The kVA rating on a primary overhead distribution transformer nameplate is a rating of:
Transformers
Question · Easy
Same battery. Which lets more through?
Short
A single-phase pole-mount transformer is rated 7,200 V primary and 240 V secondary. What is the turns ratio of the windings?
A 25 kVA single-phase pole-mount transformer is fully loaded on a 240 V secondary. What is the approximate full-load secondary current?
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A single-phase 50 kVA transformer has a 7,200 V primary. What is the approximate full-load primary current?
Question · Medium
A no-load tap changer on a primary overhead distribution transformer is intended to be operated:
What is the defining feature of a completely self-protected (CSP) overhead distribution transformer?
Before paralleling two single-phase distribution transformers on the same secondary, a line crew must verify that the units have matching:
On a conventional (non-CSP) pole-mount transformer, the primary fused cutout is installed mainly to:
Why is a wye-connected secondary preferred on a multi-grounded four-wire primary distribution system?
Three 25 kVA single-phase transformers are banked wye-wye to serve a 480Y/277 V three-phase load. What is the approximate full-load secondary line current of the bank?
Question · Hard
A 25 kVA, 240 V single-phase transformer has a nameplate impedance of 2.0 percent. What is the approximate bolted secondary short-circuit current at the terminals?
On a typical single-phase pole-mount transformer, the H1 and H2 bushings are the connections for the:
A line worker jumpers H1 to the adjacent low-voltage bushing and measures voltage from H2 to the remaining low-voltage bushing. The reading equals the sum of the high-voltage and low-voltage test voltages. The transformer polarity is:
Two identical 25 kVA single-phase transformers are connected in open delta (V-bank) to serve a three-phase load. Compared with a closed-delta bank of three such 25 kVA units, the open-delta bank can supply about:
ONAN on a substation or large distribution transformer nameplate means the unit is cooled by:
According to Ohm's law, if the voltage across a constant resistance is doubled, the current through that resistance:
Electrical Knowledge
Heating in an overhead conductor is proportional to:
On a 12.47 kV multi-grounded wye primary, the nominal phase-to-ground voltage is approximately:
A balanced three-phase primary load draws 100 A at 480 V line-to-line with a lagging power factor of 0.90. What is the approximate real power?
A 60 Hz overhead line has a series inductance of 1.5 mH per mile per phase. What is the inductive reactance per mile?
A lagging power factor on a primary feeder means the load current:
Two 6-ohm resistors are connected in parallel. The equivalent resistance is:
Kirchhoff's current law applied at a primary overhead tap states that:
The Ferranti effect on a long, lightly loaded or open-ended high-voltage line causes:
Corona on a high-voltage overhead line is best described as:
Skin effect in an AC overhead conductor means that:
A 500-foot run of primary conductor has a resistance of 0.20 ohm. If it carries 80 A, the voltage drop in that conductor is:
ACSR overhead conductor is:
Conductors
Compared with ACSR of similar aluminum area, AAC (all-aluminum conductor) is typically chosen when:
An ACSR conductor designated 26/7 has:
A circular mil is the area of a circle whose diameter is:
If conductor temperature rises and tension is free to change in a ruling span, sag will:
The ruling span of a tension section is used so that:
Armor rods are installed on an ACSR conductor at a support primarily to:
A Stockbridge damper is installed on an overhead conductor to:
Using the parabolic sag approximation D = wS² / (8T), what is the sag of a 300-foot level span if the conductor weighs 0.50 lb/ft and the horizontal tension is 2,000 lb?
The steel core in ACSR is provided primarily to:
All else equal, the ampacity of a bare overhead conductor decreases when:
A compression splice on ACSR is intended to:
ACSS (Aluminum Conductor Steel Supported) is selected instead of conventional ACSR mainly because it can:
On lower-voltage primary distribution, a pin insulator is typically used to:
Overhead Lines
On a suspension insulator string, increasing the number of disks (bells) is done primarily to:
An overhead ground wire (OHGW or shield wire) is placed at the top of a transmission structure primarily to:
Under NESC Table 232-1, the basic vertical clearance over roads, streets, or alleys subject to truck traffic for open supply conductors over 750 V to 22 kV is:
When an effectively grounded down guy or span guy crosses a road subject to truck traffic, NESC Table 232-1 requires a basic vertical clearance of:
On a joint-use pole, the communication worker safety zone between the lowest supply conductor and the highest communication facility is commonly required by the NESC to be at least:
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