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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
Circuit diagram of an electric stove plugged into the socket?
circuit diagram is the most important in electric stove plugged into the socket
Wave forms of 3 phase fully controlled rectifier for RL load?
for 3 phase r l load phase control rectifier what is the avg value?
do you mean drip loop?
its where a cable coming down a wall, loops down then up before going through the wall. means water running down the cable will not enter wall with cable
Why is a set up transformer needed in a stereo or tv set?
A stereo or tv set needs a step-up transformer because a step-up transformer increases the voltage of an appliance and a stereo or and a tv set needs a high voltage.
-------Semper Fidelis(ADC)----------
How differential protection work in a transformer?
Power flowing into a transformer must match the power flowing out (minus losses which are minimal). If this is not the case, there's something wrong.
Differential protection monitors current only; Current flowing into one side of the transformer will be equal to current flowing out the other side scaled by the turns ratio of the transformer. Since the turns ratio is equivalent to the voltage ratio, this is easily set.
What is relationship between gain and bandwidth of an op amp is?
An op amp can have a very large gain, but a limited bandwidth. If you decrease the gain, you can increase the bandwidth.
What are Block diagrams for online and offline UPS?
Online UPS is a power supply that is not interrupted during the switch-over of the power. There is a short cut-off on the offline UPS which can have an effect on affected loads during transition.
Why earthing power transmission line?
It is necessary because lightning can destroy whole phase conductors. Lightning has energy of 1MHp. So much high energy if falls on transmission line will not even destroy it but all of the distribution systems too. The reason that lightning falls on tower is that it always chosses the shortest path.
A diagram showing the connections, line terminations, etc. needed to connect a specific type of signal interface to a system.
In addition to this diagram a tabular entry giving signal specifications, connector types, etc., a figureshowing installation and mating of connectors, and a textual description of the purpose and usage of the interface are usually required in formal documentation.
During my avionics career I have had to work with systems having several thousand signal interfaces, thus requiring all of those thousands of diagrams, tabular entries, figures, and textual descriptions to appear in the Interface Control Document (ICD) for that system. Many ICDs were well over a foot thick.
Note: documents like the Software Description Document (SDD) on these systems could get over five feet thick!
What is TPS class current transformer?
TPS Class CT is used for transient performance (TP). TPS class Current Transformer has Low Leakage Flux and there is no limit for remanent flux) further there are also TPX,TPY and TPZ class CTs
1. TPX- No Limit for remanent flux due to nil air gap in the core
2. TPY - remanent flux does not exceeded 10 % due to less air gap in the core
3. TPZ- Having practically null remanent flux because there is large air gap is provide in the Core
Er. Anil Prajapati, Protection Engineer,Jaipur RVPNL
How do you increase the inductance in a inductor?
Since we know that inductance of an inductor depends on the length of inductor by the formula
L=muAN*N/l, where l is the length of inductor. So by varying the length of inductor we say that inductance of inductor varies.
How can you say that ac emf is induced in the coil?
When we place a current carrying conductor in a magnetic field emf is induced in a coil. we can knoe it by connecting voltmeter.
How do you determine the internal resistance of capacitors?
The best way is to check the data sheet and see if ESR (equivalent series resistance) is listed.
Does the motor speed double when the armature voltage is doubled?
Yes, because as the armature voltage increases, the speed also increases so they are proportional.
How could you calculate the resistance of a circuit?
A variety of techniques can be used. Node-Voltage and Mesh-current (or Loop-current) methods, for example. See related link for examples. If there is a single voltage source in the model, then find the current supplied, and Resistance = Voltage/Current. {R = V/I}
You could simulate/ model the circuit on a computer then apply the power profile and a current value will be calculated. Or if you have the circuit working, Place an amp meter into the circuit and measure the current. V/i = resistance.
What determines the power rating of a machine?
generally rating means the condition when the machine can give maximum efficiency without being overheated .In transformers and generators it is decided by core as well as copper loss(flux proportional to supply voltage,current proportional to copper loss).so both are rated in kVA whereas motors are rated as maximum output they can deliver i.e kW.
Refer to:
International Electrotechnical Commission IEC 836"Specifications for silicone liquid for electrical purposes" (Silicone Fluid Type T-1) and
ASTM D 4652 "Silicone Fluids for Electrical Insulation" specifications for repair or top-off of existing liquid-filled units.
These standards cover both the physical and electrical properties of fluid suitable for dielectric applications.
Also refer following:
IS-335/1993 - Specification for uninhibited new insulating oils.
IS-12463/1988 - Specification for inhibited mineral insulating oils.
IEC -60296/2003 - Specification for unused mineral insulating oils for transformers and switchgear. This standard cover both uninhibited and inhibited oils.
ASTM - D3487/2000-StandardSpecification for Mineral Insulating Oil used in Electrical apparatus. This standard also covers both uninhibited and inhibited oils.
Unused Mineral Insulating oils filled inNew transformers
IS -1866/2000-Code of Practice for Electrical Maintenance and supervision of Mineral Insulating oil in Equipment. (Refer Table.1 for limiting values of various parameters)
IEC -60422/1998-Supervision and maintenance guide for mineral insulating oils in electrical equipment.
In service Mineral Insulating oils:
IS -1866/2000 -Code of Practice for Electrical Maintenance and supervision of Mineral Insulating oil in Equipment.(Refer Table for limiting values of various parameters)
IS-335/1993
Appearance ------------ Clear and transparent
Density at 29.5 deg.C (Max) 0.89 g/cm2
Kinematic Viscosity (Max)
1) at 27deg.C ------------------ 27 cSt
2) at 40deg.C ------------------ Under consideration
IFT at 27deg.C (Min) ---------0.04 N/m
Flash Point (Min) --------- 140deg.C
Pour Point (Max) ---------- 6deg.C
Neutralization Value
1) Total Acidity (Max) ---- 0.03 mg KOH/gm
2) Inorganic acidity ------ Nil
Corrosive Sulphur ------- Non-corrosive
Electric Strength (BDV)
1) New unfiltered Oil (Min) 30 KV (rms)
2) After filteration (Min) If the above value is not attained, the oil shall be filtered to 60 KV (rms)
Dielectric dissipation factor (tan ) at 90deg.C(max) 0.002
Specific resistance (Resistivity)
1) at 90deg.C (Min) 35 x 10 12 ohm-cm
2) at 27deg.C (Min) 1500 x 10 12 ohm-cm
Oxidation Stability
1) Acidity (max) 0.4 mg KOH/gm
2) total sludge (max) 0.1 % by weight
Ageing characteristics
a) Resistivity (Min)
1) at 27deg.C 2.5 x 10 12 ohm-cm
2) at 90deg.C 0.2 x 10 12 ohm-cm
b)Tanδ at 90deg.C (Max) 0.20
c) Total acidity (Max) 0.05 mg KOH/gm
d) Total sludge (Max) 0.05 % by weight
Presence of Oxidation inhibitor -The oil shall contain natural anti oxidant additives.
Water content - 50 ppm
S K value - Under consideration
IS-1866/2000-Recommended Limits of Unused Mineral Oil filled in NewTransformer
Property
Highest Voltage of Equipment (KV)
< 72.5
72.5-170
>170
Appearance
Clear, free from sediment and suspended matter
Density at 29.5 deg.C (g/cm2), Max.
0.89
0.89
0.89
Viscosity at 27 deg C (cst), Max
27
27
27
Flash Point deg. C, Min
140
140
140
Pour Point Deg. C , Max
-6
-6
-6
Total acidity (mg KOH/gm), Max
0.03
0.03
0.03
Water Content (ppm), Max
20
15
10
IFT at 27 degC,(mN/m), min
35
35
35
Tanδ at 90 deg C, Max
0.015
0.015
0.01
Resistivity at 90 deg.C (x10e12 ohm cm Min.
6
6
6
BDV Kv Min
40
50
60
IS-1866/2000-Violation Limits for in service oils
Property
Highest Voltage of Equipment (KV)
< 72.5
72.5-170
>170
Flash Point deg. C, Min
Maximum decrease of 15deg.C from initial value
Pour Point Deg. C , Max
-6
-6
-6
Total acidity (mg KOH/gm), Max
0.3
0.3
0.3
Water Content (ppm), Max
No free water
40
20
IFT at 27 degC, (mN/m), min
1
1
1
Tanδ at 90 deg C, Max
1
1
0.2
Resistivity at 90 deg.C (x10e12 ohm cm Min.
1
1
1
BDV Kv Min
30
40
50
Sediment and Sludge
No sediment or precipitable sludge should be detected.
Results below 0.02% by mass may be neglected
IS-1866/2000 - Frequency of testing
Property
Frequency of Testing
Appearance
In conjunction with other Quantitative tests
Water content
After filling or refilling prior to energizing, then after
three and 12 months, subsequently along with DGA
BDV
After filling or refilling prior to energizing, then yearly
Total acidity
Yearly
IFT
After filling or refilling prior to energizing, then yearly
Resistivity
After filling or refilling prior to energizing, then yearly
Tanδ
After filling or refilling prior to energizing, then yearly
Flash Point
Yearly
Sediment and sludge
Yearly
IS-1866/2000-Recommended Actions
Property
Recommended Actions
Appearance
As dictated by other tests
Water content
Check Source of water and consider reconditioning
BDV
Recondition the oil or alternatively, if more economical or other tests dictate replace oil
Total acidity
Replace or reclaim oil
IFT
Replace or reclaim oil
Resistivity
Replace or reclaim oil
Tanδ
Replace or reclaim oil
Flash Point
Replace the oil, equipment may require inspection
Sediment and sludge
Where sediment is detected recondition the oil
IS-1866/2000 - Classification of oils in service.
Group 1:
This group contains oils that are in satisfactory condition for continued use. The frequency can be followed as described earlier.
Group 2:
This group contains oils that requires reconditioning for further service. (LOW BDV and High water content). The frequency can be followed as described earlier after reconditioning.
Group 3:
This group contains oils in poor condition that it can restore satisfactory properties only after reclaiming. Insulating oils this group should be reclaimed or replaced depending on economic considerations.
Group 4:
This group contains oils, in such poor state that it is technically advisable to dispose of them.
IEC -60296 - General Specification
Functional Properties: Viscosity, Pour point, Water content, BDV, Density, Tan.
Stability Properties: Appearance, Acidity, IFT, corrosive Sulfur, Antioxident additive
Performance Properties: Oxidation Stabillity, Sludge
HSE Properties: Flash Point, PCB content, PCA content
Ashok
Head Engineering & Project Execution
EVI, INDIA
Why are stator cores laminated?
Thin metal laminations are used to minimize the magnetic flux eddy current loss in the stator cores of high-speed, high-performance induction motors.
How do you calculate electric cable copper weight?
wire weight = material_density * 3.14159 * (0.5 * cable_diameter)² * cable_length
example for copper with 152 meter length:
----------------------------------------
material_density for copper = 8960 kg/m³
cable_diameter=0.006 meter
cable_length=152 meter
weight of wire = 8960 kg/m³ * 3.14159 * (0.5 * 0.006)² * 152 = 38.51 kg
lenght and diameter must be calculated in "meters"
density must be in "kg/m³"
How does current transformer works in a substation?
A current transformer works on the same principle as that of a simple transformer however it steps down the high current into a low level so that it can be measured using an ammeter of a suitable range. In some current transformers extra cores are provided. This is done in order to prevent the faulty currents i.e. the over currents, earth faults, differential protections. The extra cores of a C.T. gets saturated as soon as the faulty currents starts flowing and thereby does not harm the main core of the transformer and the ammeter connected. The C.T. is always connected in the line carrying current. It first steps down the current to a measureable form and further gives this current to the ammeter.
Why gain bandwidth product is constant?
The gain and bandwidth product is constant only for first order systems. However many complex systems which can be converted and studied as first order, it holds good. This is simple mathematics as in the first order system the frequency appears in the denominator. So if it increases by x times then gain (the modulus of the transfer function) is reduced by x times (approximately).
