LOAD FREQUENCY AND VOLTAGE GENERATION CONTROL

LOAD FREQUENCY AND VOLTAGE GENERATION CONTROL
Load frequency control
Automatic Generation Control
Voltage Control
Primary regulation.
Secondary regulation
real power
Why voltage control is important?

1. INTER CONNECTED POWER SYSTEM PREET PATEL LOAD FREQUENCY AND VOLTAGE GENERATION CONTROL

2. CONTENTS Load frequency control Automatic Generation Control Voltage Control 2

3. LOAD FREQUENCY CONTROL(LFC) Load Frequency Control (LFC) is the basic control mechanism in the power system operation. Whenever there is a variation in load demand on a generating unit, there is momentarily an occurrence of unbalance between real-power input and output. This difference is being supplied, by the stored energy of the rotating parts of the unit. The LFC also controls the real-power transfer through the interconnecting transmission lines by sensing the change in power flow through the tie lines. The speed/frequency variation concept can be extended from a single turbine-generator system to a power system comprising several turbine generators. The mismatch between the total power generated and the total electrical load causes the frequency change as dictated by the combined system inertia.  3

4. The governors of all the machines sense the frequency and the mechanical power outputs will be changed automatically to match the combined generation with the new combined load. This action is primary regulation . But frequency remains at a new value and set points must be adjusted, just as in single machine case for frequency restoration. This job is done by the automatic load frequency controller (ALFC) shown in figure. This process of set point adjustment is called secondary regulation . When load change occurs, frequency varies and the regulation initially for the first few seconds is due to the action of the governors of all generating units and subsequently the load frequency control system. 4

5. Excitation System AVR Voltage Sensor Frequency Sensor Load Frequency Control Valve Control Mechanism Turbine G Coupling between Generator and Turbine Valve Steam Input       5

6. The operational objectives of the LFC are to maintain reasonably uniform frequency to divide the load between generation and to control the tie line interchange schedules . The change in frequency and tie line real power are sensed which is a measure of the change in rotor angle ẟ , i.e., the error ∆ẟ to be corrected. . The error signal, i.e., ∆ and ∆ are amplified, mixed and transformed into the real power command signal ∆ which is sent to the prime mover to call for an increment in the torque. The prime mover brings change in the generator output by an amount ∆ which will change the value of ∆ and ∆ within specified limits.   6

7. AUTOMATIC GENERATION CONTROL(AGC) Automatic generation control(AGC) usually implemented in energy management system of energy control centers (ECC) consists of (1) Load frequency control to hold the system frequency within limits (2) Economic dispatch to maintain generation of each plant within the area at optimum value. (3) Interchange scheduling to maintain optimum power interchange between adjustment systems through the tie lines. Automatic generation control is synonymous with load frequency control (LFC) of power system. The purpose of LFC is to exert control over the frequency and real power load of a generator both in isolated and grid connected modes. The LFC problem is generally modelled as a linear closed loop control problem for small changes in power system which varies frequency real power load. All hydro-turbines have mechanical speed governors which perform elegantly to control the load frequency of an isolated generators called integral tie-line bias controller, which is needed for simultaneous control of frequency and power flow into o the grid power system. 7

8. The speed control mechanism includes equipment such as relays, servomotors pressure or power amplifying devices levers and linkages between the speed and governor controlled valves. The governor controlled valves regulated the water input to the hydro-turbine are normally actuated by the speed governor through the speed control mechanism. In addition, through the action of a speed changer, the speed control system may be adjusted to change the power output and also the speed of the turbine in operation. Hence, the input to the speed control system are: Speed changer position. Speed or frequency feedback through the governor. AGC is a centralized operation that operate in real time and in closed loop with a strong interface to other function oriented towards the economy and security of the power system. 8

9. Integrator Speed Sensor Turbine Exciter Speed Changer Comparator Steam Valve Amplifier Load Frequency Sensor Speed Governor Output power Rectifier and Filter Voltage sensor Frequency Hydraulic amplifier Turbine Power 9

10. VOLTAGE CONTROL A power system is said to be well designed if it gives a good quality of  reliable power supply. By good quality is meant the voltage levels within the reasonable limit. Practically all the equipment's on the power system are designed to operate satisfactorily only when the voltage level in the system correspond to their rated voltages. The variation in voltage level is allowed within the limit say ±5% at the consumer terminals. In the power system load on the supply system increases, the voltage at the consumer terminals decrease due to increase in voltage drop in the power system components and vice versa. If the voltage variation is more than a pre-specified value, the Performance the equipment suffers and the life of most of the equipment is also sacrificed. That's why voltage control is important in the power system. The voltage control is done by using various voltage control methods 10

11. Why voltage control is important? In case of incandesce lamp; it is very sensitive to voltage change, if the fluctuations in the voltage beyond certain level, life of the lamp decreases. In case of Induction motor, the torque is directly propositional to square of the terminal voltage. If the supply voltage is low, the starting torque of the motor will be very low. Most of the electronics equipments are very sensitive about voltage variation. The picture on a television set starts rolling if the voltage is low because the florescent tube refuses to glow at low voltage. Hence voltage variation must regulated and kept to a minimum level. . 11

12. Thank You 12