［ Systems・Components ］

Monitoring and Diagnostic
Systems for Power Receivingand Substation Facilities
Keywords

Tomoyuki Kawano

IoT, CBM, Facility diagnosis, Remaining life assessment, Forerunning fault, Partial discharge detection

Abstract

For the laborsaving and upgrading of maintenance service for power receiving and substation facilities such as oil-immersed power transformers andswitchgears, we have been promoting the technical development of cloud-based
remote monitoring systems and facility diagnostic systems to be applied tothese power receiving and substation facilities by utilizing Internet of Things(IoT) devices. In this approach, various sensors for current, vibration, transient
earth voltage, and others are installed in substation equipment and sensor terminals like Partial Discharge (PD) detectors are used to detect the PD which isan early sign phenomenon of equipment insulation breakdown. Using such sensors and terminal devices, the status of equipment and facilities is always monitored to grasp any early sign of an anomaly and to diagnose the abnormality. In
addition, based on the quantitative data acquired in the past, we can support
maintenance routines such as daily inspections, repair services, and facility renovation planning and can streamline the facility management.

1 Preface
Ultra-high-voltage and high-voltage powerreceiving and substation facilities consist mostly ofpower transformers, circuit breakers, and switchgears. These products support the stability and reliability of power supply. Recently, however, longer
product life has been considered more important
than facility renovation; as a matter of course,
aged facilities are increasing. In the conventional
maintenance and inspection service, Time Based
Maintenance (TBM) was carried out for which periodical maintenance actions are taken at the predetermined period for the purposes of laborsaving,streamlining of processes, and the reduction rate ofmalfunction occurrence.
Lately, however, the TBM tends to shift toCondition Based Maintenance (CBM) where a trend
leading to deterioration and maintenance service isalways monitored and carried out shortly before theoccurrence of a malfunction, only if maintenance isdetermined necessary.
Under such circumstances, we followed thesigniﬁcance of CBM and developed facility diagnostic systems by utilizing Internet of Things (IoT) devices. This paper introduces sensor terminals in-stalled in power transformers, and switchgears in
the power receiving and substation facilities, including the functions of our cloud services.

2 Outline of Facility Diagnostic
Systems and Merits of Introduction
Fig. 1 shows an outline of cloud-based facility
diagnostic system (“this system” hereafter). Thissystem is used to collect ﬁeld telemetry data fromvarious sensors installed in power receiving andsubstation equipment such as power transformers
and switchgears so that the conditions of facility
operation can be continually monitored from aremote site. In addition, it can detect an anomaly
and grasp the early sign of it through the analysis ofoperational data accumulated in the cloud. Still
more, additional cloud services are available, suchas functions that support facility operation andmaintenance, diagnostic report, and remaining life
assessment. It realizes the most effective life cycle
cost for facilities. Advantages available as a result ofintroduction of this system are as follows:( 1) Real-time monitoring of facility conditions
Conventionally, a visual check was carried out
to obtain the ﬁeld data, such as the number ofMEIDEN REVIEW Series No.181 2021 No.1

39

Cloud services

Remote monitor

System run andmaintenancecontrol support

Facility diagnostic
reportRemaininglife prediction

Smart device
Information security

Facility diagnostic algorithm
Monitor・diagnosis

Maintenance・inspection data

Data center

Online and real-time sign diagnosis
・Machine learning, AI technology
・Sign detection, remaining life assessment
Foregoing data processing
Frequency analysis
Specific data extraction

Monitor control equipment
Maintenance terminalSensor terminal

Sensor

Dissolved Transient
Vibration
gas in oil Earth Voltage(TEV)

Current・PD detector
・Communication terminal
・Substation facility monitor unit, etc.

Temperature

Imageetc.

Generator

Lightningarrester

Facilities on sitePowertransformerFig. 1Switchgear

High-tension
panel

Outline of Cloud-Based Facility Diagnostic System

An outline of cloud services and a facility diagnostic system is shown.

equipment operations, temperatures, and otherreadouts in order to grasp the trend of equipment
deterioration at the time of the periodic inspection.
After going online, however, the status of facility
operation can be checked at any location and timethrough the cloud.
( 2 ) Prevention of failures
In the case of conventional monthly and yearly
periodic inspections, any early sign of an anomaly
phenomenon occurring in the middle of the previous
and next inspection periods could not be discovered until the next inspection begins. When this system is introduced, however, it is possible to prevent
failures by making trend checks and analysis into
the measured data from facilities to identify earlysigns of anomaly phenomena at an early stage.
( 3 ) Auto-computation of remaining life
For the remaining life of a power transformer,
switchgear, or such facility equipment, this system
makes auto-computation once every day. Thanks tothis function, labor hours for conventional routines
by manual computation can be saved.
( 4 ) Measures taken against lack of technical staff
Regarding the lack of young engineers due tothe declining birthrate and retirement of skilled andwell-experienced engineers who can make an accurate grasp of facility conditions through expertise,

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MEIDEN REVIEW Series No.181 2021 No.1

there are concerns on how to pass on such expertise to the up and coming generation. When thissystem is introduced, it is then possible to support
favorable succession of techniques because thesystem can make quantitative data analysis so thatthe result of analysis can be used for visualization offacility conditions.

3 Facility Diagnosis for Power
Transformers
Fig. 2 shows the monitoring and measuring ofitems for power transformers and Table 1 shows anexample of deterioration phenomena found in oilimmersed transformers. Based on the result of
past investigation into deterioration phenomena
and abundant expertise we nurtured through many
maintenance service businesses, we selected thebasic monitoring and measuring items for powertransformers, such as load current, insulation oillevel, oil temperature, vibration of fans and pumps,
ambient temperature, and Partial Discharges (PDs).
The diagnostic functions cover transformer remaining life diagnosis, transformer condition diagnosis,
and diagnosis for fans and pumps. Fig. 3 shows atransformer diagnostic screen.

3.1 Remaining Life Diagnosis for Power
Transformers

Transformer monitoring system

Remote monitoring
Load current

CT

Oil level andtemperature

CameraTap-changer

DI

Fans and pumps

Vibration sensor

Insulation oil

Gas in oil analyzer

Ambient temperature

Camera and thermistor

PDPD detector and transient
earth voltage sensor

Surface temperature

Thermo-camera

Diagnostic functions
Transformer remaining life diagnosis
Transformer condition diagnosis
Fans/pumps diagnosis

Fig. 2

Monitoring and Measuring of Items for PowerTransformers

Monitoring and measuring of items for transformer facilities areshown.

Fig. 4 shows the remaining life diagnostic
algorithm for power transformers. The remaining life
is estimated in the comprehensive consideration of
three kinds of data shown below.
( 1) Operating conditions
Initial setting values are the years of operation,
daily operating conditions (load factor), insulation oil
temperature, various measured data and coolingsystem in installation area and environment, and oil
deterioration inhibition system.
( 2 ) Concentration
Measured values of carbon monoxide (CO)and carbon dioxide (CO2) acquired by the in-oil gas
analyzer.
( 3 ) Result of furfural analysis
Furfural is a substance dissolved from an insulation oil caused by the decomposition of deterioration generated from cellulose molecules contained
in insulation paper. Data is entered based on theresult of oil sampling and composition analysis doneat the time of yearly inspection.

3.2 Transformer Health Condition Judgment

Fig. 3

Transformer Diagnostic Screen

Measured values and present status values monitored inside thetransformer are displayed in detail.

The condition of a transformer interior can bechecked only at the time of component analysis
realized by oil sampling that is carried out during ayearly inspection, or in an overhaul inspection. In
any event, conditions of deterioration can be conﬁrmed only at the time of inspection done once ayear. To attain a better solution, we devised to enable
online gas analysis so that the inner condition canTable 1 Example of Deterioration Phenomena Found in Oil-Immersed Transformers
Outlined phenomena caused by internal deterioration in transformer tank (outline of deteriorated parts, deterioration phenomena, anddefects) are shown.
Classification
CracksPartBushing

Deterioration phenomena

Outlined defects

Generation of PD due to cracks around the Acetylene is generated due to the occurrence of feeble disshield in oil
charge caused by concentration of stresses around the rivetof mounting terminal of the shield in oil triggered by vibration
during many years of use.

Quality change CoilInsulation paper damage and insulation
Insulation paper is damaged as a result of secular deteriorationand destruction insulations breakdown due to temperature rise in coils in the vicinity of upper end lead-out of coils, and partial conduction is caused among parallel conductors.
Deformation

Insulationmaterialsof coils

As a result of generation of repeatedmechanical force, deformation and insulation breakdown are caused in insulationmaterials of coils.

Due to the repetition of external short-circuiting, buckling
deformation is caused in tap coil insulation. This has led toinsulation breakdown as a result of abrasion against neighboring coils.

Frictional wear

Oil transfer Unusual sound is generated due to friction- Unusual sound is generated in the vicinity of the bearings of thepump
al wear caused around the bearings of the oil transfer pump.
oil transfer pump.

Quality change

Oil transfer Insulation breakdown is caused due toPump motor is burned out due to insulation breakdown of thepump
thermal deterioration in the winding insula- insulation varnish used for the windings of the oil transfer pumption shield of the oil transfer pump motor.
motor as a result of secular deterioration.

※Partial excerpt from Journal of Electric Technology Research Association, Volume 61, No.3, “Sophistication of Deterioration Maintenance Technology for Enclosed
Substation Facilities”

MEIDEN REVIEW Series No.181 2021 No.1

41

Load
factorEquivalent loadfactor calculation
Operatingtemperature
calculation

Operating condition

Temperature at
installation site

Estimated polymerization degree

Winding temperature rise value/loss ratio (test data)

Conversion into estimated remaining life value

Years of operation

Overall judgment

Cooling system
Oil temperature
Oil deterioration inhibition systemConcentration

Amount of water content

CO ＋ CO2

FurfuralAmount of furfural

Conversion intoamount per unit
weight of insulation
paper

Volume of insulation paper/
Amount of insulation oilCompensation
for deaeration
treatment

History of deaeration treatment

Fig. 4

Remaining Life Diagnostic Algorithm for Power Transformers

Various data like operating condition, gas concentration, and furfural are comprehensively examined for the estimation of deterioration
status and remaining life diagnosis.

be presumed. Parameters effective to make healthcondition judgment are methane (CH4), acetylene(C2H2), and ethylene (C2H4). With these parameters,
it is possible to predict and detect a phenomenon(such as PD, thermal damage〈700℃ or above〉)
caused inside the transformer tank according to thecontent rate of each element. For this health condition judgment, we adopt the Duval Triangle (generally used for transformer health condition judgment)
as shown in Fig. 5.

80
43.7％
60
CH4,
Methane
40Cooling fans and oil transfer pumps are auxiliary machines for power transformers used to compose a cooling mechanism intended to remove heatgeneration from transformers. If these machines areout of order, transformer coils and insulations may
be subject to deterioration or ignition due to heatgeneration. In such a case, we cannot help suspending the operation of transformers.
For diagnostic service for fans and pumps,vibration sensors are newly installed. When thevibration amplitude exceeds the speciﬁed limit level,
the changing rate is calculated with the use of amoving average function based on the past data so42MEIDEN REVIEW Series No.181 2021 No.1

Low-energy discharge

4060208060
20400.0％ C2H2, AcetyleneFig. 53.3 Remaining Life Assessment for Fansand Pumps

PD

20
56.2％
C2H4,Ethylene

High-energy discharge

80

Temperature anomaly:
300℃＜t ≦700℃

Temperature anomaly
Temperature anomaly:t ≦300℃

Temperature anomaly:
700℃＜tTransformer Health Condition Judgment(Duval Triangle)

Transformer health condition judgment is shown based on composition ratio of gas-in-oil contents.

that the period toward the occurrence of failure(remaining life) is estimated. Fig. 6 shows a fan・pump remaining life diagnostic screen.
Since the cooling fans are duplicated, emergency stoppage does not occur even if a single fanshould fail. In practical management, such a faulty
fan may be replaced after the occurrence of a failure. If a fan failure can be predicted beforehand,
however, it is possible to curtail the number of fans
to be installed and this will lead to compact transformer design.

Fig. 8Fig. 6Fan・Pump Remaining Life Diagnostic Screen

VCB Diagnostic Screen

The present status of the measured values monitored in a VCB
is shown in detail.

The estimated remaining life of fans and pumps is shown.

Switchgear monitoring system

Remote monitoring
No. of VCB operations
Gas leakage
Pole motion time
VI vacuum degree
Ambient temperaturePD
Terminal loosenessCameraGas concentration sensor/camera
CT・DI
VM sensor
Thermistor
PD detector, transient earth
voltage sensor
Thermo-camera

Diagnostic functions
Detection of gas leakage sign
Trend monitoring for VCB pole motion time

Fig. 7

Monitoring and Measuring Items for Switchgears

Fig. 9Substation Equipment Monitor Unit

A monitoring and data-gathering unit is shown. It handles various sensor data acquired from power transformers and switchgears.

Monitoring and measuring items for switchgears for switchgear
diagnosis.

4 Facility Diagnosis for Switchgears
The judgment standard for switchgear maintenance is based on the frequency of circuit breaker
operations. For this reason, a counter readout isrecorded at the time of periodic inspection. In thissystem, pole open/close timing is measured eachtime the circuit breaker functions. Based on trendsof this operation timing, the state of deterioration isidentiﬁed. The pole on-off operation timing can bemeasured in the unit of 0.1 ms based on the period
from the motor starting current to the occurrence ofchange in the behavior of the contact points. Fig. 7shows monitoring and measuring items for switchgears. For remote monitoring items, the number ofcircuit breaker operations, PD, gas leakage, andvacuum degree of Vacuum Interrupter (VI) areselected. For diagnostic functions, the detection offorerunning gas leakage and trend monitoring of
Vacuum Circuit-Breaker (VCB) pole open/close timing can be itemized.
Fig. 8 shows a VCB diagnostic screen. Eachtime the VCB operates, the pole open/close timing
is numerically displayed. Based on the accumulateddata, trend graphs can be displayed.

5 Sensor Terminals
5.1 Monitoring Equipment for Power Receiving and Substation Facilities
Fig. 9 shows an external appearance of substation equipment monitor unit. This unit monitors
and gathers various sensor data of power transformers, switchgears, and high-tension panels.
Signal inputs from this unit are processed and thecollected data are managed on the cloud, relatingthem to the operating time from “ON” time of EDS/
ES and VCB closure control current/trip control curMEIDEN REVIEW Series No.181 2021 No.143

Transient earth
voltage sensor

PD detector

Fig. 10 PD Detector ( TEV Sensor)

Fig. 11 Controller Screen of the PD Detector

The unit shown is used to detect a PD that is an early sign anomaly phenomenon of insulation breakdown.

These screens are used for background noise measurement, PD
detection level setting, and waveform acquisition.

rent up to the completion of contact operation, plus
the ON/OFF status of contact points, so that thesedata can be used for remaining life diagnosis offacility deterioration. Major data to be monitored andcollected are composed of items such as PD, insulation oil temperature, vibration of fans and pumps,and tap-changing positions in the case of powertransformers, and PD, contact point parting time,pole open/close timing, power charging time, andgas pressure for switchgears. By making a setupchange, equipment to be monitored (transformer orswitchgear) can be chosen. The overall size of thisunit is W80 × H220 × D132 mm so that the unit canbe installed in substation equipment by the retroﬁt.

( 4 ) The PD detection periodicity can be identiﬁed
with the aid of software. (Periodic continuity can be
set on the customer side.)( 5 ) The device is provided with waveform acquiring function and Fast Fourier Transform (FFT)
analyzing function.
( 6 ) Irrespective of substation equipment manufacturer, retroﬁt installation is possible. (Size: W150 ×
H52.5 × D226 mm)
Fig. 11 shows a controller screen of the PDdetector.

5.2 PD Detector
For insulation deterioration diagnosis of power
equipment, the detection of PD is effective because
PD is an early sign of anomaly phenomenon leading
to insulation breakdown. PD can be detected bymonitoring the behavior of C2H2 gas, but accuracy islow. As such, we developed an exclusive PD detector where a Transient Earth Voltage (TEV) sensor isused. Fig. 10 shows the PD detector (TEV sensor).
This sensor is capable of noise removal and periodicity judgment of a high-frequency current thatﬂows along the surface of the apparatus. By doing
so, PD is detected. This device is useful for static
type substation equipment such as power transformers, switchgears, and high-tension panels. Itsfeatures are as follows:( 1) A TEV sensor is adopted.
( 2 ) It is provided with a background noise measuring function.
( 3 ) The PD detection level can be arbitrarily set oncustomer side.

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6 Postscript
This paper introduced our activities about facility diagnosis of oil-immersed power transformers
and switchgears. For maintenance and inspection
jobs for power receiving and substation facilities, byusing our diagnostic technologies, it can realize
more labor saving and advanced level service andcan support facility management works in terms offacility renovation planning.
Going forward, we will continue to develop newsensors and improve accuracies of remaining life
diagnosis through the AI analysis based on themonitored data accumulated in the past. Also, at thesame time, we will expand the application of monitoring objects to molded transformers and otherpower conversion equipment. In doing so, we would
like to establish more elaborated facility diagnosis
technologies.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.