Q2 1 } list out internal and external causes of failure of transformer

Internal Causes:
• Insulation Failure: Breakdown of insulation due to aging, overheating, or
contamination leads to short circuits.
• Winding Faults: Short circuits between turns or layers of windings due to insulation
damage or mechanical stress.
• Core Faults: Damage to the core lamination insulation causes eddy currents and
overheating.
• Overheating: Excessive load, poor cooling, or blocked ventilation leads to insulation
breakdown.
External Causes:
• Lightning Strikes: High voltage surges damage insulation and windings.
• System Faults: Short circuits or overloads in the power system cause excessive
current flow.
• Voltage Surges: Switching operations or other disturbances cause voltage spikes
that stress insulation.
• Environmental Factors: Moisture, contamination, or extreme temperatures degrade
insulation.

22]preare the trouble shooting chart [probable reasons and remedies ]for single
phase induction motor
3 ]list out the different fire extinguishers and state the advantages of co2 fire extinguisher

Different Fire Extinguishers:

1. Water: Used for Class A fires (ordinary combustibles like wood, paper, and textiles).

2. Foam: Used for Class A and Class B fires (flammable liquids like gasoline and oil).

3. Dry Powder: Used for Class A, B, and C fires (flammable gases like propane and natural
gas). Some specialized dry powder extinguishers are used for Class D fires
(combustible metals).

4. CO2 (Carbon Dioxide): Used for Class B and C fires, and especially effective for
electrical fires.

5. Wet Chemical: Used for Class A and Class F fires (cooking oils and fats).
Advantages of CO2 Fire Extinguisher:
• Non-conductive: CO2 is a gas, making it safe to use on electrical fires without the risk
of electric shock.
• Leaves no residue: CO2 dissipates into the air after use, leaving no cleanup mess,
unlike powder or foam extinguishers. This is crucial in areas with sensitive equipment
like computers or electronics.
 • Effective on flammable liquids: CO2 displaces oxygen, effectively smothering fires
involving flammable liquids.
These advantages make CO2 extinguishers ideal for offices, labs, and areas with electrical
equipment.

4 .draw the neat diagram and explain the polarity test on single phase transformer

Polarity Test on a Single-Phase Transformer

Purpose: To determine the instantaneous direction of the induced EMF in the secondary
winding with respect to the applied voltage in the primary winding. This is crucial for parallel
operation of transformers.
Types of Polarity:
• Additive Polarity: The voltage across the primary and secondary windings adds up.
• Subtractive Polarity: The voltage across the primary and secondary windings is the
difference between the two.

Procedure:
1. Connect the circuit as shown above.
 2. Apply a low AC voltage (V1) to the high-voltage (primary) side of the transformer.

3. Measure the voltage across the primary winding (V1).

4. Measure the voltage across the secondary winding (V2).

5. Connect a jumper wire between one terminal of the primary winding (H1) and one
terminal of the secondary winding (X1).

6. Measure the voltage between the other primary terminal (H2) and the other
secondary terminal (X2). Let's call this V3.
Explanation:
• If V3 = V1 + V2: The transformer has additive polarity. The dot markings (•) on H1 and
X1 indicate terminals of the same instantaneous polarity.
• If V3 = |V1 - V2|: The transformer has subtractive polarity. The dot markings would
be on H1 and X2 (or H2 and X1).
Significance:
• Parallel Operation: Transformers can only be connected in parallel if they have the
same polarity. Otherwise, a short circuit will occur.
• Autotransformers: The polarity test helps in understanding the voltage relationships
in autotransformers.
Note: The applied voltage should be low to ensure safety.
This concise explanation with the diagram should be sufficient for a 4-mark question.

Q3 1 desribe the various factors affecting preventive maintenance schedule

A preventive maintenance schedule aims to minimize breakdowns and extend
equipment lifespan. Several factors influence its design:

1. Equipment Manufacturer Recommendations: OEM manuals provide

guidelines on maintenance frequency, procedures, and necessary parts.
These are crucial for warranty adherence and optimal performance.

2. Equipment Usage and Operating Conditions: High usage or harsh

environments (dust, temperature extremes) accelerate wear and tear,
necessitating more frequent maintenance.

3. Equipment Criticality: Assets crucial for production or safety require more

rigorous and frequent maintenance to prevent downtime or hazardous
situations.
 4. Maintenance History and Data: Past maintenance records, failure patterns,
and repair data help identify recurring issues and optimize maintenance
intervals.
By considering these factors, a preventive maintenance schedule can be tailored
to specific needs, ensuring efficient resource allocation and minimizing
disruptions

2 ]explain the need and steps to conduct the reduced voltage running up test
on the three phase induction motor Need for Reduced Voltage Starting:
• High Starting Current: Direct-on-line (DOL) starting of large induction motors
draws a high inrush current, causing voltage dips in the supply system and
potentially damaging the motor.
• Torque Requirements: Some loads require lower starting torque than DOL
starting can provide.
Steps for Reduced Voltage Starting:

1. Voltage Reduction: Apply a reduced voltage (typically 50-80% of rated

voltage) to the motor terminals using a suitable starting method (e.g.,
autotransformer, resistor, reactor).

2. Starting: The motor starts with reduced current and torque.

3. Voltage Increase: Gradually increase the voltage to full value as the motor
accelerates. This can be done manually or automatically using a controller.

4. Full Voltage Operation: Once the motor reaches near-full speed, apply full
voltage for normal operation.
Common Reduced Voltage Starting Methods:
• Autotransformer Starting: Uses an autotransformer to tap a reduced voltage
from the supply.
• Resistor Starting: Connects resistors in series with the motor windings
during starting.
• Reactor Starting: Uses reactors to limit the starting current.
Note: The specific method and voltage reduction level depend on the motor size,
load requirements, and system characteristics.
3] list out dos and donts to achieve safety for electrical supervisror
while working in substation [any for points] Dos:
1. PPE: Always wear appropriate PPE (Personal Protective Equipment) including
safety glasses, gloves, hard hats, and safety shoes.

2. Lockout/Tagout: Follow proper lockout/tagout procedures before working on

any energized equipment.

3. Grounding: Ensure proper grounding of equipment before working on it.

4. Awareness: Be aware of your surroundings and potential hazards, such as

energized lines, moving equipment, and confined spaces.
Don'ts:

1. Bypass Safety Devices: Never bypass safety devices such as relays, fuses, or
circuit breakers.

2. Work Alone: Never work alone in a substation. Have a buddy system in

place.

3. Distractions: Avoid distractions while working, such as cell phones or loud

noises.

4. Assume Safety: Never assume that equipment is de-energized. Always

verify its status.

4] what are the factors to be considerd in designing of the machine

foundation
Factors to Consider in Machine Foundation Design

1. Machine Characteristics:
o Weight and Size: Determine the foundation's dimensions and load-
bearing capacity.
o Vibration Frequency: Match the foundation's natural frequency to
avoid resonance.
o Dynamic Loads: Account for forces from operation, such as impact or
unbalanced forces.
 2. Soil Conditions:
o Soil Type: Determine bearing capacity, stiffness, and potential for
settlement.
o Groundwater Level: Consider its impact on soil strength and
foundation stability.
o Seismic Activity: Design for potential earthquake forces.

3. Environmental Factors:
o Temperature Variations: Account for potential expansion or
contraction.
o Corrosion: Select materials resistant to soil and water.

4. Foundation Type:
o Block Foundation: Simple, suitable for moderate loads.
o Box Foundation: Encloses the machine, provides better vibration
isolation.
o Raft Foundation: Distributes loads over a larger area, suitable for
weak soil.

5. Construction and Maintenance:

o Accessibility: Ensure ease of construction and future maintenance.
o Cost-effectiveness: Balance performance with budget constraints.
By carefully considering these factors, engineers can design machine
foundations that are safe, durable, and minimize vibration transmission
Q4 1 state and explain the properties of transformer oil .
Transformer oil, a specialized fluid used in transformers, possesses several critical
properties that enable its effective functioning. Here are four key properties:

1. High Dielectric Strength:

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High Dielectric Strength of Transformer Oil

• This property allows the oil to withstand high voltages without breaking
down, ensuring electrical insulation between the transformer's components.
• A high dielectric strength minimizes the risk of electrical arcing and short
circuits within the transformer.
2. Good Thermal Conductivity:

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Good Thermal Conductivity of Transformer Oil

• Transformer oil efficiently transfers heat away from the transformer's
windings and core, preventing excessive temperature rise and potential
damage.
• This heat dissipation capability is crucial for maintaining the transformer's
operational stability and longevity.

3. High Flash Point and Fire Resistance:

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High Flash Point and Fire Resistance of Transformer Oil
• A high flash point indicates the minimum temperature at which the oil's
vapors can ignite.
• Transformer oil typically has a high flash point, reducing the likelihood of fire
hazards during normal operation.
4. Chemical Stability:

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Chemical Stability of Transformer Oil

• The oil should resist oxidation and other chemical reactions that can degrade
its insulating properties over time.
• Chemical stability ensures that the oil maintains its effectiveness throughout
the transformer's lifespan.
2 ] with the help of neat diagram exlain the phasing test on transformer
Phasing Test on Transformer Purpose:
 •
To determine the proper phase sequence of the secondary winding with
respect to the primary winding.
• To ensure correct polarity markings on the transformer terminals.
Procedure:

1. Connect a single-phase voltage source to one phase of the primary

winding.

2. Measure the voltage across the corresponding phase of the secondary

winding.

3. Reverse the polarity of the secondary winding and measure the voltage
again.
Diagram:

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Phasing Test on Transformer Diagram Observations:

• Case 1: If the voltage across the secondary winding increases when the
polarity is reversed, the initial polarity markings are correct.
• Case 2: If the voltage across the secondary winding decreases when the
polarity is reversed, the initial polarity markings are incorrect and need
to be reversed.
Explanation:
• When the primary winding is energized, it induces a voltage in the
secondary winding.
 •
The polarity of the induced voltage depends on the relative phase
relationship between the primary and secondary windings.
• By reversing the polarity of the secondary winding, we can determine
whether the initial polarity markings are correct or not.
Importance of Phasing Test:
• Incorrect phasing can lead to serious consequences, such as:
o Damage to equipment: If the transformer is connected in parallel
with another transformer with incorrect phasing, circulating
currents can flow, causing overheating and damage.
o System instability: Incorrect phasing can cause voltage
imbalances and system instability.
o Motor problems: If the transformer supplies power to motors,
incorrect phasing can cause them to run in the wrong direction or
fail to start.
By performing the phasing test, we can ensure that the transformer is properly
connected and operating safely.
3] state the fuction of following maintance tools.1 bearing puller 2 dial tester
3 growler 4 filler gauge
1. Bearing Puller:
• Function: Used to remove bearings from their housings without
damaging them or the surrounding components.
2. Dial Tester:
• Function: Measures small linear displacements or deviations with high
accuracy. Commonly used to check for runout, alignment, and other
critical dimensions.
3. Growler:
• Function: Detects electrical shorts in stator windings of motors and
generators. It induces an AC current in the winding, causing a humming
sound if a short circuit exists.
 •
4. Filler Gauge:
Function: Measures the clearance between two surfaces, such as the
gap between spark plugs or the thickness of a shim.
4] what are the causes of fire due to electical faults?and what precautions to
be taken to avoid fire due to electrical reasons. Causes of Electrical Fires
• Overloaded Circuits: Too many appliances drawing power from a single
circuit can cause overheating.
• Faulty Wiring: Damaged insulation, loose connections, and improper
wiring increase the risk of sparks and fires.
• Defective Appliances: Malfunctioning appliances, like frayed cords or
faulty heating elements, can ignite fires. Precautions to Prevent
Electrical Fires
• Regular Inspections: Inspect wiring, outlets, and appliances for damage.
• Avoid Overloading: Don't plug too many devices into one outlet or
extension cord.
• Use Surge Protectors: Protect electronics from power surges that can
damage them.
• Qualified Electricians: Hire qualified professionals for any electrical
work.
• Unplug Unused Appliances: Reduce the risk of electrical fires when not
in use.
5] distinguish between o.c.test and s.c.test performed on transformer any fo

Open Circuit Test (O.C. Test) Short Circuit Test (S.C. Test)

Determine core losses

Determine copper losses
Objective (hysteresis and eddy current
(winding resistance losses)
losses)
 •
Winding Low voltage (LV) winding
High voltage (HV) winding open
Condition shorted
Voltage Low voltage (5-10% of rated
Rated voltage to HV winding Applied voltage) to HV
winding

Current High current (full-load

Low current (no-load current) Drawn
current)

Q5 1 compare the difference between routine ,preventive and breakdown

maintance .
Maintenance Types
Feature Routine Maintenance Preventive Breakdown
Maintenance Maintenance
Regular, scheduled Proactive Reactive
maintenance tasks to maintenance to maintenance
Definition prevent equipment performed after
keep equipment failures before they equipment has
functioning properly. occur. failed.

Time-based intervals Time-based or

Trigger (e.g., daily, weekly, condition-based Equipment failure
monthly) intervals

Restoring
Keeping equipment in Preventing
equipment to
Focus good working order equipment failures
working condition

Cost Lower overall costs Moderate costs High costs

Significant
Minimal planned
Downtime Minimal downtime unplanned
downtime
downtime
Lubrication,
Oil changes, filter calibration,
Example replacements, visual component Emergency repairs,
inspections replacements part replacements
2] draw and explain the circuit diagram to perform noload and blocked rotor
ee phase induction motor

No-Load Test and Blocked Rotor Test on a Three-Phase Induction Motor

Purpose:
• No-Load Test: To determine the core losses, friction and windage losses,
and no-load current of the motor.
• Blocked Rotor Test: To determine the equivalent resistance and
reactance of the motor referred to the stator.
Circuit Diagram:

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Circuit Diagram for NoLoad and Blocked Rotor Test on a ThreePhase
Induction Motor Procedure:
No-Load Test:

1. Connect the motor as shown in the circuit diagram.

2. Apply rated voltage to the stator winding.

3. Measure the input power (Pno-load), input current (Ino-load), and input
voltage (Vno-load).
Blocked Rotor Test:

1. Block the rotor shaft from rotating.

2. Apply reduced voltage (around 15-25% of rated voltage) to the stator

winding.
 3. Measure the input power (Pblocked), input current (Iblocked), and input
voltage (Vblocked).
Calculations:
No-Load Test:
• No-Load Power: Pno-load = √3 * Vno-load * Ino-load * cos(φno-load)
• No-Load Current: Ino-load (measured)
• No-Load Power Factor: cos(φno-load) = Pno-load / (√3 * Vno-load *
Inoload)
Blocked Rotor Test:
• Blocked Rotor Power: Pblocked = √3 * Vblocked * Iblocked *
cos(φblocked)
• Blocked Rotor Current: Iblocked (measured)
• Blocked Rotor Power Factor: cos(φblocked) = Pblocked / (√3 * Vblocked
* Iblocked)
• Equivalent Resistance (R0): R0 = Pblocked / (3 * Iblocked^2)
• Equivalent Reactance (X0): X0 = √((Vblocked / (√3 * Iblocked))^2 - R0^2)
Explanation:
No-Load Test:
• When the motor runs at no-load, the input power is mainly consumed
by core losses, friction and windage losses, and a small amount of
copper losses.
• The no-load test helps to determine these losses and the no-load
current, which is important for motor performance analysis.
Blocked Rotor Test:
• When the rotor is blocked, the slip is 1, and the rotor impedance is very
low.
• This test simulates a short-circuit condition and helps to determine the
equivalent resistance and reactance of the motor referred to the stator.
 • These parameters are crucial for predicting motor performance under
various load conditions.
Note:
• The blocked rotor test should be performed for a short duration to avoid
overheating of the motor.
• The reduced voltage is applied to limit the current to a safe level.
By performing these two tests, the performance characteristics of a
threephase induction motor can be determined, which is essential for motor
selection and design.
Symptom Possible Causes Remedial Actions
Overload, Faulty cooling Reduce load, Check and repair
system, High ambient cooling system, Improve
Overheating
temperature, Insulation ventilation, Investigate and repair
breakdown insulation faults

Reduce load, Check and repair

Overload, Faulty cooling cooling system, Improve
High Oil
system, High ambient ventilation, Investigate and repair
Temperature
temperature, Internal faults internal faults (short circuits, loose
connections)

Loose connections, Core Tighten connections, Check core

Abnormal vibrations, Winding clamping, Check winding bracing,
Noise Investigate and repair internal
movement, Internal arcing faults
Loose connections,
Tighten connections, Replace
Damaged gaskets, Cracked gaskets, Repair or replace tank
Oil Leakage tank
3]Troubleshooting Chart for 3-Phase Transformers
Winding overheating, Investigate and repair overheating,
High Winding
Loose connections, Tighten connections, Investigate
Resistance
Internal short circuits and repair internal faults
 Moisture in oil,
Low Insulation Dry out transformer, Purify oil,
Contaminated oil,
Resistance Replace damaged insulation Deteriorated insulation

Q6 1 list out the routine ,type test and special test to be carried out on three
phase induction motor as per is -4029-1967 and is-325-1961.
Routine Tests:

1. Insulation Resistance Test: Measures the insulation resistance between

windings and frame.

2. High Potential Test: Applies a high voltage to check for insulation

breakdown.

3. No-Load Test: Determines no-load losses and magnetizing current.

4. Blocked Rotor Test: Measures rotor resistance and reactance.

5. Temperature Rise Test: Checks temperature rise under full load.

Type Tests:

1. Dielectric Test: Verifies insulation strength.

2. Overload Test: Checks performance under overload conditions.

3. Voltage Withstand Test: Assesses withstand voltage capability.

4. Vibration Test: Evaluates vibration levels.

Special Tests:

1. Noise Level Test: Measures noise generated by the motor.

2. Efficiency Test: Determines motor efficiency.

3. Power Factor Test: Measures power factor at various loads.

4. Starting Torque Test: Measures starting torque.

5. Pull-Up Torque Test: Measures pull-up torque.

Note: The specific tests and their requirements may vary depending on the
motor's size, voltage rating, and application.
2] explain with neat diagram back to back test on single phase transformer to
determine efficiency and regulation
Back-to-Back Test on Single-Phase Transformer
The back-to-back test, also known as the Sumpner's test, is a highly efficient
method for determining the efficiency and voltage regulation of two identical
single-phase transformers. It eliminates the need for a large external load,
making it particularly suitable for testing large power transformers.
Test Setup:

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BacktoBack Test on SinglePhase Transformer

1. Two Identical Transformers: The test requires two identical single-phase

transformers.

2. Primary Connection: The primary windings of both transformers are

connected in parallel to a suitable AC supply.

3. Secondary Connection: The secondary windings are connected in series,

but with their polarities reversed (i.e., in opposition).

4. Low Voltage Supply: A low voltage supply is connected across the

seriesconnected secondary windings.

5. Instruments:
o Voltmeter (V1): Measures the primary voltage. o Ammeter (A1):
Measures the primary current. o Wattmeter (W1): Measures the
total input power to the primary.
 o Voltmeter (V2): Measures the voltage across the secondary
windings.
o Ammeter (A2): Measures the secondary current.
o Wattmeter (W2): Measures the power input to the secondary.
Test Procedure:

2. No-Load Test:
o Adjust the low voltage supply to zero. o Record the primary
voltage (V1), primary current (A1), and wattmeter reading (W1). o
The wattmeter reading (W1) represents the core losses of both
transformers.
3. Full-Load Test:
o Adjust the low voltage supply to obtain rated secondary current
(A2). o Record the primary voltage (V1), primary current (A1),
wattmeter reading (W1), secondary voltage (V2), secondary current
(A2), and wattmeter reading (W2). o The wattmeter reading (W1)
represents the total losses (core losses + copper losses) of both
transformers.
Calculations:

1. Core Loss (Pi): o Pi = W1

(no-load) / 2

2. Copper Loss (Pc): o Pc =

(W1 - W2) / 2

3. Efficiency:
o Efficiency = (Output Power) / (Input Power) o Efficiency = (V2 *
A2) / (V1 * A1)

4. Voltage Regulation:
o Voltage Regulation = ((No-Load Secondary Voltage - Full-Load
Secondary Voltage) / Full-Load Secondary Voltage) * 100 Advantages
of Back-to-Back Test:
 • High Efficiency: The test is very efficient as most of the power is
circulated between the transformers.
• Accurate Results: Provides accurate measurements of efficiency and
voltage regulation.
• No External Load Required: Eliminates the need for a large external
load.
• Suitable for Large Transformers: Particularly useful for testing large
power transformers.
By performing this test, engineers can accurately determine the efficiency and
voltage regulation of single-phase transformers, ensuring their reliable and
efficient operation in power systems.
3 ]explain the classification of insulating material as per isi -1271-1958.with
class information ,insulating material [any three class wise ]and its maximum
operating temperature
Purpose of Classification:
• Safety: The classification helps prevent electrical failures and potential
hazards like short circuits, fires, and electric shocks.
• Equipment Performance: Using the correct insulation material ensures
that electrical equipment operates efficiently and reliably within its
designed temperature limits.
• Material Selection: The classification guides engineers and technicians in
selecting the appropriate insulating material for specific applications.
Key Considerations in Classification:
• Temperature: The most critical factor is the maximum temperature the
material can withstand without significant degradation of its insulating
properties.
• Electrical Properties: Factors like dielectric strength, resistivity, and
power factor are also considered.
• Environmental Factors: Resistance to moisture, chemicals, and other
environmental conditions is important.
Examples of Insulating Material Classes:
 • Class Y (Cotton):
o Max. Operating Temperature: 90°C
o Characteristics: Relatively low-temperature application, commonly
used in low-voltage applications where temperature rise is
minimal.
• Class E (Ebonite):
o Max. Operating Temperature: 60°C
o Characteristics: Good mechanical strength and electrical
properties, but limited temperature range.
• Class A (Mica):
o Max. Operating Temperature: 180°C
o Characteristics: Excellent thermal stability and high dielectric
strength, widely used in high-temperature applications like motors
and transformers.
Other Classes (Beyond the provided examples):
• Class B: Materials like glass fiber and silicone resins, with a higher
temperature rating than Class A.
• Class F: Materials like Nomex and polyesterimide, suitable for even
higher temperatures.
• Class H: Materials like ceramics and polyimide films, for the most
demanding high-temperature applications.
End of answers of summer 4