- generator step-up transformers - with the generator connected to the delta and the star connected to the system.
- substation transformers - with the delta connected to the grid, and the star connected to the load substation.
Star delta is used at transmission levels for step down
Running a 3ph motor on Single phase line?
The way that I accomplish this is to add capacitors from one of the hot leads to the third lead of the three phase motor. It creates the phantom third hot lead. However, for starting the motor I have a momentary contact switch set up, just like the the before mentioned capacitors, except the starting capacitors are much, much larger. I first turn on the motor. It rotates slowly. Then I hit the momentary contact switch which brings online the starting caps. Then varoom. The motor takes off to it's normal operating speed. The largest motor that I've tried this trick on is a 7 1/2hp. If the motor is small enough then I don't need the start switch.
How to decide the current rating of ISOLATORS?
Need to have current breaking capacities of:
Why do we go for bundled conductors in EHV lines?
We go for bundled conductors because this reduces the voltage gradient in the vicinity of the lines hence corona is reduced and also the interference with neighbouring comm. Lines. Also inductance is reduced leading to better voltage regulation and more power handling capacity.
What is form factor?
Form Factor= rms/avg… (=1.11 for sine & 1 for DC and square waveforms…)
What happens if we give 220 volts dc supply to bulb or tube light?
Bulbs [devices] for AC are designed to operate such that it
offers high impedance to AC supply. Normally they have low
resistance. When DC supply is applied, due to low
resistance, the current through lamp would be so high that
it may damage the bulb element.
How are generators rated?
Generator sets are rated in kVA at 0.8 power factor lagging.
This 0.8 power factor is not the load power factor.
It is a nominal power factor used to calculate the kW output of an engine to supply the
power for a particular alternator kVA output.
Example:
Alternator output (kVA) : 100kVA
Engine power output (kW) : 100kVA x 0.8 = 80kW
What are diversity and demand factors in power system?
An example would be a conveyor belt made up of six sections, each driven by a 2 kW motor. As material is transported along this belt, it is first carried by section 1, then each section in succession until the final section is reached. In this simple example only one section of conveyor is carrying material at any point in time. Therefore five motors are only handling no-load mechanical losses (say .1 kW) keeping the belts moving whilst one motor is handling the load (say 1 kW). The demand presented by each motor when it is carrying its load is 1 kW, the sum of the demand loads is 6 kW but the maximum load presented by the system at any time is only 1.5 kW.
The diversity factor for this system is:
∑Demand Loads 6 kW
-------------------- ----- = 4
Maximum Demand 1.5 kW
The demand factor for this system is:
Maximum Demand 1.5 kW
-------------------- ----- = 0.125
∑Connected Load 12 kW
What are the advantages of EHV Lines?
Advantages:
1. Higher generation at statns requires higher voltage transmission
2. SIL is proportional to V2 (3 V2/Zc) and long transmission lines can be loaded to SIL for stability considerations. So SIL can be increased for higher loading of lines
3. EHV also decreases the right of way requirement
4. Line costs are reduced /MW/Km
What type of conductors are used in EHV lines?
Bundled Conductors to reduce Electic field intensity in the vicinity of lines: So Corona & Radio interference are reduced…Also inductance is decreased
Expanded ACSR can also be used but it has to be handled properly to avoid distortion
400kV: 2 or 4 subconductors /ph
765kV: 8 subconductors /ph
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