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ZemkeCh7PPT.pptxElectrical Systems
Chapter 7
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What is electricity?
Energy is created by the flow of electrons.
Electrostatic charge resulting from:
Electrons repelling electrons
Protons repelling protons
Electrical current:
When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current.
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Basics of Electricity:
Electricity is much like water it has pressure, flow and resistance.
Voltage
Electrical pressure, the force that move electricity measured in volts. Like water, pressure (voltage) drops over distance
Amperes
Electrical current or flow measured in amps.
Ohms (Resistance)
The tendency to resist the current or flow measured in ohms; "1 Ohm" is the resistance between two points in a conductor where the application of 1 volt will push 1 ampere. Wiring (conductor), equipment, etc., all have some level of resistance.
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Ohm’s Law: Measuring Electricity
The basis for all electricity measurements is Ohm’s Law.
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E = Volts – electrical pressure
I = Amperes (amps) – electrical current (flow)
R = Ohms (Ω) – resistance to electrical flow
Measuring Electricity
Q: A mixer plugged into a 110V electrical receptacle, draws 5.5 amps. What is the electrical resistance (measured in ohms)?
A: ? Ω
Q: A microwave oven plugged into a 110V circuit with 15 ohms (Ω) of resistance draws how many amps.
A: ? amps
Q: A Keurig coffee maker draws 10 amps of power and has 21 ohms (Ω) of resistance. What is the voltage of the electrical circuit?
A: ? volts
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Measuring Electrical Power
Electricity is measured in units of power called watts.
Amps × Volts = Watts (A×V=W)
Kilowatt = 1,000 watts (power used now, demand power)
Kilowatt-hour = overall power consumed, power used over a period of time.
Power is a measurement of how much energy you're using over time. To find the total amount of energy, you multiply the power used by the total number of hours used (kWh). A 1000 watt toaster operating for 1 hour uses 1 kilowatt (kWh) of energy; the same amount as using a 2000-watt toaster for 0.5 hours or a 100-watt lamp for 10 hours. See how it works?
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Measuring Electrical Power
Q: A microwave oven plugged into a 110V circuit draws 7.0 amps of power. How many watts of power are consumed?
A: ? watts
Q: A refrigerator is plugged into a 110V circuit and draws 6.0 amps. If it runs continuously for 30 days, how many kilowatt-hours (kWh) will it use?
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Measuring Electrical Power
1. Determine watts
V × A = 660 watts
2. Convert to kilowatts
660/1000= .66 kWh’s
3. Multiple by time (hrs)
30 days x 24 hrs = 720 hrs
4. (110 × 6 /1000) × (30 × 24) = .66 × 720 = 475.2 kWh’s
or 110 × 6 × 30 × 24 / 1000 = 475.2 kWh’s
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Power – don’t confuse this with current
Power is electricity that is used
Power is measured in watts
Watts = Volts x Amps
Kilowatt (kW) = 1,000 watts
We use power:
Right now – watts or kilowatts (kW)
Over time – watt-hours or kilowatt-hours (kWh)
Current is the flow of electrons, creating electricity
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Electrical Circuits
A circuit overload occurs when it is trying to draw more than it is designed to carry
Amperage draw is critical when determining electrical circuits
Drawing too much power from a circuit is a main cause of tripped breakers /blown fuses
Q: An office has the following appliances plugged into a 10A circuit:
Scanner 1.5A
2 desk lamps @ 0.5A each
Laptop computer 0.75A
Printer 0.8 A
Microwave oven 3.0A
Mini-refrigerator 3.0A
What will happen?
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Electrical current is provided as:
Direct current – no change in polarity
We usually get DC current from:
Batteries
Generators
Solar photovoltaic (PV) panels
Alternating current – polarity alternates between positive and negative
We usually get AC current from:
Electric company
Inverter – take DC current from solar panel, generator, or battery and convert it to AC current
Frequency (Hz): how often the polarity changes each second
North America: 60 Hz
Europe: 50 Hz
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AC vs. DC
AC
Alternates, moves in both directions,
Generated by power company
AC cheaper to produce
Transmit easily over long distances
Easy to step-up / step-down
Convert AC to DC (rectifier)
DC
Direct/constant, current flows one way
Requires additional input as it travels
Great for small appliances/electronics
Advent of solar = resurgence of DC
Generators, batteries
Convert DC to AC (invertor)
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Frequency
AC is supplied with positive and negative polarity meaning the current alternates between a positive and negative charge.
Measured in hertz (Hz), the rate it cycles between polarities per second. Simply stated, frequency is the number of times a sine wave completes a cycle.
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60 Hz or 50 Hz
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Frequency Issues for Guest
Devices like hairdryers and electric razors rated at 110V/60Hz (US) will run faster/hotter at 220V/50Hz, the inverse is just the opposite, both can cause failure. Use transformers to decrease or increase v/Hz accordingly.
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How is electricity usually generated?
A generator uses a turbine
Metal coils are attached to a shaft
The coils spin around in a field of magnetic coils, creating an electrostatic charge
The turbine turns the shaft
What turns the turbine?
High pressure steam
Water
Wind
Sources of energy: coal, natural gas, nuclear, solar, hydro, wind.
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Turbine Generated Power
Hoover Dam Hydroelectric Turbines
17 hydroelectric turbines
4 billion kWh’s annually
1.3 million people in NV, AZ, CA
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Power Generation Distribution
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Fuel Cell Power Generation
Sierra Nevada Brewing Co., Chico, CA
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You can also generate electricity with photovoltaic panels
Photovoltaic (PV) panels take light and convert it to electricity
PV chips are semi-conductors
The system generates DC current
Must either use DC motors to use the electricity or use an inverter to convert DC to AC current
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Residential Solar
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Power Plant Generated Electricity
Utility companies used to generate both AC & DC power
Distributed at high voltage
The voltage must be reduced, or “stepped-down”, using a series of step-down transformers to the end users
The electricity utility company usually owns the transformers, although your building will also have its own transformers
Once at your building your transformers will either “step-up” increase or “step-down” decrease depending on voltage required
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Where are transformers located?
Above-ground
On an electric pole, connected to electrical wires
On the ground, in a transformer box
Below-ground:
Usually in urban areas where land is scarce
Transformer is place in a vault, which is under the sidewalk; a grate will cover the vault to permit heat to escape
You may also have transformers inside your building’s mechanical and electrical areas
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Transformers
Transformers can either be used to increase or decrease power depending on the needs/use of the consumer
Above-ground transformers
Below-ground transformers, in a vault
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Transformers are hot!
They are hot and must be cooled
May be air-cooled or oil-cooled using a specially-formulated oil
Older transformers that are oil-cooled may have oil containing polychoryl biphenols (PCBs). PCBs are carcinogenic, especially when burned
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All hospitality managers should know:
Where the property’s transformers are located
Whether the transformers are air-cooled or oil-cooled
If oil-cooled, does the oil contain PCBs?
This is important because if your transformers catch fire, you need to communicate this information quickly to the Fire Department so they can knock the fire down quickly and correctly
This is particularly true if you oil-cooled transformer has PCBs, since the PCBs create a serious environmental hazard when burning
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Because transformers get hot, they tend to catch fire
Animals are also curious and investigate transformers…with sad results
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Power Disruption’s Small Enemy
Each marker represents a documented squirrel-induced power outage since 1987 (Cyber Squirrel 1).
Source: https://www.washingtonpost.com/news/wonk/wp/2016/01/12/a-terrifying-and-hilarious-map-of-squirrel-attacks/?postshare=5781453142437501&tid=ss_mail
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Electrical distribution: Exterior to Panel
Electricity enters the building
Goes through a meter to measure consumption and demand
Possibly through a transformer
Travels to distribution panel
Circuit breakers
Fuses
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Electrical distribution: Distribution Panel
Electricity is distributed through wiring, this wiring is called a circuit. Series circuits most common.
Lighting
Wall outlets (receptacles)
Appliances
Combination: Lighting, receptacles
Each circuit is protected by a circuit breaker or fuse. They prevent the circuit from drawing too amps by “breaking the circuit” or interrupting the power on that circuit.
Circuit breakers can be reset
Fuse is a one-time use, when circuit is overdrawn the fuse burns and breaks the circuit.
Circuit protection protects the wire, not the device/appliance
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Electrical Circuits
Series circuit is most common: multiple outlets, outlet and lights, etc. all on one circuit (same breaker, fuse, etc.)
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Additional circuit protection: GFCI
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The ground-fault circuit interrupter (GFCI)
Fast acting, as quick as 1/40 of a second
Monitors power directly at receptacle
Any power discrepancy in the receptacle or equipment
Most common in wet areas
Wiring:
Commercial buildings have different electrical codes and requirements than residential buildings. May appear to be stricter; however, just appears so.
Wiring types:
Non-metallic sheathed cable, Romex, primarily residential
Armored cable (AC) or BX
Closed raceway: rigid conduit or flexible metal conduit (FMC), Greenfield.
Raceway: surface or sub-floor
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Wiring Review
A D
B E
C F
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Emergency Power
Emergency generators
Usually diesel-powered; may also be natural gas (nat-gas) fired
May be required by code
What should be connected to emergency power?
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Back-up/Clean Power Source
Uninterruptible Power Supply (UPS) systems
Small battery-back up systems for computers, servers and other electronic equipment
15-60 min., opportunity to shut-down/save data
Provides “clean” power for sensitive electronics
Takes buildings AC power, converts to DC (rectifier), stores DC power in a battery, UPS draws from DC source, converts back to AC (inverter)
Computers, electronics plug into the UPS
Dedicated line/circuit
Only computers, servers, sensitive electronics plugged into the circuit.
UPS & Dedicated circuits will eliminate “noise”/static
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Power Quality
Surge/”overvoltage”: too much voltage
Transients: intense burst of high voltage from power company or lighting
Sags/”undervoltage”: too little voltage
Brownouts: electrical sag greater than 5%
Blackout: complete loss of power
Electrical noise: static, voltage variations
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Load-shedding systems
In Chapter 4, we will discuss how to manage electric bills, including consumption and demand
A load-shedding system will help you manage your demand costs
Load: any electrical appliance that is drawing electricity right now
Demand is based on how much power we are using right now (not over time); measured in kW
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Peak-shaving/load-shedding
The goal of a peak-shaving system is to shave the tops off of the peaks, or spikes, in our demand
If we can lower the peaks, we can lower the demand charges on our electric bill (which are very expensive, especially in the summer period)
A load-shedding system will monitor the demand meter in real-time
When the system sees a demand spike forming during on-peak periods, it will automatically shut down appliances (loads)
When the load-shedding system sees that we are leaving the on-peak “danger zone” for demand charges, it will turn the equipment back on
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Electrical system safety practices
Lock-out/tag-out program
Prevent accidentally turning on de-energized equipment
Prevent employee injuries
Arc flash safety program
All electrical equipment capable of arcing
Temp can exceed 35,000°F
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Electrical system safety (cont.)
Engineering department employee procedures
Non-engineering employee safety measures
In case of a fire:
Someone needs to cut power to the area on fire as soon as possible!
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