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Energy Use Analysis > Electrical Power > Flashcards

Electrical Power Flashcards

1
Q

What is electrical demand?

A

A measurement of power, in kW, based on a customer’s highest use within a given unit of time.

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2
Q

What is contract demand?

A

The addition of all of a utilities customer demand so that they can estimate the maximum overall generating capacity they need to provide.

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3
Q

Electric utilities sell two products:

A

Usage and demand

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4
Q

What is Usage?

A

The overall flow of electricity over time, in kWh

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5
Q

What is Demand?

A

The simultaneous use of power, in kW. Demand becomes the load the utilities must provide.

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6
Q

What is peak demand?

A

The most power, in kW, used over a specific time period.

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7
Q

T/F Most medium and large commercial customers pay for demand.

A

True

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8
Q

What is Load Factor?

A

The relationship between kWh consumption and kW demand for the same billing period. It describes the profile of the electrical use of a facility.

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9
Q

Load factor for a given time period =

A

Average kW in time period / Peak kW in time period

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10
Q

Average kW =

A

Total kWh / # of hours in time period

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11
Q

A high load factor means power use is relatively ______.

A

constant

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12
Q

A low load factor means power use is ________.

A

inconsistent, with high and low peaks.

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13
Q

For an industrial facility, a ____ load factor is ideal.

A

high

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14
Q

What are baseload plants?

A

Power plants that operate constantly to provide the minimum amount of power needed around the clock.

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15
Q

What are some typical baseload plants?

A

Coal, natural gas, nuclear, hydroelectric dams, geothermal, biomass

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16
Q

What are intermediate plants?

A

Power plants that operate daily or seasonally to follow the large but predictable swings in demand. Dispatched during baseload outage or maintenance.

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17
Q

What are some typical intermediate plants?

A

Natural gas, hydroelectric, solar thermal, solar VP, wind farms

18
Q

What are peaking plants?

A

Power plants that are used only sporadically and for short periods of time to accommodate peak demand that exceeds the intermediate plants.

19
Q

What’s the most expensive type of plant to run?

A

Peaking plants, because they sit idle most of the year.

20
Q

What are some typical peaking plants?

A

Natural gas, oil and diesel generators, hydroelectric dams

21
Q

How much excess capacity beyond peak needs are utilities required to have as a margin of safety?

A

10-20%

22
Q

What are Demand Side Management strategies?

A

Strategies offered or incentivized by utilities to reduce the power use of its customers during time of extreme demand, done cooperatively.

23
Q

What are some DSM strategies?

A

Large lighting, motor, or HVAC retrofits, rescheduling large loads to off-peak hours, interruptible loads, curtailable loads,

24
Q

What’s an interruptible load?

A

One that the utility can remotely turn off at certain times of the day or year during peak times. The customer is offered a financial incentive, like a yearly rebate.

25
Q

What’s a curtailable load?

A

One that a customer is willing to turn off if given sufficient notice by the utility. They work best for manufacturing facilities with significant inventory.

26
Q

What is Alternating Current (AC)?

A

The electrons oscillate between positive and negative voltage, relative to ground. The higher the voltage, the higher the sine wave.

27
Q

What is three-phase voltage?

A

Three separate lines carry the electricity and the AC voltage in each line is offset 1/3 from each other, allowing for a more constant power generation.

28
Q

What percentage of all electricity produced is lost in transmission due to the resistance of the wires?

A

7%

29
Q

What are substations?

A

Stations where voltage is stepped down to lower levels that can be safely distributed by local distribution lines to each customer.

30
Q

Where are step-down transformers?

A

At or near each customer. They make the final voltage adjustment.

31
Q

For most residential buildings, electricity enters as _________________.

A

120/240 volt single-phase service (two hot wires + 1 neutral carrying wire)

32
Q

For larger commercial buildings and industries, electricity enters as _________________.

A

277/480 volt three-phase service (3 hot wires + 1 neutral carrying wire)

33
Q

What is Real Power?

A

Power that is put directly to work lighting, turning, or burning something in watts.

34
Q

What is reactive power (phantom power, negative power, wattless power)?

A

Occurs when certain types of induction loads such as transformers or motors induce a magnetic field to produce work. The fields cause the current to fall out of phase, and when multiplied with voltage it produces power that dos not show up on the power meters as positive watts. Measured in kilovars of kVAR.

35
Q

What is apparent power (total power)?

A

The total amount of power needed to provide both real power and reactive power. Computes as the vector sum (hypotenuse) of real and reactive power. Measured in volt-amps.

36
Q

Power Factor =

A

Real power (kw) / Apparent power (kVA)

37
Q

Why does the utility care about power factor?

A

Even though reactive power doesn’t show up as watts, it still represents electrons that need to be generated by the utility. If a facility has a low power factor, the utility must supply more current than is necessary for the actual power.

38
Q

T/F The power factor of a facility should be as high as possible.

A

True

39
Q

When do utilities generally charge a customer for power factor?

A

When the customer’s power factor falls below a certain percentage, such as 90%.

40
Q

What are some power factor correction strategies?

A

Eliminate the inductive loads that generate kVAR, replace inductive motors, install capacitors designed to correct power factor by temporarily providing the reactive power, real-time metering

41
Q

T/F A typical single facility meter can be used to determine overall power factor but it can’t determine what?

A

The cause

Energy Use Analysis (4 decks)

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