In active power and frequency control, a. Frequency should remain constant b. A considerable drop in frequency could result in low magnetizing currents in induction motors and transformers. c. The frequency of a system is dependent on reactive power balance. d. Relatively closed control of frequency ensures constancy of the speed of induction motors. Which of the above statements are incorrect?

In active power and frequency control, a. Frequency should remain constant b. A considerable drop in frequency could result in low magnetizing currents in induction motors and transformers. c. The frequency of a system is dependent on reactive power balance. d. Relatively closed control of frequency ensures constancy of the speed of induction motors. Which of the above statements are incorrect? Correct Answer b and c

Active power and frequency control:

• For satisfactory operation of a power system, the frequency should remain nearly constant.
• Relatively close control of frequency ensures constancy of speed of induction and synchronous motors.
• Constancy of speed of motor drives is particularly important for satisfactory performance of generating units as they are highly dependent on the performance of all the auxiliary drives associated with the fuel, the feed-water and the combustion air supply systems.
• In a network, considerable drop in frequency could result in high magnetizing currents in induction motors and transformers.
• The extensive use of electric clocks and the use of frequency for other timing purposes require accurate maintenance of synchronous time which is proportional to integral frequency. As a consequence, it is necessary to regulate not only the frequency itself but also its integral.

Frequency of the system:

• The frequency of the system is dependent on active power balance.
• As frequency is a common factor throughout the system, a change in active power demand at one point is reflected throughout the system by a change in frequency.
• As there are many generators supplying power into the system, some means must be provided to allocate change in demand to the generators.
• A speed governor on each generating unit provides the primary speed control function, while supplementary control originating at a central control centre allocates generation.