Lecture #6 Power System Reactive power and voltage control Dr.Qi Huang School of Energy Science and Engineering,UESTC
Lecture #6 Power System Reactive power and voltage control Dr. Qi Huang School of Energy Science and Engineering, UESTC
Contents Introduction Concept of Reactive power in power system Control and management of reactive and voltage Difference between active power frequency regulation Importance of voltage control Measures for voltage control Rules of reactive compensation and voltage control Excitation control of generator 电力拿镜广城洲量写控制四川省童点实验蜜 家电
电力系统广域测量与控制四川省重点实验室 Contents Introduction Concept of Reactive power in power system Control and management of reactive and voltage Difference between active power & frequency regulation Importance of voltage control Measures for voltage control Rules of reactive compensation and voltage control Excitation control of generator
Concept of reactive power Power in an electric circuit is the rate of flow of energy past a given point of the circuit.In alternating current circuits,energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. 口 The portion of power that,averaged over a complete cycle of the AC waveform,results in net transfer of energy in one direction is known as real power. The portion of power due to stored energy,which returns to the source in each cycle,is known as reactive power. 电力拿镜广城洲量写控制四川省童点实验蜜 家电网
电力系统广域测量与控制四川省重点实验室 Concept of reactive power Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power. The portion of power due to stored energy, which returns to the source in each cycle, is known as reactive power
Concept of reactive power The instantaneous product of voltage and current is the 0 power flow;however,only the in-phase part can be used to do work(for example 0.010.020.030.040.050.060.070.080.09 0.1 current overcome friction in a motor, voltage or heat an element) the portion of power flow that is temporarily stored in the 2 form of magnetic or electric fields,due to inductive and 0 0.010.02 0.030.040.050.060.070.080.09 0.1 Im capacitive network elements, and then returned to source, is known as reactive power. 电力集镜广城测量与控制四川省重点实脸室 家电
电力系统广域测量与控制四川省重点实验室 Concept of reactive power The instantaneous product of voltage and current is the power flow; however, only the in-phase part can be used to do work (for example overcome friction in a motor, or heat an element) the portion of power flow that is temporarily stored in the form of magnetic or electric fields, due to inductive and capacitive network elements, and then returned to source, is known as reactive power. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -4 -2 0 2 4 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -4 -2 0 2 4 current voltage
Concept of reactive power The active power is used to keep the normal operation of appliances,converting electrical energy into other forms(mechanical,light or heat) Reactive power is used to exchange energy (electric field and magnetic field).It does not do work,but just help exchange the energy.Any appliances that have coils would consume reactive power. Reactive power is not useless!Motor needs to build up a magnetic field,driving mechanical movements; Transformer needs to build up magnetic field, helping induction of voltage. 电力拿镜广城洲量写控制四川省童点实验蜜 家电网
电力系统广域测量与控制四川省重点实验室 Concept of reactive power The active power is used to keep the normal operation of appliances, converting electrical energy into other forms (mechanical, light or heat) Reactive power is used to exchange energy (electric field and magnetic field). It does not do work, but just help exchange the energy. Any appliances that have coils would consume reactive power. Reactive power is not useless! Motor needs to build up a magnetic field, driving mechanical movements; Transformer needs to build up magnetic field, helping induction of voltage
Concept of reactive power 食蜜 Figure 2-29.Reactive Power Inclined Plane Analogy 家电
电力系统广域测量与控制四川省重点实验室 Concept of reactive power
Concept of reactive power Under normal operation condition,appliances not only absorb active power,but also reactive power.If the reactive power is not enough,then electromagnetic field cannot be built,causing the decrease of voltage,hence affecting the operation of appliances. Reactive power may affect the power system in following aspects: 0 (1)reduce the active power output of generator (2)reduce the power delivery capability of transmission and transformers (3)increase the voltage loss and power loss on transmission line (4)cause voltage drop and operation under low power factor condition,under which the nominal capacity cannot be fully used 电力拿镜广城洲量写控制四川省童点实验蜜 国家电网
电力系统广域测量与控制四川省重点实验室 Concept of reactive power Under normal operation condition, appliances not only absorb active power, but also reactive power. If the reactive power is not enough, then electromagnetic field cannot be built, causing the decrease of voltage, hence affecting the operation of appliances. Reactive power may affect the power system in following aspects: (1)reduce the active power output of generator (2)reduce the power delivery capability of transmission and transformers (3)increase the voltage loss and power loss on transmission line (4)cause voltage drop and operation under low power factor condition, under which the nominal capacity cannot be fully used
Control and management of reactive power and voltage Objective of reactive power and voltage management: guarantee power quality and reduce active power loss methods Balance and Voltage Limit of voltage optimization of RP regulation oscillation Condition Measures Mode Condition Measures Target Computation Predictable Generator, method voltage transformer, Stochastic Connect to large system; variation reactive ↓ and impulse Shunt capacitor compensation Voltage Contrary, Transformer, voltage devices pivot natural, reactive fluctuation Connect phase modifier constant compensation control of Connect reactor devices voltage 电力拿镜广城洲量写控制四川省童点实验蜜 家电网
电力系统广域测量与控制四川省重点实验室 Control and management of reactive power and voltage Objective of reactive power and voltage management: guarantee power quality and reduce active power loss methods Limit of voltage oscillation Voltage regulation Predictable voltage variation Generator, transformer, reactive compensation devices Voltage pivot Contrary, natural, constant control of voltage Stochastic and impulse voltage fluctuation Transformer, reactive compensation devices Connect to large system; Shunt capacitor Connect phase modifier Connect reactor Balance and optimization of RP Condition Measures Target Mode Computation method Condition Measures
Difference between voltage reactive power regulation and frequency active power regulation Active power source:only generator ->uniqueness Reactive power sources:generator, reactive power compensation devices (capacitor,reactor,phase modifier, static VAR)->diversity ■Active power source consumes primary energy, while reactive power source does not 电力拿镜广城洲量写控制四川省童点实验蜜 家电网
电力系统广域测量与控制四川省重点实验室 Difference between voltage & reactive power regulation and frequency & active power regulation Active power source: only generator ->uniqueness Reactive power sources: generator, reactive power compensation devices (capacitor, reactor, phase modifier, static VAR)->diversity Active power source consumes primary energy, while reactive power source does not
Difference between voltage reactive power regulation and frequency active power regulation Frequency of whole system is the same. Frequency regulation is only in power plant,can only be realized by regulating the output of prime mover. Voltage level at different point in power network is different.Voltage regulation can be done dispersedly.There are various type of voltage regulation measures.Voltage regulation: hierarchical regulation and local balance In power network, reactive power consumption is much larger than active power. 电力拿镜广城洲量写控制四川省重点实验蜜 家电网
电力系统广域测量与控制四川省重点实验室 Difference between voltage & reactive power regulation and frequency & active power regulation Frequency of whole system is the same. Frequency regulation is only in power plant, can only be realized by regulating the output of prime mover. Voltage level at different point in power network is different. Voltage regulation can be done dispersedly. There are various type of voltage regulation measures. Voltage regulation: hierarchical regulation and local balance In power network, reactive power consumption is much larger than active power
