Core Topics 2013

Question 1

The inducing of an EMF in a coil or conductor by magnetic flux lines generated in another coil or conductor is called

Answer 1

Mutual Induction

Question 2

The construction of a basic transformer consists of the following components:

Answer 2

• Primary winding
• Secondary winding (s)
• Magnetic circuit
• Enclosure

Question 3

The _______ winding is the winding where energy is applied. It may be either the high voltage or low voltage winding. Usually the _______ from the core in power transformers.

Answer 3

Primary

Furthest

Question 4

The mathematical expression for the transformer voltage turns ratio is:

Answer 4

Ep/Es = Np/Ns
or
Ep Ns = Es Np

Question 5

The _________ is the ratio between the currents in the primary and secondary of a transformer and is in __________ proportion to the turns-ratio

Answer 5

current ratio

inverse

Question 6

__________ are the most common type used in the transfer of electrical power.

Answer 6

Iron core transformers

Question 7

The cores of iron core transformers are designed to:

Answer 7

• Minimize flux leakage.
• Accommodate various winding configurations.
• Accommodate specific size requirements

Question 8

In an __________ the windings are wound around an insulation or non-magnetic form.

Answer 8

air-core transformer

Question 9

__________ consist of a single winding serving as both the primary and secondary.

Answer 9

Autotransformers

Question 10

__________ can be designed with multiple taps or slider to provide a wide range of input and output voltages

Answer 10

Adjustable transformers

Question 11

__________ maintain a constant output voltage with varying input voltage.

Answer 11

Regulating transformers

Question 12

In a __________ connected transformer winding, one end of each of the leads is connected together. The three remaining leads are connected to the load or power source.

Answer 12

Wye

Question 13

In the __________ connection, the windings are connected in series to form a closed loop

Answer 13

Delta

Question 14

What were the two Root Causes leading to multiple failures associated with the Main Bank Transformer.

Answer 14

RC1 – Inappropriate material performance of the silicon polymer insulation prevented proper control of environmental contamination

RC2 – Engineers did not adhere to sound engineering principals by not using applicable codes and standards in the design of the CCVT.

Question 15

EXPLAIN the function of the Capacitive Coupled Voltage Transformers (CCVTs).

Answer 15

The Capacitive Coupled Voltage Transformers (CCVTs) are necessary in high voltage transmission and distribution systems for relaying and metering.

Question 16

The two methods by which the IDD system will use to identify a problem bushing and abnormality are:

Answer 16

1. Measured capacitance of one phase is greater than the other phases by observing an increase in leakage current
2. Power factor indicates a phase angle different from 120

Question 17

The IDD ALERTS! associated with abnormalities within the IDD itself are:

Answer 17

• Maintenance Mode – IDD records data, but does not analyze the data
• Unable to obtain information – Information processing not functioning properly
• Unable to obtain recording – Hardware issue between IDD and Bushing CTs

Question 18

The IDD ALERTS! associated with abnormal trends are

Answer 18

• Power Factor
o Slightly changed - Closely monitor
o Moderately changed - Investigate at earliest opportunity
o Severely changed - Investigate imediately

• Capacitance – Provides the same ALERTS! as Power Factor

Question 19

Name three types of fittings used for Electrical Penetrations @ DCPP

Answer 19

• Swagelok Fittings (Most common)
• Hi-Seal
• Gyrolok

Question 20

Name the three levels of FR clothing

Answer 20

Single-Layer Flame Resistant (SLFR): minimum rating of 8 cal/cm2.

Double-Layer Flame Resistant (DLFR): minimum rating of 15 cal/cm2

Suited: (15 cal/cm2 to 100 cal/cm2)

Question 21

State the purpose of the brushless exciter

Answer 21

The Brushless Exciter is Designed to produce the generator field voltage and current required from no load to rated load. This provides rated output of the generator during normal and grid transient conditions

Question 22

Name the 4 major components of the brushless exciter

Answer 22

1. Permanent Magnet Generator (PMG)
   • Provides a continuous source of AC power for excitation without the use of brushes or collector rings
2. AC Exciter Stator
   • Provides a continuous magnetic field.
3. AC Exciter Rotor
   • Induces an AC voltage in the three-phase exciter rotor windings.
4. Rectifier/Fuse Wheel.
   • Converts 300Hz, 3 phase AC from the AC exciter into DC for application to the generator field.

Question 23

How does the permanent magnet generator produce electricity without the use of brushes or slip rings?

Answer 23

Magnets rotate around conducting wires, this rotation creates electricity

Question 24

AC Exciter is composed of what two parts

Answer 24

a Stator and a Rotor

Question 25

Name the components make up the Fuse Wheel (rotating rectifier)

Answer 25

Diodes (120)
Full-wave rectifier
Fuses

Question 26

a localized dielectric breakdown of a small portion of electrical insulation. It can be initiated by voids cracks or inclusions within a solid dielectric.

Answer 26

Partial Discharge

Question 27

PD generally occurs in systems operating at voltages of _______ or above

Answer 27

3000