Phase 6 Full Questions T1 + T2 Theory Flashcards
4 advantages of home automation
Cost effective
Can dim lights
Can be on time clock
Can be controlled by phone
Triac - can conduct in both waves
Thyristor - can only conduct in half wave
Draw a labelled block diagram showing the 5 main components of a PLC
The purpose of an opto-coupler is to provide electrical isolation between input and output devices.
A signal is sent to the diode making light, this is received by a photo transistor.
There is no electrical connection
List 4 types of input device used in home automation ?
Occupancy sensor- light automatically come in when senses occupant in building
Daylight sensor - when senses daylight , the light will dim.
Temperature sensor - prevents temperature rising above set temp
PIR - will automatically turn lights on/off
Describe how a bus topology system can provide control in a large automation system and give 2 benefits ?
Bus topology is one continuous cable
Data can be shared among other sub systems
Sub systems can be removed without interrupting others
2 benefits
System is faster
Controls closer to plant
Draw a connection diagram of a DC, short Shunt compound motor, identify the series and shunt windings and describe how they influence the performance of the motor
Explain the typical operation of a TRIAC, and state typical applications
It has a 2 directional thyristor which is triggered on both Half’s of the AC cycle.
Used for dimming lamps and controlling speed of motors.
What is the purpose of the D1 diode ?
Draw a flywheel diode circuit.
D1 is a flywheel diode, used to dissipate the energy in the coil of the transistor.
Describe the 3 steps required to connect a large three-phase synchronous motor to the mains electrical supply ?
- Must run to synchronous speed
- Should produce voltage as main supply
- Once EMF is in phase the motor can be connected.
Draw a PLC star topology
State one main advantage, and one disadvantage of the operation of a synchronous motor
Advantage - improves PF
Disadvantage - not self starting
Outline the main reason why automatic tap changes are used in the windings of electrical power distribution transformers
Used when high demand is on the transformers
Increases transformer voltage
Describe the term voltage regulation
The difference in voltage in the secondary winding between no-load and full load as a percentage of the no load voltage
What are the two types of transformer losses?
- Copper losses
- Iron losses
What do we find buy doing an open circuit test on a transformer?
An open circuit test will measure iron losses
What do we find if we do a short circuit test on a transformer?
A short circuit test on the transformer will measure copper losses
Describe 2 different methods employed to cool oil filled powertransformers ?
Air cooled - natural ventilation
Oil cooled - forced ventilation
Explain how to carry out an insulation test on a three phase power transformer?
Transformer must be isolated
Need to connect, L1, L2 and L3 together
L1 L2 L3 and Neutral
L1 L2 L3 and Earth
High-voltage test meter is connected in turn
Draw a suitable diagram of two single phase transformer, connected in parallel
List a typical reading for the instruments, which would indicate it was safe to parallel the transformers
Why do we connect transformers in parallel?
To share the Load and for security of supply
2 ways a bucholz relay can operate?
Air leaks - air entering the transformer due to faulty gland or oil pumps
Low oil level - the leak in the transformer tank or fittings
Why do we use arcing horns or surge protectors?
Arcing horns and surge protectors protect the transformer windings by diverting the surge current.
How do arcing horns work?
Arcing horns are connected between the incoming line and the Earthed tank of the transformer. If a high voltage surge happens, will cause the arc to jump the air gap between the horns and discharge to earth.
Explain how to carry out an insulation test on a three phase power transformer
The transformer is isolated and proved to be isolated
You need to connect, L1, L2 and L3 connections together, and L1, L2, L3, and neutral connections together
A high voltage 10 kv insulation test meter is connected in turn between phases
Results have to be greater than 1 mega ohm
Describe the procedure required to connect A large 3 phase synchronous motor to the main electrical supply.
Must be ran up to synchronous speed
An EMF should be produced
It may now be connected to the mains supply
The field current can be switched on
What is armature reaction?
Armateur reaction takes place when amateur current causes the armature to become an electromagnet
State two methods of overcoming armature reaction in a DC motor or generator
Install compensating windings (extra winding)
Install inter poles ( improves commutation)
Describe the aid of a diagram of the operation of a single end of line alarm circuit and give one advantage
Monitors cable , if it was to be short circuited the EOL would detect a change in current and sound the alarm.
Explain How
A. both windows may be opened without activate the alarm panel when the system is unset
B. The system is activated on the opening of one or both windows on the alarm system when the system is set
A. Contacts shunted by diodes when the system is set the current flows through the circuit
B. The Diodes are reverse polarity when the window open the current is ceased setting off the alarm.
In relation to intruder alarms, describe the operation of the following
- Panic button
- Inertia sensor
1- when the panic button is pressed it sends a duress signal which sets off the alarm, when the system resets the panic button is restored.
2- when there is impact to the door the ball of the inertia sensor moves and sets off the alarm
- Conventional
- Addressable
Name three types of fire alarm sounders and one suitable application for each?
Siren - factory
Bell - schools
Public system - airports
Name three types of intruder alarm and give one suitable application for each
Panic button - bedside
Inertia sensor - windows frame
Pressure mat - inside front door/window
What is the minimum number of sound or bell circuits required to be connected to a fire alarm control panel
2
One suitable type of cable for fire alarm installation
Fire resistant Ph30 cable
What is the purpose of the diodes ?
When the system is off, the polarity is opposite, which stops the current from flowing and sounding the alarm
Compare the use of smoke detectors to heat detectors when used in fire alarm system and state one advantage and one application for each type of detector
Smoke detectors, cover more floor area and false alarms Can occur from dust
Adv - gives early warning
Application - classrooms
Heat detectors
Adv - withstands environmental conditions
Allocation - kitchens
What does L, P and M stand for ?
Automatic detectors for the Protection of life
Automatic detector for the Protection of property
Manual detectors
Max and main fire alarm dB level
Min - 75db
Max - 118db
State maximum floor area for a single fire detection zone
2000 m²
Explain the use of isolators connected in addressable fire alarm layout
The isolator is used so if there is a fault to one of the instrument, only turns off the zone which is connected to the isolator and the rest of the system will still be on
List suitable locations within a building for the installation of the main control fire panel
Main exit/entry
Place with low fire risk
Good lighting
Easily accessible
Explain the reason why electrical utility operators offer maximum demand tariffs to large, commercial, electricity consumers
Because they always use electricity at peak times
List the benefits of electrical, smart metering for consumers and electrical utility operators
Saves money on meter readings
Can monitor electricity being used
How is ark extinction achieved through MCB’s ?
The arc is extinguished through V splitter plates, this increases the length of the arc and de-ionises it. The gas is then vented from the sec chamber
State four advantages of MCB’s in comparison with the fuses
Can easily spot a tripped MCB
They do not age
Can not be switched on while fault occurs
Tamperproof
Give five advantages of using all insulated switchgear compared to metalclad switch gear
Corrosion resistance
Easy to assemble
Easy to drill
Reduce weight
Reduce cost
Explain the reason why a main fuse is installed in a domestic consumer unit consisting of a miniature circuit breaker
Higher breaking capacity
Backed up with a fuse
Cut off current is less than the short circuit current
List of procedures required to carry out the verification of operation of 30 mA single phase AC type RCD
Should be verified by injecting a test residual current and recording the time of operation by means of a proprietary instrument, specifically designed for the purpose
Define the following terms
- ring conductor
- earth termination
-reference earth electrode
1- mounted to structure
2- to discharge lightning
3- capable of being isolated for testing
In relation to the design of a lightning protection system, state two factors that should be considered
Location of building
Structure of building
Height of building
Components of building
What are the three main effect of a lightning strike?
List four factors that must be considered when assessing a building ?
Electrical
Mechanical
Thermal
- The location of the Building
- The structure of the building
- The area of the building
- The contents of the building
State two main functions of a UPS system?
Provide backup power
Provides surge protection
Condition, electrical supply
When selecting a rotary diesel powered UPS system list, two factors that need to be considered before the installation
Noise
Fuel storage
The Load
Draw a single line diagram of a solid state uninterruptible power supply system and give one suitable application
On-line system
In relation to the installation of electrical circuits and potentially explosive atmospheres defined, the term intrinsically safe circuit and with the aid of a sketch. Describe how an electrical circuit is made intrinsically safe.
A. Current and voltage is limited through a zener diode so no Spike can cause an explosive atmosphere.
B.
In relation to potentially explosive atmospheres state three ways in which combustable dust can be ignited by electrical apparatus ?
Sparking of electrical equipment
Mechanical, sparking
Surface temperature too high
Electrostatic charge
In relation to the installation of electrical circuits and potentially explosive atmospheres explain the meaning of a flameproof enclosure
Flameproof enclosure is an enclosure that protects against explosions of flammable gas
Explain the meaning of the component parts of the apparatus label
T6 - temperature class
11 - Gas group
C - gas type
E - protection flame proof
Ex - European mark
List of key electrical components required to connect a solar photovoltaic array to the national electric grid, and describe the function of each compound
Inverter - covert AC to DC
Battery - Stores DC power
Solar PV - Collects solar rays
DC sw - isolator
AC sw - isolator
When verifying the operation of a grid tied micro generator at the commissioning stage, list the tests that are required to be carried out
Over / under voltage test
Over / under frequency
Mains test
List four places where the warning sign should be located in a building that’s connected to both the National Grid and on site generator
At the micro generator
At all isolation points
At main fuse board
And all fuse board between the micro generator and the ESB metering point
What form needs to be filled out to connect A microgenerator to the grid
NC6 form
In relation to microgeneration, do you always need to install an export import meter?
No, but they are needed to apply for payment
Is there a cost to the customer for installing an import export meter?
Yes, ESB networks charge €340
State 4 advantages of microgeneration
Reduce electricity bills
Reduce carbon emissions
Independent supply
It’s possible to sell back to the grid
List four advantages of addressable fire alarm panel
Easier to identify the location of fire
Easier maintenance
Panel can be programmed to the clients needs
Save money on labour
List the three categories that smoke detectors can be divided into and a location where they should not be placed
Photoelectric detectors
Ionisation detectors
Combination detectors
Smoke detector should not be placed in the kitchen
What are three main reasons of using instrument transformers
Enables the use of standard equipment
Increased safety
Measurement instruments can be changed without isolation
Provide 4 advantages and 1 disadvantage of CTS
Adv -
Makes metering of large loads easier
Reduces cost
Safety increased
Provides electrical insulation
Disadvantage-
Cannot open circuit on load as large voltage could build up on terminals
List three criteria equipment for save selection and potentially explosive atmospheres
Area classification
Gas classification
temperature classification
Explain the meaning of a brown and black out
Brown out are caused when main supply is unable to cope with demand, these can last several hours
Blackouts are total Brakes in the supply which can be between milliseconds to hours , they can be caused by line faults thunderstorms etc
Describe the aid of a diagram an off-line and online UPS system
List the places where a UPS unit should not be located
On top floor of a building
On an outside wall
Close to lightning attractions
Close to large currents
List the four main parts of a UPS system and briefly explain what they do ?
Inverter - coverts DC to AC
Rectifier - used to change AC to DC power
Battery - Provides emergency power
Static bypass switch - used to bypass the ups normal operation
State three locations, where a standby UPS system may be used
Hospitals
Schools
Supermarkets
What is an exposed conductive parts?
Any metal part that has electrical cables within
What is an extraneous conductive parts?
Any metal part that is in contact with earth has no electrical cables within, can become live under fault conditions.
Earthed equipotential bonding?
All the conductive parts within that area and connecting them by means of earthing conductors (bonding )
Three Advantages and disadvantages of relay outputs ?
Adv -
Can switch AC and DC
Higher currents than a transistor
Polarity is not an issue
Disadvantage-
Moving parts make it slower
Mechanical wear
Noise
Advantages and disadvantages of a transistor output
Adv - no mechanical movement
More reliable than realise
Disadvantage- polarity is critical
Only switches DC
Switching current limited to Low max current
What effect has armature current on a motor ?
Armature current is directly proportional to the torque produced by a DC motor so the more armature current, the more torque
What effect has field excitation on a motor ?
The stronger the magnetic field , the more torque
Why do we use a bi directional Triac?
A bi directional Triac allows current to flow in both directions, which is useful for dimming lights
What is the minimum decibel level of an external bell box?
70db
Draw a VSD
What is side flashing?
Risk of flashover from the protection system to other metal on the Structure
Draw a diagram of a magnetic contact and explain Briefly
Magnetic contacts consist of a reed switch on a fixed Magnet. The magnet is fixed and to the opening , reed sw fixed fixed to the frame. The magnet moves away example the window opens and switch opens, setting off the alarm.
What are the four most common types of microgeneration?
PV
Wind
Micro-hydro
CHP
Max search area in a fire detection zone ?
30m
Three control panel functions
Mute alarms
Sound alarms
Reset alarms
In relation to a sound activated bellbox Mounted to the exterior of the building state of Max permissible audible time
30 mins
State one component that’s necessary for an SAB to have to continue operation
Rechargeable battery and it’s own tamper circuit
What is Peak lopping ?
Using generators in the evening, time to bring down the price of electricity
Draw a conventional fire alarm system
The purpose of resistor 1 to 4 is the limit to excessive starting current.
As the motor picks up speed the handle is moved through the resistors, reducing the level of starting resistance.
When contact is made with stud 5 it completely cuts out all external resistance
