Talk On Safety in Substations for Security Personnel 24th Nov 2011

Yesterday I've been requested by the Support Police (Polis Bantuan) of Tenaga Nasional Berhad to give a talk on the safety in substation. The talk would be given to a group of contracted security personnel in order to help them understand how to ensure their safety during their job guarding TNB substations. I accepted the invitation with high spirits as I have the opportunities to share my experiences and help in preserving the high safety culture in TNB organizations.

Preparing the hardware to start the presentation. 

So today as promised, I started my presentation at 11.30am to a crowd of 35 gentlemen which are all have non-technical background. I am deeply honored to be given the chance to share safety tips to these security personnel. It is because I have high respect towards their dedication in ensuring all TNB assets in substations are safe from theft and trespassing. While you and me are sleeping, they make sure their eyes are wide open to see if there are anything suspicious happening in the substation.

Ice Breaking Session. Don't ask me why there is no ice in the picture.

The talk was in Bahasa Melayu as not all security personnel knows and understand English. I have set my presentation material to be as simple as possible so that although they don't have technical background, they can still understand and can practice all the safety tips which I've informed them.

My First Slide for the Talk. 

I started my talk by introducing them to the flow of electricity supply system in Malaysia starting from generation until distribution of electricity to consumer. This is important because on each level of electricity supply system, there are several types of substation which are critical for them to know such as Main Intake Substation (Pencawang Masuk Utama-PMU), Main Distribution Substation (Pencawang Pembahagian Utama-PPU) and Substation (Pencawang Elektrik-PE). Each substations have different roles and voltage levels.

Going through the content of my presentation. Luckily no one fall asleep yet.

Next I introduced them to the basic electrical components in a substation. In order for them to avoid hazard and ensure their own safety, they need to know what are the components which will bring hazard to them. It is the same when you want to tackle a hot chick. First you need to know her, study her interests, know her hobby, find about food and drinks which she likes, TV shows that bring tears to her beautiful eyes and her favourite colour. After you have gathered all this information, then you can straightaway plan a strategy to win her heart. After you have won her heart, marry her and stay in your bedroom for the whole month.

The crowd was very supportive and attentive. 

After that I explained about why they need to take care of their safety when they are in substations. I go through topics of injuries caused by electricity. I also shown them videos on real flashover accident involving an electrician and a bear going up an electricity pole.

Sharing Session where one of the participant asked questions about safety

Then I gave them four tips which will ensure their safety in substations. I told them if they follow these four tips, they can prevent any electrical accident from happening to them even though they do not have any technical knowledge about electricity.

1. Never touch any electrical components in a substation
2. If you meet an unconscious person with an electrical wiring touching his/her body while patrolling the substation area, separate it using insulated material such as wood
3. Do not follow orders from TNB personnel (either CEO, Bosses or Engineer) which involved touching electrical components inside substation.
4. If you hear any weird sound (crackling, hissing, alarm) from electrical components or see any irregularities in the substation, do not investigate yourself. Contact TNB personnel or TNB Polis Bantuan.

Finally I arrived at the climax of my safety talk which is the review of fatal and nonfatal electrical accidents in TNB. In this review, I showed some electrical accident pictures, explained what went wrong and how can they prevent the same accident from happening to themselves. The pictures are disturbing but I think the pictures succeed in showing the participants the importance of safety in TNB substations.

Below are pictures from my presentation slides:

Suspected thieve lying on top of 11kV transformer already dead and well cooked

Another thieve trying to steal cooper strip in TNB Substation. He did not succeed. Instead he become super crispy...and dead.

Tools of the thieve - metal saw, pouch bag and mineral water. Too bad now the thieve cannot drink the water again.

Cable Thief case. Picture on the left is the place where the power cable being stolen. Picture on the right is the thieve. He actually tried to cut a live cable. Superman would be proud of him - not! 

The pictures above are scary right? It is not good to steal others' properties. TNB suffers millions of losses every year because of theft. Instead of stealing TNB properties, better they steal a lady's heart. Then marry her and be satisfied all night long bebeh.

Answering one of the participant's question

I would like to thank Ketua Gerakan Negeri TNB Pulau Pinang En Dzahiruddin and Sarjan Saiful Yezin for inviting me to give the safety talk. I would also like to thank my Chief Engineer Mr Lim Yew Soon for allowing me to give the safety talk.

Towards the end of my talk. I am lucky to be blessed with such a wonderful crowd

This is a part of my contribution towards society as an electrical engineer. Am always proud to work as a TNB engineer. You should be proud too.

My slide can be downloaded by clicking the address below

http://www.4shared.com/document/S8wbtlCM/Taklimat_Safety_in_Substation_.html?

Effect of Moisture inside SF6 Gas Insulated Switchgear

Water is important to us and other living things in this world. Without water, life could not be sustained. Water can be found anywhere even in the air around us in the form of moisture. That is why we can see condensation on a cold glass of water. The water is not from the inside of the glass but it is from the moisture in the air. We use the term Humidity in order to measure the content of moisture in the air.

A glass of cold coke with a slice of lemon on top and condensation at the outer glass. You want it, don't you? Too bad it's already inside my stomach...except for the glass.

I live in Malaysia and my country is one of the country which has a very high humidity. In other words, Malaysia has a high moisture content in its air. This humid condition affects not only people and other living things but also non living things such as electrical equipment, your boss's car, your friend's stinky stocking, and other examples which I don't want to list here in order to prevent taking up more space on your computer RAM.

In my experience working in the electricity industry as an electrical engineer, various ways are being applied in order to reduce the effect of moisture to High Voltage (HV) Equipment. Moisture is conductive in nature so the existence of moisture on HV equipment will not only lower the effectiveness of the insulation coordination but it will also cause deterioration on the HV equipment insulation. The deterioration will lead to a catastrophic damage to the HV equipment. In this blog entry I will explain on the Effect of Moisture inside SF6 Gas Insulated Switchgear.

Moisture maybe bad for HV equipment but women use moisturizer to increase  moisture content on their skin so they always look radiance, subtle and fresh. Please don't ask for the phone number of the woman in the picture, she's not my office colleague.

All SF6 Gas Insulated Switchgear (GIS) in Tenaga Nasional Berhad and most parts of the world are fully encapsulated in order to hold the SF6 gas. To connect one encapsulation to the other components, heavy duty gaskets (or O-Rings) are used. However because of the aging factor, thermal or mechanical stress, these gaskets lost its flexibility and deform. The deformation of these gaskets not only leads to SF6 leakage, but also the entrance of air to the encapsulated SF6 gas chamber. These air will bring moisture along with them.

One of my apprentice engineer asked me about the effect of moisture entering the SF6 GIS. I answer to him:

"Do you think i'm a walking google website?" 

Just joking. Of course I explained to him all the effects of moisture to the SF6 GIS. It is good to share knowledge with other fellow engineers. The next paragraph is what I have explained to him.

Men also use moisturizer. Please don't be shy to admit. The guy above is not a gay.

When switching is done in a SF6 Gas insulated switchgear, arching will occur. This is because there is a high impedance on the breaker switch when the switch is opened and high voltage current tries to flow through the impedance. The arching release immense heat and SF6 gasses will quench the arching in order to prevent it from spreading.

It is generally known that the rule of chemistry said any substance (either solid, liquid or gas) will experience chemical reaction in the presence of heat. Same as SF6, the immense heat will break the chemical bonding of SF6 and create Sulfur atom and Florin molecule. Because this chemical reaction takes place in an encapsulated area filled with SF6, the Sulfur atom and Fluorine molecule will combine back to become SF6 as usual.

However when there is a leakage and air enters the SF6 gas compartment, it will bring along the moisture. Air and moisture will prevent the Sulfur atom and Fluorine molecule to combine back. In immense heat, highly mobile hydrogen molecules will combine with Fluorine molecule and form Hydrogen Fluoride which is corrosive in nature. Hydrogen Fluoride can be seen as a thin layer of white precipitation on busbars. Because of its corrosive nature, the busbar will be corroded and metal ions will be released into SF6 compartment. This metal ions will combine with Fluorine molecule and becomes Metal Fluoride. Metal Fluoride will also precipitate on the busbar.

Both precipitation will create uncertainties on the electric field of the busbar which result in Ultrasound generation. At the same time busbar will slowly becomes corroded. In times the busbar will fail and cuase catastrophic damage to the whole switchgears.

Moisture - good for women and some men but bad for HV equipment.

Solid Insulation Breakdown - Internal Discharge

In Greek Mythology, there is a story about Trojan War where the city of Troy is attacked by the Army of Greeks led by the King of Sparta. The war lasted for 10 years until the Greeks used a wooden horse to trick the people of Troy. The Greeks constructed a big wooden horse and place a group of elite soldiers inside it. The horse was left outside the Troy city wall and the Greeks pretend to retreat. 

The Trojan Horse and some Greek soldiers. It is confirmed that the fart's gas is not SF6

The people of Troy thought the war was over and the Greeks were really retreating. They also thought that the wooden horse is a gift from the Greeks and they took the wooden horse inside their city wall without realizing there were a group of elite soldiers inside the wooden horse. At night, the elite soldiers killed the Troy city guards, opened the city gate and let the other Greeks army to enter Troy. The people of Troy is caught off-guard and The city of Troy falls to the hand of the Greeks.

But wait, why there is a boring history lesson inside a high voltage blog?

The baby is also bored and no, this is not the son of Santa Claus

Actually the mechanism and phenomena of Internal Discharge in solid insulation breakdown is closely related to the story of the Trojan Horse in the Trojan War. The explanation below will enlighten this relationship.

Cavities and voids can be formed in insulation materials of high voltage equipment due to mishandling during operation, mechanical force during high voltage fault, insulation material aging, thermal effect or chemical  reaction. Cavities and voids can also be readily exist in insulation material because of the defect in manufacturing processes. These cavities and voids are the Trojan Horses which will lead to the failure of the insulation. It is like you are having an enemy within you, waiting for the right time to destroy you from within just like what the elite soldiers inside the Trojan Horse did to the city of Troy.

11kV XLPE Aluminium Single Core 500mm2 with voids. The white dots in red circle are not your dandruff so please don't wipe your monitor. They are actually cavities/voids.

The picture above shows an 11kV Aluminium Single Core 500mm2 cable which uses Cross Linked Poly Ethylene (XLPE) as its insulation. The cavities / voids inside the XLPE layer (circle in red) is automatically filled with air which has a lower dielectric constant from XLPE. Do take note that the dielectric constant of air is 1 and dielectric constant of XLPE is 2.35. Because of a lower dielectric constant in the cavity / void, higher charges will be available inside the cavity / void which in turn increases the electric field strength inside it. When the high electric field strength exceed its breakdown value, breakdown in the form of discharge (spark) will occur.

Can you see a spark or discharge inside the cavity on the teeth? I can't...because it's a teeth Bro, not a  high voltage equipment

When the discharge occurs, the electric field inside the cavity / void will be zero. However, the same process will be repeated again and again. Charges in the cavity / void will start to accumulate again, electric field strength in the cavity / void will be increasing and when the electric field strength exceed the breakdown value, breakdown in the form of discharge will occur again.

Equivalent circuit of a cavity/void in an insulation. C1 is capacitor representing the cavity /void, C2 representing insulation in series with the cavity/void, C3 representing the rest of the insulation.

The severity of the discharge depends on the operation voltage of the XLPE cable. Operation voltage of 33kV has much more severe discharges compared to 11kV discharges. On the other hand, the frequency of the operation supply will determine the number of the discharge and how frequent the discharge will occur. For example, numbers of discharge in a 50Hz electricity supply is less than in 60Hz electricity supply . The more frequent the discharge occurs, the faster the insulation will deteriorate.

The discharges inside the void will create positive ions and electrons which in turns move and hit the surface of the void because of the availability of electric field. The collision will break the chemical bonding on the void surface thus making it bigger. The frequent numbers of discharges will dissipate heat inside the void. The heat will carbonized the void surface and cause an erosion. This erosion will make the void bigger. If the void keeps getting bigger, catastrophic breakdown can happen as the insulation can no longer withstand the electrical stress. 

So beware of the "Trojan Horses" inside the insulation of your new or existing high voltage equipment. Make sure you always do necessary tests (Insulation Resistance Test, Pressure Test, Transient Earth Voltage, Ultrasound) before commissioning new HV components, after maintenance of HV components or after any repairing work. 

How SF6 works as electrical insulation

People knows what is H2O. Lots of people knows what is OMG. And some even know WTF is..haha. But what is SF6? Why is it so good that some electrical engineers swear that SF6 is their best friend?

Before I explain further, let me go to the toilet first and release my own "SF6" gasses first.

Just joking. In my previous posts, i have explained thoroughly what is SF6 and its capability of quenching any arching activity. In this post, i will give a real life situation which explains how SF6 works as electrical insulation.

Tamco VY30M25D 33kV Switchgear

The picture on the left shows a single switchgear feeder with 3 phase 33kV supply in PPU National Semiconductor substation in Pulau Pinang. The brand of the switchgear is Tamco VY30M25D and it uses air insulated busbar. The width of the switchgear around 1.2m and the length is 1.75m. It is considered very big as it will take 2 person to rack out the breaker from switchgear. Imagine it to be as big as a 2 door wardrobe. You can easily fit 3 person inside the breaker compartment.

Tamco GIS Switchgear

The picture on the right is also a single switchgear feeder with 3 phase 33kV supply fitted in PPU Hospital Substation in Pulau Pinang. It is also made by Tamco and uses SF6 gas as insulation for busbars. Usually it is called Gas Insulated Switchgear (GIS). The width of the switchgear around 0.5m and the length is 1m. The built is very compact and has less floorprint compared to the switchgear in Pic 1 although both of them operate at the same voltage level. 

The usage of SF6 as insulation gives advantage of equipment spacing inside a switchgear. This will lead to a lesser floorprint which means that the whole land area of a substation can be greatly reduced. In a country where land is considered a scarcity such as Japan or in a metropolitan area where land is considered a premium like Kuala Lumpur, GIS technology is preferred. Breakdown voltage of SF6 is higher than breakdown voltage of air so the busbar of each phase can be placed as close as the breakdown voltage permits. You can refer to my post on Gas Insulation (Saturday, 9th April 2011) to know more on this. In the future with the current R&D done throughout the world, new insulation gas will come out and eventually will further reduce the size of switchgears with its superior insulation capabilities.

SF6 Gas Insulated Switchgear also has a longer lifetime compared to their air insulated switchgear counterpart. According to electrical gas breakdown phenomena, we have 2 types of discharge: i) Non-sustaining and ii) Self-Sustaining. The discharge will start as non-sustaining at first and will soon develop to self sustaining discharge. That is why we will see an increase of partial discharge activity if we do a trending on any switchgear with partial discharge irregularities. This non-sustaining discharge if not properly controlled or rectify will lead to self sustaining discharge and further leads to breakdown avalanche. By then it is already to late. 

In Air Insulated Switchgear, air cannot absorb the electrons created by the non-sustaining discharge. The abundance of electrons available from the non sustaining discharge will further propel the process of creating a self sustaining discharge thus less time is needed for a self sustaining discharge to form. This will greatly reduce the equipment lifetime.

In SF6 Gas insulated Switchgear, SF6 gas has a tendency to attach to electrons created by the non-sustaining discharge so longer time is needed for a self sustaining discharge to form thus the equipment lifetime will not be reduced. SF6 gas will 'arrest' any free electrons created by the non-sustaining discharge on the spot. The SF6 and electrons attachment will prevent these free electrons from creating any self sustaining discharge.

3 electrons being captured by SF6 Special Squad (I bet the red one is the leader)

The picture above is only a gimmick to entertain your mind after reading my long explanation. You will not find these guys inside your switchgears...

Except if they are crazy enough to steal the copper busbars.

Liquid Insulation

In current power industry nowadays, High Voltage Apparatus with gas (SF6) insulation is the main player. Nearly all new main intake substations are using Gas Insulated Switchgears (GIS). It seems that a lot of people in the industry tends to think that GIS is better than liquid insulated switchgears. There are some who feels that liquid insulated switchgears are already obsolete and GIS is the way of the future. I have asked some of my colleague on which is the better insulation between SF6 and oil. Not suprisingly all of them says SF6 has better insulation capability than oil.

My Staff filling up the Transformer Insulation Oil into On Load Tap Changer Chamber

However this is not true. In the previous post in Gas Insulation, Paschen's Law states that the breakdown voltage is the function of pressure multiply by distance of gap (Vs=f(p x d). ). We know that liquid is denser than gas which means that liquid has more pressure. When we relate this with Paschen's Law, it is proven that liquid acts as a far better insulation than gas. Liquid also quench the arc faster than gas and has the capability to dissipate the heat better than gas.

Electron movement in Gas Insulation

Electron Movement in Liquid Insulation

The picture above shows the movement of electron from cathode to anode in two different types of insulation. In gas insulation medium, the distance between molecules of the gas is wide apart so electron can move easily. So avalanche can easily occur which in turn will create insulation breakdown. However in liquid insulation medium, the configuration of molecules is very near and the number of molecules are much higher than in gas insulation medium. This means that liquid is much denser than gas and leave a little space for electron to move.

The concept is as same as when you are speeding on a highway like a Mat Rempit. If there are a lot of cars on the highway, you cannot ride your motorcycle very fast. But if there are only two or three cars on the highway, then you can speed like the highway is owned by your father. A word of advice, please ride and drive carefully.

Brief Info on Sulphur Hexaflouride (SF6)

Sulfur hexafluoride (SF₆) is an inorganic, colorless, odorless, non-toxic and non-flammable greenhouse gas. SF₆ has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule. Typical for a nonpolar gas, it is poorly soluble in water but soluble in nonpolar organic solvents. It is generally transported as a liquefied compressed gas. It has a density of 6.12 g/L at sea level conditions, which is considerably higher than the density of air.

SF₆ is used in the electrical industry as a gaseous dielectric medium for high-voltage circuit breakers, switchgear, and other electrical equipment, often replacing oil filled circuit breakers (OCBs) that can contain harmful PCBs. SF₆ gas under pressure is used as an insulator in gas insulated switchgear (GIS) because it has a much higher dielectric strength than air or dry nitrogen. This property makes it possible to significantly reduce the size of electrical gear. This makes GIS more suitable for certain purposes such as indoor placement, as opposed to air-insulated electrical gear, which takes up considerably more room. Gas-insulated electrical gear is also more resistant to the effects of pollution and climate, as well as being more reliable in long-term operation because of its controlled operating environment.

(Taken from http://en.wikipedia.org/wiki/Sulfur_hexafluoride)

Gas Insulation

Air around us is a good insulator. It is abundance and self restored after electrical breakdown process. Air is commonly used as insulator in switchgears and overhead transmission line. However as demand for electricity supply increases especially in dense urban area, the need for a smaller and compact high voltage apparatus arise. Researchers realize that air is not the viable to fulfill this needs. Thus a new gas insulation technology is born - The Sulphur Hexaflouride (SF6). Air has Critical Breakdown Voltage of 24.5kV/cm which means that for one centimeter gap between a different phase, or between phases and ground, air can withstand 24.5kV. If the voltage exceeds this value, breakdown will occur.

Breakdown Voltage of Air

On the other hand, SF6 gas has Critical Breakdown Voltage of 88.4kV/cm which means that for one centimeter gap between a different phase, or between phases and ground, air can withstand 88.4kV. Breakdown will occur if voltage exceeds this value.

Breakdown Voltage of SF6 gas

Explanation on why SF6 has higher breakdown voltage than air

In the previous section, I have stated that the breakdown voltage of SF6 is higher than air. In this world everything happens for a reason and same goes to this. SF6 has added characteristics which makes it more superior than air in terms of breakdown voltage. The reason is SF6 has higher dielectric strength and has arc quenching capability.

Molecular Structure of SF6 Gas

The Townsend Breakdown criterion for air is given by:

 where gamma is the Townsend Second Ionization Coefficient and alpha is Townsend Second Ionization. However for SF6 gas, the Townsend Breakdown Criterion is given by:

 which we can see there is an additional coefficient added and it is called the attachment coefficient. The attachment coefficient is introduced to Townsend Breakdown Criteria in order to describe the behaviour of SF6 gas molecules which will attach itself to excess electrons during the first ionization and the second ionization. This behavior is the one which contribute to more superior dielectric strength and higher arc quenching capability compare to air.

Effect of Pressure Towards Gas Breakdown Capability (Paschen's Law)

In 1889, Friedrich Paschen made a discovery when he was experimenting the breakdown voltage of a parallel plate in a gas with respect to gap distance and pressure. He realize that as pressure of gas decrease, the density of gas will also decrease thus providing more space for electron to move. At some point, increment in gap distance will also increase breakdown voltage. Below is the Paschen's Law

where p is the gas pressure and d is the gap distance. The graph below shows different Pachen's Curve for CO2, Air and H2.

 

Noted that each gasses shows increment in breakdown voltage one the (pd) value increase. In my experience, 33kV GIS switchgear has a pressure of 1.2 bar compared to 132kV GIS switchgear which could reach to 5 bar.