher excitation
current. Additionally, the phase angle between the applied voltage and the transformed voltage is
also measured and is included in the results.
4.1.2 Voltage Ratio and Turns Ratio
It is important to understand the differences between transformer voltage ratio and transformer
turns ratio. The voltage ratio is the ratio of rated voltages of two windings but the turns ratio is
exactly the ratio of the number of turns of two sets of windings. For a single-phase Transformer,
the Turns Ratio is the same as the Voltage Ratio, however for a three-phase transformer they may
be different.
As an example, consider a single-phase transformer schematic with a primary side and a
secondary side. The primary side nominal voltage which is written on the nameplate is 6900V and
from the manufacturing data, we know it consists of 15000 turns. And secondary side nominal

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Preliminary
voltage written on the nameplate is 230V which consists of 500 turns from manufacturing data. The
following equations are valid:
 
  
 
  

With three-phase transformers of different configurations, turns ratio and voltage ratio can be
different.
Figure 3: Three-phase transformer schematic with Dyn11 vector group
For example, Figure 3 shows a three-phase transformer schematic with a delta connection on the
primary and star connection on the secondary side. 120000V and 20000V are written as primary
and secondary rated voltages respectively on the nameplate. The rated values are always line-line
voltages and the voltage ratio can simply calculate as follow:
 
  
Here, turns ratio is different from the voltage ratio because the low voltage side connection is star
and line-line rated voltage is different from the phase voltage. So, a factor of is required as
follow to calculated the nominal turns ratio:

When we know the number of turns from the manufacturing data, the turns ratio can be calculated
directly. Consider that for the current example the number of turns is 93531and 9000 for each
primary and secondary winding respectively. The following equations are valid:
 
  

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Preliminary

 
4.1.3 Relative Error
Turns ratio error can be calculated by comparison of the measured value and the reference rated
value using the following formula:
󰇟󰇠 
 
The calculated error can be compared with a limit value. Generally, there are limit values for the
turns ratio relative error. A typical limit value according to IEEE C57.12.00-2010 is 0.5%. This limit
value can be used to judge if the test is passed or failed.

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Preliminary
4.2 DC Resistance Test
4.2.1 Principle
The winding DC resistance test is one of the most important tests. Many power transformer faults
such as shorted turns, tap changer problems and loose connections can be detected.
Figure 4 represents the summarized winding resistance measurement circuit of the mini-ATOS. It
utilizes the 4-wire measuring technique for each measurement. 2 wires to inject current and 2 wires
to measure voltage. The test measuring cables and clamps are Kelvin type which means that the
user does not have to hook up separately additional cables to the transformer for measuring.
Figure 4: Summarized schematic of mini-ATOS winding resistance measuring circuit
The mini-ATOS has two power supplies with the same output power which can be used to
measure both high and low voltage side winding simultaneously.
The maximum output voltage and current of each power supply are different to provide optimal
output for each side. One power supply has more output voltage which is suitable for the high
voltage side with a bigger resistance and the other one has more output current which is suitable
for the low voltage side with a smaller resistance.
During the measurement, because of the high inductivity, the core and winding must be charged
and only after charging, stable and accurate measuring is possible. The following equation
represents the relation between the current injected into the winding, 󰇛󰇜, and the voltage drop
value, 󰇛󰇜, across the winding. is the winding resistance value that is aimed to be measured
and is the equivalent value of the inductivity.
󰇛󰇜󰇛󰇜󰇛󰇜

The voltage drop value consists of two parts; the first part is the voltage drop because of the
resistance, and the second part is the voltage drop because of the inductivity. After charging, the
second part tends to zero and then the Resistance value can be calculated:
󰇛󰇜
  
󰇛󰇜󰇛󰇜 


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Preliminary
The mini-ATOS winding resistance circuit is also equipped with heavy-duty discharge circuits that
are very unique in design to dissipate the stored energy in the transformer windings.
4.2.2 Temperature Correction
The DC resistance measured values can be corrected to the desired reference values by
employing the following equation based on IEEE C57.12.90:


Where: 󰇟󰇠
󰇟󰇠
󰇟󰇠
󰇟󰇠
󰇟󰇠
Temperature constant values for copper and aluminum are :
Table 1: Cu and Alu temperature correction values
Material
󰇟󰇠
Copper
234.5
Aluminum
225
Alloyed aluminum
Can be up to 230
The other form of temperature correction formula is:
󰇛󰇛󰇜󰇜
Where: 
and have the following relationship:

 󰇛󰇜
For example, by considering that the value of for copper is 0.00393 at 20°C, is:

󰇛󰇜

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Preliminary
4.2.3 Resistance Deviation
For a 3-phase test object, the DC resistance values of each phase are supposed to be almost the
same. Hence, it is possible to measure a deviation value from the average value for each phase as
follows:
󰇟󰇠

󰇟󰇠
 
󰇟󰇠
 
󰇟󰇠
 
The calculated deviations can be compared to a maximum deviation limit value to find out if the
result is passed or failed. There is a limit in IEEE C57.12.152-2013, which is 2%. However other
values are also possible with agreements.
Please note that if the temperature of phases is not the same during the resistance measurements,
the deviation values may be higher. In this case, it is better to calculate the deviation values of the
temperature-corrected resistances.

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Preliminary
4.3 Demagnetization
After transformer shutdown or a measurement with a direct current, there is always residual
magnetism or remanence in the transformer magnetic core. There are various reasons that this
remanence should be removed. One reason is that energizing a transformer with remanence can
cause a much higher inrush current and this may cause deformation of the winding. The other
reason is that the remanence will affect the results of some tests such as SFRA, magnetic balance
and excitation current, which may lead to a wrong diagnosis.
The mini-ATOS includes a very efficient, fast and modern demagnetization feature. During the
demagnetization, all important parameters are measured, calculated and monitored continuously
and each cycle of the demagnetizing is adjusted and performed according to the previous cycles.
Figure 5: A) A real example of a demagnetization with mini-ATOS. B) Closer look at the same curve in A.

90297-0.24 Instruction Manual mini-ATOS
Page 18 of 125
Preliminary
Figure 5-A shows an actual example of a hysteresis curve during demagnetization which is
performed using the mini-ATOS. Figure 5-B is a closer look at the same curve. The depicted
parameters are described below:
- 󰇟󰇠: Magnetic flux with the unit of volt-seconds or weber. It will be measured as integral
of the inductive part voltage over time. The value of the Vs is related directly to the
magnetic flux density with the unit of tesla, by considering that the cross-section area of the
transformer magnetic core is a constant value:

 

- 󰇛󰇜: Magnetic field strength with the unit of ampereturn/meter. The number of the
turns and length of the magnetic path is usually unknown but since they are constant
values, the magnetic field strength is in direct relation to the injected current to the winding
which can be measured directly:

 


- : Maximum positive or negative flux at saturation point
- : The initial value of the residual magnetism flux or remanence flux before
demagnetization
- : The final value of the remanence flux after performing the demagnetization
- : Maximum positive or negative remanence flux remains in the magnetic core which
is normally happened after saturation.
4.3.1 Raytech SPP Demagnetization Method
To achieve a very small residual magnetism, the mini-ATOS use a special method to perform the
final cycles of the demagnetization, called SPP, Smart Pattern Predictor, which is based on pattern
recognition. This is very useful when special measurements like SFRA are desired to perform.
This method recognizes the properties and shape of the demagnetization of previous cycles to
achieve a very small remanence, the shape and properties of the final cycles are predicted and
then the final cycles will be performed in a way to achieve the best and the smallest possible
residual magnetism state.
4.3.2 Three-Phase Transformer Demagnetization
For a core-type three-phase transformer with three limbs, the demagnetization is usually performed
from the middle phase. Many times, it is enough to achieve a safe residual magnetism state to
connect the transformer to the power grid without the risk of high inrush current. However, it is not
always like this. Sometimes the demagnetization should be performed from all three phases. The
following items can be a reason to consider a three-phase demagnetization:
- When the core consists of 4 limbs or 5 limbs
- When the transformer is a shell-type
- When the aim is to achieve a very small residual magnetism to perform special tests like
SFRA
The mini-ATOS can use the advantage of the automatic multiplexer to perform demagnetization
from each phase automatically and without changing the connection setup.

90297-0.24 Instruction Manual mini-ATOS
Page 19 of 125
Preliminary
4.4 Magnetic Balance
Raytech mini-ATOS performs the magnetic balance test by applying AC voltage on each winding
of the three-phase transformer from the high voltage side and measuring induced voltage into
other windings on the same side. The applied voltage produces magnetic flux in the core which is
distributed to other parts of the core and induces a voltage into other windings. Any problem or
fault in the magnetic core may change the distribution of flux.
For a healthy core-type transformer with a demagnetized 3 limb core, the magnetic balance test
results should be in the form of Table 2:
Table 2: Typical magnetic balance pattern of a core-type transformer with 3 limbs
Phase




 
 
 

 
 
 

 
 
 
The sum of and should be almost and it is supposed to be greater than :
 
The index TCI [%], Transformer Core Imbalance, introduced by Raytech for easy diagnosing of
magnetic balance test results. It is calculated using the following formula:
󰇟󰇠󰇧 
          󰇨 
Please note that when the core is not fully demagnetized, the TCI value may be high. For a correct
magnetic balance test, it is highly recommended to always demagnetize the core beforehand. On
the other hand, by performing the magnetic balance test, it is possible to find out if the transformer
core is demagnetized or not.
miniATOS uses 10Hz as test voltage frequency. The reason why is at low frequencies, the flux
distribution is less affected from the stray capacitances and so it is better for magnetic circuit
diagnosis.

90297-0.24 Instruction Manual mini-ATOS
Page 20 of 125
Preliminary
4.5 Short Circuit Impedance
4.5.1 Principle
The short-circuit impedance/leakage reactance test is helpful in detecting mechanical deformations
in the windings. It is performed by applying AC voltage to each phase on the primary side while
shorting the circuit on the other side. The performed voltage, injected current, and phase difference
will be measured. From the measured values, the short-circuit impedance, leakage reactance, and
AC resistance will be calculated:
󰇟󰇠
󰇛󰇜󰇟󰇠
Where: 




The equivalent three phases short circuit impedance, AC resistance and leakage reactance will be
calculated as follows:
󰇟󰇠
󰇛  󰇜
󰇛 󰇜󰇟󰇠
With the Nominal voltage and base power, it is also possible to calculate the values in percents:
  

󰇟󰇠󰇟󰇠
 
󰇟󰇠󰇟󰇠
 
󰇟󰇠󰇟󰇠
 