215

Figure 215.51 The transformer shown in Figure 215.51 has two separate secondary windings that are rated for 12/24 volts. The primary winding is rated for 208 volts. Which connection diagram shown below is correct if the required control circuit is to be 12 V? Select one: a. b. c. d.

not a

Normally, 44 amps of current is flowing through a transmission line and 19.36 kW of power is lost in the conductors. However, during a peak period a current of 100 amps is pushed through the conductors. The I2R losses (power lost) in the conductors is ___ kW. Select one: a. 44 b. 19.36 c. 100 d. 193.6 e. none of these

not a

Which of the following is NOT correct? Select one: a. NP ÷ NS = EP ÷ ES b. NP ÷ NS = IS ÷ IP c. IS ÷ IP = EP ÷ ES d. IS ÷ IP = ES ÷ EP

not a

A low-voltage lighting system is supplied through a transformer. The transformer ___. Select one: a. is an isolating type b. secondary circuit is limited to 25 amps c. delivers power at 30 volts or less d. is supplied from a branch circuit of 20 amps or less e. all of these

not b

A small 1Ø transformer (500 VA) can be used as a "step-up" transformer but the output voltage will be smaller than expected because there is turns ratio ___ on the low voltage windings. Select one: a. variation b. deration c. compensation

not b

Which of the following situations would produce destructive heat within an encapsulated .5 KVA transformer that has a primary rating of 480 volts and a secondary rating of 120 volts? I. installing the transformer in a NEMA 3R enclosure II. connecting a .3 kW load to the secondary Select one: a. I only b. II only c. either I or II d. neither I nor II

not b

Typically, leads (instead of bus-bar terminations where lugs would be installed) are provided on which of these Group I 1Ø transformers? (Re: Y2 Annex B) Select one: a. .50 KVA b. 250 VA c. 15 KVA d. a and b only e. a, b, and c

not c

The "hot" from a load is passed through an ammeter clamp three times, as shown above in Figure 215.31. The load draws 1.2 amps from the circuit. How much current will be indicated on the meter display? Select one: a. 3.6 b. 0.4 c. 1.2 d. 2.4 e. 0

not d

A 120 VA load is the only load connected to the secondary of a 250 VA transformer. To supply this load, the transformer must be supplied with at least ___ VA of power on the primary. Select one: a. 57.6 b. 2.08 c. 250 d. 120 e. 125

not a

A 1Ø transformer has a power rating of 37.5 KVA with a 480-volt primary and a 120/240-volt secondary. The transformer is delivering power to a 22 KVA load at 240 volts. The transformer is supplying ___ amps of current to the load. Select one: a. 78 b. 92 c. 313 d. 156 e. 183

not a

Figure 215.11 With current flowing in the completed primary circuit, 240 volts is ___ on the secondary winding of the pole-mounted transformer shown above in Figure 215.11. Select one: a. turned b. rectified c. induced

not a

77 Which of the secondary transformer connections, shown below, is correct to supply the proper voltage to the 120/240-volt load? Select one: a. b. c. d.

a

Transformers ___ change an input frequency of 60 Hz to an output frequency that is 10% higher or lower than the input frequency. Select one: a. cannot b. can

a

A liquid-filled transformer has a primary voltage of 12,470 volts. The transformer is surrounded by a 6-foot-high fence. The overall height of the fence must be extended 1 foot with at least ___ strands of barbed wire on top of the fence. Select one: a. 1 b. 3 c. 2 d. no minimum required

b

A transformer enclosure that is non-ventilated ___ allow air from outside the enclosure to circulate through it. Select one: a. does b. does not

b

A 480 primary to 120/240-volt secondary single-phase transformer is actually supplied by 496 volts. If no tap changes are made, what line-to-neutral output voltage will be available? Select one: a. 240 b. 116 c. 248 d. 124 e. 120

d

A dry-type transformer uses ___ to dissipate excess heat that is generated by current passing through the windings. Select one: a. deflection b. cores c. oil d. air

d

Figure 215.21 Refer to Figure 215.21. Primary power = ___ mW. Select one: a. 6 b. 2880 c. 4.17 d. 144 e. none of these

d

Figure 215.51 The transformer shown in Figure 215.51 has two separate secondary windings. The transformer is rated at 15 KVA and its secondary windings are rated 120/240 volts. The secondary windings are connected for 120/240-volt operation. If several 120-volt loads are connected to X4 and X3 this winding can supply a maximum of ___ amps to those 120-volt loads. Select one: a. 125 b. 8 c. 31.25 d. 78.125 e. 62.5

e

Refer to the "Connection Diagrams" that appear in Y2 Annex B. The transformer shown in ___ is a shielded transformer. I. Diagram 13 II. Diagram 23 III. Diagram 58 Select one: a. II only b. II & III only c. I only d. III only e. I, II & III

e

___ amps are supplied from a transformer to a 11.5 kW 120-volt load. The transformer has a 2-wire secondary and a nameplate rating of 15 kVA with a 480-volt pri--120-volt sec. Select one: a. 11.5 b. 62.5 c. 125 d. 47.9 e. 95.8

e

An ___ has no direct electrical connection between the primary and secondary windings. I. autotransformer II. isolation transformer Select one: a. I only b. II only c. both I & II d. neither I nor II

b

Askarel-insulated transformers are permitted to be installed outdoors only. Select one: a. True b. False

b

If 800 kW of power is produced at 2160 volts but will be transmitted across a long distance at 13.8 kV, the current flowing in the transmission wires is ___ amps. Select one: a. 37.037 b. 57.97 c. 579.7 d. 370.37 e. none of these

b

Table215.4 Maximum Ambient Temp Maximum Percentage of Loading 40°C (104°F) 100% 50°C (122°F) 92% 60°C (140°F) 84% A 100 KVA rated transformer installed in an ambient temperature of 50ºC has a derated value of ___ kVA. Refer to Table 215.4. Select one: a. 108.696 b. 92 c. 100 d. 104.167 e. none of these

b

Temperature rise in a transformer is the ___ without damage occurring to the windings. Select one: a. maximum ambient temperature that can occur inside a transformer enclosure b. maximum temperature above the surrounding air temperature that can occur in the windings c. maximum temperature that can occur in the windings

b

The minimum clearance from the bottom of a 240-V pole-mounted transformer to the ground is ___ feet. Select one: a. 14 b. 8 c. 10 d. no minimum required

b

Transformers that hum are defective and should be replaced immediately. Select one: a. True b. False

b

When a transformer is used as a step-down transformer the output voltage is ___ than the input voltage. Select one: a. higher b. lower

b

You need to change from 240 volts to 480 volts to operate a piece of equipment that will require 25 KVA at 480 volts. You must use a transformer that is built specifically for step-up applications. Select one: a. True b. False

b

40ºC = ___ºF Select one: a. 90 b. 167 c. 104 d. 140

c

A transformer with a 120/240-volt secondary can deliver power at the proper voltage to ___. Select one: a. 120-volt loads b. 240-volt loads c. both a and b d. neither a nor b

c

An example of an autotransformer is a ___. Select one: a. a ballast in a fluorescent luminaire b. a ballast in an HID luminaire c. both a and b d. neither a nor b

c

BIL is a measure of the ability of the transformer's insulation system to withstand very high-voltage, short-time surges cause by ___. Select one: a. lightning b. equipment switching c. either a or b d. neither a nor b

c

Cross-country power transmission lines are made more efficient by increasing the transmission ___. Select one: a. height b. current c. voltage d. none of these

c

FCBN is an abbreviation for ___ taps. Select one: a. Frequency Charged Before New b. Ferro- Conductive Basic Numbering c. Full Capacity Below Normal d. Fixed Cathode Backbone Network

c

Figure 215.11 Refer to Figure 215.11. The turns ratio for the substation transformer is ___. Select one: a. 52:3 b. 3:52 c. 100:13 d. 13:100 e. none of these

c

Figure 215.21 Refer to Figure 215.21. Transformer voltage ratio = ___. Select one: a. 4:1 b. 1:20 c. 20:1 d. 2:1 e. none of these

c

If the nameplate of a transformer shows the primary rated at 120 volts and the secondary rated at 12 volts, the ___ is 10 to 1. I. voltage ratio II. turns ratio Select one: a. I only b. II only c. both I & II d. neither I nor II

c

Individual dry-type transformers rated over 112½ kVA shall be enclosed in a fire-resistant room with materials having a ___-hour minimum fire rating. Select one: a. 2 b. 6 c. 1 d. 3

c

NEMA Type 3R enclosures can be used ___. Select one: a. outdoors b. indoors c. either a or b d. neither a nor b

c

Statement(s) ___, shown below, is (are) true. I. efficiency = output power ÷ input power II. output power = input power - losses Select one: a. I only b. II only c. both I & II d. neither I nor II

c

Taps are provided on some transformers to "correct" for an input voltage that is ___ normal rated voltage. Select one: a. above b. below c. either a or b d. neither a nor b

c

The ___ the number of turns on the primary and secondary windings determines the output voltage. Select one: a. sum of (or Tp + Ts) b. product of (or Tp x Ts) c. ratio of (or Tp ÷ Ts) d. difference between (or Tp - Ts)

c

Transformer "tap" connection points are associated with the "___" leads or lugs on a transformer. Select one: a. X b. H c. A or B

c

Transformers are ___ efficient when the windings are cooled. Select one: a. equally b. less c. more

c

Voltage surges can damage electrical equipment (including transformers). Voltage surges can be caused by ___. Select one: a. electrical equipment in the system opening and closing b. lightning strikes c. either a or b d. neither a nor b

c

Within a CT scan, that is part of a 600 amp 277/480 volt service, each of the service entrance conductors is routed through a ___ transformer. These transformers are connected to the metering equipment provided by the utility (CenterPoint Energy for example). Select one: a. control b. distribution c. current d. isolation

c

___ is a transformer design type. Select one: a. Oil filled b. Dry c. Both a and b d. Neither a nor b

c

A transformer has a nameplate rating of 480-volt primary - 120/240-volt secondary. If instead of rated voltage the applied primary voltage is 440 volts, a 5 KVA transformer could deliver a maximum output of ___ kVA without overloading. Select one: a. 4 b. 5.45 c. 6.25 d. 4.58

d

A transformer has a primary rated at 240 volts and a secondary rated at 120 volts. A 120-volt load connected to the secondary of the transformer is pulling 10 amps. The transformer is supplied from a 2-pole breaker in a 120/240-volt 3Ø, 4-wire panelboard. ___ amps is flowing in the circuit conductors that connect to the primary. Select one: a. 120 b. 2.5 c. 10 d. 5 e. 12

d

A transformer has a primary rated voltage of 120 and a secondary rated voltage of 24. If you measure an output on the secondary of 16 volts, ___ volts has been applied to the primary. Select one: a. 120 b. 30 c. 180 d. 80 e. 50

d

Electricity is moved through transmission lines at a high voltage (on the order of 13.8 kV) instead of the lower voltage used by customers because ___. Select one: a. it is cheaper b. I2R = P losses are reduced c. efficiency is improved d. all of these

d

Generally, transformers have an efficiency of ___. Select one: a. less than 10% b. less than 50% c. between 60 & 70% d. more than 90%

d

Table215.4 Maximum Ambient Temp Maximum Percentage of Loading 40°C (104°F) 100% 50°C (122°F) 92% 60°C (140°F) 84% A transformer that is hung above a lay-in ceiling, where the temperature is 122ºF, can deliver no more than ___ kVA when the transformer is rated at 100 kVA. Refer to Table 215.4. Select one: a. 108.7 b. 83.7 c. 100 d. 92

d

The turns ratio for a transformer with a primary rated voltage of 120 and a secondary rated voltage of 24 is ___. Select one: a. 1:4 b. 1:5 c. 4:1 d. 5:1 e. none of these

d

Transformers operate on the principle of ___. Select one: a. phase shift b. lagging transference c. hysteresis d. electromagnetic induction e. none of these

d

Turns ratio can be written as ___. Select one: a. T.R. = Np ÷ Ns b. T.R. = Tp/Ts c. T.R. = Tp ÷ Ts d. either a or b or c

d

Voltage ratio can be written as ___. Select one: a. T.R. = Tp/Ts = Ep/Es b. V.R. = Tp ÷ Ts = Ep ÷ Es c. T.R. = Np ÷ Ns = Vp ÷ Vs d. either a or b or c

d

When a ventilated dry-type distribution transformer is to be used outdoors, it can be equipped with weathershields to attain a ___ rating. Select one: a. NEMA 2 b. duty c. classification d. NEMA 3R

d

When operated within its ratings a transformer can be expected to operate for about ___ years. Select one: a. 5 to 10 b. 15 to 20 c. 10 to 15 d. 20 to 25 e. 1 to 5

d

A clamp-on ammeter is placed around a single circuit conductor as shown below at the right. When current is flowing in the conductor, a voltage is induced in the clamp.The meter clamp serves as the ___ winding and the meter components serve as the load (completing the circuit). Select one: a. secondary b. primary

a

A load that uses 7.35 kVA of power is using ___ volt-amperes. Select one: a. 7350 b. .00735 c. .735 d. 735 e. none of these

a

A step-down transformer's primary winding is connected to ___. Select one: a. the power source b. the load

a

An isolation transformer is routinely used where "clean power" is required to operate delicate electronic equipment such as computers. Select one: a. True b. False

a

Copper loss is a power loss (reduction of efficiency) caused by the voltage dropped in the (resistive) windings in a transformer. Select one: a. True b. False

a

Figure 215.52 Which of the secondary transformer connections, shown in Figure 215.52, is correct to supply the proper voltage to the 240-volt load? Select one: a. I b. II c. III d. IV e. none of these

a

If a transformer "hums" after it is energized, ___. Select one: a. the transformer is operating normally b. the transformer is defective and should be de-energized immediately

a

Ignoring small losses, is this a true statement for a transformer? Is x Es = Ip x Ep Select one: a. Yes b. No

a

Large dry-type distribution-type transformer enclosures have steel bottoms that are punched so that ___. I. a grounding electrode conductor can be run through the bottom without drilling a hole II. proper air circulation occurs so that the windings are not overheated III. the shipping weight is reduced Select one: a. II only b. II & III only c. III only d. I & II only e. I, II & III

a

Power is transferred from the primary winding to the secondary winding of a transformer using magnetic coupling. Select one: a. True b. False

a

Power loss in conductors is wasted energy. This wasted energy is dissipated into the air in the form of heat. Select one: a. True b. False

a

Power losses in transmission lines can be reduced by ___ conductor size. Select one: a. increasing b. decreasing

a

Standard industry practice is that transformers be rated in ___. Select one: a. VA b. W

a

Temperature ___ is the difference in temperature between the transformer windings and the ambient temperature surrounding the transformer. Select one: a. rise b. differential c. either a or b d. neither a nor b

a

The NEMA standard BIL rating for transformers 600 volts and below is ___ kV. Select one: a. 10 b. 25 c. 15 d. 20

a

To allow for adequate ventilation or dissipation of heat, transformers are required to be marked with a minimum distance or clearance from walls or other obstructions. Select one: a. True b. False

a

Typical "pole-mounted" transformers are filled with ___. Select one: a. oil b. non-conductive cellulose c. fiberglass insulation d. water

a

When a 7.5 KVA transformer is required to deliver 32 amps at 240 volts the transformer is ___. Select one: a. overloaded b. operating within its ratings

a

___ is abbreviated BIL. Select one: a. Basic Impulse Level b. Built- In Laminations c. Basic Intensity (current) Level d. Busbar Insulation Limiters

a

___ loss is loss caused by the induced currents that are produced in metal parts that are being magnetized. Select one: a. Eddy current b. Conductivity c. Hysteresis d. Copper

a