A 37.5 kVA single-phase pole-mount transformer is fully loaded on a 240 V secondary. What is the approximate full-load secondary current?
Transformers
Question · Easy
H1 and X1 markings on a distribution transformer identify which terminals?
Oil in a liquid-filled overhead distribution transformer is used primarily to:
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On a completely self-protected (CSP) overhead distribution transformer, the secondary overload device is typically:
A 50 kVA single-phase transformer has a 7,620 V primary. What is the approximate full-load primary current?
Question · Medium
Three 25 kVA single-phase transformers are banked closed-delta. What is the three-phase bank rating?
A single-phase transformer is rated 7,200 V primary and 240 V secondary. If the primary winding has 1,500 turns, how many secondary turns are required for that voltage ratio?
A delta-wye transformer bank is commonly used to serve 480Y/277 V three-phase loads from a delta primary feeder because the wye secondary:
A no-load tap changer (NLTC) on a distribution transformer is intended to be operated:
Before paralleling two single-phase distribution transformers on the same secondary, a line crew must verify that the units have matching:
A 225 kVA three-phase pad-mount transformer is fully loaded on a 12.47 kV wye primary. What is the approximate full-load primary line current?
Question · Hard
A 50 kVA single-phase transformer with a 240 V secondary has 2.0 percent impedance. What is the approximate secondary bolted-fault current?
A 480 V source is applied across a 24 Ω resistive load. What is the current?
Electrical Knowledge
A single-phase 120 V circuit supplies 15 A to a resistive load. What is the real power?
In a parallel circuit, which quantity is the same across every branch?
A balanced three-phase load draws 80 A at 4,160 V and 0.90 power factor. What is the approximate real power?
Shunt capacitor banks are installed on a distribution feeder primarily to:
Inductive reactance of a line conductor increases when:
Apparent power on a circuit is measured in kVA. Real power equals apparent power multiplied by:
All else equal, voltage drop on a supply circuit increases when:
A balanced 480 V three-phase feeder carries 175 A at 0.80 lagging power factor. What is the approximate real power?
A three-phase motor load draws 100 A at 0.80 power factor. If capacitors improve the power factor to 1.00 while real power stays the same, the line current becomes approximately:
What does ACSR stand for on overhead line conductors?
Conductors
Compared with aluminum of the same circular-mil size, hard-drawn copper overhead conductor has:
Ampacity of an overhead conductor is the current it can carry continuously without:
A single-phase circuit carries 90 A. The round-trip conductor resistance is 0.30 Ω. What is the conductor voltage drop?
After an overhead conductor is sagged, which change increases sag the most, all else equal?
An ACSR designation of 26/7 means the conductor has:
Compared with AAC of the same diameter, ACSR is generally selected when the line needs:
Which condition reduces the allowable ampacity of an overhead conductor?
A conductor weighs 0.40 lb/ft, the span is 300 ft, and the horizontal tension is 2,500 lb. Using the parabolic sag formula d = wS² / 8T, what is the sag?
Overhead sag charts distinguish initial (stringing) sag from final sag primarily because aluminum conductors:
Which code governs the safety of utility overhead electric supply lines up to the service point?
Overhead Lines
On a jointly used distribution pole, supply conductors are generally placed:
The NESC communication-worker safety zone between supply space and communication space is commonly maintained at about:
The South Carolina Public Electrical Utility contractor classification includes which of the following in addition to distribution line construction?
Under the NESC, the clearance from a supporting structure, support arm, or attached equipment to a fire hydrant shall be not less than:
For construction equipment working near an overhead line of unknown voltage up to 350 kV, OSHA 1926.1408 Option (1) requires that no part of the equipment, load line, or load get closer than:
Phase-to-phase spacing on an overhead line is increased as operating voltage rises mainly to:
A dead-end (strain) structure differs from a tangent structure because the dead-end:
A down guy is attached 36 ft above ground and the anchor is 27 ft from the pole. What is the guy length, neglecting hardware take-up?
A distribution-class surge arrester on a transformer pole is installed to:
NESC Grade B construction, rather than Grade C, is required at locations such as:
Armor rods and vibration dampers are installed on overhead conductors primarily to:
The ruling span used when sagging a line that has several different span lengths is:
A short span next to a long span can develop uplift in cold weather. What is the practical concern?
Before excavating for a URD trench, vault, or pole hole in South Carolina, the excavator must first:
Underground Lines
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