Chapter 11 Flashcards
The __________________________station of power generation and distribution enables power to be produced at one location for immediate use at other distant locations.
Central
Without the use of _______________________ to efficiently raise and lower voltage levels, the widespread distribution of electrical power would be impractical.
Transformers
High voltages are used in transmission lines to reduce the transmission ___ .
a. Resistance
b. Current
c. Power
d. Power factor
B
- Relatively large diameter conductors are used in electrical utility transmission systems.
__________ (True/False)
- The higher the level of the distribution voltage, the more difficult and expensive it becomes to provide for adequate insulation of the conductors.
__________ (True/False)
- Three-phase power is usually supplied to commercial and industrial customers.
__________ (True/False)
F
T
T
For the distribution system shown in Figure 3-1, determine the value of the current transmisison
r
Compared to the low-voltage side, the high-voltage side of a power transformer draws ____ current.
a. More
b. Less
c. The same
d. A fixed amount of
b
Substations contain __________________________ ________________________ that reduce the transmission voltage levels.
step-down
Transformers
The three major sections of the unit substation are:
a. ___________________________
b. ___________________________
c. ______________________________
High voltage primary switch gear
Transformer Section
Low-Voltage Distribution
- The unit substation is left open on the back for convenient access to all parts.
__________ (True/False)
- Before attempting to open the primary switch on a unit substation, you should disconnect the loads from the transformer.
__________ (True/False)
- Electrical distribution systems within buildings are required to safely deliver electrical energy without any component overheating or unacceptable voltage drops.
__________ (True/False)
F
T
T
Correct selection of conductors for feeders and branch circuits must take
into account \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ , \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, and \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ .
Ampacity
Short Circuit
Voltage Drop
In installing motors and motor controllers, which of the following needs to be adhered to (accurately followed)?
a. NEC
b. State and local codes
c. Manufacturer’s instructions
d. All of these Answer: _______
d
. Identify the three
major sections of the
electrical
distribution system
shown in the
diagram.service entrance
feeders
branch circuits
Identify the three types of raceways shown in figure 3-3:
a. ________________________________
b. ________________________________
c. ________________________________
Rigid and flexible conduit
Busway
Cable Tray
Conduit capacity is generally based on a _______ fill ratio.
a. 90%
b. 80%
c. 60%
d. 40%
Answer: _______
d
A panelboard is usually supplied from a switchboard and further divides the power distribution system into smaller parts.
T
What is the value of the line-to-neutral voltage for the three-phase four-wire panelboard feeder circuit shown in Figure 3-4?
480/root 3
277 for
. The proper grounding and bonding of an electrical distribution system ensures that any person who comes in contact with any
______________________ parts of the installation will not receive an electric shock.
energized
- The impedance of the ground path is kept to a maximum.
__________ (True/False) - The equipment grounding bus is noninsulated and connects directly to the panelboard metal enclosure.
__________ (True/False)
- Main lug type panelboards contain a main breaker that is an integral part of the panelboard.
__________ (True/False)
- A motor control center is normally designed to accommodate plug-in-type motor control units.
__________ (True/False)
F
T
F
T
Correctly identify the three-phase buses (A-B-C) for the panel bus arrangement shown in Figure 3-5.
c
B
a
Identify the components of the transformer circuit shown in Figure 3-6.
a. ____
b. __
c. ___
d. ___
e. __
f. ______
Primary winding 2nd winding core magentic flux path AC source Load
- The principle of operation of a transformer is based on __ induction.
a. Mutual
b. Self
c. Primary
d. Secondary
Answer: _______
- Movement of coils within a transformer produces the transformation of voltage.
__________ (True/False)
A
F
- For an ideal transformer, the power input is equal to the power output.
__________ (True/False) - Transformer power is rated in volt-amperes instead of watts.
__________ (True/False) - The voltage ratio of a transformer is equal to its turns ratio. __________ (True/False)
- A step-up transformer is one in which the secondary winding current is greater than the primary winding current.
__________ (True/False)
T
T
T
F
For the transformer circuit shown in Figure 3-7 determine the:
a. Turns ratio: _______________________________
b. Value of the secondary voltage: ____________________
5:1
120 Volts
- The efficiency of a transformer is typically in the __ range.
a. 90 percent
b. 80 percent
c. 60 percent
d. 40 percent
Answer: _______
- If the secondary circuit of a transformer becomes overloaded, the primary circuit will not be affected.
__________ (True/False)
a
F
- When the secondary winding of a transformer is disconnected from the load:
a. Zero current flows in the primary
b. Very little current flows in the primary
c. The primary current remains the same as under load
d. The primary current becomes very high Answer: _______
- A transformer is being designed to increase the voltage from 12 V to 120 V. If the primary requires 400 turns of wire, how many turns are required on the secondary?
b
4000 turns
For the transformer circuit shown in Figure 3-8 determine the:
a. Value of the secondary current flow: ___________________
b. Value of the primary current flow: _____________________
c. Value of the primary voltage: __________________________
20a
5a
480V
- The high-voltage winding on a single-phase transformer are identified as Xl and X2.
__________ (True/False) - On a transformer, when the lead marked H1 is instantaneously positive, the lead marked X1 will be instantaneously____ .
Answer: ______________________
F
Positive
- A transformer has subtractive polarity when terminal HI is adjacent to terminal Xl.
__________ (True/False) - What is the most popular operating voltage of commercial and industrial motor control systems?
a. 120 V
b. 208 V
c. 440 V
d. 600 V
Answer: _________
T
A
The primary of the three-phase transformer connection shown in
figure 3-10 is connected in a _________________ configuration and the
secondary is connected in a __________________ configuration.
delta
Wye
- In three-phase transformer systems, the constant ______ is used because the transformer phase windings are 120 electrical degrees apart.
a. 3
b. 2.5
c. 1.73
d. 0.707 Answer: _______
- In a Delta-connected transformer secondary, the phase and line voltages are equal. __________ (True/False)
C
T
For the Wye distribution system shown in Figure 3-11, if the voltage between any two line leads is 208 V, the voltage from any line lead to neutral would be __________ V.
120 V
- An autotransformer has electrical isolation between the primary and secondary circuits.
__________ (True/False) - An autotransformer motor starter reduces the starting current to the motor by:
a. Inserting resistance in series with the motor
b. Reducing the value of the applied voltage
c. Reducing the load on the motor
d. Reducing the frequency of the applied voltage
Answer: _______
F
B
- The secondary low-voltage side of a potential instrument transformer is usually wound for:
a. 5 volts
b. 10 volts
c. 24 volts
d. 120 volts
Answer: _______
- For the circuit of Figure 3-12, transformer X is a _________________
transformer, while transformer Y is a _________________transformer.
d
potential
current
- Instrument transformers provide insulation between the instrument and the high voltage of the power circuit.
__________ (True/False)
- A current transformer should always have its secondary shorted when there is current flow in the primary winding but no load connected to the secondary.
__________ (True/False)
T
T
For Wye connections
what is equation for line voltage when you know phase voltage
eLine=ePhase x 1.73
For “wye” connections, what is the formula for calculating phase voltage (EPhase) when you know line voltage (Eline)?
ePhase=eLine/1.73
For “wye” connections, what is the relationship between line (ILine) and phase (IPhase) currents?
iLine=iPhase
For “delta” connections, what is the relationship between line (ELine) and phase (EPhase) voltages?
eLine=ePhase
For “delta” connections, what is the formula for calculating line current (ILine) when you know phase current (IPhase)?
iLine=Iphase*1.73
For “delta” connections, what is the formula for calculating line current (ILine) when you know phase current (IPhase)?
iPhase=iLine/1.73
Delta lady
LIPS
LINE phase times 1.73
Wye
They are both lisp but for eye connection it’s the current that’s he same
