Midterm

90°

In a pure inductive circuit, the current lags the voltage by _____

Np / Ns = Is / Ip

The number of turns needed for a full scale range of a amperes can be calculated using the formula_______

heat

If ______is not removed from transformer, it will build up to an extremely high temperature and eventually destroy the insulation in the transformer

Variac or Powerstat

If a rotary switch were to be removed and replace with a sliding tab that may contact directly with the transformer winding, the turns ratio Could be adjusted continuously. This type of transformer is commonly referred to as a _____Depending on the manufacturer.

Ep / Es = Np / Ns

If the amount of voltage applied to the load is to be computed, the formula______can be used.

Declination

The angular difference between true North and magnetic north is known as the angle of

No line isolation

The auto transformer has one disadvantage since the load is connected to one side of the powerline, there is_____between the incoming power and the load.

X

The current-limiting property of the inductor is called the reactance and is symbolized by the letter_____.

E = I x R

The formula for Ohm's law is

Ephase = Eline / 1.732

The formula used to compute the voltage in a Wye-connected system is_____

Maximum symmetrical

The minimum interrupting rating permitted for a fuse or circuit breaker in a specific installation is the______fault current available at the location of the protective device.

Rise to its maximum value

When a resistive load is suddenly connected to a source of direct current, the current will instantly______

Center-tapped

When a transformer bank must supply both three-phase and single phase loads, the utility company will often provide an open-Delta connection with one transformer_______

Inductive Reactance

____ is an induced voltage and is, therefore, proportional to the three factors that determine the Induced voltage

Fuses or circuit breakers

______Can be used as the branch circuit protective devices in circuits supplying power to transformers

Percent

______Impedance is an empiracal value that can be used to predict transformer performance

primary winding

_______Of a current transformer must be connected in series with the load.

Three inductors are connected in parallel. inductor 1 has an inductance of 2.5 H, inductor 2 has an inductance of 1.8H, and inductor3 has an inductance of 1.2H. The total inductance of this circuit is_____H

0.559

case

A dialectric oil provides electrical insulation between the windings and the _____

(L1 x L2)/(L1 + L2)

A formula that can be used to find the total Inductance of parallel Inductors is LT =______

30

Assume that an isolation transformer has 240 turns of wire on the primary and 60 turns of wire on the secondary. This is a ratio of 4:1 (240/60 = 4) Now assume that 120V is connected to the primary winding. The voltage of the seconday winding is____V

95% to 98%

Autotransformers have very high efficiencies, most in the range of_____

1.732

High-leg voltage can be computed by increasing the single phase center tapped voltage by_____

star

The Wye, or_____, connection is made by connecting one end of each of the three phase windings together.

maximum

The ability of a fuse or circuit breaker to open under the _____fault current is expressed as the interrupting rating of the device

Power

The amount of Core material needed for a particular transformer is determined by the_____rating of the transformer

Induced

The amount of _____voltage in an inductor can be computed if the resistance of the wire in the coil and the amount of current are known

An = A1 + (A2-A3)

The amount of current flow in a neutral conductor will be the sum of the unbalanced load between lines L2 and L3, with the addition of the current flow in the high leg, L 1. To determine the amount of neutral current, use the formula______

Turns of wire

Two factors that determine the number of flux lines produced by an electromagnet are the number of_____And the amount of current flow through the wire

heating

Will demagnetize an object

Toroid

_______Transformer is a transformer constructed with a hollow core, similar to a donut in that it has a hole in the middle

Zero

If power is applied to the transformer bank before the Delta connection is closed. The voltmeter should indicate_____ volts.

3 x Ephase x Iphase

If the phase values of voltage and current in a three phase circuit are known, the apparent power can be computed by using the formula VA =______

125

If the primary current is 9 Amps or more, the fuse or circuit breaker size is set at _____% of the primary current

9

If the primary current is _____amperes or more,it is permissible to increase the fuse size to the next highest standard rating

Three-phase

If three phase transformation is needed and a three phase transformer of the proper size and turns ratio is not available, three single phase transformers can be connected to form a_______ bank

Delta

In a ______connection, line voltage and phase voltage are the same

100,000,000

In a magnetic measurement,______lines offlux are equal to one weber(wb)

Ammeter

The percent impedance is measured by connecting a ______ across the low voltage terminals and a variable voltage source across the high-voltage terminals

The primary winding of a transformer is Between points B and N, And has 120 V applied to it. There are 120 turns of wire between points be an in. The secondary of the transformer contains 40 turns of wire. Assume that the law connected to the secondary has an impedance of 10 ohms. The amount of current flow in the secondary circuit is.... Amps

4

Silicon

A ____Diode has a forward voltage drop of approximately .7 V regardless of the current flowing through it

secondary

CTs are designed to operate with_______Winding Shorted

1.732

The phase Windings of an alternator are connected in Wye. The alternator produces is a line voltage of 440 V and supplies power to two resistor gloves. One load contains resistors with a value of 4 ohms each connected in Wye. The second load contains resistors with the value of 6 ohms each, connected in Delta. Both loads are connected directly to the output of the alternator. To determine the amount of line current needed for load 2, use the following formula: I l(load 2) = I p(load 2) x______.

Buck or boost

The polarity of a transformer windings can be determined by the connecting one lead of the primary to one lead of the secondary and testing for an increase or decrease in voltage. This is often referred to as a _____connection.

Air core

When a coil is wound around a non-magnetic material such as wood or plastic it is known As a____ magnet.

One-line

A ______Diagram, which illustrates a delta-Wye Connection, is generally used to show the main power distribution system of a large industrial plant

Henry

A coil has an inductance of one____When a current change of one ampere per second results in an induced voltage of one volt

Teaser

A connection involving the use of two transformers to supply three phase power is the T-connection. In this connection, one transformer is generally referred to as the main transformer and the other is called the_______transformer

300

A current of a transformer has a ratio of 600:5 If the primary power wire is inserted through the opening, it will require a current of 600 A to the deflect the meter full scale. If the primary power conductor is looped around and inserted through the window a second time, the primary now contains two turns of wire instead of one. It requires_____Amps of current flow in the primary to deflect the meter full scale

23.1

A delta connected alternator is connected to a Wye connected resistive load. The alternator produces a line voltage of 240, and the resistors have a value of 6 ohms each. Using ohms law, we determine the amount of phase current, I p(load) =______A.

138.57

A delta-connected alternator is connected to a Wye- connected resistive load. The alternator produces a line voltage of 240 V, and the resistors have a value of 6 ohms each. If El(load) = 240V, then E P(load) = _____V

Diode

A device often used to prevent induced voltage spikes when the current flow through an inductor is stopped is the____

Their lowest scale value is too high to accurately measure low-current values

A problem with many clamp-on ammeters is that_______

VA = 1.732 x El x Il

A three phase motor is connected to a 480 V, 60 Hz line, a clamp-on ammeter indicates a running current of 68 A at full load, and a three phase wattmeter indicates a true power of 40,277W. To solve this problem, first find the amount of Apparent power in the circuit using the formula______

Winding voltage

A transformer nameplate does not list the current rating of the windings. The current rating for a winding can determined by the dividing the kVA rating by the_____

Most homes and many businesses

A very common type of isolation transformer is a distribution transformer which is used to supply power to______

voltage spike

A_____occurs when the current flow through an inductor stops, and the current decreases at an exponential rate also

X1 - X2

According to ANSI rules, the high-voltage leads of a transformer are to be marked H1 -H 2 and so forth' and the low-voltage leads are marked____, and so forth.

wrap multiple turns of wire around a jaw of the ammeter to change the secondary scale value

An ammeter with a full-scale range of 0-6 amperes would not be able to measure accurately a current flow of .2 amperes. The answer to this problem is to_____

VARs

An electrical measurement called _____ is used to measure the reactive power in a pure inductive circuit.

0.398 A

An inductor has an inductance of .8 H and is connected to 120 V, 60 Hz line. How much current will flow in the circuit if the wire resistance of the inductor is negligible?

2

And auto transformer has 2:1 turns ratio. A voltage of 480 volts is connected across the entire winding. Since the transformer has a turns ratio of 2:1, a voltage of 240 volts will be supplied to the load. Ammeters connected in series with each winding indicate the current flow in the circuit. It is assumed that the load produces a current flow of 4 amperes on the secondary. A current flow of_____amperes is supplied to the primary.

125

Assume line L1 has a current flow of 100 A, line L2 has a current of 75 A, and line L3 has a current low of 50A. The amount of current flow in the neutral conductor would be _____amps.

31.25

Assume that a single phase transformer is 2400/480V 15kVA transformer. The full load current rating of the secondary winding is______A.

250

Assume that an amateur provides range values of 5 A, 2.5 A, one amp, and .5 A. Also, assume that the meter movement requires a current flow of 100 Milla amps to deflect the meter pool scale and that the primary of the current transformer contains five turns of wire. The number of turns needed for a full scale range of 5 A is_______ turns

AC ammeters

Current transformers are used to change the full scale range of_____

63.2%

Each time constant in an exponential curve is equal to _____% of some value.

120°

In a delta connection where one transformer is center tapped to form a neutral conductor, the two lines are 180° out of phase when compared with a center tap. In the Wye connection, lines will be _____out of phase

One of the transformers to be larger

In a given circuit, three phase loads has a power requirement of 75 kVA, and the single phase load requires an additional 50 kVA. Three 25 kVA transformers could be used to supply the three phase power needed. The addition of a single phase load,however, requires_____.

Carry the vector sum of the unbalanced current

In a given three phase transformer connection with a delta connected primary and Wye connected secondary, the secondary has been center tapped to form a neutral conductor. The neutral conductor will_____

Changing resistance values

In a given transformer bank, the three loads form a delta-connected load. If these three loads are intended to be used as single-phase loads, they will in all likelihood have______

El / 1.732

In a three phase transformer, the phase value of the primary voltage can be computed using the formula Ep(primary) =_____

English

In the_____System, the term used to describe the total force producing a magnetic field, or flux, is magnetomotive force(mmf)

eddy current

Iron-core inductors cannot be used for high frequency applications because of______Loss and hysteresis loss in the core material

27,800

It takes______ dynes Two equal a force of 1 ounce

Domains

Magnetic materials contain tiny magnetic structures in the molecular material known as magnetic______

diamagnetic

Materials are either metal or nonmetal materials that cannot be magnetized

Less than noncontinuous load plus 125% of the continuous load

NEC 215.2A states that the rating of a branch circuit shall not be_____

Saturation

Occurs when all the molecules of the magnetic material are lined up

I = VA / E

One of the formulas for determining current in a single phase circuit is_____

Diametrical

One of the most common three phase 6-phase connections is the _______connection.

75

One reason why three phase power is superior to single phase power is that in a balanced three phase system, the conductors need to be only about______% of the size of conductors for a single phase 2 wire system of the same KVA rating

voltage and current

Only phase values of______ Can be used when computing transformer values

440

The phase windings of an alternator are connected in wye. The alternator produces a line voltage of 440 V and supplies power to 2 resistive loads. One load contains resistors with a value of 4 ohms each, connected in Wye. The second load contains resistors with a value of 6 ohms each, connected in Delta. Both loads are connected directly to the output of the alternator. The line voltage for both Loads 1 and 2 will be the same,_____V

Left hand rule

The polarity of an electromagnet can be determined using the _____ rule.

Ep / Es = Is / Ip

The primary current can be computed by using the formula______

40

The primary winding of a transformer is between points b and N, and has 120 volts applied to it. There are 120 turns of wire between points B and N. the selector switch is set to point D, and the load is now connected between points D and N. The secondary of this transformer contains 40 turns of wire. The amount of voltage applied to the load is_____V

1.732

The primary windings of three single phase transformers have been connected to form a wye connection. In a wye connection, the phase voltage is less than the line voltage by a factor of_______

Induction

The principle of magnetic_____ States that whenever a conductor cuts through magnetic lines of flux, the voltage is induced into the conductor.

Underwriters Laboratories

The temperature readings of devices such as circuit breakers, fuses, and terminals are found in the ______product directories

Amount of power needed

The type of three-phase transformer connection to use is generally determined by the ______

Primary winding

The volts per turn for any transformer is determined by the_____

Potential

The_____Transformer is basically an isolation transformer with a high voltage rating on the primary winding and that is Intended for use in metering circuits

Colbalt

There are actually only three substances that form natural magnets: Iron, nickel and _____.

Speed

Three factors that determine the amount of voltage that will be induced in a conductor; the number of turns of wire, the strength of the magnetic field(flux density) And the_____ of the cutting action.

1.5 H

Three inductors are connected in series, Inductor 1 has inductance of .6 Henry, inductor 2 has inductance of .4 Henry and inductor 3 has an inductance .5 H. The total inductance of the circuit is____H

Ip(load) = Ep(load) / R

Three single phase transformers are connected to form a wye-delta bank. Once the voltage across each of the load resistors is known, the current flow through the phase of the load can be computed using the formula_____

Is / Ratio

To calculate the current flows applied to the primary, use the formula Ip =

Only one

To use the clamp on type of AC ammeter, clamp the jaw of the meter around______of the conductors supplying power to the load.

Isolation, Auto, and current

Transformers can be divided into several classifications, which include_______