- Positive plates become dark brown in colour and negative plates become grey.
- Specific gravity of sulphuric acid increased from 1.8 to 2.3V
- Voltage of each cell rises from 1.8 to 2.3V
- Energy is absorbed in the cell
- . Cell delivers gazing when the charging is completed
LIST FOUR (4) ADVANTAGES OF A TRANSFORMER. (4 MARKS)
1. It’s one of the economical devices to transmit electrical power at high voltage and current. Can also be reduced at the designed voltages when required.
2. Its efficiency is very high in comparison to other electrical machine.3. It can be operated very easily with little operation.
4. It maintenance cost is less, in comparison to other electrical machineries.
5. Number of tappings can be taken out from the secondary windings for voltage in only one transformer, which is used for transistor and low voltage appliances.
6. It can be taken from place to place very easily and it’s even used in house industry.
7. This can be designed for very high voltages, as there is much space to insulate winding
BRIEFLY EXPLAIN THE PRINCIPLE OF OPERATION OF THE FOLLOWING SPEED-CONTROL METHODS OF A D.C MACHINE
(I) Fux control. (Ii) Rheostat control. (III) voltage control
1) Flux control: For shunt motor, flux control method is frequently used because it’s simple and inexpensive. In this method, a variable resistance (known as shunt field Rheostat) is placed in series with shunt field windings.For series motor, in this method the flux produced by the series motor is varied and hence the speed. The variation of flux can be achieved in the following ways.
(I) Field diverters. (Ii) Armature diverters (III) tapped field control (IV) paralleling field coils.
(2) voltage control method: In this method, the voltage source supplying the field current is different from that which supplies the armature. This method avoids the disadvantages of poor speed regulations and low efficiency as in armature control method. However, it’s quite expensive.
3) Rheostat control DC shunt motor: In this method, speed variation is accomplished by means of variable resistance in series with the shunt field. An increase in controlling resistance will reduce the field current with a reduction in flux and an increase in speed
REQUIREMENTS FOR A TRANSMISSION AND DISTRIBUTION STATION
- It must provide at all time the power that consumers need
- It must maintain a stable normal voltage that doesn’t range more than ± 10%
- It must be able to maintain a stable frequency that doesn’t vary more than ± 0.1%
- It must supply energy at an acceptable price.
- It must meet/agree with the safety standard
- It must be environmentally friendly.
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