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Substation Year 3 Level 4 > Substation Operation And Maintenance Power Transformers 1 > Flashcards

Substation Operation And Maintenance Power Transformers 1 Flashcards

(61 cards)

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1
Q

What is a transformer?

A

A device that transmits AC power from one circuit to another by electromagnetic induction.

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2
Q

Why are transformers used in power systems?

A

To increase voltage for efficient transmission and reduce voltage for distribution to consumers.

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3
Q

What are the essential parts of a transformer?

A

Primary winding, secondary winding, and a core.

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4
Q

What is the primary winding?

A

A coil of insulated wire connected to a circuit that supplies AC power.

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5
Q

What do the labels H1 and H2 represent?

A

The leads of the primary winding, generally indicating higher voltage connections.

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6
Q

What is the secondary winding?

A

A coil of insulated wire connected to a circuit with a load.

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7
Q

What do the labels X1 and X2 represent?

A

The leads of the secondary winding, generally indicating lower voltage connections.

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8
Q

What is the core of a transformer made of?

A

Typically laminated metal to reduce energy loss.

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9
Q

Is there a direct electrical connection between transformer windings?

A

No, the core and windings are insulated.

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10
Q

What creates the magnetic field in a transformer?

A

Alternating current flowing through the primary winding.

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11
Q

How is voltage induced in the secondary winding?

A

Through electromagnetic induction as the magnetic field cuts across it.

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12
Q

What determines the difference in voltage between primary and secondary windings?

A

The transformer’s turns ratio.

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13
Q

What is a transformer’s turns ratio?

A

The number of times the primary wire is wound around the core compared to the secondary wire.

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14
Q

If the primary has 8 turns and secondary has 2, what is the turns ratio?

A

4:1

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15
Q

How does a turns ratio of 4:1 affect voltage?

A

It reduces the voltage to 1/4 of the primary voltage.

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16
Q

What is a step-down transformer?

A

A transformer that reduces voltage.

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17
Q

What is a step-up transformer?

A

A transformer that increases voltage by having more turns on the secondary than the primary.

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18
Q

If the turns ratio is 1:5 and the primary voltage is 100 volts, what is the secondary voltage?

A

500 volts.

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19
Q

What are the three types of transformers commonly found in substations and switchyards?

A

Power transformers, current transformers, and potential transformers.

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20
Q

What is the main function of a power transformer?

A

To transfer electrical power between circuits at different voltage levels.

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21
Q

What are current transformers (CTs) used for?

A

To reduce high current levels to a lower, safer level for measurement and protection equipment.

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22
Q

What are potential transformers (PTs) used for?

A

To reduce high voltage levels to lower levels suitable for metering and protective relays.

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23
Q

How do these transformer types differ from each other?

A

Each type is designed with unique features based on its function: power handling (power transformers), current sensing (CTs), and voltage sensing (PTs).

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24
Q

What distinguishes power transformers from other substation equipment?

A

Power transformers are large, stationary units designed to transfer electrical energy between circuits at different voltage levels.

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25
What are bushings on a transformer?
Insulated devices that allow conductors to pass through the transformer tank without contact.
26
Why are transformer bushings important?
They maintain electrical insulation and mechanical support where conductors enter or exit the transformer.
27
What is the transformer tank filled with?
Usually filled with insulating oil that helps cool and insulate internal parts.
28
What are radiators on a transformer?
External components used to dissipate heat from the transformer oil to the surrounding air.
29
How does oil move through the radiators?
Either by natural convection or by using pumps to circulate the oil.
30
What is the function of cooling fans on transformers?
To increase the rate of heat transfer from radiators, improving cooling efficiency.
31
Why do power transformers need to be cooled?
Because they generate significant heat during operation, which must be managed to prevent overheating and equipment failure.
32
What are the two main cooling methods for transformers?
Natural cooling and forced cooling.
33
What is natural cooling?
A method where heat is dissipated without external assistance—typically using radiators and convection.
34
What is forced cooling?
A method where cooling is enhanced using fans or pumps to move air or oil and increase heat dissipation.
35
What are the two most common types of transformer cooling systems?
Oil-immersed self-cooled (OA) and oil-immersed forced-air cooled (OA/FA).
36
How does OA (Oil-immersed Self-cooled) work?
Heat generated in the transformer is carried by oil to the radiators, where it is dissipated naturally into the surrounding air.
37
How does OA/FA (Oil-immersed Forced-air cooled) work?
It uses fans to blow air over the radiators to enhance cooling.
38
What type of oil is typically used in transformers?
Mineral oil is the most common, though some use silicone or other less flammable alternatives.
39
What is the function of insulating oil in transformers?
It provides both electrical insulation and cooling for internal components.
40
What does a conservator tank do in a transformer?
It allows for oil expansion and contraction due to temperature changes without exposing the oil to the outside atmosphere.
41
What is the purpose of a breather in a conservator system?
It filters and dries air entering the conservator to prevent moisture contamination of the oil.
42
How does the conservator system reduce oxidation?
By minimizing the oil’s exposure to air, it helps reduce oxidation and contamination.
43
What is a bladder or diaphragm used for in some conservator systems?
To separate the oil from the air completely, offering better protection against moisture and oxidation.
44
What is the purpose of a sealed-tank transformer?
It prevents contact between the insulating oil and outside air, reducing contamination and moisture absorption.
45
How do sealed-tank transformers accommodate oil expansion?
By using flexible diaphragms or nitrogen gas cushions to handle internal pressure changes.
46
What role does nitrogen gas play in some sealed transformers?
It provides a pressure cushion and prevents air (and moisture) from contacting the oil.
47
Why are pressure relief devices important in sealed transformers?
To vent excess internal pressure safely, protecting the tank from rupture.
48
What is the function of a pressure/vacuum gauge on a sealed transformer?
It monitors internal pressure and alerts operators to abnormal pressure conditions.
49
How is oil condition typically monitored in a sealed transformer?
Through sight glasses and sample ports for inspecting oil levels and testing quality.
50
What is a load tap changer (LTC)?
A device used to adjust the transformer's output voltage under load without interrupting power.
51
Where is a load tap changer usually located?
Inside a separate compartment attached to the main transformer tank.
52
What does the LTC do when system voltage changes?
It adds or removes winding taps to raise or lower the output voltage accordingly.
53
What is the benefit of using an LTC?
It helps maintain steady voltage levels to customers despite changes in system load.
54
What is an important maintenance consideration for LTCs?
Regular inspection and servicing are crucial due to their moving parts and arcing contacts.
55
What kind of fluid is often used in LTC compartments?
Insulating oil, similar to or the same as in the main transformer tank.
56
What is a no-load tap changer (NLTC)?
A device used to change the transformer voltage ratio, but only when the transformer is de-energized.
57
How does an NLTC differ from a load tap changer (LTC)?
An NLTC can only be adjusted when the transformer is offline, whereas an LTC operates under load.
58
When is an NLTC typically used?
During installation or scheduled maintenance, to match system voltage requirements.
59
How many tap positions are usually available in an NLTC?
Typically 5 positions: 2 above nominal, 2 below, and 1 at nominal voltage.
60
Why must the transformer be de-energized for NLTC adjustment?
To prevent arcing and equipment damage, as the device is not built for live switching.
61
What is the main purpose of both LTCs and NLTCs?
To regulate and optimize voltage for system stability and customer service quality.

Substation Year 3 Level 4 (3 decks)

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