Bearing Size & Code Reading

Bearing Codes
Example:              6002

Here 6à  is denoting to Type of a bearing.

Here 2à  is denoting to Internal Diameter of a bearing.

• Different Types of Bearings are:-

Bearing Number	Type
1101	Self Element Bearing
6201	Ball Bearing
6301	Ball Bearing
5200	Thurst Bearing
3200	Roller Bearing
7200	Anguller Bearing

• Bearing Shaft Size Details from Bearing Type

Bearing	Calculation	Shaft Size in MM
6200	0	10
6201	0	12
6202	0	18
6203	0	17
6204	4*5	20
6205	5*5	25
6206	6*5	30
6207	7*5	35
6208	8*5	40
6209	9*5	45

Insulation Testing for Motor & Alternators

Few people knows this formula for Insulation testing for a motor or alternator/ Transformer. I am saying this because i got this formula after long discussion with colleges. so you are lucky
  

Formula of LT Motor/Alternator  Insulation resistance  


Insulation resistance for LT motor = 1+ (Motor Ratted Voltage in KV) In Mega Ohm 

LT Motor (415volt) internal resistance should be 90~100 Mega Ohm.


Acceptable Internal Resistance for Motor = 2 ~ 10 Mega Ohm 

Note:- For LT equipment we used 500 V (500 Volt) Meggar.

Formula of HT Motor/Alternator Insulation resistance

Insulation resistance for HT motor = (Voltage in KV *2)+3  In Mega Ohm

For example : 11 kv HT Motor IR   = (11*2)+3 =25 Mega Ohm

Note:- For HT equipment we used 5 KV (5000 Volt) Meggar.

For Alternator or Transformer winding testing we withstand the 5KV voltage for around 2 minutes.

Synchronizing Method & Parameters for Alternators

When I was a student I study about alternator, so being a fresher & student I was willing to see how it works and synchronizing procedure. Fortunately I joined Utility Department purely electrical i.e. large machine including all Electrical costly & large machines by size and by cost too. 

The operation of paralleling two alternators is known as synchronizing, and certain conditions must be fulfilled before this can be affected. The incoming machine must have its voltage and frequency equal to that of the bus bars and, should be in same Phase with bus bar voltage.

A SYNCHRONIZING PANEL WITH ACESSARIES   

Synchronizing can be done with the help of

(i) Dark lamp method or 
(ii) By using synchro-scope.    

                                                                          

In Dark Lamp method we synchronize alternator with the dark and light glow of bulb. When in synchroscope method we synchronize alternator when frequency is matched in same direction. 
There are certain parameters are already feed in digital protection relay. Synchronizing process is completed after check synchronizing relay. It protects synchronizing circuit. These relays are used to verify that the voltages on either side of a circuit breaker are synchronized, and in the proper phase and magnitude relationship to allow automatic closing.

DOUBLE FREQUENCY METER 

DOUBLE VOLT METER

SYNCHROSCOPE

A Synchronizing panel have following mounting or auxiliary’s i.e.

Ø Double Frequency Meter

Ø Double Voltage Meter

Ø Synchroscope

Ø Master Trip Relay

Ø Check Synchronizing Relay

Ø DC Ampere meter

Ø DC Voltage meter

Ø Bulbs for Dark Lamp method

Ø Indication bulbs

Ø Equipment selector switch for selection

Ø Manual/Auto synchronizing selector switch

 Synchronizing Check Relay Settings

   df offset  = 0.20 Hz

   Max df    = 0.25 Hz (50.25Hz)

   Min df = 0.18 Hz (49.82Hz)

   dv Max = 3.00%  (10670 ~11330 Volt)

   Syn. Time Pulse = 0.20 Sec 

   Closing time pulse for CB = 80 mile sec

Note:- These all setting are for 3.9 MW Alternator, prime mover - gas engine 

Calculation of a ACB or VCB for a AC Generator

Before calculation of a LT/HT breaker you should take care all large machines in a power plant are rated in KVA. So keep this in mind.

Example :- 

Give a specification of a LT (415 Volt) breaker  for a 2000 KVA Alternator.
For any designing in electrical machines we need to get full load current of a machine, then add the percentage of safety factor & other factor too.

Generator Power = 2000 Kva

                P= 1.7321V*I 

             Now Current will be = 2000*1000/415*1.7321 Volt  
                                               = 2782 Ampere 
Now breaker selection will add different safety factors in ratting, with short circuit current. I don't know the exact method for selection of a breaker. but here we used 3200 Ampere because of nearest Breaker in ratting is 3200 Ampere with SF.

Same method you can also apply for transformers too for current calculation in primary & secondary side.

Thanks,
Anuj Tyagi