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Distribution Code [4] Motor Control [5] Grounding System, [6] Fuses,... etc
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Transformer parts are:1)BUCHHOLZ RELAY: it is a very sensitive gas and oil operated instrument which safely detect the formation of gas
or sudden pressure inside the oil transformer.
2) CONSERVATOR: it is used to provide adequate space for the expansion of oil when transformer is loaded or
when ambient temperature changes.
3) SILICA GEL BREATHER: it sucks the moisture from the air which is taken by transformer so that dry air is taken
by transformer.
Transformer Oil Deterioration
The Oil inside power transformers have a vital role to play in the transformer's functioning. The function of the
transformer oil is two-fold, to provide cooling to the transformer windings and to provide insulation. However,
over a period of many years, the transformer oil deteriorate owing to many factors. This deterioration causes a
change in the physical and chemical properties of the oil.
Some of the reasons for transformer oil deterioration are
Oxidation of the oil. The transformer breather permits the entry of air into the transformer, although it filters the
moisture. The air which flows inside the transformer oxidizes the oil and forms a sludge of hydrocarbons. This
process, though, usually occurs gradually over a period of many years. The sludge thus formed hinders the cooling
of the transformer and causes heating. The sludge, sometimes, blocks the cooling ducts of the transformer. Higher
temperatures inside the transformers, in turn, cause further sludge formation.
Thermal Decomposition. At high temperatures, the organic compounds in the transformer oil break down due to a
phenomenon known as pyrolysis. This results in the formation of unwanted carbon compounds, sludge, etc.
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Moisture contamination. Under ideal conditions, the oil in a transformer is protected against the entry of moisture
by means of the silica gel filter in the breather. The silica gel changes color from blue to pink when it gets saturated
with moisture. If the silica gel is not renewed in time, moisture may pass through the filter contaminating the oil.
4) DOUBLE DIAPHRAGM EXPLOSION VENT: it is used to discharge excess pressure in the atmosphere when
excess pressure is developed inside the transformer during loading.
5) OIL LEVEL INDICATOR: it is used to show the oil level in the transformer.
6) Winding temperature indicator: used to show the temperature of transformer winding.
7) RADIATORS: these are used for cooling of the transformer oil.
PARTS OF A POWER TRANSFORMER (1)
What are the name of the basic parts of a Power Transformer?
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We cannot deny the fact that only a handful of electrical engineering students are presently familiar with power
transformers especially on what it looks like. Unlike a transformer we found in our homes, a power transformer’s
appearance and construction is somewhat more complicated. It is not just a simple winding with a primary and
secondary terminal although basically any transformer has one. The function that a power transformer plays in an
electrical system is very important that an electric utility can not afford to loss it during its operation. Our discussion
here will focus more on the basic parts and functions of a power transformer that are usually tangible whenever you
go to a substation. Although not all power transformers are identical, nonetheless they all have the following listed
parts in which the way of construction may differ.
1. Transformer Tank – this holds the transformer windings and its insulating medium (oil-filled). Transformer tanks
must be air-tightly sealed for it to isolate its content from any atmospheric contaminants.
2. High Voltage Bushing – this is the terminals where the primary windings of the transformer terminates and serves
as an insulator from the transformer tank. Its creapage distance is dependent on the voltage rating of the transformer.
3. Low Voltage Bushing – like the high voltage bushing, this is the terminals where the secondary windings of the
transformer terminates and serves as an insulator from the transformer tank. Low voltage bushing can be easily
distinguished from its high voltage counterpart since low voltage bushings are usually smaller in size compared to the
high voltage bushing.
4. Cooling Fins/Radiator – in order for the transformer to dissipate the heat it generated in its oil-insulation, cooling
fins and radiators are usually attached to the transformer tanks. The capacity of the transformer is dependent to its
temperature that is why it is imperative for it to have a cooling mechanism for better performance and higher
efficiency.
5. Cooling Fans – can be usually found attached to the cooling fins. Cooling fans can be either be a timer controlled
or a winding/oil temperature controlled. Cooling fans helps raises the transformer capacity during times when the
temperature of the transformer rises due to its loading. Cooling fans used on the transformer are actuated by the help
of a relaying device which when senses a relatively high temperature enables the fan to automatically run.
6. Conservator Tank – An oil preservation system in which the oil in the main tank is isolated from the atmosphere,
over the temperature range specified, by means of an auxiliary tank partly filled with oil and connected to the
completely filled main tank.
7. System Ground Terminal – system ground terminals in a power transformer are usually present whenever the
connection type of the transformer windings has wye in it. This terminal can be found in-line with the main terminals
of the transformer.
8. Drain Valve – can be usually found in the bottom part of the transformer tank. Drain valves are used whenever oil
replacement is necessary. Through this valve, the replacement of oil in an oil-filled transformer can be easily done
simply by opening this valve like that of a faucet.
9. Dehydrating Breather – Dehydrating breathers are used to prevent the normal moisture in the air from coming in
contact with the oil in electrical equipment as the load or temperature changes. This reduces the degeneration of the
oil and helps maintain its insulation capability. When used with conservator system with a rubber air cell it reduces
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moisture accumulation in the cell. Some breathers are designed for sealed tank transformers and breathe only at preset pressure levels. ABB
10. Oil Temperature/Pressure gauges – these are used for monitoring the internal characteristics of the transformer
especially its windings. These gauges help the operator in knowing the level of temperature and pressure inside the
transformer (oil & winding). This will also serve as an alarm whenever a certain level is reached that could be harmful
to the transformer windings.
11. Bushing Current Transformers – modern transformer construction today now includes current transformers.
These are usually found around the transformer terminals which will be later be used for metering and relaying
purposes. Its terminals are found in the control panels attached to the transformer.
12. Control Panel – this houses all of the transformer’s monitoring devices terminals and auxiliary devices including
the terminals of the bushing current transformers and cooling fans. Control panels are very useful especially when a
remote control house is needed to be constructed, this will serve as their connection point.
13. Surge Arresters – this type of arresters are placed right directly before and after the transformer terminals in
order to minimize the exposure of the transformer. Like any other surge arresters, its purpose is to clip sudden
voltage surge that can be damaging to the winding of the transformer.
ⒿⓄⒾⓃ ⓄⓊⓇ ⒷⓁⓄⒼ
http://www.electricaltechnology.org/
Transformer OIL Testing
Acidity Or Neutralisation Number (Nn) Test Method: ASTM D974
Acids in the oil originate from oil decomposition/oxidation products. Acids can also come from external sources
such as atmospheric contamination. These organic acids are detrimental to the insulation system and can induce
corrosion inside the transformer when water is present. An increase in the acidity is an indication of the rate of
deterioration of the oil with SLUDGE as the inevitable by-product of an acid situation which is neglected.
The acidity of oil in a transformer should never be allowed to exceed 0.25mg KOH/g oil. This is the CRITICAL
ACID NUMBER and deterioration increases rapidly once this level is exceed.
Interfacial Tension (Ift) Test Method : ASTM D971
The Interfacial Tension (IFT) measures the tension at the interface between two liquid (oil and water) which do not
mix and is expressed in dyne/cm. The test is sensitive to the presence of oil decay products and soluble polar
contaminants from solid insulating materials. Good oil will have an interfacial tension of between 40 and 50
dynes/cm. Oil oxidation products lower the interfacial tension and have an affinity for both water (hydrophilic) and
oil. This affinity for both substances lowers the IFT. The greater the concentration of contaminants, the lower the
IFT, with a badly deteriorated oil having an IFT of 18 dynes/cm or less.
IFT-NN Relationship
Studies have shown that a definite relationship exists between acid number (NN) and Interfacial Tension(IFT). An
increase in NN should normally be followed by a drop in IFT. The IFT test is a powerful tool for determining how
an insulating oil has performed and how much life is left in the oil before maintenance is required to prevent sludge.
The IFT provided an excellent back up test for the NN.
IFT not accompanied by a corresponding increase in NN indicates polar contamination which have not come from
normal oxidation. Although a low IFT with a low NN is an unusual situation , it does occur because of
contamination such as solid insulation materials, compounds from leaky pot heads or bushings, or from a source
outside the transformer.
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Quality Index System
Dividing the Interfacial Tension (IFT) by the Neutralisation Number (NN) provides a numerical value that is an
excellent means of evaluating oil condition. This value is known as the Oil Quality Index (OQIN) or
Myers Index Number (MIN).
A new oil , for example has a OQIN of 1500.
OQIN = IFT 1500=45.0(typical new oil)
NN 0.03(typical new oil)
TRANSFORMER OIL CLASSIFICATIONS*
Description
1.
Good Oils
3.
Marginal Oils
4.
Bad Oils
0.00 - 0.10
2.
Proposition
A Oils
0.05 - 0.10
NN
0.16 - 0.40
5.
Very Bad
Oils
0.41 - 0.65
6.
Extremely
Bad Oils
0.66 - 1.50
0.11 - 0.15
IFT
30.0 - 45.0
27.1 - 29.9
24.0 - 27.0
18.0 - 23.9
14.0 - 17.9
9.0 - 13.9
MIN
300-1500
271 – 600
160 – 318
45 - 159
22 - 44
6 - 21
Colour
Pale Yellow
Yellow
Bright Yellow
Amber
Brown
Dark Brown
7.
Oils in Disastrous
Condition
1.51 or more
Black
The four functions of insulating oil is to provide [1] cooling, [2] insulation, [3] protection against chemical attack
and [4] prevention of sludge buildup.
Transformer Cases Operating in Parallel
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Case 1: Equal Impedance, Ratios and Same kVA:

The standard method of connecting transformers in parallel is to have the same turn ratios, percent impedances, and kVA
ratings.

Connecting transformers in parallel with the same parameters results in equal load sharing and no circulating currents in the
transformer windings.

Example: Connecting two 2000 kVA, 5.75% impedance transformers in parallel, each with the same turn ratios to a 4000 kVA
load.





Loading on the transformers-1 =KVA1=[( KVA1 / %Z) / ((KVA1 / %Z1)+ (KVA2 / %Z2))]X KVAl
kVA1 = 348 / (348 + 348) x 4000 kVA = 2000 kVA.
Loading on the transformers-2 =KVA1=[( KVA2 / %Z) / ((KVA1 / %Z1)+ (KVA2 / %Z2))]X KVAl
kVA2 = 348 / (348 + 348) x 4000 kVA = 2000 kVA
Hence KVA1=KVA2=2000KVA
Case 2: Equal Impedances, Ratios and Different kVA:

This Parameter is not in common practice for new installations, sometimes two transformers with different kVAs and the same
percent impedances are connected to one common bus. In this situation, the current division causes each transformer to carry
its rated load. There will be no circulating currents because the voltages (turn ratios) are the same.

Example: Connecting 3000 kVA and 1000 kVA transformers in parallel, each with 5.75% impedance, each with the same turn
ratios, connected to a common 4000 kVA load.
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


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Loading on Transformer-1=kVA1 = 522 / (522 + 174) x 4000 = 3000 kVA
Loading on Transformer-1=kVA2 = 174 / (522 + 174) x 4000 = 1000 kVA
From above calculation it is seen that different kVA ratings on transformers connected to one common load, that current division
causes each transformer to only be loaded to its kVA rating. The key here is that the percent impedance are the same.
Case 3: Unequal Impedance but Same Ratios & kVA:

Mostly used this Parameter to enhance plant power capacity by connecting existing transformers in parallel that have the same
kVA rating, but with different percent impedances.


This is common when budget constraints limit the purchase of a new transformer with the same parameters.
We need to understand is that the current divides in inverse proportions to the impedances, and larger current flows through the
smaller impedance. Thus, the lower percent impedance transformer can be overloaded when subjected to heavy loading while
the other higher percent impedance transformer will be lightly loaded.

Example: Two 2000 kVA transformers in parallel, one with 5.75% impedance and the other with 4% impedance, each with the
same turn ratios, connected to a common 3500 kVA load.



Loading on Transformer-1=kVA1 = 348 / (348 + 500) x 3500 = 1436 kVA
Loading on Transformer-2=kVA2 = 500 / (348 + 500) x 3500 = 2064 kVA
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It can be seen that because transformer percent impedances do not match, they cannot be loaded to their combined kVA rating.
Load division between the transformers is not equal. At below combined rated kVA loading, the 4% impedance transformer is
overloaded by 3.2%, while the 5.75% impedance transformer is loaded by 72%.
Case 4: Unequal Impedance & KVA Same Ratios:

This particular of transformers used rarely in industrial and commercial facilities connected to one common bus with different
kVA and unequal percent impedances. However, there may be that one situation where two single-ended substations may be
tied together via bussing or cables to provide better voltage support when starting large Load.


If the percent impedance and kVA ratings are different, care should be taken when loading these transformers.
Example: Two transformers in parallel with one 3000 kVA (kVA1) with 5.75% impedance, and the other a 1000 kVA (kVA2) with
4% impedance, each with the same turn ratios, connected to a common 3500 kVA load.



Loading on Transformer-1=kVA1 = 522 / (522 + 250) x 3500 = 2366 kVA
Loading on Transformer-2=kVA2 = 250 / (522 + 250) x 3500 = 1134 kVA
Because the percent impedance is less in the 1000 kVA transformer, it is overloaded with a less than combined rated load.
Case 5: Equal Impedance & KVA Unequal Ratios:

Small differences in voltage cause a large amount of current to circulate. It is important to point out that paralleled transformers
should always be on the same tap connection.

Circulating current is completely independent of the load and load division. If transformers are fully loaded there will be a
considerable amount of overheating due to circulating currents.

The Point which should be Remember that circulating currents do not flow on the line, they cannot be measured if monitoring
equipment is upstream or downstream of the common connection points.

Example: Two 2000 kVA transformers connected in parallel, each with 5.75% impedance, same X/R ratio (8), transformer 1
with tap adjusted 2.5% from nominal and transformer 2 tapped at nominal. What is the percent circulating current (%IC)

%Z1 = 5.75, So %R’ = %Z1 / √[(X/R)2 + 1)] = 5.75 / √((8)2 + 1)=0.713
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






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%R1 = %R2 = 0.713
%X1 = %R x (X/R)=%X1= %X2= 0.713 x 8 = 5.7
Let %e = difference in voltage ratio expressed in percentage of normal and k = kVA1/ kVA2
Circulating current %IC = %eX100 / √ (%R1+k%R2)2 + (%Z1+k%Z2)2.
%IC = 2.5X100 / √ (0.713 + (2000/2000)X0.713)2 + (5.7 + (2000/2000)X5.7)2
%IC = 250 / 11.7 = 21.7
The circulating current is 21.7% of the full load current.
Case 6: Unequal Impedance, KVA & Different Ratios:


This type of parameter would be unlikely in practice.
If both the ratios and the impedance are different, the circulating current (because of the unequal ratio) should be combined with
each transformer’s share of the load current to obtain the actual total current in each unit.

For unity power factor, 10% circulating current (due to unequal turn ratios) results in only half percent to the total current. At
lower power factors, the circulating current will change dramatically.


Example: Two transformers connected in parallel, 2000 kVA1 with 5.75% impedance, X/R ratio of 8, 1000 kVA2 with 4%
impedance, X/R ratio of 5, 2000 kVA1 with tap adjusted 2.5% from nominal and 1000 kVA2 tapped at nominal.









%Z1 = 5.75, So %R’ = %Z1 / √[(X/R)2 + 1)] = 5.75 / √((8)2 + 1)=0.713
%X1= %R x (X/R)=0.713 x 8 = 5.7
%Z2= 4, So %R2 = %Z2 /√ [(X/R)2 + 1)]= 4 / √((5)2 + 1) =0.784
%X2 = %R x (X/R)=0.784 x 5 = 3.92
Let %e = difference in voltage ratio expressed in percentage of normal and k = kVA1/ kVA2
Circulating current %IC = %eX100 / √ (%R1+k%R2)2 + (%Z1+k%Z2)2.
%IC = 2.5X100 / √ (0.713 + (2000/2000)X0.713)2 + (5.7 + (2000/2000)X5.7)2
%IC = 250 / 13.73 = 18.21.
The circulating current is 18.21% of the full load current.
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The different types of transformer’s windings
1. Concentric windings:
i.
Cross-over
ii.
Helical
iii.
Disc.
2. Sandwich windings
I. Concentric windings. Refer Fig. 10. These
windings are used for core type transformers. Each
limb is wound with a group of coils consisting of
both primary and secondary turns which may be
concentric cylinders. The l.v. windings are placed
next to the core and h.v. winding on the outside. But the two windings can be sub-divided, and interlaced with high
tension and low tension section alternately to reduce leakage reactance. These windings can be further divided as
follows:
i.
Cross-over windings. Cross-over windings are used for currents up to 20 A so they are suitable for the h.v.
winding of small transformers. The conductors are either cotton covered round wires or strips insulated with paper.
Cross-over coils are wound over formers and each
coil consists of a number of layers with a number of
turns per layer. The complete winding consists of a
number of coils connected in series. Two ends of
each coil are brought out, one from inside and one
from outside. The inside end of a coil is connected
to the outside end of the adjacent coil.
ii.
Helical winding. A helical winding
consists of rectangular strips wound in the form of a
helix. The strips are wound in parallel radially and
each turn occupies the total radial depth of winding.
Helical coils are well suited for l.v. windings of large transformers. They can also be used for h.v. windings by
putting extra insulation between layers in addition to the insulation of conductors.
iii.
Continuous disc winding. This type of winding consists of a number of flat strips wound spirally from
the inside (radially) outwards. The conductor is used in such lengths as are sufficient for complete winding or
section of winding between tappings. The conductor can either be a single strip or a number of strips in parallel,
wound on the flat. This gives a robust construction for each disc. The discs are wound on insulating cylinders spaced
from it by strips along the length of the cylinder. The discs are separated from each other with press board sectors
attached to the vertical strips. The vertical and horizontal spacers provide ducts for free circulation of oil which is in
contact with every turn.
iv.
Sandwich coils. Sandwich coils (Fig.11) are employed in transformers of shell type. Both high and low
voltage windings are split into a number of sections. Each high voltage section lies between the voltage sections.
The advantages of sandwich coils are that their leakage can be easily controlled and so any desired value of leakage
reactance can be had by the division of windings.
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Philippine Distribution Code – Important Notes
Page 8 of 16
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Motor Calculation Steps
( NEC Article 430 )
Feeder Circuit
Conductor
Branch Circuit
Short Circuit
Protection
Feeder Circuit Short
Circuit Protection
Motor Circuit
Conductor
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Thermal
Overload
Protection
Motors
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The following steps adhere to Article 430 of the NEC
Step 1: Determine the FLC of the given motor(s)
for Single Phase – see Table 430.248 based on NEC 2011 ed
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for Three Phase – see Table 430.250 based on NEC 2011 ed
Step 2: Select the overload protection
The service factor SF and the temperature rise ratings of the motor(s) must be known.
SF is the percentage of the overloading the motor can handle for short periods of time only.
The temperature rise is the difference between the motor winding temperature running at its full potential and the ambient
temperature. If the temperature rise does not exceed 400C when running at its full potential, the motor will not be harmed.
SF no less than 1.15 = 125% · FLC
Temperature Rise not over 400C =125% · FLC
All other motors = 115% · FLC
On cases where overload trips too early to start the motor, modifications are permitted as follows:
SF no less than 1.15 = 140% · FLC
Temperature Rise not over 400C =140% · FLC
All other motors = 130% · FLC
Step 3: Size the Motor Circuit Conductor
Multiply FLC by 125%
then use Table 3.10.1.16 for the correct motor conductor.
Step 4: Determine the Branch Protection
Multiply FLC by corresponding value from
Table 430.52
If the computed value is not standard, choose:
next size up
See Table C for Standard sizes of fuses and fixed
trip circuit breakers.
Step 5: Size the Feeder Conductor
Multiply FLC of the Largest Motor in the group by
125%,
then add all the FLC of the remaining motors
then use Table 3.10.1.16 for the correct feeder
conductor.
Step 6: Determine the Feeder Protection
Take the largest Branch Circuit Protection in the
group
then add all the FLC of the remaining motors
If the computed value is not standard, choose: next
size down
See Table C for Standard sizes of fuses and fixed
trip circuit breakers.
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FUSES
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Table C. Standard sizes for fuses and fixed trip circuit breakers, are:
15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800,
1000, 1200, 1600, 2000, 2500, 3000, 4000 5000, and 6000 amps. Additional standard fuse sizes are 1, 3, 6, 10, and 601 amps
Class G fuses. Developed for use in lighting and appliance panel boards with a special fusibleswitch unit, these non-renewable cartridge fuses are intended for use only in AC circuits where
interrupting ratings to 100kA rms symmetrical are required.
Class J fuses. A 600VAC fuse rated to interrupt a minimum of 200kA. They are labelled as
“Current-Limiting” and are not interchangeable with other classes. J are fast-acting fuses.
Class K fuses. These non-renewable fuses are subdivided into three individual classes, defined
as Class K-1, K-5, and K-9. All are available in 250VAC and 600VAC ratings, with current
ratings from 0A to 600A. Class K fuses are available with DC ratings.
Class L fuses. These non-renewable fuses are current-limiting. They’re designed for the
protection of feeders and service entrance equipment.
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Distribution Code [4] Motor Control [5] Grounding System, [6] Fuses,... etc
Class H fuses. This cartridge fuse, is suited for general purpose branch circuit,
circuit lighting
circuit, and the protection of non
non-inductive equipment like electric ovens and resistance
heaters.. Class H fuses are available in renewable and non
non-renewable
renewable models. Renewable types
allow the user to replace the internal fusible link after the fuse operates.
Class R fuses. These non-renewable
renewable fuses are made in 250VAC and 600VAC ratings, with
current ratings from 0A to 600A. An R-Rated fuse, is intended to provide short circuit, protection
of medium voltage, motors and motor controllers.
controllers It is a current limiting, high interrupting rating,
fuse. R-rated
rated medium voltage fuses are back-up
back
fuses and are not designed or intended to open
under overload, conditions. R--rated fuses for motor circuit protection.
Class T fuses. These non-renewable
renewable fuses are current-limiting
current
and are designed for protection of
feeders and branch circuits in accordance with the NEC. Current ratings range from 0A to 1200A
for 300V rated fuses, and 0A to 1,200A for 600VAC rated fuses. Class T fuses are available with
DC ratings. The interrupting rating is 200kA rms symmetrical.
Class CC fuses. These non-renewable
renewable fuses are current-limiting
current limiting and intended for the protection
of components sensitive to short
short-time overloads, noninductive loads, and short-circuit
short
protection
of motor circuits.
GROUNDING
The PRIMARY goal of the grounding system throughout any facilities is SAFETY.
SAFETY
Why ground at all?
1. PERSONNEL SAFETY FIRST
2. EQUIPMENT PROTECTION SECOND
The three main types are:
1. EQUIPMENT GROUNDING (SAFETY)
2. SYSTEM GROUNDING
3. LIGHTNING/SURGE GROUNDING
Role of Grounding
1. Provides a low impedance path to the flow of
lightning discharge current
2. Limits the ground potential rise
3. Limits ground resistance to be as low as possible < 10 Ω
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Grounded vs. Grounding
The terms grounded and grounding are very similar, but
their meanings are quite different.
In any electrical circuit,
there are two wires needed
to complete any circuit.
One is called the "hot
wire" and the other is
called "neutral" or
"grounded". Sometimes
the neutral wire is referred
to as a grounded wire. It is
most correctly referred to as a "grounded neutral
conductor," but most times referred to as "the neutral" or
"the ground wire".
Since the neutral or grounded wire is a necessary part of the
electrical path, grounded wires carry electrical current
under normal operating conditions. A grounded wire is required by the National Electrical Code
to be white or gray in color on the customer side of the meter. Grounded wires on the utility side
of the system do not generally have insulation.
A "grounding" wire on the other hand is a safety wire that has intentionally been connected to
earth. The grounding wire does not carry electricity under normal circuit operations. Its purpose
is to carry electrical current only under short circuit or other conditions that would be
potentially dangerous. Grounding wires serve as an alternate path for the current to flow back to
the source, rather than go through anyone touching a dangerous appliance or electrical box.
Confusion arises because it is commonly referred to as a ground wire even though it is more
correctly called a "grounding" wire. Some people will refer to this wire as the "case ground"
since this wire is typically connected to the cases or outer parts of electrical boxes and appliances
and tools.
The grounding wire is required by the National Electrical Code to be a bare wire, or if insulated,
a green or green with yellow colored insulation.
This is a STOLEN COPY if it does bear
the original signature of the author.
Page 13 of 16
COMPILED NOTES on [1] Transformer Parts: [2] Cases of Parallel Operation [3] Parts of Philippine
Distribution Code [4] Motor Control [5] Grounding System, [6] Fuses,... etc
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Types of insulators
These are the common classes of insulator
Pin type insulator - As the name suggests, the pin type insulator is
mounted on a pin on the cross-arm on the pole. There is a groove on
the upper end of the insulator. The conductor passes through this
groove and is tied to the insulator with annealed wire of the same material as the conductor. Pin type
insulators are used for transmission and distribution of communications, and electric power at voltages
up to 33 kV. Insulators made for operating voltages between 33kV and 69kV tend to be very bulky and
have become uneconomical in recent years.
Post insulator - A type of insulator in the 1930s that is more compact than traditional pin-type insulators
and which has rapidly replaced many pin-type insulators on lines up to 69kV and in some configurations,
can be made for operation at up to 115kV.
Suspension insulator - For voltages greater than 33 kV, it is a usual practice
to use suspension type insulators, consisting of a number of glass or
porcelain discs connected in series by metal links in the form of a string.
The conductor is suspended at the bottom end of this string while the top
end is secured to the cross-arm of the tower. The number of disc units
used depends on the voltage.
Strain insulator - A dead end or anchor pole or tower is used where a
straight section of line ends, or angles off in another direction. These poles
must withstand the lateral (horizontal) tension of the long straight section
of wire. To support this lateral load, strain insulators are used.
For low voltage lines (less than 11 kV), shackle insulators are
used as strain insulators. However, for high voltage
transmission lines, strings of cap-and-pin (suspension)
insulators are used, attached to the cross arm in a horizontal
direction. When the tension load in lines is exceedingly high,
such as at long river spans, two or more strings are used in
parallel.
Shackle insulator - In early days, the shackle insulators were used as strain insulators. But nowadays,
they are frequently used for low voltage distribution lines. Such insulators can be used either in a
horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the
cross arm.
Bushing - enables one or several conductors to pass through a partition such as a wall or a tank, and
insulates the conductors from it.[9]
Line post insulator
This is a STOLEN COPY if it does bear
Station post insulator
the original signature of the author.
Cut-out
Page 14 of 16
COMPILED NOTES on [1] Transformer Parts: [2] Cases of Parallel Operation [3] Parts of Philippine
Distribution Code [4] Motor Control [5] Grounding System, [6] Fuses,... etc
Power Plants
rdsjr
This is a STOLEN COPY if it does bear
the original signature of the author.
Peaking power plants : Peaking power plants, also known as peaker plants, and occasionally
just "peakers", are power plants that generally run only when there is a high demand, known as
peak demand, for electricity. Because they supply power only occasionally, the power supplied
commands a much higher price per kilowatt hour than base load power. Peak load power plants
are dispatched in combination with base load power plants, which supply a dependable and
consistent amount of electricity, to meet the minimum demand.
A peaker plant may operate many hours a day, or it may operate only a few hours per year,
depending on the condition of the region's electrical grid. Because of the cost of building an
efficient power plant, if a peaker plant is only going to be run for a short or highly variable time,
it does not make economic sense to make it as efficient as a base load power plant.
Peaker plants are generally gas turbines that burn natural gas. A few burn biogas or petroleumderived liquids, such as diesel oil and jet fuel, but they are generally more expensive than natural
gas, so their use is limited to areas not supplied with natural gas. However, many peaker plants
are able to use petroleum as a backup fuel, as storing oil in tanks is easy.
Base load power plants : The opposites of peaking plants are base load power plants. Nuclear
and coal burning plants operate continuously. stopping only for maintenance or unexpected
outages.
Intermediate load following power plants such as hydroelectric operate between these
extremes, curtailing their output on nights and weekends when demand is low. Base load and
intermediate plants are used preferentially to meet electrical demand because the lower
efficiencies of peaker plants make them more expensive to operate.
Renewable Energy
For countries that are trending away from coal fired baseload plants and towards intermittent
energy sources such as wind and solar, there is a corresponding increase in the need for peaking
or load following power plants and the use of a grid intertie.
Hydroelectric Dams
Hydroelectric Dams are intentionally variable; they can generate less during off-peak and
quickly respond to peak demands, consequently hydroelectricity may function as load
following or a peaking plant and with sufficient water, a base load plant.
Technical advantages and disadvantages of both AC and DC Systems.
Page 15 of 16
COMPILED NOTES on [1] Transformer Parts: [2] Cases of Parallel Operation [3] Parts of Philippine
Distribution Code [4] Motor Control [5] Grounding System, [6] Fuses,... etc
rdsjr
Advantages of DC Transmission
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There are two conductors used in DC transmission while three conductors required in AC transmission.
There are no Inductance and Surges (High Voltage waves for very short time) in DC transmission.
Due to absence of inductance, there are very low voltage drop in DC transmission lines comparing with AC (if
both Load and sending end voltage is same)
There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required.
A DC System has a less potential stress over AC system for same Voltage level. Therefore, a DC line requires
less insulation.
In DC System, There is no interference with communication system.
In DC Line, Corona losses are very low.
In High Voltage DC Transmission lines, there are no Dielectric losses.
In DC Transmission system, there are no difficulties in synchronizing and stability problems.
DC system is more efficient than AC, therefore, the rate of price of Towers, Poles, Insulators, and conductor are
low so the system is economical.
In DC System, the speed control range is greater than AC System.
There is low insulation required in DC system (about 70%).
The price of DC cables is low (Due to Low insulation)
In DC Supply System, the Sheath losses in underground cables are low.
DC system is suitable for High Power Transmission based on High Current transmission.
In DC System, The Value of charging current is quite low, there fore, the length DC Transmission lines is greater
than AC lines.
Disadvantages of DC Transmission:
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Due to commutation problem, Electric power can’t be produce at High (DC) Voltage.
For High Voltage transmission, we can not step the level of DC Voltage (As Transformer can not work on DC)
There is a limit of DC Switches and Circuit breakers (and costly too)
Motor generator set is used for step down the level of DC voltage and the efficiency of Motor-generator set is low
than transformer.
so the system makes complex and costly.
The level of DC Voltage can not be change easily. So we can not get desire voltage for Electrical and electronics
appliances (such as 5 Volts, 9 Volts 15 Volts, 20 and 22 Volts etc) directly from Transmission system.
AC Transmission:
Advantages of AC Transmission System
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This is a STOLEN COPY if it does bear
the original signature of the author.
AC Circuit breakers is cheap than DC Circuit breakers.
The repairing and maintenance of AC sub station is easy and inexpensive than DC Substation.
The Level of AC voltage may be increased or decreased step up and Step down transformers.
Disadvantages of AC System.
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In AC line, the size of conductor is greater than DC Line.
The Cost of AC Transmission lines are greater than DC Transmission lines.
Due to Skin effect, the losses in AC system are more.
In AC Lines, there is Capacitance, so continuously power loss when no load on lines or Line is open.
Other line losses are due to inductance.
More insulation required in AC System
Also corona Losses occur In AC System,
There is telecommunication interference in AC System.
There are stability and synchronizing problems in AC System.
DC System is more efficient than AC System.
There are also re-active power controlling problems in AC System.
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