This document summarizes control of active and reactive power in a power system. It discusses that active power control is related to frequency control, while reactive power control is related to voltage control. It then discusses how active power and frequency are controlled through load-frequency control (LFC) to maintain a constant frequency for satisfactory power system operation. The document also discusses generator response to load changes and how speed governing works to reduce speed variations through a transfer function relationship between electrical and mechanical torques. It describes how system load responds to frequency deviations and provides an overall system block diagram.

1. CONTROL OF ACTIVE
POWER & REACTIVE
POWER
SUBJECT : POWER SYSTEM ANALYSIS
PRESENTER: PAVITHRAN SELVAM (E15010009)

2. INTRODUCTION
Influenced by different
control actions
 Active power control : Related to frequency control.
 Reactive power control : Related to voltage control.
 Important Factors :
• Constant of frequency & voltage :
to determine quality of power supply, control of active power & reactive
power.
Active Power
Reactive
Power
Fairly independent
of each other

3. Active power & Frequency control
Description :
• Considerable drop in frequency could result in high magnetizing
current in high magnetizing current in induction motors &
transformers.
• Frequency of a system is dependent on active power balance.
• Change in active power demand at one point is reflected
throughout the system by a change in frequency.
• To control of frequency , generation within each area has to be
controlled.
• Control of generation & frequency is referred to as load-
frequency control(LFC).
Constant frequency = Satisfactory operation of P.S

4. 11.1.1 - Fundamentals of Speed Governing
 Generator Response to Load Change
If load change, then instantaneous change in Te
Mismatch between the Tm and the Te
Speed variations
CAUSES
RESULTS

5. TransferFunction:
Relationshipbetweenrotorspeedasafunctionof
theelectrical&mechanicaltorques
• Relationship between Power(P) & Torque(T)
(11.1)
By considering a small deviation (denoted by prefix Δ) from initial
values (denoted by subscript 0), we may write
(11.2)

6. From equation 11.1,
The relationship between the perturbed values, with higher-
order terms neglected by
Therefore,
Since, in the steady state, electrical & mechanical torques are
equal, Tm0 = Te0. With speed expressed in pu, ω0 = 1.

7. Figure 11.2 can now be expressed in terms of ΔPm and Δpe as
follows:
• Within the range of speed variations, the turbine mechanical
power is essentially a function of valve or gate position and
independent of frequency.

8.  Load Response to Frequency Deviation
• For resistive loads, such as lighting and heating loads, the
electrical power is independent of frequency.
• For motor loads, such as fans and pumps, the electrical power
changes with frequency due to changes in motor speed.
Overall frequency-dependent characteristics of a composite load:
• D = percent change in load for one % change in frequency.
• Typical values of D are 1-2%.
• If D=2 means 1% change in frequency
2% change in load

9. • The system block diagram including the effect of the load
damping:
Can be reduced

10. • Absence of speed governor:
- the system response to a load change determined by the
inertia constant and the damping constant.
• Steady –state speed deviation:
- the change in load exactly compensated by the variation in
load due to frequency sensitivity.