How To Eliminate Harmonic In Electrical System?

What Is Harmonics in Electrical System?

Harmonic define as any Non-Linear Current or Voltage in an electrical distribution system.

The presence of harmonics in electrical systems means that current and voltage are distorted and deviate from sinusoidal waveforms.

Harmonic shouldn’t be thought of as an acoustic or vibration harmonic, but simply any electrical device that draws current unpropotionally to voltage.

Harmonic currents are currents circulating in the networks and which frequency is an integer multiple of the supply frequency.

Cause of Harmonic.

Harmonic currents are caused by non-linear loads connected to the distribution system. A load is said to be non-linear when the current it draws does not have the same waveform as the supply voltage. The flow of harmonic currents through system impedances in turn creates voltage harmonics, which distort the supply voltage.

Harmonic are commonly produced by non-linear loads or devices that rectifies AC Voltage into DC Voltage. The most common non-linear loads generating harmonic currents are power electronics equipments such as variable speed drives, rectifiers, inverters, lighting and computer.

Other loads such as inductors, resistors and capacitors are linear loads and do not generate harmonics.

Why Harmonic Need To Be Eliminate?

One of the major effects of harmonics is to increase the current in the system. This is particularly the case for the third (3^rd) harmonic, which causes a sharp increase in the zero sequence current, and therefore increases the current in the neutral conductor. This effect can require special consideration in the design of an electric system to serve non-linear loads.

In addition to the increased line current, different pieces of electrical equipment can suffer effects from harmonics on the power system.

Despite the reason above, there are numbers of other reasons why harmonic need to be eliminate. The tabulation below shows the effect of harmonic to the electrical equipments that will be the main reason for eliminating the harmonic.

Equipment	Effect of Harmonic
Motor	Overheating, production of non-uniform torque, increased vibration
Transformer	Overheating and insulation failure, noise
Switchgear and cables	Neutral link failure, increased losses due to skin effect and overheating of cables
Capacitors	Life reduces drastically due to harmonic overloading
Protective Relays	Malfunction and nuisance tripping
Power electronic equipment	Misfiring of Thyristors and failure of semiconductor devices
Control & instrumentation Electronic equipment	Erratic operation followed by nuisance tripping and breakdowns
Communication equipment / Computer	Interference
Neutral cable	Higher Neutral current with 3rd harmonic frequency, Neutral over heating and or open neutral condition
Telecommunication equipment	Telephonic interference, malfunction of sensitive electronics used, failure of telecom hardware

How to Eliminate Harmonic?

To ensure a good and proper operation of the electrical installation, both harmonics (Current Harmonic and Voltage Harmonic) need to be eliminated.

Current Harmonic can be eliminated by adding Line Choke or by installing Isolating Transformer to the harmonic producing equipments.

Voltage Harmonic can be eliminated by installing Tuned Capacitor.

Other than the above method, you might consider equipments with a low Current Total Harmonic Distortion (THD).

What Is Ultimate Breaking Capacity (Icu) & Service Breaking Capacity (Ics)

To all engineers…you must know what MCCB is! But have you notice the Icu and Ics percentage indicate at the MCCB?

For example; the above MCCB shows that the Ics = 50% Icu

Those values are actually the breaking capacity of the circuit breaker namely as per below;

Icu: Rated Ultimate Short-circuit breaking capacity (in kA) 

Ics: Rated Service Short-circuit breaking capacity (in kA) 

The purpose of those braking capacity is to ensure the Circuit Breaker fulfill and without fails its main purpose to protect the electrical installations against overcurrent.

Icu is the abbreviation for Rated Ultimate Short-circuit breaking capacity. This is the current for which the prescribe conditions according to a specific tests sequence do not include the capacity of the circuit breaker to carry its rated current continuously after the test.

Ics is the abbreviation for Rated Service Short-circuit breaking capacity. This is the current for which the prescribe conditions according to a specific tests sequence include the capacity of the circuit breaker to carry its normal rated current continuously after the test.

Ics is expressed as a percentage of Icu (value to be chosen by the manufacturer from 25%, 50%, 75% or 100%). This is the maximum current that the breaker can break!

To explain the differences between those two, we took the weight lifting event as an example.

We compare this two guy; Mr. A and Mr. B (consider both guy lifting the same weight..even though its obviously not in the picture)

Mr. A can lift the weight to its ultimate but Mr. B only can lift the weight up to half of Mr. A’s ultimate.

Now, we assume Mr. A and Mr. B is the same guy (same MCCB) but Mr. A is the Ultimate Current (Icu) and Mr. B is the service current (Ics).

By looking to the picture, we can conclude that both Mr. A and Mr. B can lift the weight to its ultimate but only during servicing both Mr. A and Mr. B can only operate at 50% of their ultimate current(Icu).

So, we go back to the standard percentage of Ics (normally 25%, 50%, 75% or 100%); as an engineer: What is the percentage that you prefer for your Ics compared to Icu?

It is you to decide…

How To Joint Faulty Underground Cable

First of all, all you need todo is to identify the faulty cable.

Once you identify the faulty cable, remove the PVC outer sheath (roughly about 2 feet length) until you see the steel armor.

Remove the armor until you see the internal cable.

Cut those cables.

Insert the jointing sleeve and do crimping the jointing sleeve by using crimping tool.

Now you have finish jointing one side of the cable.

Insert the heat shrinkable sleeve (the red and black colour). Please ensure the sleeve is fully covered the jointing areas.

Do the jointing with the other end.

This is how it look like.

Use the HT Tape to wrap the surrounding jointing area.

Then, cover the wrapped HT Tape with the heat shrinkable sleeve (red colour) and heat it up to let it shrink. 

Now, connect the steel amour with braided tape.

Joint to the other end.

Once finish, use the heat shrinkale sleeve (black colour) to cover the whole jointing area. Heat up the heat shrinkable sleeve to let it shrink.

The End.

Flush Floor Trunking ; The Wrong Things That Most People Do!

This is the things that engineers and site workers must avoid when installing flush floor trunking (FFT); cable congested in FFT.

FFT normally consist of single, 2 compartments and 3 compartments of internal trunking. These compartments are segregated between each other and each compartment shall not be shared together.

Based on IEE Wiring Regulation, cabling in enclose enclosure should comply with 40% space factor.

Meaning to say, all cables should only occupy only 60% of overall internal dimension of FFT.

However, designer must consider the internal flyover inside three compartments in FFT. This area can be considered as unused space in FFT. Therefore, the actual usable space is much lesser than 60%.

Calculating the space factor without considering this unused space will result congested cable in FFT (see figure below).

Light Fitting Categories (Cat 1, Cat 2 and Cat 3).

There are three categories of light fitting listed in The Chartered Institution of Building Services Engineer (CIBSE’s) namely Category 1, Category 2 and Category 3.  These types of lighting are differed according to their luminance limit angle.   Category 1 limit angle is 55, Category 2 is 65 and Category 3 is 75 as shown in figure below;

Categorizing these light fitting is not indicating that category 1 is not ‘better’ than category 2 ‘better’ than category 3. The correct category must be selected for each individual installation otherwise undue installation and energy costs are likely to be incurred.

Light output ratio is another aspect of the installation when choosing the ‘right’ category. This ratio must be determined so that the luminance is evenly distributed as can be seen in the figure below.

From this information it can be ascertained that in general Category 1 (reflector luminance less than 200cd per sq.m from an angle of 55^o)luminaires are recommended where there were a high density of VDU (Video Display Terminal) in an area, and where usage is sustained over long periods of time, or is of an intensive nature or where errors are critical.

Category 2 luminaires (reflector luminance less than 200 cd per sq.m from an angle of 65°) are recommended where there would be fairly wide spread use of VDT in an area where one VDT per desk for general use.

Category 3 luminaires (reflector luminance less than 200 cd per sq.m from an angle of 75°) are recommended where the density of VDT is low and where computer use is casual. 

Credit to PCO Lighting

How To Identify Faulty Underground Cable

It happens at one of my project....the underground cable from main substation experience a faulty.

This faulty cable causing the Main Switch Board to trip over certain period of energizing (not an instantaneous tripping).

Since the underground cable are laid over more than 150 meter, the location of the faulty cable may not be seen through naked eye.

In order to identify the fault location, voltage injection need to be apply to the faulty cable. This is to ensure the faulty cable will produce spark.

The spark that appear below ground will produce sound (sounds like dup...dup..dup). The sound was so soft that you need microscopic equipment to hear it.

By using that microscopic equipment, place the equipment on the ground and walk along the routing of the faulty cable until the sound are stronger. Once the fault location are found, the digging process started and cable rectification to be done.

This is how the video look like during the process.

Enjoy....

How To Test LV Cable

GENERAL TESTS PROCEDURES (For Low Voltage Power Cables)

CABLE RATED VOLTAGE FROM 6.6kV to 33kV

Generally, there are 2 types of tests that need to be done for each individual cable namely a) Electrical and b) Non-Electrical Test.

1) Electrical Test. (This test shall be conducted for every cable drum produced)

a) Voltage Test
Voltage shall be applied between the conductors and the metallic screen (earth) for designated duration. The voltage shall rise gradually to the testing voltage of 35Uo and kept at the testing voltage for 5 minutes. Values of single-phase test voltage for the standard rated voltages as per table below. No breakdown of insulation shall occur. [IEC 60502-1 clause 15.3].

b) Measurement of Electrical Resistance of Conductor
DC resistance of each conductor shall be measured using a suitable measuring bridge at ambient temperature and then corrected to a temperature of 20oC and 1 km length in accordance to the factor given in IEC 60228. The resistance corrected shall not exceed the appropriate maximum value specified in IEC 60228. [IEC 60502-1 clause 15.2].

c) Insulation Resistance Test
The insulation resistance test shall be made at ambient temperature. Each cable shall be measured using a 500V Insulation Resistance Measuaring Bridge between each cores (phases) and screen (earth). No breakdown of insulation shall occur.

2) Non-Electrical Test
This test shall be conducted at frequency of 10% of the number of quantity in any contract [IEC 60502-2 clause 17].

a) Measurement of thickness and / or diameter of the cable construction shall be conducted on random samples. The items measured value obtained shall not be less than the minimum value as stated in the specifications. Typical measurement done as follows:

i) Insulation thickness
ii) Metallic screen thickness and overlapping
iii) Inner and outer sheath thickness
iv) Other test specified (i.e Tensile Test for Steel Wire Armored etc)

b) Hot Set Test
Sampling and test shall be conducted in accordance with IEC 60811-2-1 clause 9 shall comply with the following specifications:

How To Test MV Cable

GENERAL TESTS PROCEDURES (For Medium Voltage Power Cables)

CABLE RATED VOLTAGE FROM 6.6kV to 33kV

Generally, there are 2 types of tests that need to be done for each individual cable namely a) Electrical and b) Non-Electrical Test.

1) Electrical Test. (This test shall be conducted for every cable drum produced)

a) Partial Discharge Test
Voltage of 1.73 Uo shall be applied between the conductors and metallic screen. The magnitude of the discharge at the test voltage shall not exceed l0pC [IEC 60502-2 Clause 163]

b) Voltage Test
Voltage shall be applied between the conductors and the metallic screen (earth) for 5 minutes. The voltage shall rise gradually to the testing voltage of 35Uo and kept at the testing voltage for 5 minutes. Values of single-phase test voltage for the standard rated voltages as per table below. No breakdown of insulation shall occur. [IEC 60502-2 clause 16.4].

c) Measurement of Electrical Resistance of Conductor
DC resistance of each conductor shall be measured using a suitable measuring bridge at ambient temperature and then corrected to a temperature of 20oC and 1 km length in accordance to the factor given in IEC 60228. The resistance corrected shall not exceed the appropriate maximum value specified in IEC 60228. [IEC 60502-2 clause 16.2].

d) Insulation Resistance Test
The insulation resistance test shall be made at ambient temperature. Cable after HV test shall be tested by using suitable measuring instrument for 1 minute. No breakdown of insulation shall occur.

e) Current Test on Non-Metallic Sheath
A DC voltage of 8kV per millimeter of specified nominal thickness of the extruded over sheath shall be applied for 1 min between the underlying metal layer at negative polarity and the outer conducting layer subject to a maximum voltage of 25kV.
The outer conducting layer may consist of a coating of graphite applied to the extruded over sheath or obtained by immersion in water for the duration of test. No breakdown of over sheath shall occur [IEC 60229-2 clause 3.1].

2) Non-Electrical Test
This test shall be conducted at frequency of 10% of the number of quantity in any contract [IEC 60502-2 clause 17].
a) Measurement of thickness and / or diameter of the cable construction shall be conducted on random samples. The items measured value obtained shall not be less than the minimum value as stated in the specifications. Typical measurement done as follows:

i) Semi conductive screen and XLPE insulation thickness
ii) Metallic screen thickness and overlapping

iii) Inner and outer sheath thickness

iv) Other test specified (i.e Tensile Test for Steel Wire Armored etc)

b) Hot Set Test

Sampling and test shall be conducted in accordance with IEC 60811-2-1 clause 9 shall comply with the following specifications:

How To Do Wiring For 1 Way, 2 Way and Intermediate Switch?

As for wiring for light fitting, there 3 method of switching that can be used; 1 Way, 2 Way and Intermediate Switch.

1 way is the basic of all switching method. The circuit only using single switch to control all lighting connected to that particular circuit.

2 way switch normally used for a long span of corridor, staircase, sharing toilet (with 2 doors) and room that has a two access doors.

User will have an option to switch ON or OFF the light fitting at either side of those switches. This is the advantage of using the 2 way switch compared to 1 way switch.

The other switching method is using the intermediate switch whereby more than three switches being used to control the same lighting.

These 3 types of wiring using different type of switches. Therefore, it is crucial for you to identify what type of switch to be use…otherwise the wiring won’t work.

At the front plate of switches..all looks the same, you only can identify the differences by looking at the back of those switches (the cable terminal). Figure below illustrate the differences of those switches.

Okay, by now you should knew the concept and switches to be used..this is the final part, how to do the wiring!

Figure below illustrate the wiring diagram for 1 way, 2 way and intermediate switch.

Wish you all the best..tq.

Generator Set..What Supplier Might Not Telling You!

Today I learned a very important thing...the thing that some of the Generator Set (genset) supplier hidden from you or maybe something that the supplier overlook into...the coolant for genset!

Due to some incident at other projects..the Client requesting us to inspect on the coolant’s  liquid for those genset installed at site.

Surprisingly, we notice that those genset are only filled with water inside its radiation system but there are no coolant being added in. We taking sample of the coolant liquid and the colour are plain white. It indicate that, no coolant liquid being added and the radiator is only filled with water.

Normally, the coolant liquid are coloured green (some might colour red).

Water is actually one of the cooling agents. However, as the genset generally made from metal, using water are not advisable as the metal tend to rust.

So, those water need to be drained out and the radiator must be fully flushed. Then, refill the coolant into the radiator...make sure you witness the process!

So guys, BEWARE..do check the coolant liquid for your genset.

How To Calculate The Size Of Projection Screen

Below is the sample calculation to calculate the projection screen.

You must first indentify the furthest distance of audience. Let says10m.

By using the aspect ratio of 10/6 (based on AV formats: video or NTSC (4:3), HDTV (16:9)), you can identify the screen height.

Screen Height           = 10/6

                                                            = 1.67m

                                                            = 5.5 ft

                                                            = 66 inch

Then, you need to define the video format screen (assume you using 16:9 format)

Therefore, screen width       = 16/9 x 66 inch

                                                                        = 117.3 inch @ 2.97m

Based on the calculation above, the standard projection screen of size: 116" x 65" is proposed.

Once you have the size of projection screen, you need to determine the projector luminance.

           

Projector luminance = (Width x Height x Room Lux Level) / screen gain

Normally the screen gain will be unity = 1 and Room Lux Level = 300 lux

            Therefore projector luminance = (2.97m X 1.67m x 300 lux) / 1

                                                                = 1487 ANSI Lumens

Therefore the standard luminance of 2000 ANSI for projector will be proposed.

Below is the size of projection screen according to their aspect ratio for your reference.

Video Format (4:3 Aspect Ratio)
Image Diagonal	Image Height	Image Width
60"	36"	48"
72"	43"	57"
84"	50"	67"
96"	57"	77"
100"	60"	80"
120"	69"	92"
150"	87"	116"
180"	105"	140"
200"	120"	160"
210"	123"	164"
240"	141"	188"
HDTV Format (16:9 Aspect Ratio)
Image Diagonal	Image Height	Image Width
92"	45"	80"
106"	52"	92"
110"	54"	96"
119"	58"	104"
133"	65"	116"
159"	78"	139"
188"	92"	164"
216"	106"	188"
220"	108"	192"
AV Format (1:1 Aspect Ratio)
Image Diagonal	Image Height	Image Width
71"	50"	50"
85"	60"	60"
99"	70"	70"
108"	60" (5')	90" (7.5')
119"	84"	84"
120"	72" (6')	96" (8')
130"	72" (6')	108" (9')
136"	96" (8')	96" (8')
151"	84" (7')	126" (10.5')
153"	108" (9')	108" (9')
170"	120" (10')	120" (10')
173"	96" (8')	144" (12')
204"	144" (12')	144" (12')
238"	168" (14')	168" (14')
272"	192 (16')	192 (16')
305"	216 (18')	216 (18')

Source: www.da-lite.com