ELO 21 chapter 14,15,19,20

Why is there a greater hazard working on an energized secondary close to a transformer rather than farther away?

Close to a transformer, the fault current on the secondary bus or service is very explosive.

What influences the amount of voltage drop in a circuit? Answer text

Customer demand, conductor size and length, daily and seasonal peak loads, reactance in a circuit.

What can be seen or heard when a line is subject to harmonic interference? Answer text

Customers with sensitive electronic equipment complain, for example, that a computer acts erratically.

When two or more transformers are connected with the positive terminal of one transformer connected to a negative terminal of another transformer, what kind of interconnection is it?

Delta or series connections.

Why is separating the primary neutral from the secondary neutral a hazard for linemen?

During a line-to-ground fault somewhere on the system, there can be a high voltage between the neutral and ground.

To conduct a turns ratio test on a transformer, why is it necessary to energize the high-voltage coil with a low voltage such as 120 V?

Energizing the low-voltage coil would induce a hazardous high voltage on the primary coil, which would also be more difficult to measure.

What methods are used to inspect insulated jumpers?

Ensure that the insulated jumper has been tested as scheduled. Do a visual inspection for damaged rubber.

Why should a worker wait until the lamp is at normal brilliance or approximately 30 seconds before doing a voltage check on a gaseous-discharge luminaire?

Gaseous-discharge lamps need a high voltage to start the initial electric arc. A ballast will step up the 120 V supply voltage to provide a 750 V to 4,000 V output. The voltage should settle to its normal operating voltage when the light is at normal brilliance.

Which of the following lamps are high-intensity discharge lamps?

High-pressure sodium, Mercury-vapor

Identify the formula for voltage drop and power loss.

IR = voltage drop I2R = power loss

Why should the primary neutral of a wye-delta transformer bank be left floating (ungrounded)? Answer text

If the H2 bushings were connected to the system neutral, the transformer bank would carry extra current not related to the current needed to supply the normal service load. If the primary wye circuit is unbalanced, extra current flows through the delta secondary as it tries to balance itself through the secondary of the transformer bank. If the transformer neutral were grounded and one primary phase were opened, the transformer bank would become an open-delta bank and continue to supply three-phase power at a 57% reduced capacity, exposing the bank to a burnout because of an overload.

Name three possible causes of a low-voltage trouble call.

Increased load on customer's service Length and size of secondary Transformer tap on wrong setting Upstream regulator not working Time clock on switched capacitors incorrect Poor phase balance overloading one phase

Which of the following are considered measures used by a utility to reduce disturbances to a power system?

Install voltage regulators, Install capacitors, Install surge arresters, construct a dedicated feeder

How does a set of capacitors installed on a distribution feeder benefit the electrical system?

Installing a capacitor is the most economical way to improve the voltage on a feeder and also benefit the whole electrical system. When the power factor of the circuit improves, there is less apparent power needed to feed the load and, therefore, less current and less voltage drop. Capacitors can be in a substation or downstream on a distribution circuit.

What two kinds of tests can be carried out on a transformer using a 1,000 V Megger?

Insulation resistance and continuity tests.

What are the three main sources of TVI complaints caused by utility equipment?

Loose hardware, defective insulators, corona discharge.

Using watts and lumens as units, how is the efficiency of a lamp defined?

Lumens per watt.

Is it acceptable to use a 2.5 inch (6.4 cm) wire (lifting) tong as a link stick to hold conductor tension on a corner?

No

Can a single-bushing transformer be installed on a delta circuit?

No, the primary coil is connected phase-to-phase and needs two insulated bushings.

Why should doing a job "hot" not be the first option?

One of the basic principles of managing safety is to eliminate the hazard if possible. Doing the work on an outage and the installation of protective grounds would eliminate the electrical hazard.

A center-tapped 120/240 V secondary coil has the two parts of the coil inside the tank arranged in parallel. What would be the voltage between the X1 and the X3 terminals?

Placing the two secondary coils in parallel allows the complete coil to be used to provide 120 V. The voltage between X1 and X2 would measure 120 volts, but between X1 to X3 would measure zero because nothing would be connected to X3.

What hazard exists when a socket base meter is plugged into a meter base with the source wires energized?

Plugging in the meter is like closing a switch. If there is a lot of load or a short circuit at the customer's premises, then an explosive arc could occur at the meter.

Revenue metering involves the measurement of one or more of the three kinds of power and/or energy used by a customer. What are they?

Real, apparent, and reactive power

What type of lighting system is common at airport runways, and why?

Series lighting systems can feed long distances from one source.

Why should rubber-glove protectors not be used as work gloves even after they are no longer used as rubber-glove protectors?

Someone monitoring the work or a safety watcher cannot easily see if rubber gloves are being worn when needed.

What can be done to reduce exposure to toxic chemicals such as mercury, sodium, and phosphor found in the bulbs of gaseous-discharge lamps?

Staying outdoors and upwind when working with these lights reduces the risk of exposure.

What is the load (tension) on holding tong A, given that the conductor weight is 500 pounds, length A is 10 feet, and length C is 10 feet?

Tension on holding tong A = Length of A (10) × conductor weight (500) ÷ length of C (10) = 500 pound tension

Why is there a higher risk when working on an energized secondary next to a transformer rather than a span away? Answer text

The closer the source, the higher the available fault current. A high fault current can be explosive.

The leads going in and out of a set of voltage regulators are very small compared to the main line conductors. Will the relatively small leads affect the capacity of the feeder to supply the load?

The leads are large enough to carry the current and short enough that the voltage drop is minimal.

What is the purpose of blocking the automatic reclosing feature of a source circuit breaker or recloser?

The nonreclose feature guarantees that a circuit will not be re-energized once it does trip out. When the circuit is not automatically re-energized, the exposure time to the electrical hazard is reduced, and it will allow a safer rescue effort if needed. Damage or injury may be limited by the reduced exposure to the high-fault current that can occur during a fault.

Why would a time delay of 10 seconds on a voltage regulator not be considered a good practice? Answer text

The regulator would be constantly reacting to temporary changes.

if a streetlight stays on in daylight, what could be the cause?

component failure or dirt on the photocell will keep the contact closed

Name three kinds of defects to look for when doing a visual inspection of rubber gloves.

cracking and cutting damage, embedded wood or metal splinters, unusual swelling of rubber

a large inductive load causes the power factor to go ______

down

A customer pays a utility more per kWh when power is supplied at a primary voltage. (true or false)

false

What can a utility do to reduce the risk of being the cause of tingle voltage at a customer?

good grounding system

What is a common fix for poor-quality power?

improved system grounding

How can the second point of contact be eliminated when doing rubber-glove work?

isolate all secondary points of contact. (cover-up, PPE)

Name four advantages an electronic (smart) meter has over an electromechanical meter.

it can register the time of use, can be used to check the voltage and current in each phase, the meter can check itself for proper function, it can register killowatt demands

If the outer bulb of a mercury-vapor lamp breaks while replacing the lamp,to what hazard is the worker exposed?

it is possible for the inner bulb to continue to emit an unseen ultraviolet radiation without the outer bulb acting as a filter.

What extra steps can be taken to prevent a wire (lifting) tong from sliding through a saddle?

leave the set of blocks on the stick

Total consumption (kWh) ÷ peak demand (kW) x hours in a month = ________________ factor.

load factor

One current coil and one potential coil working together is defined as _____________. Answer text

one element

Why is the second point of contact considered a hazard when working hot? Answer text

persons body is in contact with another object at a different potential causing electrical shock

The kilowatt peak ÷ the kilovolt-ampere peak = _____________ factor.

power factor

How much energy is being used by a customer when a meter with a Kh of 7.2 has 10 rotations of its disk? If the 10 rotations occurred in 40 seconds, what is the power being drawn?

the customer has used 10 × 7.2 = 72 watt hours energy.

what is meant by peak demand?

the highest amount of instantaneous power used by the customer during a billing period

Why can a break in a series lighting circuit be hazardous to a lineman? Answer text

A hazard to linemen is that the voltage across any break in a series circuit will be equal to the output voltage of the source transformer.

Name three possible sources for flickering lights.

A loose neutral, large motors, inadequate capacity of feeder transformer.

chapter 15

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chapter 18

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chapter 19

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Name three possible causes of a high-voltage trouble call.

1. If the voltage is high and the customer is close to a distribution substation or close to a voltage regulator, the voltage could be set too high. 2. A transformer can occasionally suffer some shorted-out turns in the coil and cause high voltage to customers. 3. A voltage regulator or LTC at the substation transformer could be stuck in a high position.

How much current can be expected in the leads feeding a 450 kVAR capacitor bank on a 25/14.4 kV system?

10.4 A

What would be the expected full-load current (100% loaded) on the 240 V secondary of a 100 kVA, 7,200/240 V transformer?

100,000/240 = 417 A full-load current

Name three types of three-phase services that three single-phase units with a 120/240 V secondary can serve.

120/208 wye, 240/416 wye, 240 delta, and 120 delta services.

A transformer with a 240 V secondary has a 60-to-1 turns ratio. What is the primary voltage feeding this transformer?

240 × 60 = 14.4 kV

What length of clear insulating section of a live-line tool should be maintained when working on a 115 kV circuit?

3 feet 2 inches phase to ground 4 feet 3 inches phases to phase

The disk of a meter with a Kh constant of 3.6 rotates 100 times. How much energy was used?

3.6 × 100 = 360 watt hours

An insulated or bare jumper should be carrying at least________percent of the load current before cutting a conductor.

30-33%

What is the purpose of a ballast in a gaseous-discharge lamp?

A ballast is a large inductor or reactor that limits current flow while it lowers the voltage as the lamp tube begins to conduct.

If a gaseous-discharge lamp replacement is very frequent at a specific location, what are possible causes?

A ballast with a higher wattage than the lamp will cause premature burnout of gaseous-discharge lamps.

Why is there a high-voltage hazard when there is current flowing through the primary of a current transformer while the secondary is open circuited?

A current transformer is like other transformers; the input V × I = the outputV × I. When the current is stepped down, the voltage is stepped up at the same ratio. A voltage drop brings the voltage to a safe level when the secondary is shorted or connected to the meter current coil.

The lights in part of the customer's premises are very bright, and in another part the lights are very dim. What is the likely cause?

A poor or open neutral connection blocks the normal return path from 120 V appliances. The current will travel back to the source through the other 120 V leg or through 240 V equipment. The 240 V equipment will operate normally.

What does quality power look like?

A quality power supply is one where the AC and voltage rise and fall at a rate that can be represented by a sine wave. Any deviation in the magnitude or frequency of the 60 Hz sine wave is considered a power-quality disturbance.

When a secondary bus is fed from many transformers connected in parallel, what kind of secondary system is it? Answer text

A secondary network.

When using plastic guard equipment what kind of insulation does a lineman depend on for electrical protection?

Air gap

What is the difference between a self-contained and a transformer-rated meter?

All the current being measured goes through a self-contained meter. Only a representative current from a current transformer goes through a transformer-rated meter.

How can one CT be used to meter a 120/240 V three-wire service?

Both 120 V conductors go through one CT. To have the current in the two opposite polarity 120 V legs go through the CT in the same direction, the two wires go through the CT from opposite directions. The current from the two legs adds together to double the secondary current.

The neutral and the safety ground are normally tied together at the transformer supplying the service and also at the service panel. What happens when the safety ground is tied together downstream on the customer's premises?

The safety ground wire will then share with the neutral the job of carrying current back to the source. The resulting ground currents can cause tingle voltage as well as disturbances to the normal operation of electronic equipment in the customer's premises.

Can the wye secondary of a wye-wye bank be connected to the same bus as the wye secondary of a delta-wye bank of the same secondary voltage?

There is always an angular displacement or phase shift with a wye-delta or a delta-wye transformer bank. The secondary will be 30° out of phase with the primary. This means that a wye secondary of a wye-wye bank, which has a 0° angular displacement, cannot be connected in parallel with a wye secondary of a delta-wye bank, which has a 30° angular displacement.

Can two phases of a delta primary supply a three-phase, open-delta service?

To feed an open-delta three-phase secondary service, three primary wires are needed. A wye primary would need two phases and a neutral, and a delta primary would need three phases.

Why do distribution circuits have larger conductors than what is needed for ampacity?

To reduce voltage drop and line loss as well as keep the fault current level higher.

Rubber gloves should not be the sole protection between a lineman and a potential fatal shock. ( True or False)

True

How many elements are in a meter that is normally used in a three-wire service?

Two, typically, energy can be metered with one less element than the number of wires in the service.

How can ferroresonance be prevented when energizing a three-phase transformer bank?

Use a three-phase gang switch. Keep some load on the transformer. Temporarily ground the floating neutral.

When a circuit is temporarily fed in reverse through a regulator, what adjustments should be made at the regulator?

When a circuit is temporarily fed in reverse through a regulator, the regulator continues trying to adjust the voltage on its load side, which is now the source. The voltage sensor measures the input instead of the output voltage. The regulator tries to change the input voltage, though it is not able to do so. Typically, the regulator goes to the maximum boost or to the maximum buck position. To avoid these problems, the regulator should be bypassed and removed from service before the circuit is fed in reverse.

At the main panel, the phase-to-phase voltage readings of a delta 240 V service are lower than normal and one phase-to-phase voltage reading is 0 V. For example, the readings are 210 V, 210 V, and 0 V. What is the likely cause?

When one phase of a primary feeder loses power, the voltage at a wye-delta transformer bank will have a reduced voltage on two of the phase-to-phase readings and 0 V on the third phase-to-phase reading.

Why is a transformer-rated meter used for some services?

When the voltage and/or current is too high for a self-contained meter

What precautions should be taken to reduce the risk of overreaching when working with rubber gloves?

Work at arm's length. Wear rubber sleeves. Work from an insulated platform.

What solution is available to a utility to correct a corona problem that is causing TVI interference? Answer text

Workmanship and design require that all sharp points on energized parts be smooth or rounded off.

A transformer coil must have a potential difference across it in order to operate. What two types of connections are possible to get a voltage across a transformer coil?

Wye or delta (parallel or series).

When two or more transformers are connected with the positive terminal of each transformer connected to a phase and all the negative terminals connected together, what kind of interconnection is it?

Wye or parallel connections.

Energy consumption is the volts × amperes used by a customer. What is the largest variable measured by a kilowatt-hour revenue meter?

amperes

How can the probability of a voltage surge be reduced while working with live-line tools on a transmission line? Answer text

block the automatic reclosure on all circuit breakers connected to circuit, do not work when lighting is in the area

When a capacitor is isolated with the intent to re-energize, why is it necessary to wait 5 minutes before re-energizing?

the voltage on the capacitor to drain before re-energizing. If a charged capacitor is returned to service, the line voltage builds up well above normal. There is a danger when energizing capacitors with a fuse cutout because, if proper contact is not made the first time, any immediate second strike to retry closing the cutout results in double the line voltage across the cutout terminals.

why would a utility charge extra for peak demand?

they have to generate transmit and transformer the energy to supply the peak load

A voltmeter can be used to verify that a socket-based meter will not be plugged into a short circuit. (true or false)

true

The comfort of a lineman carrying out barehand work depends on an electric field not penetrating into a conducting sphere; therefore, there will be no current flow inside a sphere. (True or False)

true

True or False: A bypass switch at a voltage regulator can be closed after the regulator has been zeroed.

true

True or False: Capacitors improve the voltage upstream from the capacitor installation.

true

Name four types of disturbances to power quality that can be continuous.

• An unacceptable range of voltage rise and fall • Intentional voltage reductions (brownouts) during periods of peak load • Unbalanced voltages between phases • Harmonic distortion • Tingle voltage • Electrical noise (radio and television interference)