NCCER LEVEL 3 Module 7 'Transformers'

Conductors connected to the high leg of a four-wire delta system be color-coed with what color of insulation or tape?

Orange (NEC Section 110.15)

Dry-type transformers rated at 112.5kVA or less may be located out in the open provided they are separated from combustible material by a distance of ____.

12"

If the power factor is improved by the addition of a capacitor, the motor running overcurrent device must be selected based on the ___.

reduced current

Except for motors starting service, insulated conductors used for connections between resistors and motor controllers must be rated at not less than ___.

90 C

A transformer reads zero volts across the output terminals. The cause is most likely ____.

an open circuit

When performing maintenance on dry-type transformers, check for cracked insulation on transformers over ____.

1,000V

The main purpose of a transformer is to ______________ .

Change the output voltage

The three parts of a basic transformer are the ___.

primary winding, secondary winding, and core

When AC flows through a transformer coil, the field generated around the coils is a ___.

magnetic field

When the field from one coil cuts through the turns of a second coil,?

voltage will be generated

What causes voltage to be induced in a transformer?

Mutual induction

The three basic types of iron core transformers are ___.

closed core, open core, and shell

One effect caused by a magnetic leakage in transformers is a ___.

lower secondary voltage

If one of the transformers is damaged in a delta system, the configuration that may be used to temporarily carry the load is called a(n) ___.

open delta configuration

The windings in an autotransformer ___.

share part of a winding in common

Most control transformers are ___.

dry-type step-down

The power factor of a circuit can be improved by increasing the ___.

capacitance

A dry-type transformer must be housed in a vault if rated at more than ___.

35kV

A symptom of a transformer with an open circuit is ____.

no output on the secondary

The meter used to measure insulation resistance is called a(n)___.

megger

The coil that receives energy from the line voltage?

Primary

Coil that delivers energy to the load?

Secondary

What article states the specific rules for installation and protection of capacitors other than surge capacitors or capacitors that are part of another apparatus.

NEC Article 460

What NEC article covers the installation of separate resistors and reactors on electric circuits?

NEC Article 470

What is provided to either increase or decrease the secondary voltage?

Taps

A transformer can be checked for shorted turns using a(n)

TTR tester

Which transformer system provides three-phase power while allowing lightning to be connected between any of the secondary phases and the neutral?

Delta-Wye Transformer

What two leads connected increase secondary voltage by 5%? What two leads connected decreases secondary voltage by 5%?

7-2 increases by 5% and 5-4 decreases by 5%.

Where would you find 120V in a Delta - Delta 120V /240V transformer? Where is the 240V?

120V is between the center-tapped terminal and each ungrounded terminal and 240V across the full windings of each phase.

In an AC circuit how many horses are always working at varying lengths?

3 horses inductance capacitance and true power

Which of the following types of transformers can be ventilated, air-cooled, or sealed?

Dry-type transformers

which of the following types of Transformers are installed in a vault?

oil insulated Transformer