Chapter 3 Review
The higher the level of the distribution voltage, the more difficult and expensive it becomes to safely insulate between line wires, as well as from line wires to ground.
True
Potential transformers are used
with instruments and relays
The __________ current sets up an alternating flux in the core of a transformer.
Exciting
A current transformer is a transformer that is designed to be connected in parallel with the circuit to be monitored.
False
A step-up transformer is one in which the secondary winding current is greater than the primary winding current.
False
Compared to the high voltage side, the low voltage side of a transformer draws _________ current.
More
The principle of operation of a transformer is based on ________ induction.
Mutual
The transformer winding coil that connects to the power supply is known as the _________ coil winding.
Primary
The transformer winding coil that delivers power to the load is known as the _________ coil winding.
Secondary
A transformer has subtractive polarity when terminal H1 is adjacent to terminal X1.
True
If the phase-to-neutral voltage is 120 volts in a Wye transformer system the phase-to-phase voltage would be
208v
Current transformers are used to
supply a small amount of current that is proportional to the main current
Conduit conductor capacity is generally based on a _______ fill ratio.
40%
The secondary winding of a current transformer is designed to produce a standard current of
5a
For a given amount of power delivered, doubling the transmission voltage cuts the electrical loses by _________.
75%
The efficiency of a transformer is typically in the _______ range.
90%
High voltages are used in transmission lines to reduce the transmission __________.
Current
An autotransformer has electrical isolation between the primary and secondary circuits.
False
If the secondary circuit of a transformer becomes overloaded, the primary circuit will not be affected.
False
Movement of the coils within a transformer produces the transformation of voltage.
False
Relatively large diameter conductors are used in electrical utility transmission systems.
False
Single-phase power is usually supplied to an industrial customer.
False
The low-voltage winding leads on a single-phase transformer are identified as H1 and H2.
False
The switchboard is usually supplied from the panelboard.
False
Conductors that deliver energy from the service equipment to the final branch circuit overcurrent device are known as
Feeder Conductors
Substations contain step-down _________ that reduce the voltage.
Transformers
For an ideal transformer, the power input is equal to the power output.
True
In a Delta-connected transformer, the phase and line voltages are equal.
True
Instrument transformers provide insulation between the instrument and the high voltage of the power circuit.
True
The voltage ratio of a transformer is equal to its turns ratio.
True
When a 240/480 volt dual primary control transformer is to be operated from a 240 volt system the primary winding are connected in parallel.
True
Without transformers the widespread distribution of electrical power would be impractical.
True
When the secondary winding of a transformer is disconnected from the load,
Very little current flows in the primary
Three-phase transformers are normally connected in_________ or _________.
Wye Delta
The low-voltage windings leads on a single-phase transformer are marked
X1 and X2
A control transformer is used to
reduce the voltage for motor control circuits
An autotransformer motor starter reduces the starting current to the motor by
reducing the value of the applied voltage
A motor control center is a modular structure designed specifically for plug-in-type control units and motor control.
True
The unit substation is completely enclosed on all sides with sheet metal so that no live parts are exposed.
True
Transformer power is rated in volt-amperes instead of watts.
True
Transmitting large amounts of electric energy over fairly long distances is accomplished most efficiently by using high-voltages.
True
The phase windings of a three-phase transformer are _______ electrical degrees apart.
120
The secondary low-voltage side of a potential instrument transformer is usually wound for
120v
What is the operating voltage of most commercial and industrial magnetic control systems?
120v
