Phrantech technologies

29/08/2022

How to calculate the value of Current Transformer transformers mounted on both sides of the transformer

*Transformer 80MVA

1- Current current value from the side of 110KV

Power (S) = 1.73 x V x I

I = 80000/(1.73 x 110)
I = 420 A

Of course there is no current transformer ratio of 420 so the largest value is used and we choose a current transformer of 500

2- Current current value from the side of 20KV

I = 80000/ (1.73 x 20)
I = 2313 A

And the same thing there is no current transformer in this ratio so the largest value is used and we choose a current transformer 2500

Note when choosing the value of the power adapter is according to the available percentages of the power transformers produced by companies

*There is no problem in choosing a higher current adapter ratio for example a transformer. Stream 1500 and there is no of it in the manufacturers or stores of the company A current transformer is installed at a higher rate of 1600 and there is no important problem not less than the current value calculated from the equation.

* Most companies resort to the production of multi-ratio transformers, for example, when changing the transformer from 25MVA to 40MVA, we need a transformer with a higher ratio, so the transformer is not changed as it used to happen previously

But the ratio of the current transformer from both ends of the primary or secondary coil is changed

The third current transformer on the neutral breakeven point is specific to REF restricted ground leakage and its value is the same value on the one hand.
The 110KV

Choosing the correct ratios of current transformers on both sides of the transformer is an important thing and we make sure of the correct ratios when making Diff Relay differential protection calculations and also when balancing the transformer Stability Test.

18/08/2022

03/08/2022

uestions & Answers on Batteries & troubleshooting - Part 1

1-List down the applications of auxiliary DC power supply system in Power plants? -Protections relays -Circuit breakers -DCS -Trip circuits -Signaling -Telephone system & communication -Emergency lighting -Transmitters & Positioners -Emergency oil pumps -Metering panels

2-List down the various DC voltages & their applications in power plants 220 VDC & 110 VDC - Protection system / Emergency lighting / Trip & closing coil of circuit breakers / Operating mechanisms . 48 VDC - Telephone communication +/- 24 VDC - Control circuits / Measuring instruments / Static relays

3-What is the power source for DC supply? Main power source is lead-acid storage battery & AC/DC rectifier set

4-What are the installation requirements for lead acid battery ? The room should be isolated from other system Room should have adequate lighting & ventilation The room walls & floor should have acid proof tiles Battery cells should be installed on insulated racks Racks should be placed on insulator generally porcelain insulators Cables should be acid proof The DC bus bars should be of round or flat copper materials Bus bars connections are made by soldering or brazing The positive terminal of the battery is Red & negative terminal should be blue.

5-How do you calculate the maximum discharge current of batteries? Maximum discharge current = (Continuous load (W1) + Short time Load (W2)) / Rated Voltage

6-How do you specify the batteries? -Batteries have following specification: -Rated voltage -No. of cells -AH capacity -Arrangement of cells -Details of charging equipment

7-What do you mean by AH of batteries? AH (Ampere hour) is the capacity of battery. It is the product of current and total time required for discharge. It depends on the magnitude of discharge current.

8-How do you decide the number of batteries for a particular battery bank? No. of battery cells = Bus bar voltage / Voltage of one cell

9-What are the various charging methods employed for batteries? -Initial charging -Quick charging -Trickle charging

10-What do you mean by trickle charging? & what is its significance? Trickle charging is constant charging current that is supplied to battery to compensate its discharge current. Batteries get discharge when not in use. Hence to avoid sulphating, the batteries should be kept continuous charging by trickle charging.

11-What do you mean by primary cells (dry cell) & secondary cells? Primary cells are non rechargeable cells & Secondary cells are storage batteries

12-What are anode, cathode & electrolyte in Lead-acid batteries? Cathode: Sponge lead Anode: Lead Peroxide (PbO2) Electrolyte: Sulphuric acid & water

13-What is the voltage level of lead acid batteries that are generally employed? It is 2 V

14-What is the voltage level of fully charged & fully discharged lead acid battery? Voltage of fully charged cell is 2.5 V & 1.75 V for fully discharged cell

02/08/2022

Questions & Answers on Power Transformers - Part 1

1-What do you mean by power transformer?
It is a static Electro-magnetic machine which transforms alternating current from one AC voltage to another AC voltage at same frequency & at the same apparent power (KVA).

2-What is the principle of Power transformer operation?
Power transformers work on the principle of electromagnetic induction. Which states that, EMF induced in a closed conducting circuit when the magnetic flux linking with that circuit changes in time.

3-What is the main function of a power transformer?
Generally, it is used for stepping up or stepping down of Voltage to desired level

4-What are the various parts of power transformer?
-Casing
-Core
-Primary & secondary windings
-LV & HV bushings
-Radiators & cooling system
-Conservator
-Breather
-Protection devices like Buchholz relay, relief valves, temperature sensors.

5-Why does the oil conservator is placed at higher elevation?
Oil conservator is placed at a slightly higher level than that of the tank. It accommodates the contraction & expansion of oil level during lower & higher loads respectively. At higher load, oil temperature rises and hence level in the conservator rises & at lower load, oil temperature decreases & level in conservator drops down.
The above cushioning in oil level is by cushioning bag present in conservator, the air cushion in the conservator permits expansion & contraction of the oil tank without contact with moist air.


6-What is the function of breather in Transformers?
Breather is installed in a pipe from conservator. One end is connected to air cushion bag in the conservator, other end is connected to external air.
Breather is filled with dry silica jel, generally pink in colour. When oil in the conservator rises, air is let out through the breather. During low load when oil level in the conservator decreases, air is sucked into the cushion bag through breather. Silica jet absorbs the moisture & lets only dry air. Wet silica jells are blue in color.

7-What is the function of Buchholz’s relay?
It is fitted in the pipe between conservator tank & main oil tank. It operates by gas during arcing or short circuits

8-What are the various cooling methods employed in Power transformers?
-ONAN: Oil Natural & Air Natural
-ONAF: Oil natural & Air forced
-OFAF: Oil forced & Air forced
-OFWF: Oil forced & water forced
-AN: Air natural

9-What is the function of Pressure relief valve in Transformers?
It is fitted on tank to vent out the gases formed in oil & hence protects the transformer from explosion.

10-What do you mean by small, medium & large transformers?
-Small transformers: < 5 KVA
-Medium transformers: 5 to 500 KVA
-Large transformers :> 1 MVA

10/07/2022

3 phase motor wiring

09/07/2022

Three phase motor wiring.

06/06/2022

Direct on line

28/05/2022

Engineering to world.