Electrical Instruments, Power, and Energy Measurements

Flashcards testing knowledge of single-phase and three-phase power measurement instruments, phase sequence meters, electromechanical watt-hour meters, demand meters, smart meters, and submetering systems.

What is the definition of a linear electrical circuit?

A circuit in which both the voltage and the current can be described as a sine function.

How does a single phase wattmeter measure power?

It measures current, voltage, and the lead or lag of the current with respect to the measured voltage.

Under what condition will a single current transformer (CT) suffice for a three phase power meter?

A single CT will suffice if the load is balanced.

How many current transformers (CTs) are needed for three wire, three phase applications when the load is unbalanced and monitoring currents in all three phase conductors is unnecessary?

Exactly $2$ CTs will suffice.

What parameters can a general power analyzer provide details on?

Currents, voltages, power factors, power, VARS, VA, frequency, phase sequence, lead/lag angles, and nonlinear current characteristics.

What can the power quality analyzer shown in Fig. 5 simultaneously display?

Traces of $5$ voltages and $2$ currents.

How are current measurements made for panel mounted digital power quality meters versus traditional portable power analyzers?

Panel mounted power quality meters use permanently installed toroidal CTs, whereas portable power analyzers use clamp-on CTs.

What standard sequence marking is used when connecting an incoming three phase electrical source to a power distribution center or motor control center?

Sequence A to T1, B to T2, and C to T3.

What happens to connected three phase motors if the source connection sequence is wired as A to T1, C to T2, and B to T3?

Motor rotation will be reversed and incorrect, which can result in severe damage to property as well as injury to personnel.

What conductor color coding sequence is frequently used in the United States for $480\text{-}3\text{-}60$ three phase circuits?

The sequence "brown-orange (or violet)-yellow".

What color coding is typically used for conductors above $480\text{ VAC}$?

Black conductors are usually used and are not color coded.

How does a non-contact phase sequence meter determine phase sequence?

By clamping its probes over the insulation of the conductors being analyzed.

How did traditional electromechanical watt-hour meters measure energy consumption?

A miniature motor drove a disc at a rotation rate proportional to power; total disc rotations were proportional to watt-hours consumed and drove a register logging kilowatt-hours.

What standard do many US states require new watt-hour meters to meet?

The accuracy requirements of ANSI Standard 12.1, with an accuracy requirement much better than $1\%$.

What do demand meters typically measure for billing larger commercial and industrial customers with three phase service?

Peak usage of either current or power (in $\text{kW}$, not $\text{kWh}$).

What is the most popular sampling duration for demand meters, and how many readings are taken in an average billing period?

A duration of $15\text{ minutes}$ is most popular, taking over $2800$ readings in an average billing period.

Why is the value indicated by a traditional demand meter's pointer not a true maximum peak usage?

The value indicated by the pointer is an integrated value over the predetermined sampling period rather than an instantaneous peak.

What were the primary features and limitations of early AMI (Advanced Metering Infrastructure) meters in the 1990s?

They electronically recorded and stored electric consumption by hour of the day for TOU (Time of Use) programs, but lacked real-time, two-way communications.

What term did Public Service of Oklahoma use instead of "smart meter"?

"advanced digital meter".

What term did Philadelphia Electric Company revert to when referring to their meters?

"Advanced Metering Infrastructure".

What is the two-part definition of smart metering provided in the text?

A concept embracing meters that use new technology to capture complex energy use information, and communication systems that can capture and transmit energy use information as it happens or almost as it happens.

What is the functional difference between a smart grid and a smart meter?

Smart grids are fitted with sensing devices to provide real-time condition information of an electrical distribution system, whereas smart meters offer information to shift peak loads to off-peak times.

What two main issues raised by consumers caused early adverse press for smart meters?

Fears of adverse health effects from periodic radio signal emissions and privacy concerns regarding the monitoring of power usage and living habits.

How do smart meters assist utilities during a power outage?

They immediately alert the utility to the outage condition, allowing the utility to quickly determine problem extent and dispatch line crews faster.

Where are submeters commonly installed?

At marinas, condominiums, mobile home parks, RV parks, apartments, home owners associations, or for tracking usage by internal departments within an industrial facility.

Which US state publishes a list of approved submeters and disallows non-listed meters?

The State of Maryland.