Download Chapter 1 electrical Fundamental 2014

Mechanical and Electrical Systems
[CIV 311]

Comprehensive coverage of mechanical systems, electric al systems, plumbing, fire
protection, security, vertical transportation, lighting, acoustics and communications. The
course includes analysis techniques and design principles for each system. A
comprehensive design project is required for a major building project.. Psychrometry
and process of air. Cooling load estimation. Refrigeration cycles. Water chiller systems.
Air handling system. Cooling towers. Equipment selection. Installation, operation and
maintenance of air conditioning systems.

Basic knowledge of data communication: data transmission technology, transmission
media, signal interference, etc. Network topology: logical aspect and physical aspect.
Local area network technology. Networking equipment: repeaters, signal transceivers
converters, switches/hubs, connectors/interfacing equipment, etc.

Principles of lighting, lighting design for buildings which includes artificial lighting, point,
line and area light sources, types and properties of luminaries, polar curves, design
methods and calculations, glare index, lighting design standard, luminaire heat recovery
system and lighting energy management, hybrid lighting, daylighting of buildings, effect of
climate on lighting

T01
PART ONE ELECTRICAL
Chapter 1
Electrical fundamental
T02
Electricity
General Electricity
• Development can be measured by a
nation’s electricity consumption
• Electricity usage is divided into:
a) Industrial
b) Commercial and residential
c) Agriculture and irrigation
• Electricity important input for
industry
3
Electricity
General Electricity
• How can electricity supply shortage
be solved?
a)
Renovation and modernization of plants, transmission and
distribution systems
b)
Demand side management with the utilization of energy
efficiency technologies
c)
Awareness raising among energy users
4
Electricity
Generation & Distribution
Transmission
system
Power plant
Generator
GT
10.6 KV
Distribution system
22 or 11 KV
220 KV
Distribution
Step down
transformer
380/220 V
5
Electricity
Generation & Distribution
•
AC generators (“alternators”) generate electricity
• Electricity generated at 9-13 KV
• Power generated from 67.5 to 1000 MW
•
Power stations: generating transformers (GTs) to increase voltage
to 132-400 KV
•
Substations: step-down transformers to reduce voltage before
distribution
6
Electricity
Generation & Distribution
Benefits of high voltage transmission
•
Less voltage drop: good voltage regulation
•
Less power loss: high transmission efficiency
•
Smaller conductor: lower costs
7
Electricity
Phase of Electricity
Single phase AC circuit:
• Two wires connected
to electricity source
• Direction of current
changes many times
per second
-3phases of an electric system
(Wikipedia contributors, )2005
Three phase systems:
• 3 lines with electricity from 3 circuits
• One neutral line
• 3 waveforms offset in time: 60-50cycles/second
8
Electricity
Phase of Electricity
Star connection
Delta connection
9
Electricity
Active and Reactive Power
•
Active power (kW): real power used
•
Reactive power (kVAR): virtual power that determines load/demand
•
Utility pays for total power (kVA)
kVA =  (KW)2 + (KVAR)2
Source: OIT
10
Electricity
Power Factor Correlation
11
Electricity
PF Correction: Capacitors
•
kVAR demand should be as low as possible for the same kW
output
Figure: Capacitor as kVAR generator
12
Electricity
PF Correction:
Capacitors
•
Act as reactive power
generators
•
Reduce reactive power
•
Reduce total power
generated by the utilities
Figure: Fixed capacitor banks
Source: Ecatalog
13
Electricity
PF Correction: Capacitors
Advantages for company:
•
One off investment for capacitor
•
Reduced electricity costs:
•
Total demand reduced
•
No penalty charges
•
Reduced distribution losses
•
Increased voltage level at load end, improved
motor performance
14
Electricity
PF Correction: Capacitors
Advantages for utility:
•
Reduced reactive component of network
•
Reduced total current in the system from the source end
•
Reduced I2R power losses
•
Reduced need to install additional distribution network capacity
15
Electricity
Electrical Load Management
Goal: reduce maximum electricity demand to lower the electricity
costs
•
Load curve predicts patterns in demand
KVA
•
Daily load curve of an
engineering industry
(National Productivity
Council, India)
Hours
16
© UNEP 2006
Electricity
Electrical Load Management
Strategies to manage peak load demand:
•
Shift non-critical / non-continuous process
loads to off-peak time
•
Shed non-essential loads during peak time
•
Operate in-house generation or diesel
generator (dg) sets during peak time
•
Operate AC units during off-peak times and
utilize cool thermal storage
•
Install power factor correction equipment
17
Electricity
Electricity Billing Mechanism
•
Energy charges
• Actual charges based on active power
• Charge based on apparent power
•
Maximum demand charges
• Based on maximum demand registered
• Penalty for peak load
18
Electricity
Electricity Billing Mechanism
•
Power factor penalty or bonus
•
Fuel costs
•
Electricity duty charges
•
Meter rentals
•
Lighting & fan power consumption
•
Time of Day (TOD) rates
19
Electricity
Electricity Billing Mechanism
Utility uses trivector meter for measurement during billing cycle
(usually month):
•
Maximum demand
•
Active energy in kWh
•
Reactive energy in kVArh
•
Apparent energy in kVAh
20
Electricity
Electricity Billing Mechanism
•
Demand
measured in
time intervals
•
Maximum
demand is
highest reading
•
Customer
charged on
highest
maximum
demand value!
A Typical Demand Curve
(National Productivity Council)
21
Electricity
Transformer
•
Static electrical device that
transforms electrical energy
from one voltage level to
another
•
Two or more coils linked
magnetically but electrically
insulated
•
Figure 12: A view of a
transformer
(Indiamart.com)
Turns Ratio: turns on 2nd coil (connected to load)
turns on 1st coil (connected to power source)
22
Electricity
Transformer types
Transformers are classified based on:
•
Input voltage
•
Operation
•
Location
•
Connection
23
Electricity
•
Electricity is the flow of electrons in a conductor.
•
The electrons must have a path to and from its
source.
•
This path is called a circuit.
24
Normal, Open and Short Circuits

Normal Circuit
◦ When normal current is flowing through the circuit

Open Circuit
◦ When the current flow is interrupted by switch or
fuse
◦ Circuit break presents an extremely high resistance.

Short Circuit
◦ When the current flowing through the circuit is
following a “shorter” low resistance path between the
power source terminals.
◦ Allows high current to flow in the circuit
T025
Electricity
 Various
electrical devices are used as a
part of the circuit.
 These
devices are used for a variety of
activities, such as turning the electricity
off and on, providing electricity to various
lights or appliances, etc.
Types of Electrical Currents
Electrical current comes in two forms: 
Direct current (DC) ◦
Flows in only one direction. 
It is usually generated by battery-base electrical systems 
and used in the electrical systems of internal combustion
engines or flashlight batteries.
Alternating current (AC) ◦
Reverses the direction of flow of current many times 
each second.
AC is the type used in homes, factories, etc. 
Electrical Service
 Service
is provided to homes, businesses
and other small users of electricity by
three wires from a utility pole.
 Two
of the wires are “hot,” each carrying
220 volts.
 The
other wire is “neutral,” and provides
the return path for electricity.
Electrical Service (cont.)
 These
wires are connected to a service
entrance, which is where the electricity
enters a building.
A
meter is used in the service entrance
to measure the amount of electricity
being used.
Electrical Service (cont.)
 The
service entrance is grounded with a
wire connected to a ground rod driven
several feet into the ground.
 It
is needed to provide a return path to
the ground and to carry away stray
electrical current out of the system.
Service Panel
Follows the meter. 
It houses the circuit 
breakers for the
system and is used
to distribute the
power to individual
circuits throughout
the system.
Overcurrent
 When
a circuit uses too much electricity, an
overcurrent causes a circuit breaker to trip,
shutting down the power to that circuit.
 The
excessive heat caused by an overcurrent
condition may burn or damage a conductor’s
insulation and cause a fire.
A
circuit breaker is a heat-sensitive switch,
which automatically trips when electricity
demand is too great which causes the
temperature in the conductor to get too hot.
Amps Volts Watts
The following relationship exists between Amps,
Volts and Watts.
 Amperes
are a measure of the rate of flow of
electricity in a conductor.
 Volts
are a measure of electrical pressure.
 Watts
are a measure of the amount of energy
or work that can be done by amperes and
volts.
Amps Volts Watts (cont.)
Thus, the following relationship exists.
Work = Pressure x Flow
Or
Watts = Volts x Amperes
Amps Volts Watts (cont.)
 This
formula is commonly referred to as
the West Virginia Formula
W=VA
 When
we know any two variables of the
formula, we can calculate the other.
Amps Volts Watts (cont.)
Formulas
Watts = Volts x Amps
Volts = Watts / Amps
Amps = Watts / Volts
Calculating Amperage
If we have a 100 watt lamp plugged into a 120 volt
receptacle, we can determine the rate of flow or the
amperes for that circuit.
Amps = 100 Watts / 220 Volts
100 / 220 =.4545 Amps
Calculating Watts
If a water heater operates at 20 amps on a 240 volt
circuit, what is the wattage of the appliance?
Watts = 220 Volts x 20 Amps
4800 Watts =220V x 20A
Watts=4400
Calculating Volts
If an electric motor operates at 2880 watts and 12
amps, what would be the voltage requirement for
that motor?
Volts = 2640 Watts / 12 Amps
2640 / 12 = 240 Volts
Maximum Minimum Average

Find the max and min load of the
following domestics daily curve
Hour
6
8
9
12
14
16
18
20
24
2
4
6
Kw
2
10
12
14
4
6
8
20
6
4
4
2
T040
T041
Transformer Rating
T042
Example Design
1.High rising building consists of 12 level
Each level 4 flats (4 bed room, reception and two bath room)
If each flat has the following equipment
The main building has the following
3 lefts
15 hp
0.8 pf
3 water pump
12hp
0.7 pf
Outdoor light
10kw
1 pf
Calculate
•Total power design the electrical installation of the building
•Main cable and branch cable cross section
•Switchboard main and sub switchboard flat switchboard
•No of transformer
Dishwasher
Air condition
Water heater
Washer
Light
Numbe
r
1
3
1
1
total
power
Power factor
2.5 KW
5 hp
4 KW
6 KW
7 KW
0.7
0.6
1
0.8
1
T043
T044