Transformers Lvl II Test Prep

a reactor should have about ? impedance to reduce notch depth by about 50%

3%

A ? reduction in notch depth is enough to eliminate extra zero crossovers that cause problems

50% Note: Higher impedance may cause problems with sensitive equipment because the wider notch may be seen as a loss of voltage. Lower impedance may not reduce the notch depth enough to eliminate problems.

which of the following is used for the imput reactors. a. A motor drive causes notching b. Low line impedance allows high inrush current c. Power factor correction capacitors are used d. All of the above

All of the Above

a ? is a reactor used to reduce common-mode noise current generated by the rapid switching of a motor drive or a signaling device

Common-mode choke

? is a type of electromagnetic interference induced on power or communication lines

Common-mode noise

A saturable- Core reactor consists of one winding

False

Drive isolation transformers cannot provide protection from common mode transients that originate with the primary source t/f

False

Electrostatic shield can prevent common-mode noise from transferring from the transformers primary to the secondary only if the secondary is grounded

False

With 3-phase motor drives that use SCR 6-pulse (6-diode)rectifiers, only one SCR can be on at any given time

False

in a saturable- core reactor, large amounts of DC current can be controlled by a small amount of AC current

False

Which of the following are benefits associated with grounding the secondary of a drive isolation transformer? I. Grounding provides superior transient and impulse immunity to the load side of the transformer. II. Grounding reduces common-mode noise coupling from primary to secondary. III. Grounding prevents induced ground current from transferring upstream into the primary system. IV. Grounding will reduce the total harmonic distortion in the primary of the system.

Grounding provides superior transient and impulse immunity to the load side of the transformer. Grounding reduces common mode noise coupling from primary to secondary Grounding prevents induced ground current from transferring upstream into the primary system.

Which of the following is not a basic function of a drive isolation transformer? a. Common-mode noise reduction b. Increase of notch depth c. Reduction of drive-induced ground currents d. Voltage change

Increase of notch depth

Which of the following is not a basic function of a drive isolation transformer.a. Common-mode noise reduction b. Increase of notch depth c. Reduction of drive-induced ground currents d. Voltage change

Increases notch depth

A drive isolation transformer is designed with additional ? to reduce power quality problems associated with non linear loads a. flux b. reactance c. resonance d. shielding

Reactance

A ? is a coil added in series with a load to reduce inrush current voltage notching effects and voltage spikes. a. capacitor b. polarized-frequency relay c. reactor d. silicon-controlled rectifier

Reactor

All two-winding transformers are isolation transformers

True

Drive isolation transformers and like reactors both provide reactive control of distorted like current harmonics and line notching t/f

True

Drive isolation transformers protect the primary source from common energies that originate with motor drive system and can prevent ground current from transferring back through primary ground system t/f

True

Electric motors typically draw many times their full-load current during startup.

True

Nonlinear rectified power supplies are a common cause of power quality problems. t/f

True

Rectifiers are used in the starters of large synchronous motors to provide a voltage to the AC coil of the polarized-frequency relay. t/f

True

The secondary of a drive isolation transformer represents a separately derived system t/f

True

With a variable-frequency drive, unwanted pulses of current are caused by fast-changing voltages from the drive

True

Zero-crossovers are often used for timing signals and to activate equipment

True

A ? is a reactor used to restrict the current to AC or DC drives in the case of short circuits in the drive itself. a. capacitor b. choke c. polarized-frequency relay d. silicon-controlled rectifier

choke

to reduce notching a reactor can be used to add impedance. the added impedance. Increases or decreases Notch widens or narrows Width

decreases notch depth and widens notch width

A ? is a distortion in a voltage waveform where the voltage quickly drops toward zero and then returns to the correct value.

notch

? help eliminate voltage spikes by slowing down the rate of change in the drive out put voltage

output reactors

Match corresponding letter of the saturable core transformer

pg 159

The opposition to current flow that is only present in AC is ? .

reactance

A ? is an inductor whose inductance is controlled through the use of a magnetic field created by a second winding wound around the same iron core as the primary winding.

saturable-core ractor