EET402 -M4-Ktunotes.in.pdf ,NOTES ON ESD

MODULE 4
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Module 4
Industrial Power and Lighting Installations (9 hours):
Industrial installations –classifications- Design of electrical distribution systems with main
switch board, sub switch boards and distribution boards with ACBs, MCCBs and MCBs as the
case may be, for feeding power (mainly motors) and lighting loads of small and medium
industries.
Selection of armoured power cables (AYFY, A2XFY, YWY) – calculation of ampacity, voltage
drop, short circuit withstand capacity etc.
Design of MSB & SSB including Motor Control Centre (MCC) for motor controls - selection of
bus bars and switchgears.
Selection of 11kV indoor and outdoor transformer substations upto 630kVA - selection of
switchgears and protective devices –Preparation of schedule of works and bill of quantities (cost
estimation excluded).
Short circuit calculations and earthing design for the HV and LV sides of an 11 kV substation of
capacity up to 630 kVA.
Pre-commissioning tests of 11kV indoor/outdoor substation of an HT consumer.

Industrial Installation
Design of industrial installation is more sophisticated.
Industrial installation has diverse loads.
Main aspects of industrial installation are
✔Easiness of maintenance
✔Fault location
✔Economic considerations
✔Energy conservation

Classification of Industrial Buildings
•For the purpose of evaluating the electrical requirements as per NEC ,
industries are classified taking into consideration three basic criteria
1) Fire hazard
2) Power consumption
3) Pollution hazard

1) Classification based on fire hazard
National Building Code classifies the industrial buildings in group G from the
safety point of view.
• Group G1-Buildings used for low fire hazard industries.
These industries have low combustibility and the process/operations are not
liable to self propagation of fire and only damage to life and property may
arise out of panic, fumes or smoke or fire from an external source.
Eg:- cement, glass, rice, soap detergent ,sugar industry etc.

• Group G2-Buildings of moderate fire hazard
Those industries in which the process/operations may give rise a fire which
will burn with moderate rapidity and give rise to considerable volume of
smoke. These fires will not result in explosion.
Eg:-Ship repairing, coir, flour mills, fertiliser plants etc.
• Group G3:-Buildings with high fire hazards
Those industries in which the process/operations may give rise a fire which
will burn with extreme rapidity and give rise to considerable volume of
poisonous fumes and lead to explosion.
Eg:-alcohol distillery, explosive manufacturing, petrochemicals etc.

2) Classification based on power consumption
NEC classifies industrial building according to the power requirements as
✔ Light industries(Small)
✔ Average industries(Medium)
✔ Heavy industries(Large)

Description Average power
requirement(kVA)
Examples
Light industry Upto 50 kVA Garment making,
ornament making
Average industry Above 50 up to 2000
kVA
Furniture, pottery, glass,
tobacco,textiles
Heavy industry Above 2000 kVA Heavy electrical
equipment, steel mills,
ship building, chemical
plants, paper mills,
petrochemicals

3) Classification based on Pollution degree Level
Pollution degree is a classification according to the amount of dry pollution and
condensation present in the environment.
Pollution degree1:-No pollution or only dry nonconductive pollution occurs.
Pollution degree 2:-Normally nonconductive pollution occurs. Temporary
conductive pollution occurs due to condensation.
Pollution degree 3:- Conductive pollution or dry nonconductive pollution that
becomes conductive due to condensation occurs.
Pollution degree 4:-Pollution generates persistent conductivity caused by
conductive dust, rain or snow.

Electrical Installation in small industries
• Small industries contain motor in the installation.
• Each motor must be controlled by a main switch
• A 3 phase motor need a triple pole switch with fuse in each phase and also a
starter is required for starting and stopping the motor.
• Size of switch fuse unit and starter will depend upon the rating of the motor.
• Depending upon rating of the motor ,PVC cables of suitable size are to be used.
• For large capacity motors ,3 phase underground cables are used.
• Cables are enclosed in a rigid heavy gauge conduit.

• If there are more number of motors, power to the various machines is distributed
from the main switchboard located at a convenient position.
• Main switch fuse unit consist of different switch fuse units to control the
incoming and outgoing circuits .
• The outgoing circuits feed different sub distribution boards which will be placed
at various locations.

Design of Electrical Installation in Small Industries
(1) Motor current
✔ When the motor is first connected to the line ,it will draw more current than its
rated current. This is called the starting current.
✔ When the motor pick up its speed, it carries full load .
✔ When the motor is overloaded ,the current increases and it will overheat.
✔ Current rating of the cable used for supplying power to the motor is based on full
load current of the motor, but the rating of fuse is based on starting current.
✔ The rating of fuse should be greater than twice the rating of cables.

(2) Deciding the cable size
The cable shall have a current carrying capacity of not less than 150 percent of
motor full load current.
For example
For dc motor

(3) Determination of the size of conduit
Size of conduit depends upon three factors:
✔ No. of cables to be installed
✔ Cross sectional area of the cable
✔ The permissible conduit fill
The maximum permissible number of cables that can be drawn into conduit is given
by the below table.

(4) Deciding the fuse rating
Fuse has to carry starting current safely.
Starting current is taken as 1.5 times the full load current.

(5) Deciding the starter, distribution board and Main switch
Specification of distribution board is decided from the number of circuits to be fed from it.
Voltage rating of DB is decided by the voltage rating of the circuit and current rating is the highest
starting current of the circuit.
Current rating of the Main Switch should be equal to the starting current of the motor of highest
rating plus the full load current of the remaining motors.

Bus-bar system of a Motor Control Centre (MCC)
•A bus-bar system is an important component of a Motor Control Centre
(MCC), which is used to distribute power to the motor starters and other
electrical equipment within the MCC.
•The design of the bus-bar system must meet certain criteria to ensure safe
and reliable operation of the MCC.

The following are some of the criteria that should be considered in the design of a
bus-bar system for an MCC:
• Current carrying capacity: The bus-bar system must be designed to carry the
maximum current that can be drawn by all the loads connected to it.
• Voltage drop: The voltage drop along the length of the bus-bar should be kept within
allowable limits to ensure proper voltage regulation at the load terminals.
• Short-circuit rating: The bus-bar system must be designed to withstand the
maximum fault current that can occur in the system without damage.
• Mechanical strength: The bus-bar system must be designed to withstand the
mechanical stresses that can occur during installation, operation, and maintenance.
• Insulation coordination: The bus-bar system must be designed to ensure proper
insulation coordination with other components of the MCC, such as the switchgear
and motor starters.
• Maintainability: The bus-bar system must be designed for ease of installation,
inspection, and maintenance.

Designing an Main Switch Boards and SubSwitch Boards with MCC for motor
controls.
The following are the design procedures that need to be considered:
• Load Analysis: Conduct a load analysis to determine the peak demand, power factor, and
the number and sizes of motors required.
• Selection of Main Switchboard (MSB) and Sub Main Distribution Board (SSB): Based on
the load analysis, select the appropriate ratings for the MSB and SSB. The MSB is usually
rated for high current and fault levels, while the SSB is rated for lower current and fault
levels.
• Selection of MCCs: Select MCCs according to the number and size of motors. Each MCC
should be able to handle the maximum current and fault levels of the connected motors.
• Busbar System Design: Design a busbar system that can handle the maximum current and
fault levels, and provide proper voltage regulation at the connected loads.
• Protective Devices Selection: Select protective devices such as circuit breakers, fuses, and
relays to ensure safety and reliability of the system.
• Enclosure Selection: Select an enclosure that can withstand the environmental conditions
and safety requirements of the industry.
• Cable Sizing and Termination: Size the cables according to the maximum demand load,
voltage drop, and short-circuit levels.
• Grounding System: Design and install a grounding system in accordance with local codes
and standards to ensure safety and protection against electrical hazards.

Short Circuit Study
• The initial current that flows in a power system due to short circuit , will not be
purely sinusoidal in nature.

Short circuit current

Fault Level computation & Earthing Design

Earthing
Earthing means connections of the neutral point of a supply system or the non current
carrying parts of electrical apparatus to the general mass of earth so that if a discharge
occurs it will not cause any danger.
Purpose of earthing
• To ensure that no current carrying conductor rises to a potential with respect to general
mass of earth than its designed insulation
• To avoid electric shock to human beings
• To avoid risk of fire due to earth leakage current through unwanted path.

Resistance of earth
• The resistance of earth should be low enough to cause flow of current to earth
during an earth fault.
• Maximum permissible values of earth resistance in different areas are
Large power station – 0.5 to 1 ohm
Small substation – 2 ohm
In all other cases – maximum 5 ohm

Factors influencing earth resistance
• Condition of soil
• Temperature of soil
• Moisture content of soil
• Size and spacing of earth electrodes
• Depth at which electrode is buried
• Material of conductor
• Quality of coal, dust and charcoal in the earth pit.

Earth electrode and Earthing lead
• Any wire, pipe, rod or metal plate embedded in earth for the purpose of making an
effective connection with earth is known as earth electrode.
• The wire which connects overhead earth wire to the earth electrode is known as
earthing lead.

Methods of earthing
Earthing can be done in many ways. The various methods employed are
(1) Strip or wire earthing
In this type of earthing, a copper strip electrode of cross section not less than
25mmX1.6mm is buried in a horizontal trench of depth not less than .5m. When
using round conductors made of galvanized steel or iron, the cross sectional area
should not be less than 6mm2
. The length of the conductor buried should not be less
than 15m.This type of earthing is used at places which have rocky soil.

(2) Rod Earthing
Rod earthing is similar to pipe earthing. In
this method of earthing a copper rod of
diameter 12.5 mm or 16mm diameter
galvanized steel or a hollow section of
25mm galvanised iron pipe of length not
less than 2.5m is buried vertically
underground. The pipe can be buried
manually or using pneumatic hammer.
This system is suitable for areas which are
sandy .

(3) Plate Earthing
In this type of earthing, a plate made up of
galvanized iron or copper is buried vertically at
a depth not less than 3m from the ground level.
The dimension needed for galvanized iron plate
is 60cmX 60cmX 6.35mm and that for copper
plate is 60cmX 60cmX 3.18mm.The plate is
embedded in alternate layers of coke and salt.
The earth wire is bolted to the earth plate with
the help of a bolt ,nut and washer made of same
material of that plate.

(4) Pipe Earthing
It is the most common type of earthing system. In
this type of earthing system, a perforated pipe
made of galvanized steel/iron of approved length
and diameter is buried vertically. The size of the
pipe used depends on the magnitude of current and
the amount of moisture content in the soil. The
diameter of the pipe is usually 40mm and length
2.75m for normal soil. The amount of soil
moisture determines the length of the pipe.

Substation Earthing
• Substation earthing system has buried horizontal mesh of rods and vertical electrodes
welded to the mesh.
• Before 1960s the design criterion of substation earthing was low earth resistance (below
0.5 ohm for hv installation).
• New criteria for design is that the substation earthing system should have low earth
resistance, low touch potential and low step potential.
• Conventional criteria is in practice for substations and power stations upto and including
220 kV.

The functions of grounding systems or earth mat include:
Ensure safety to personnel in substations against electrical shocks.
Provide the ground connection for connecting the neutrals of star connected
transformer winding to earth ( neutral earthing ).
Discharge the overvoltages from overhead ground wires or the lightning masts to
earth. To provide ground path for surge arresters.
To provide earth connections to structures and other non-current carrying metallic
objects in the sub-station (equipment earthing).

Parts of the Earthing system
• An underground horizontal earth mesh (earth mat or earthing grid)
• Earthing Electrodes or Earthing spikes
• Earthing Risers
• Earthing Connection
An underground horizontal earth mesh is known as earth mat. A number of rods when
joined together through copper conductors constitute an earthing mat .It reduces overall
grounding resistance.
Several identical earth electrodes are driven vertically into the soil and are welded to
the earthing rods of the underground mesh. (Larger the number of earth electrodes ,
lower will be the earth resistance).

• Earthing risers are usually the mild steel rods bent in vertical and horizontal
shapes and welded to the earthing mesh at one end and brought directly up to
equipment or structure foundation.
• Earthing connections are galvanized steel strips or electrolytic copper flats or
strips/ stranded wires/ flexibles. These are employed for final connection between
earthing riser and the points to be grounded.

• Step Potential is the potential
developed between the two feet on the
ground of a man or animal when short
circuit occurs.
• Touch potential is a potential which is
developed between living body
touches the faulty structure. When
operating personnel touch an electrical
equipment during short circuit
condition, fault current flows through
the human body.

EARTH MAT DESIGN
• Earthing mats are provided for earthing in substations.
• It consist of horizontally buried earth conductor grid and vertically buried earth
electrodes.
• Earth mat design is based on permissible body current , fault duration and magnitude
when a person becomes a part of accidental earth circuit.
• The design will limit the voltages (step and touch)to a safe level.
• Resistance of earthing system = ρ/4r +ρ/L
ρ – Soil resistivity
r- radius in meters of circle having the same area as that occupied by the earth mat.
L – length of conductor buried in meters

Steps involved in the design are:
• Step 1:Prepare substation layout plan
• Step 2:Determine mat area
• Step 3: Measure site soil resistivity
• Step 4: Determine fault and design current
• Step 5: Determine fault duration
• Step 6: Design conductor size, spacing length, mat resistance.
• Step 7: Mat layout
• Step 8: Mat construction and adjustment if required.

Calculate number of GI earthing pipe of 100 mm diameter, 3 meter length.
System has fault current 50KA for 1 sec and soil resistivity is 72.44 Ω-Meters.

• Max. allowable current density = 7.57×1000/(√ρt) A/m2
(ESD handbook page
No:34)
• Max. allowable current density = 7.57×1000/(√72.44X1) = 889.419 A/m2

• Surface area of one 100 mm dia. 3 meter long Pipe = 2 x 3.14 x r x L = 2 x 3.14 x 0.05 x3
= 0.942 m2
• Max. current dissipated by one Earthing Pipe = Current Density x Surface area of
electrode
• Max. current dissipated by one earthing pipe = 889.419 x 0.942 = 837.83 A say 838 A
• Number of earthing pipe required = Fault Current / Max. current dissipated by one
earthing pipe.
• Number of earthing pipe required = 50000/838 = 59.66 Say 60 No’s.
• Total number of earthing pipe required = 60 No’s.

• Resistance of earthing pipe (isolated) R = 100xρ /2×3.14×L×(loge
(2L/d)) (ESD
handbook page no:33)
• Resistance of earthing pipe (isolated) R = 100×72.44 /2×3.14×300×(loge
(2×300/10)) = 15.74 Ω/Pipe
• Overall resistance of 60 no of earthing pipe = 15.74/60 = 0.26232 Ω.

Number of transformer substation
Main characteristics to be considered for deciding the number of substations are
▪ Surface area of the industrial building.
▪ Total power demand in comparison with std transformer capacities.
▪ Load distribution.
Normally one substation is preferred in view of supervision, maintenance and control.
Factors that lead to more than one substation are
• A large surface area( > 25000 m2
)
• Power demand greater than 2500 kVA
• Sensitivity to interruption and need to maintain redundancy.

Number of distribution transformers
It depends upon several factors such as
▪ Surface area of the building site
▪ Total installed power capacity
▪ Sensitivity of circuits to power interruptions
▪ Sensitivity of circuits to disturbances
▪ Future expansion
Factors that lead to more than one transformer are
▪ Large connected load( > 1250 kVA):- Even though transformer upto 2000 kVA are available ,it is
preferable to have multiple units of smaller capacity for ease of replacement and lower space.
▪ Large surface area of the building( > 5000m2
):-If the area is large it is better to have more than one
transformer close to the load centers because this reduces the cable cost
▪ Separation of and disturbing loads:- If the load mix includes large volume of sensitive loads (IT loads) and
large motor loads ,it is favorable to have separate transformers.

Selection of transformers
Factors deciding selection of transformers
✔ Maximum demand
✔ Future expansion
✔ Spare capacity
✔ Statutory requirements
✔ Site condition

Standard rated output in kVA
•Standard rating of Distribution Transformers (11/0.433kV) are 50, 63,
80, 100, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600 and
2000 kVA.

Classification of substations
• Substations are classified in different ways such as on the basis of
i) Nature of duties
ii) Service rendered
iii) Operating voltage
iv) Importance
v) Design

• Classification of substations on the basis of nature of duties
1) Step up or primary substations:- These substations are generally associated with generating
stations. Generated voltage is usually stepped up to primary transmission voltage by step up
transformers.
2) Primary Grid substations:-These substations are located at suitable load centers. In these
substations primary transmission voltage is stepped down to different suitable secondary
voltages. These secondary transmission voltages lines are carried over to secondary
substations where the voltage is again stepped down primary distribution voltage.
3) Step down or distribution substations:-These substations are located at load centers where
primary distribution voltages are stepped down to secondary distribution voltage ( 415 / 230
V). These substations feed consumers through distribution network and service line.

•Classification of substations on the basis of service rendered
1) Transformer substations:-Transformers are installed to transform voltage from
one level to other level.
2) Switching substations:- These substations are meant for switching operation of
power lines without transforming voltage. At such substations different
connections are made between various transmission lines.
3) Converting substations:- These substations convert either ac to dc or vice
–versa or converting frequencies.

•Classification of substations on the basis of operating voltage
1) High voltage substations:- Substations involving voltages between 11 kV and 66
kV.
2) Extra high voltage substations: - Involving voltages between 132kV and 400 kV.
3) Ultra high voltage substations:-Operating voltage above 400 kV.

•Classification of substations on the basis of importance
1) Grid substations:-These are substations from where bulk power is transmitted
from one point to another in the grid. These substations are important because
any disturbance may cause failure of the grid.
2) Town substations :- These substation stepped down the voltage at 33/11 kV for
distribution in towns and any failure may result in the failure of supply for the
whole town.

•Classification of substations on the basis of design
1) Indoor substation :- All apparatus are installed in the substation building. Such
substations are usually for a voltage upto 11 kV but can be erected for 33 kV
and 66 kV when the surrounding atmosphere is contaminated.
2) Outdoor substations :- These substation are erected in open areas.

OUTDOOR SUBSTATION
• There are two types of outdoor
substation.
Pole mounted substation:
• They are erected for mounting
distribution transformers of capacity
upto 250 kVA.
• Single pole or H pole and 4 pole
structures with suitable platforms are
used for transformers .
• Gang operating switch (G.O) or Air
Break switch is used for switching ON
and OFF of HT transmission line.
• HT fuse unit is installed for the
protection of HT lines.

Type Capacity
Single Pole Upto 25 kVA
H pole Upto 125 kVA
4 Pole Above 125 kVA

SINGLE LINE DIAGRAM OF A POLE MOUNTED DISTRIBUTION
SUBSTATION

• H-pole structure, base channel of 100mmx50mm size
• Erected at a height of 2.44m from ground level
• 11kV Lightning arrestors(3 numbers) are erected at the top .
• 3 and 1/2 core cable is taken from the L.T side of the transformer bushings to L.T Main
Switch.
• To control LT side iron clad low tension switch with fuses are installed.
• Main switch with fuse unit provide the protection of transformer against feeder faults.
• L.T Main Switch is connected to the L.T Distribution Switch.
• L.T cables are selected according to the capacity of the transformer.
• Substation is earthed at two or more places.

Foundation Mounted Outdoor
Substation
• They are built in open and usually
enclosed by a fence for safety.
• Substations for primary and secondary
transmission and for primary
distribution (above 250KVA) are
foundation mounted outdoor type.

ADVANTAGES OF OUTDOOR SUBSTATION
• Fault location is easier.
• Extension of installation is easier.
• Time required for erection is less.
• Cost of switchgear installation is low
DISADVANTAGES OF OUTDOOR SUBSTATIONS
• Supervision is to be done in open air during all kinds of weather.
• Rapid fluctuation in ambient temperature.
• More space is required.
• Protection devices are required to be installed for protection against lighting
surges.

INDOOR SUBSTATION
• All apparatus are installed in the substation building.
• They are usually for voltages upto 11KV.
• Switchgear on the primary side will have oil circuit breaker.
• Secondary side is connected to bus bar and from the busbar various feeders
emerge out.
• Each feeder consist of isolator switch, circuit breaker and measuring instruments.
• Reverse power relay is employed for the protection of feeders.
• For transformer protection Buchholz’s relay is employed.
• Other auxiliary equipments are i) storage batteries ii) fire fighting equipments
such as water buckets, fire extinguishers etc.

Single line diagram of indoor substation

Layout of indoor substation

Consider 20% for future expansion

Selection of HT Cable
It is based on HT side fault MVA (minimum 150 MVA as per KSEB and normally fault
MVA is taken as 250 MVA)

•Selection of LT cable
Based on full load secondary current of the transformer.
3-1/2 core cable ------------- cable is selected from the table taking into
consideration the factor of safety and future load requirements.

•Selection of LT bus bar

•A factory has the following connected load:
•i. Large motor of 150 kW - 1 no.
•ii. Machine shop with 7.5 kW motors - 6 nos.
•iii. Painting booth of 22.5 kW
• iv. 10 kVA welding transformers - 4 nos.
•v. Water pumping station load 15 kW
•vi. Lighting load 5 kW
Select the transformer rating and design an indoor substation including
the schematic diagram showing the details of switchgear and cable sizes.
Assume a diversity factor of 1.2.

Eg-AYFY means Aluminum conductor,PVC
insulated steel strip armored and PVC sheathed
cable

Selection of cables
All cables consist of a low resistance conductor which carries current and insulation
to isolate the conductors from each other and from their surroundings.
The main factors which are to be taken into account for the selection of cables are as
follows:
• The power and voltage rating for which the cables are being used
• Choice of material used in cable
• Conditions of installation at the site
• Current carrying capacity of the cables
• Voltage drop in the cables
• Short circuit capacity of the cables
• Availability of the selected size of the cables.

1) Voltage rating
• Main consideration for cable selection is it must withstand system voltage.
• Design voltages for cables are expressed in the form of U0
/U.
Where U0
-voltage between conductor and earth
U- voltage between conductors
• Power cables manufactured in India are designated as 650/1100V, 1.9/3.3 kV or
6.35/11 kV or 22kV or 33kV.

2) Conditions of installation
Different methods are adopted for laying of cables. Different methods for laying the
cables are listed in the table.
Refer Databook Page No:55

3) Choice of material used in cable
• Copper and Aluminium are best choice of conductors for cables.
• Copper has high conductivity but cost is high.
• Aluminium has low mass density.
• Insulating material used in cables are broadly divided as follows
a) Impregnated paper:-It is derived by chemical treatment of wood pulp. Thickness
of paper used is from 65 to 190 micrometer. Paper is to be protected from
moisture. So metallic sheath are to be provided around it.

b) Synthetic dielectrics:-Different synthetic dielectrics used are Polyvinyl Chloride
(PVC),Polyethylene (PE), Ethylene Propylene Rubber (EPR), Cross-linked polyethylene
(XLPE).
PVC-Economical, easy to process and hardly combustible. But used only for medium
voltage cables upto (6.6 kV),generation of hydrochloride in case of fire, softening at higher
temperature etc.
PE – Excellent electrical characteristics and used for medium and high voltage cables. But
it is combustible, life affected by partial discharge .
EPR-Better long term resistance to aging and electrical properties. But processing is
difficult, cost is more.
XLPE-High mechanical strength, higher continuous operating temperature. But process is
difficult, reduced life.

4) Current carrying capacity of the cables
During service operation, cables suffer electrical losses which appear as heat in the
conductor, insulation and metallic components.
The current rating is dependent on the way the heat is transmitted to the cable
surface and dissipated to surrounding.

5) Short circuit ratings
During short circuit there is sudden inrush of current for a few cycles.
Short circuit rating are derived from the eqn
Isc
= K× A/√ t
K- constant combining temperature limits and properties of conductor materials
A- area of cross section in mm2
Isc
-short circuit current in A
t- time duration of fault in seconds.

6) Voltage drop calculation
• When designing distribution systems ,it is important that the voltage drop from the
point of commencement of supply to the farthest apparatus shall not exceed 3% of
the system voltage.
• Voltage drop is determined by multiplying the complex value of line current by the
complex impedance value.
VD
=IL
× ZC

Calculation of ampacity of cables
•Ampacity refers to the maximum current that a cable can carry safely
without exceeding its rated temperature.
• The ampacity of a cable depends on various factors such as the cable's
size, insulation material, ambient temperature, installation method, and
cable length.

The following steps are to be considered for calculating ampacity:
• Determine the cable's size: The cable size is typically specified by its cross-sectional
area, which is measured in square millimeters (mm²).
• Determine the insulation material: Different insulation materials have different
temperature ratings. Maximum temperature rating of the insulation material used in the
cable should be known for calculating ampacity.
• Determine the ambient temperature: The ambient temperature is the temperature of the
air surrounding the cable. Temperature of the environment where the cable will be
installed should be known.
• Determine the installation method: The ampacity of a cable also depends on the
installation method. For example, the ampacity of a cable installed in conduit will be
different from a cable installed in free air.
• Calculate the derating factor: The derating factor adjusts the ampacity of the cable based
on the installation method and the number of cables installed.

Pre-commissioning tests of 11kV indoor/outdoor substation of an HT
consumer
• Insulation resistance test: This test measures the insulation resistance of the
substation equipment, including the cables, busbars, transformers, and switchgear.
The purpose of this test is to ensure that the insulation is adequate and to detect
any faults that could cause breakdowns.
• High voltage test: This test is used to verify the dielectric strength of the
equipment, and is typically performed by applying a high voltage to the
equipment for a specified period of time.
• Continuity test: This test verifies the continuity of the wiring, connections, and
grounding systems of the substation.

• Transformer testing: This includes checking the insulation, winding resistance, and polarity of
the transformer.Some of the transformer test are i) Transformer Turn Ratio Test ii) Operational
Checks on protection System iii) Winding resistance measurement iv) Magnetic Balance test
v) Temperature Rise Test (Oil And Winding):
• Circuit breaker testing: This includes verifying the operation of the circuit breakers, testing the
trip time, and checking the contact resistance.
• Protective relay testing: This includes verifying the operation of the protective relays, testing the
trip time, and checking the contact resistance.
• Control system testing: This includes verifying the operation of the control system, checking the
wiring and connections, and testing the interlocks.
• Commissioning of the substation: This includes energizing the substation and verifying that it is
operating as designed, with all protection systems and control systems functioning correctly.

EET402 -M4-Ktunotes.in.pdf ,NOTES ON ESD

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