Chapter 5-3-5 Auto-control Frequency and Active Power

Article 519. Required Functions of Auto-control Frequency and Auto Power

The active power generated by each power plant shall be adjusted automatically or by load dispatch center. The purposes are as follows.

-Frequency deviation on the power system is limited within the allowable value.

-Power flow on each power line in the power system is adjusted appropriately in order to maintain stability of the power system.

Article 520. Frequency Fluctuation Requirements

The speed regulation of the autocontrolfrequency and active power system equipped in generator shall be selected appropriately in order to restrain frequency fluctuation on the power gird and adjust the distribution of load among generators rationally in case of load fluctuation on the power grid.The speed regulation is defined as the following equation.

Moreover, the value of this speed regulation shall be adjustable at the site because this value has to be adjusted according to the conditions on power plants and loads.

(N2 − N )

α = (P1 − P2 )Nn Pn

N1, N2: Rotating speed before and after load change respectively P1, P2: Output of generator before and after load change respectively Nn: Rated rotating speed

Pn: Rated output of generator

Article 521. Required Components

Controlling signal shall be received from auto-controlled frequency and active power system of higher dispatch level.

Equipment for auto-control of frequency and active power in load dispatch centers shall detect actual deviation against stipulated mode, establish and transmit controlling operation to lower level load dispatch centers and power plants which are involved in power auto-control process.

Auto power regulator at power plant shall satisfy the following requirements.

-To receive and set up controlling operations which come from higher load dispatch level and establish signals for controlling action at power plant level.

-To establish controlling action for each block of generator unit

-To maintain power of each block according to received controlling action

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aforesaid components are also used to remove adverse affect which prevent protective relays from currying out their functions.

Remote control facilities shall ensure sending information on power flow to other power system which this power system is connected to, and transmitting control signals from auto active power control device to controlled equipment as well as transmitting necessary information to senior management agencies.

For hydropower plant, power control system shall be equipped with auto devices to secure the start and stop of generator unit, and if necessary, such auto devices can switch generator unit to either synchronous compensation mode or generation mode, depending on conditions and operation method.

In hydropower plants of which output power is decided according to water flow condition, auto power regulator by water flow shall be equipped.

Chapter 5-3-6 Auto-prevention of Disturbances

Article 522. Required Functions of Auto-prevention of Disturbances

A device for auto-prevention of disturbance can make change of operation mode of series and shut compensation devices and other devices of power transmission line such as shunt reactor, autoexcitation regulator of generator, etc. It also will reduce active power of power plant in case that fault mentioned at the below items (1) and (2) occursTherefore,. this device limits amount of power to avoid further load shedding by frequency in power system or other adverse affect on power system.

The device for auto-prevention of disturbance can be applied in the following cases.

(1)Normal power lines as well as fault power lines are disconnected when protective relay and onephase auto-recloser operate at one phase earth fault. Such situation can occur on heavy load power lines. Automatic devices can be applied if the failure of operation of the automatic devices doesn’t cause further load shedding.

(2)Power line is de-energized when protective relay operates at multi-phase short circuit.

(3)Circuit breaker fails to be interrupted at switchingf ostandby device in case thatshort circuit occurs in normal operation mode of power system.

(4)Asynchronous power lines are separated from power system in normal operation mode.

(6)There are quick-act auto-reclosers or auto-reclosers operating in normal diagram and normal modes.

Auto-out-of-step protective device can be used for the following purpose.

(1) To disconnect partly generators of hydropower plant, and to disconnect generator of thermal power plant, if necessary.

(2)To reduce or increase output of steam turbine-generator promptly at permissible rate of thermal power plant

(3)To shed partially load of consumers which can endure transient outage

(4)To dived power system

(5)To reduce promptly and transiently load on turbine rotor.

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Priority of control signal of the device for auto-prevention of disturbance shall be decided according to influence caused by each operation or phenomenon.

Chapter 5-3-7 Auto-elimination of Asynchronous Mode

Article 523. Required Functions of Auto-elimination of Asynchronous Mode

The device for auto-eliminating asynchronous mode shall carry out methods to alleviate synchronous loading conditions as follows at first.

-To increase promptly load of turbine or to reduce part of load of consumers

-To reduce output of generator or to de-energize generators partly

Automatic separation of power system at assigned points shall be only carried out after asynchrony occurs if the aforesaid measures cannot recover the synchronyto power system after passing some stipulated oscillation periods or in case that asynchronous mode lasts longer than allowable duration.

Chapter 5-3-8 Auto-prevention of Frequency Decrease

Article 524. Required Functions of Auto-prevention of Frequency Decrease

The functions of the device for auto-prevention of frequency decrease are as follows.

-To energize standby system automatically by frequency

-To shed load automatically by frequency

-To shed load further

-To re-energize outage parts after recovery of frequency

In case that frequency decreases, firstly, standby source shall be automatically energized to reduce load shedding or outage duration of electricity supply to consumersEnergizing. standby source includes the measures below.

-To connect spinning reserve in thermal power plant to power grid.

-To start up automatically hydraulic turbine-generators which are in standby

Article 525. Load Shedding in the event of Frequency Decrease

Automatic load shedders by frequency must be equippedin substations in power system. heseT devices can be also equipped at consumers’ sites, but are managed by the power sector.

Amount of load to be shed shortage occurs shall be indentified based on the efficiency in case that any power shortage occurs. Sequence of load shedding shall be considered so that it causes minimum loss due to outage. If necessary, several automatic load shedders by frequency with multi-level operation can be applied. Important loads are usually shed lastly.

Automatic load shedder by frequency shall be operated in combination with autorecloserand auto switching power supply device.

Further load shedding device shall be applied if automatic load shedding by frequency is not sufficient at both amount of load to be shed and shedding speed.

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Power system management unit will decide the necessity of further load shedding, amount of load to be shed and detailed method of load shedding.

Power plants or generators are disconnected to make balance between generated power and load.The generators which supply electricity to auxiliary system of the power plant are also disconnectedThe. purposes are as follows.

- To maintain power supply to auxiliary system of power plant

- To prevent electricity lost in entire power plant in case that device for-p eventionauto of frequency decrease fails to operate

-To ensure supply of electricity to very important consumers

-To replace further load shedding in case that separation of power plant is more preferable than further load shedding

Necessity to apply further load shedding method, amount of load to be shed and energized, calibration level of time, frequency and other parameters for frequency decrease limiter shall be decided based on actual operation of power system.

Article 526. Re-energizing after Load Shedding

In arranging devices and allocating load by order, outage parts should -beenergized after the recovery of frequency considering importance of load, ability to reduce amount of load by automatic

load shedder by frequency, complexity and delay time of recovering power lines which are not equipped with automation equipment.

Usually, sequence of reenergizingoutage parts after recovery of frequency is decided according to the reverse order of the sequence for load shedding by automatic load shedder by frequency.

Chapter 5-3-9 Auto-prevention of Frequency Increase

Article 527. Required Functions of Auto-prevention of frequency Increase

The auto-tripping protective relay shall firstly disconnect some generators of hydropower plants. Secondly, thermal power plants from hydropower plants, but the remaining load for the thermal power plants should be as close as the capacity of the thermal power plant.

For the power system where only hydropower plants exist, device to prevent frequency from increasing due to electrical faults shall be equipped to such power system.

For the power system where only thermal power plants exist, device to preventdurationthe of frequency increase from exceeding the allowable value for the load of the generator unit.

Chapter 5-3-10 Auto-prevention of Voltage Decrease

Article 528. Required Functions of Auto-prevention of Voltage Decrease

Auto-prevent voltage decrease devices not only monitor voltage on power system but also check other parameters such as voltage variable rate, etc. In addition, these devices should have function to intensify forced excitation for synchronous electrical equipment and forced compensators, or to deenergize reactors.

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