TRANSFORMER AND SWICTH GEAR
TRAINING
prepared by
Masresha Asfaw
2025
T 1. Type of Transformer by construction
1.1Conservator type
1.2. Hermetically sealed type
1.3. Dry type
2. Installation of distribution transformer
2.1 Pole mounted
2.2 Indoor type
3. protection of a transformer
•
t
4. Current and power rating of a transformer
5. Winding of a transformer
5.1 Star & Delta
6. Step up and step down process
7. Types of a transformer test
7.1 Dry test
7.2 Wet test
8. Transformer oil
8.2 Insulation: Fluidity, viscosity,
8.3 Break down voltage
9. Switch gear :-
9.1Types of switching devices
9.2 switching procedures
10. Quenching media
Oil , SF6 gas , Vacuum
11. Ring main unit (RMU)
12. Low voltage switch gear
13. Cable
13.1 Types of cable
13.2 Sizes of cable
13.3 Cable treatment
1.1conservator type
Conventional transformer .
It can be installed in and out door .
Filled with oil
Built in an active and inactive parts.
Built in H.T bushing
L.T stud
Has a primary and secondary winding
Has a silica gel
• .
• Has a core
1.2Hermitically sealed
.It is not exposed for atmospheric air
. Oil refilling process conducted with special precaution.
. Be mounted on selected area.
. Maintenance free .
1.3Dry type
. No oil filled
. The core made from hard epoxy resin material .
. Needs ventilation i.e cooling fan.
. Maintenance free
.
.
• Installation of distribution transformer
• .Pole mounted with pole seat ( concrete ).
• . With H type pole ( wooden, concrete)
• In door type
• .Enclosed with prefabricated compact substation
• .Installed in Net station.
• .
• 3.Protection of a transformer
• .Primary , drop out fuse, powder fuse, liquid fuse , M.V
circuit breaker .
• . Secondary HRC , MCCB
• 4.Current and Power Rating of a transformer
• In KVA or KW and in AMP
• 5. Windings of a transformer
• 5.1Primary Delta Secondary Star.
•
• 6. Step up and step down process
• primary and secondary winding ratio
• N1/N2=V1/V2= I2/I1
• 7. Types of a transformer Test
• 7.1 Dry test
• Test conducted with out any electrical source
• dead circuit.
• Insulation (Megger)test winding , oil , Resistance test
• 7.2 Wet test
• Test conducted while there is an electrical source
• (live circuit) Voltage, Current , Phase sequence
insulation Resistance of Transformer Coil
Transformer Coil M Min.IR Value Dry
Voltage Megger Size Type T/C
0 – 600 V 1KV 500 MΩ
600 V To 5KV 2.5KV 5,000 MΩ
5KV To 15KV 5KV 25,000 MΩ
15KV To 69KV 5KV 50,000 MΩ
8. Transformer oil property
8.2 Insulation : Fluidity, viscosity, of a fluid
(liquid or gas) viscosity, resistance to a change in
shape, or movement of neighboring portions relative
to one another
Viscosity denotes opposition to flow. The
reciprocal of the viscosity is called the fluidity
a measure of the ease of flow.
8.3 Break down voltage (BDV) of oil is the maximum
voltage at which the oil's insulating properties fail. It's also
known as the dielectric strength of the oil.
9. Switch gear :-
Different kinds of switching devices in an electrical
circuit that are using for making and breaking a
circuit at different times mechanically and electrically
, They are operated locally, remotely and SCADA
controlled.
Examples
Load break switch, disconnecting switch, isolating
switch, Earth switch, areal section switch circuit
breaker.
9.1 Switching procedure
.A load break switch and a circuit breaker
closing and opening and operating with load .
. Isolating switch, disconnecting switch
operate while with no load but the presence of
voltage.
. Earth switch is operating with a dead circuit
i.e with no load and voltage at all.
9. Switch gear :-
Different kinds of switching devices in an electrical
circuit that are using for making and breaking a
circuit at different times mechanically and electrically
, They are operated locally, and remotely or SCADA
operated .
Examples
Load break switch, disconnecting switch, isolating
switch, Earth switch, areal section switch ,circuit
breaker.
10. Quenching media
Oil , SF6 gas, Vacuum etc.
Serves in load bread switch, circuit breaker by
arc quenching and spark diminishing.
Except vacuum oil and SF6 gas is refilled in a
circuit breaker and in a load break switch
sealed tank . It can be monitored with oil or
SF6 gas monitoring gauge .
11. Ring main unit (RMU)
Redundancy: Power can continue to flow even if one
section of the ring is damaged.
Easy maintenance: Compact and self-contained design
allows for simple replacement and servicing.
Improved power quality: Can help manage voltage
fluctuations by isolating faults quickly.
A Ring Main Unit (RMU) is considered an important
component in electrical power distribution networks,
primarily used .
Consists of : (If GIS ) load break switch, Earth switch,
M.V Circuit breaker, fuse switch , capacitive indicating
light, MV current transformer, Voltage transformer, SF6
gas can , Gas monitoring gauge.
12 Low voltage switch gear
Consists of:-
Main circuit breaker (MCB), MCCB Current transformer
, for Metering, Ammeter , volt meter Voltage
transformer and Energy meter ,L.V Bus. DZ fuses ,
surge arrester,
13. What is the definition of a cable?
A cable is a thick wire, or a group of wires inside a
rubber or plastic covering, which is used to carry
electricity or electronic signals.
13.1 Types of cables overhead (ABC)and underground
power cables.
voltage level medium voltage, low voltage
Construction single core, three core
Insulation XLPE plastic, PVC plastic, impregnated
paper oil insulation .
13.2The size (cross sectional area) of the cable
determines the current carrying capacity.
Copper cable can carry current more than
aluminum.
The size of the XLPE insulation of the cable
determines the level of the voltage .
In most cases the size (cross sectional area) of the
low voltage neutral conductor approximately half
size (Cross sectional area) any of the three phase
Treatment of medium voltage three core cable
1. Remove the outer PVC insulation as per the installation manual
given.
2. Remove the inner sheath (insulation) .
3. Remove the paper jute and rope .
4. Temporarily fasten the copper screen back to the direction of the
cable run.
5. Remove the copper tape away from the cable.
6. Peel carefully the semi conductive material as per the required
length.
7. Remove the XLPE insulation as equal as the measured length of the
cable lug plus 5mm.
8. Clean the XLPE insulation with a cleaning agent .
9.Put the stress control tube 5mm above the semi conductor
to the direction of the XLPE.
10. Shrink the stress control tube properly.
11 Crimp the cable lug for all phases.
12. Shrink the anti tracking tube .
13. Shrink the lug sealing for all phases.
14. Mark or shrink the phase identification color i.e (RYB)
15. If it is out door shrink the rain shades on each phase
following the installation manual.
16. Put the color identification of each phase (BYR).
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