FIELD OF INVENTION
The invention relates to the method of monitoring SF6 gas condition, system primary
parameters such as voltages and currents, equipment’s condition and operation status
together with the auxiliary system voltages and currents of a Gas Insulated Switchgear
using a reliable and modular unit which consists of input & output modules, data
acquisition modules and a processor.
BACKGROUND OF THE INVENTION& PRIOR ART
In a power system, one of the key elements is a high-voltage switchgear. The
switchgear contains numerous types of high-voltage equipment elements such as
circuit-breakers, dis-connectors, earth switches, current and voltage transformers
together with surge arresters. The Gas Insulated Switchgear (GIS) is a better option
when compared to the Air Insulated Switchgear (AIS). The proliferation of the GIS has
been observed on account of its modular, compact and simplicity in structure, better
dielectric properties of SF6 and ability to handle very high voltages upto the range of
about 1200kV. It also offers an economical solution to complex switchgear applications
with high reliability. The GIS is a metal encapsulated switchgear consisting of Voltage
Transformers, Current Transformers, Circuit Breakers, Dis-connectors and Earth
Switches using SF6 gas for insulation.

Encapsulation makes it difficult to check the abnormal conditions and faults in the
components. It is difficult to rectify the faults inside the GIS without fault information
and fault location. On account of an increase in the adaptability of the GIS switchgear
due to its technical feature, the power system becomes more complex while the quality
of power also needs to be improved with the application of new technologies. Hence, a
condition-monitoring equipment will enhance the performance and reliability of a GIS
system by monitoring its critical parameters on-line by acquiring the information
required for diagnosis.
With the increase in demand for GIS station installations and the revolution in the
electronics field, the development of monitoring systems for Power Apparatus has been
started a few years ago. The patents, which already have been filed in this field are as
follows:
US 20110309939A1 describes mainly the monitoring of SF6 gas density, Arc faults’
detection and partial discharge measurement. It does not mention anything about the
monitoring of the GIS equipment information such as the status of breakers, dis-
connectors & earth switches together with motor currents’ monitoring while it also does
not mention anything about the number of SF6 gas chambers that can be monitored
using this monitoring unit. The invention does not describe the technique about the
monitoring of circuit breaker parameters such as contact travel time, operating times,
contact wear and cumulative breaking-current measurement.

US 20140028324A1 is applicable only for Cubicle Type gas insulated switchgear consists
of a Circuit Breaker and a Bushing, which is used in the distribution system. This
invention speaks about the GIS switchgear assembly i.e. the breaker mechanism, its
operation and the sensors which are mounted on it. There are two units in which one is
a Slave-data acquisition unit connected to the Switchgear Unit and a Master-data unit,
which is interfaced to a number of Slave-data units. The Master-data acquisition system
(M-DAS) determines the deterioration and analysis of the data received from Slave-data
acquisition systems(S-DAS). This mainly performs analysis for the breaker-operation
times together with its coil (coil pressure sensor) continuity, gas pressure (sensor),
partial discharge (sensor) and contact-travel (stroke sensor) distance.
US 20150308938A1 comprises the measurement of Gas density, trends of gas density,
temperature at different points on the surface of a gas chamber, ambient temperature,
atmospheric pressure, atmospheric sound levels and also the electrical conditions such
as AC & DC voltages and currents. This invention mainly focused on the algorithm of
measurement of gas pressure in a Gas Insulated Switchgear chamber. The input
channels capability for reading sensors’ data is limited and the developed-GUI mainly
describes the trends of a gas pressure with the respective time and temperature. In this
invention, no information has been mentioned about the multiple chamber
measurements, other GIS equipment monitoring while there is no mention about the
breaker parameters’ monitoring such as operating times, contact wear also.

EP2820731B1 discloses the gas insulator switchgear SF6 pressure monitoring has been
presented and it also gives the information about monitoring of the primary current. It
also mention about pre- and post-discharge current with the respective gas pressures
to monitor the faults inside the gas insulated switchgear compartment. This invention
presents only the current and SF6 gas pressure monitoring at a given frequency in a
graphical manner, which also enables the determination of the rate of change in the
current amplitude with respect to time (di/dt) in between two successive
measurements. If the current slope value exceeds the reference value it gives an alarm.
Similarly, if the pressure level with respect to the reference values drops to the level
limits, it gives an alarm. In this invention, the ambient temperature has been measured
and if it goes out of pre-defined range it disables the ‘generation of alarm’.
JP2008022670A describes the methodology for the monitoring of the Gas Insulator
Switchgear system. In this method, the monitoring of the gas insulated switchgear
status has been done through the remote monitoring system. The architecture of this
invention consists of a sensor unit, a signal-processing (monitoring) unit, central
processing unit and a remote monitoring system. The monitored data or fault
diagnostics data is transferred to the remote monitoring system through the
HTTP/SMTP protocol. In this technique, each signal-processing (monitoring) unit has
been implemented using a single processor and this unit is interfaced with another
processor unit to enable communication to the remote GUI computer system. This

method/realization of implementation may be expensive to monitor the complete GIS
system.
OBJECTS OF THE INVENTION
The main objective of this invention is that a reliable, modularized unit should be
provided to monitor the condition of a Gas Insulated Switchgear and its equipment
status, and the auxiliary system parameters.
This invention describes the various analog & digital signals’ data acquisition, hardware
filtering architecture, the method of interfacing with the processor board and also the
communication with the remote GUI system.
This invention also includes the objective of monitoring of SF6 gas pressure of all
chambers, ambient temperature, primary system voltages & currents, operating times &
status of switchgear equipment while including the monitoring of the auxiliary system
parameters for a complete GIS bay using a single-processor board. This also describes
the manner of visualizing/displaying the above parameters on a Graphical User
Interface.
Another objective of this invention is that the method should determine the breaker
operating times such as contact-travel distance, velocity, open-time, break-time, close-
time, make-time, arcing and pre-arcing times.

SUMMARY OF THE INVENTION
This invention proposes the unique modular hardware architecture which consists of the
input and output modules, the filtering module, the data acquisition & signal-processing
module which is required for monitoring the condition of a single-bay GIS system.
These modules are housed in a 19” EMI/EMC compliant rack. An embedded-processor
module has the communication capability to interact with the graphic user interface
module. The field signals’ data acquisition, monitoring and measuring functions are
realized on the embedded-processor module while suitable add-on modules are used to
enhance the analog signal-handling capability of the unit. Algorithms have been
implemented in real-time functioning for data acquisition, filtering, measurements and
analytical functions such as breaker operation-times’ computation, Contact wear,
Cumulative breaking current and control of spring-charging motor currents. In-built
software features of the embedded-processor had been used extensively to implement
critical functions with various cycle durations, which are required for successfully
monitoring the GIS. The standard communication protocols have been implemented to
communicate with the Local & Remote HMI for user interaction.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 depicts the Hardware Architecture of the GIS Monitoring System

Figure 2 depicts the Interconnection scheme of the I/O modules and the Processor
module
Figure 3 describes the Circuit Breaker Operation Time calculation during ‘Open’
operation in the form of a flow chart
Figure 4 describes the Circuit Breaker Operation Time calculation during ‘Close’
operation in the form of a flow chart
Figure 5 presents the Circuit Breaker primary current, contact’s travel-distance,
open coil current and close DI signal status trends during ‘Open’ operation
Figure 6 presents the Circuit Breaker primary current, contact’s travel-distance,
close coil current and close DI signal status trends during ‘Close’ operation
Figure 7 describes the methodology for measuring Contact Wear of a Circuit
Breaker in the form of a flow chart
Figure 8 describes the methodology for measuring Cumulative Breaking Current of
a Circuit breaker in the form of a flow chart
Figure 9 describes the methodology to control the spring-charging Motor Current of
a Circuit Breaker in the form of flow chart

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
The Modular GIS Monitoring System [100] as presented in Figure 1, consists of input
and output modules such as Digital input & output modules [103], Isolator modules
[104], Current Transformer & Potential Transformer (CTPT) modules [106] together
with a Filter Module [105] to attenuate un desirable frequency signals, which get
superimposed on the power frequency signals, and a processor module [101] along
with Analog add-on modules [102] for data acquisition, digital filtering and analytical
functions.
The Architecture of various modules’ placement in a unit is shown in Figure 1.
The [106] Module acquires the field inputs viz. currents & voltages in the form of
analog signals in the range of 63.5V/110V or 1A /5A. The field inputs consist of AC and
DC types. These inputs must be stepped down to a level acceptable to the processor
circuit, which is done by means of current transformers & potential transformers in case
of AC voltages and AC/DC currents, which are PCB-mountable type instrument
transformers. The field DC voltage signals (Battery bank voltages) are stepped down by
using a resistor divider circuit. The current transformer used here is a Hall-Effect
transformer, which can handle both AC & DC signals. The current signals from the
current transformer are converted into voltage signals by using suitable resistors. Since

the processor can operate only in the digital domain, these field inputs need to be
converted into digital data using the 16-bit A/D conversion circuit, whose input ranges
are ±10V. This transformation of the field inputs must be very precise to avoid any
error in the finally computed values. Since the equipment is expected to operate in the
most harsh environment under severe fault conditions it is very essential to protect the
system from high voltage & high frequency noise entering the system either by
conduction or radiation. A pre-filtering circuit consisting of an Inductor & Capacitor (LC)
circuit is provided on the primary side of the instrument transformer for this purpose. In
addition, a Metal Oxide Varistor (MOV) is also used to protect from voltage surges. The
cut-off frequency for the LC pre-filtering circuit is set so as to bypass all the high
frequency signals. The low voltage dc signal (obtained from Battery bank) is also
provided for isolation from noise before feeding it to the A/D converter using an op-amp
circuit.
The [105] Module main function is to attenuate the undesirable harmonics, which may
even pass through the [106] module before reaching the A/D converter. Each channel
of this filter module is built up of the following stages:
o A non-inverting unity gain amplifier for providing high input impedance to
minimize loading on the CT.
o A scale-changer for amplitude correction.
o A phase-correction circuit.
o A second-order low-pass chebyshev filter.

The field signal that reaches the [106] module is free of high-frequency signals before
being fed into the [105] module, some undesirable harmonics that may pass through
the [106] module get attenuated on the [105] module. The desired amplification is
also available on the [105] module to facilitate the scaling of the input to the A/D
converter. This data is then processed by the [101] module according to an algorithm.
The results of this processing are used for metering & analytical purposes.
The [104] Module, whose main function is to provide the high-voltage isolation
between the input & out terminals while regenerating the input signal at the output
terminals. The inputs to this module are 4-20 mA signals coming from various sensors
passes through a PCB mountable isolator, which uses as isolation amplifier, where the
signal is isolated and regenerated at the output terminals as 4-20 mA signal. This 4-
20mA signal is converted into a voltage signal by employing resistors of suitable ratings.
This voltage is fed into an A/D converter for further processing by the microprocessor.
The [103] modules concerned with monitoring of the binary states of the large number
of switches associated with the status of the switchgear. The status of the switches,
which need to be monitored in the GIS consist of circuit breaker open/close status, dis-
connector open/close status, earth switches open/close status, spring charge status
among others. The status signals originating from switches is either 0Vdc or 220Vdc.
When the switch is open a 0Vdc voltage is available and when it closes the voltage
available is 220Vdc. In such a situation, where the field and monitoring

equipment are at very different voltage levels, the link between the two is preferably
optically isolated, to protect the monitoring equipment hardware from over-voltage
damage. The Optical isolation is necessary to provide isolation between the 220 Vdc in
the field and the 5 Vdc at the micro-processor input. Digital outputs utilizes the TTL
level signal from the processor to drive the optically-isolated relay on the output side,
which can be used for switching ON or OFF for circuit such as spring-charging motor.
The rating of this output is decided by the application to which it is connected.
The [102] modules have been used to fulfill the requirement of enhanced Analog signal
handling capability of the [100] unit.
The [101] module has been used to implement digital signal processing and analytical
functions, and also used to realized communication protocols, which are required to
communicate to Local as well as remote GUI system.
The [107] module has an input 230Vac/220Vdc of the standard value and the desired
24 Vdc was derived from the module, which is fed an input to the other modules in
need of it.
The inter-connection of the modules for the respective functions are as shown in Figure
2. A local touch-screen Human-Machine Interface (HMI) terminal [108] facilitates the
design & configuration of all the parameters of the system, which is interfaced with the

processor board. This [108] is intelligent and programmable, operating in an
embedded WIN CE environment. The Remote HMI [201], realized in PC provides
communication with the [100] over an Ethernet Cable using TCP/IP Communication
Protocol.
The operator can view various parameters through the display on-line and can edit
settings using the touch-screen tabs. Alarms and Event records can be read from the
front panel of the graphic display which can be used in post-fault analysis. All the
records are stored in a cyclic buffer for viewing at a later time.
A typical Modular GIS Monitoring System [100] Configured for a single GIS bay is as
follows:
> Three nos. of [106] modules, each of which caters to 1 AC voltage (63.5V), 3
DC voltages and 12 AC/DC current channels.
> Two nos. of [104] modules, each of which caters to 16 channels.
> Two nos. of [103] modules, each of which caters to 18 no’s of digital input
channels and 4 nos. of digital output channels.
> One [105] module, which caters to 16 no’s of low-frequency filter channels.
> One [101] module, having a Central Processor Unit (CPU) of 1.6GHz, RTC and
battery-backed RAM.

> Three Analog add-on PC104 [102]modules, each of which has 16 nos. of Analog
input channels, 4 nos. of Analog output channels, 8 nos. of Digital input channels
and 8 nos. of Digital output channels.
> A Universal power supply [107] module, with 230Vac/220Vdc Input and output
voltage of 24Vdc.
> One [201] no. of local touch-screen HMI terminal
Methodology adopted for calculating Circuit Breaker Operation Times
The method for calculating the breaker operating parameters such as open-time, close-
time, break-time make-time, arcing-time, pre-arcing time, and travel speed is depicted
in the flowcharts as shown in Figure 3 and Figure 4. The breaker timing calculations
activity has been realized using the GUI software facility. During the breaker’s ‘open’ or
‘close’ operation, the event recording function gets activated and stores data for a
duration of 250 ms before and after an event. These timing calculations are performed
by using the previously recorded data which is stored in memory. The adopted
methodology for calculating parameters has been confirmed through a Real-Time
testing by interfacing the [100] unit with a 420 kV GIS circuit breaker at the Extra High
Voltage Lab in our campus.
The Circuit Breaker primary current, trip/close coil currents and travel sensor voltages
are monitored by interfacing with the analog I/O module of the [100] unit. Digital

Inputs such as breaker’s ‘open & close’ status are connected to the digital I/O module
of the [100] unit. In the simulation test set-up, the breaker primary current is given as
1 A (rms). The 220 Vdc supply is provided for the open/close contacts’ status and
trip/close coils. The desired voltages and currents are then monitored during the circuit
breaker operation using our Monitoring Unit. The monitored data is fetched and the
plots are generated in the remote GUI.
The breaker parameters’ curves during the ‘open’ operation are shown in Figure 5,
where [501] depicts the primary current through the breaker, [502] depicts the
breaker’s contact travel distance, [503] depicts the trip coil current and [504] depicts
the ‘Close’ signal’s DI status. From the Figure 5, it shows that the trip coil current [503]
increases after a ‘trip’ command is given and [502] shows the travel sensor voltage
which indicates the contact starts moving. When the contacts get separated the current
[501] through the breaker becomes zero and the ‘close’ signal DI status [504] becomes
a logic ‘0’, which indicates that the breaker is open.
The breaker parameters’ curves during the ‘close’ operation are shown in Figure 6,
where [601] depicts the primary current through the breaker, [602] depicts the breaker
contacts travel distance, [603] depicts the close coil current and [604] depicts the
‘close’ signal DI status. From the Figure 6, it shows that the ‘close coil’ current [603]
starts increasing from zero when the ‘close’ command is given and contact’s travel
distance sensor voltage increases [602] indicates that the contact starts moving.

Subsequent to the issue of the ‘close’ command the current through the starts flowing
and the ‘close’ signal DI status becomes high, which indicates that the breaker contacts
are closed [604].
All these results are obtained by using an attractive and user-friendly GUI. This makes
the system very convenient for achieving the results accurately for diagnostic purposes.
Breaker ‘Open’ Operation
The Figure 3 shows the methodology adopted for the breaker operation times’
calculations during the ‘open’ operation. Each element in the flowchart has been
assigned a label which refers a specific operation which has been described below.
[301], indicates the operation in which the data of samples of primary current, travel
sensor voltages which depends on the plunger movement of a breaker, trip coil
currents, open & close coil currents are read from the inputs.
[302], indicates the operation about when the breaker trip/open command is
given/received to the breaker for ‘open’ operation.
[303], indicates the operation about the time-instant ‘t1’ when the trip coil current
starts increasing from zero during this operation.

[304], indicates the operation about the time instant ‘t10’ when the travel distance
sensor voltage is examined for a linear gradient after the trip coil energisation and the
voltage sample is recorded as a first point for calculation of contact travel speed.
[305], indicates the operation about the time-instant ‘t2’ when the ‘arcing contacts
separation’ starts and at this instant the breaker ‘close’ status signal becomes a ‘logic
low’ while the ‘open’ status digital input becomes a ‘logic high’.
[306], indicates the operation about the time instant ‘t20’ which is the second point for
linear gradient of contact travel sensor voltage sample is recorded. This is usually taken
at 10-15 ms after the first point referred as ‘t10’.
[307], indicates the operation about the time-instant ‘t3’ when the breaker contacts
separation starts and the primary current through the breaker becomes zero.
Open time
The ‘Open time’ is the interval between the instant (t1) [303] when the trip coil current
starts increasing from zero for a previously closed circuit breaker and the instant (t2)
[305] when the arcing contact separation starts in all the poles while the breaker
‘close’ status signal becomes a ‘logic low’ and the breaker ‘open’ status signal becomes
a ‘logic high’.

Arcing Time
The ‘Arcing time’ is the interval between the instant (t2) [305] when the contact
separation starts and the instant (t3) [307] when the primary current through the
breaker becomes zero for a previously closed breaker.
Break Time
It is the summation of the ‘Open Time’ and the ‘Arcing Time’ .i.e. the time interval
between the instant (t1) [303] when the trip coil current starts increasing from zero
and the instant (t3) [305] when the primary current through the breaker becomes
zero.
[308], indicates the operation related to calculation of the open time and Arcing time
from the recorded data samples and displayed on the GUI.
[310], indicates the operation related to calculation of the break time which is derived
from ‘open & arcing’ times and displayed on the GUI.
Contact-Travel speed
The contact-travel speed is calculated based on the intermittent data concerned with
the linear slope of displacement curve during the ‘open’ operation. The starting
point/value is chosen at the time instant (t10) [304] when the open/close signal status
changes and the second point is chosen at 10ms to 15 ms (t20) [306] after the
starting point.

Contact travel speed = Contacts travel distance between two points / Time taken to
travel that distance
Contacts travel distance between two points = Sensor voltage/ADC value at the starting
point to Sensor voltage/ADC value at the second point
[309], indicates the operation related to calculation of the contacts travel speed from
the recorded data at time instants ‘t10’ [304] & ‘t20’ [306].
Breaker ‘Close’ Operation
The Figure 4 shows the methodology adopted for the breaker operation times’
calculations during the ‘close’ operation. Each element in the flowchart has been
assigned a label which refers a specific operation which has been described below.
[401], indicates the operation in which the data of samples of primary current, travel
sensor voltages which depends on the plunger movement of a breaker, trip coil
currents, open & close coil currents are read from the inputs.
[402], indicates the operation about the breaker close commend is given/received to
the breaker for ‘close’ operation
[403], indicates the operation about the time-instant ‘t4’ when the close coil current
starts increasing from zero during this operation.

[404], indicates the operation about the time instant ‘t11’ when the travel distance
sensor voltage is examined for a linear gradient after a close coil energisation and the
voltage sample is recorded as a first point for calculation of contact travel speed.
[405], indicates the operation about the time-instant ‘t5’ when the primary current
starts flow through the breaker.
[406], indicates the operation about the time instant time instant ‘t22’ which is the
second point for linear gradient of contact travel sensor voltage sample is recorded.
This is usually taken at 10-15 ms after the first point referred as ‘t11’.
[407], indicates the operation about the time instant ‘t6’ when the contacts touches
during this operation and at this instant the breaker ‘close’ status signal becomes a
‘logic high’ & the ‘open’ status digital input becomes a ‘logic low’.
Close time
The ‘Close time’ is the interval between the instant (t4) [403] when the circuit breaker
close coil current starts increasing from zero for a previously opened circuit breaker and
the instant (t6) [407] when the contacts touches during the breaker close operation
while the breaker ‘close’ status signal becomes a logic high and the ‘open’ status signal
becomes a ‘logic low’.

Make Time
The ‘Make time’ is the interval between the instant (t4) [403] when the circuit breaker
close coil current starts increasing from zero and the instant (t5) [405] when the
primary current starts flow through the breaker.
Pre-Arcing Time
It is the difference in time between the Close Time and the Make Time [408] .i.e. the
interval between the instant (t5) [405] when the primary current through the breaker
starts flow and the instant (t6) [407] when the breaker contacts touches for a
previously opened breaker.
[408], indicates the operation related to calculation of the Close time and Make Time
from the recorded data samples and displayed on the GUI.
[410], indicates the operation related to calculation of the Pre-Arcing which is derived
from ‘Close & Make’ times and displayed on the GUI.
Contacts Travel speed
The contact-travel speed is calculated based on the intermittent data concerned with
the linear slope of displacement curve during the ‘close’ operation. The starting
point/value is chosen at the time-instant (t11) [404] when the open/close signal status
changes and the second point is chosen at 10ms to 15 ms after the starting point (t22)
[406].

Contact travel speed = Contacts travel distance between two points / Time taken to
travel that distance
Contacts travel distance between two points = Sensor voltage/ADC value at the starting
point to Sensor voltage/ADC value at the second point
[409], indicates the operation related to calculation of the contacts travel speed from
the recorded data at time instants ‘t11’ [404] & ‘t22’ [406].
Methodology used for Calculating Contact Wear of a Circuit Breaker
The contact wear of a breaker is useful to estimate the life of a breaker and in manner
that their maintenance can be properly planned. The contact wear depends on the
interrupting current and the interruption time of a breaker. The procedure for
measuring the contact wear of a breaker is depicted in the flow chart presented in the
Figure 7. Each element in the flowchart has been assigned a label which refers a
specific operation which has been described below.
[701], indicates the operation related about the breaker close signal DI status. This is
examined for its change from ‘logic 1 to logic 0’. Subsequently, if the status satisfies
desired status the control program starts calculation of the ‘contact wear’. If the status
is not as required, then it goes to the next step which involves checking of the ‘close’
signal DI status.

[702], indicates the operation in which the contact wear measurement variables are
forced to zero.
[703], indicates the cycle time for the software thread to run to measure the contact
wear.
[704], indicates the operation in which breaker close signal DI status is checked. If it is
a ‘logic zero’ & the current through breaker becomes more than reference current value
then control program starts measurement of the contact wear. If it is a ‘logic one’ it
goes to the beginning of the loop.
[705], indicates the operation in which the breaker contact wear is measured for one
iteration. The measured contact wear is added to a previous value during one
operation. The contact wear for one iteration is computed as Icw = Ic×Ic×k×cycle
time/1000. Ic = Current through breaker, k=multiplication factor.
[706], indicates the operation in which the breaker’s close signal DI status changes
from ‘logic 0 to 1’. Otherwise, if the current through the breaker becomes lower than
the reference current value then the measurement of contact wear is known to be
complete.
[707], indicates the operation in which the total contact wear is measured by adding
the present contact wear value to the previous value stored in memory.

Methodology used for Calculating the Cumulative Breaking Current of a
Circuit Breaker
Circuit breakers do have the rated short-circuit breaking duties as these short-circuit
breaking currents could severely erode the breaking contacts. Hence, the measurement
of the cumulative breaking current is useful to evaluate the state of the circuit breaker
poles. The procedure for measuring the cumulative breaking current during the ‘open’
operation of a breaker is depicted in the flow chart presented in the Figure 8. Each
element in the flowchart has been assigned a label which refers a specific operation
which has been described below.
[801], indicates the operation in which the trip coil current is compared with the
reference current value or breaker ‘open signal DI’ status is checked. If any one of
these are satisfied then control program begins the measurement of cumulative
breaking current.
[802], indicates the operation in which the current through breaker is measured,
current positive sample value & negative values are assigned to the corresponding
variables.
[803], indicates the operation in which the current positive peak of the present sample
is compared with the previous sample value. If the present value exceeds the previous

value then the swapping operation is initiated and the present value replaces the
previous value.
[804], indicates the operation in which the maximum positive peak of the current is
determined by swapping the previous value with the present value.
[805], indicates the operation in which the current negative peak of the present
sample is compared with the previous sample value. If the present value exceeds the
previous value then the swapping operation is initiated and the present value replaces
the previous value.
[806], indicates the operation in which the maximum negative peak of the current is
determined by swapping the previous value with the present value.
[807], indicates the cycle time for the software thread to run to measure the
cumulative breaking current.
[808], indicates the operation in which the control program checks the breaker ‘open
signal DI’ status and current through the breaker by comparing it with the reference
current value for a lower value. If these conditions are satisfied then it initiates the
calculation of the cumulative breaking current. Average current (Iavg) =
((IbrkoldP+IbrkoldN)/2); Breaking current (Irms) = Iavg/1.414.

[809], indicates the operation in which the breaker cumulative current measured for
one operation. The cumulative current is measured and added to the previous value
stored in a memory.
Methodology used for Control of spring-charging Motor Current
Most of the circuit breakers have spring/hybrid operating mechanism and the charging
of spring is done using an ac motor. The motor current/operation can be controlled
during the unbalanced and open-phase supply condition. In this case, during the
abnormal condition it stops the supply fed to the ac motor by initiating a control action.
The procedure to control the spring-charging motor current of a breaker is depicted in
the flow chart presented in the Figure 9. Each element in the flowchart has been
assigned a label which refers a specific operation which has been described below.
[901], indicates the operation in which the breaker ‘spring-charge’ status is checked by
the control program by observing the ‘spring-charge DI signal’ status. If the DI signal
status is a ‘logic 1’ then it indicates that the spring is fully charged and it terminates the
program loop. If it is not a ‘logic 1’ then it initiates the motor operation by closing the
motor current path switch.
[902], indicates the operation in which the control program generates the motor
current control switch DO status as a ‘logic 1’, which facilitate the closing of the current
path of the motor following which all the currents are measured.

[903], indicates the cycle time for the software thread to run the motor current control
program.
[904], indicates the operation in which all the three phase current are added and
compared with the reference value. If this total is lower than the reference value then it
indicates that at least one phase path could have opened or some unbalance in the
currents could exist. In this case, it gives a protection signal to control the switch to cut
off the power supply to the motor. Otherwise, the motor starts running to energies the
spring.
[905], indicates the operation in which the control program generates the motor
current path control switch DO status as a logic ‘0’ following it cuts off the power supply
to the motor to prevent an unbalance operation.
[906], indicates the operation in which the time required for charging the spring is
calculated.
[907], indicates the operation in which the spring charging status is checked. If it is
fully charged then it gives a signal to motor current path switch DO status as logic ‘0’.
Otherwise the program loop continues to run to charge the spring.
[908], indicates the operation in which the motor current path switch DO status is
observed as a ‘logic 0’ to open the current path.
[909], indicates the operation in which the total spring charging time is calculated.

WE CLAIM
1. A monitoring system (100) for a gas insulated substation in a modular configuration,
comprising digital input and output modules (103), isolator modules (104), current
transformer & potential transformer (CTPT) modules (106), filter modules (105),
processor module (101), analog add-on modules (102) in addition to universal
power supply module (107) and human- machine interface (HMI) terminal (108),
wherein the I/O modules are interconnected to execute the system.
2. The system as claimed in claim 1, wherein the CTPT modules (106) comprising, PCB
mountable instrument transformers, resistor divider circuit for dc voltages, A, pre-
filtering circuit to bypass undesirable signals, metal oxide varistor for protection from
voltage surges, configured to acquire field inputs, viz; currents/voltages and step-
down the same accordingly, acceptable to the processor.
3. The system as claimed in claim 1, wherein, the filter module (105) to attenuate
undesirable harmonics in the input signal, passing through the module (106) and
render desired amplification to facilitate scaling of the input to the A/D converter.
4. The system as claimed in claim 1, wherein, the isolator module (104), a PCB
mountable isolator used as isolation amplifier to regenerate signal at output terminal

at higher (ma) rating and subsequently converting to voltage signals for A/D
converter by employing resistors of suitable rating.
5. The system as claimed in claim (1), wherein the digital I/O modules (103) to
monitor binary states of assorted switches of circuit breaker, dis-connector, earth
switch in addition to spring charge condition of ON-OFF operation of the switches
through motor, optically isolating field and monitoring voltage level at the
microprocessor input.
6. The system as claimed in claim (1), wherein, analog add-on module (102) to
enhance analog signal handling capability of the system.
7. The system as claimed in claim 1, wherein, processor module (101), to implement
digital signal processing and analytical functions, communication protocols to
communicate with the Local and remote graphical user interface.
8. The system as claimed in claim 1, wherein, the power supply module (107) having
an input of 230 Vac/220Vdc and 24 Vdc for feeding to the modules as applicable.
9. The system as claimed in claim 1, wherein human-machine interface terminal (108)
facilitating the design & configuration of all the parameters of the system interfaced
with the processor.

10.The monitoring system of GIS as claimed in claim 1 includes methods of determining
operation times of circuit breaker, contact wear to estimate the life of a breaker,
cumulative breaking current, control of spring charge of motor, SF6 gas pressure of
the system.
11.The method of determining operation times of circuit breaker as claimed in claim 10,
wherein operation times include open time, arcing time, break time, contact travel
speed during break, close time, make time, pre-arcing time, travel speed during
make, calculated through graphical user interface, using recorded data stored in
memory and confirmed through real time testing by interfacing the system in the
laboratory.