Part 7

LOAD DISPATCH COMMAND – OPERATION

Chapter 1 LOAD DISPATCH COMMAND

Article 386. General provision

National dispatch center, dispatch center region and local domain and all units operate electrical equipment such as transformers, transmission lines, power plants, etc., responsible for securing the following obligations.

1. Reservation of hot standby and spinning reserve

Each operator shall endeavor to secure the following as a supply capability of the supply area.

-- Reserve margin: 8-10%

-- Operation reserve capacity oncurrent day: It is not less than 5%of the anticipation maximum electric power of the operation day.

-- Spinning reserve: It is about 3% of system capacity.

2.Frequency control

- - About 1-2% of system capacity shall be reserved in principle frequencyas control capability (Load Frequency Control Capacity).

-- Frequency deviation: 95% or more staying in the ranges of 50.0 Hz plus minus 0.1 Hz

-- Time deviation: Within plus minus 15 seconds

3.Target voltage

taken into consideration of setting up the target voltage of system voltage.

(1)System configuration, arrangement of generator, and capacity of phase modifying equipment.

(2)System characteristic, load characteristic, and performance of voltage adjustment equipment

(3)Permission voltage range of electric power system equipment

(4)Reservation of system stability

(5)Range of permission change of voltage supplied to customer

(6)Conservation of the proper reactive power balance of power system

(7)Reduction of electric power loss

-Voltage range in normal operation mode:

• Voltage level of the electrical system must be determined according tothe operating mode, load the largest and the smallest load. In normal conditions, the voltage is allowed to fluctuate in the range from -5% to +5% from the nominal voltage and is determined on the secondary side of the transformer supplying power to the households use electricity and from -5% to +10% at the connection points for power plants

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•When the power network is not stable, then the voltage is allowed to fluctuate in the range of -10% to +5%.

•In normal working conditions of the supply power center, during the time when the total load reduction of 30% of the maximum load, the voltage at the busbar must be kept at normal voltage of electrical network

•In normal working conditions of the transmission power network, the voltage at the busbar allows the operator to ± 10%.

-Scope of voltage fluctuations in power distribution networks (circular 32-2010 MOIT)

1.In the single incident or in the process of restoring stable operation after the incident, allowing the range of the voltage at the connection point with customers using electricity directly affected by the incident in the range of +5 % and -10% from the nominal voltage.

2.In the critical incident power transmission systems or disaster recovery, allowing the voltage in the range ± 10% of nominal voltage.

-Scope of voltage fluctuation in the power transmission network (circular 12-2010 MOIT)

1.In the case of electricity transmission system crash elements, serious incidents, in a state of emergency or in the process of restoring the system, allowing the range of the temporary grid voltage is greater than ± 10 % of nominal voltage but not exceed ± 20% of nominal voltage.

2.During the incident, the voltage at the scene of an incident and the neighborhood can reduce the value of 0 in phase with the incident or more than 110% of the nominal voltage in the phase is not a problem for until the problem has been eliminated.

Article 387. Load dispatching instruction

It shall be necessary to install the following devices in thesubstation and the power station, etc.and the load dispatching center to be operated the power system by a certain load dispatching command at normal and the accidental situations. Details shall depend on a related standard.

(1)The communication equipment for stay in touch

(2)Dispatching data transmission equipment (transmission equipment of telemetering data, switching condition and current and voltage value etc. of equipment to be controlled)

Article 388. Submission of annual schedule on overhauls and repairs

The national load dispatch center settles on the supply and demand programto secure necessary reserved capacity for the demand for Vietnam, and tokeep the service reliability. When supply and demand program is settled on, the following items should be taken into consideration.

-Equipment outage program including inspection and repair program etc. on each power plant

-Equipment outage program including inspection and repair program etc. on transmission and substation equipment for bulk power system

Decide the timing of implementation of the above-mentioned equipment outage program of the power plant and the transmission and substation equipment based on the following matters.

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Table 388 Consideration matters of developing the equipment outage program

Article 389. Allowable load capacity of electrical equipment and power transmission lines

It is necessary to set the permissible operation capacity of the power equipment and conductors of the power station and the substation equipment, etc. from the viewpoint of theprevention of equipment destruction when operating them.

The system operator and the owner of equipment shall set the above capacity under consideration of the following items.

-Timing of reviewing permissible operation capacity

+When the rated capacity and the overload capacity of equipmentare changed by the equipment replacement and repair (However, the permissible operation capacityis set the minimum value among the permissible operation capacity of various equipment which is series connection)

+When the overload capacity of the transformeris changed by the result of dissolved gas analysis for transformer etc. (When the overload capacity is changed by the aged deterioration of the equipment)

+Items to review when the permissible operation capacity was modified.

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+ Relay setting for over current protection (prevention of malfunction and failurethe ofrelay operation caused by the change of power flow)

+ Relay setting for automatic load limiter (Automatic load limiter : When transmission line overload is detected, partial load will be limited automatically to resolve the overload)

Article 390. Load curve of hydropower plants

The operation of the hydropowerstation where is provided the amount oftailwater by the water demand in the downstream shall be followed the below.

-As for the output of the power station, it is calculated based on the amount of tailwater (volume of water for power generation) and in consideration of theeffective head, the water turbine and the generator efficiency. The power generation program shall be scheduled along the volume of water for power generation.

-The operator shall operate according to the power generationrogram,p record the operation activities, and keep the record.

Article 391. Keeping of assigned load curves and spinning reserves of power plants

The national load dispatchcenter develops the total demand curve in the entire system in consideration of the demand change factor of the social environment, the season and the weather etc.

When supply and demand curve forpower plant generation is made, it is necessary to consider the following items.

-Select the operating power plant, and decide the economical load dispatch among the above power plant in consideration of the generation characteristic of each power plant.

-Decide the economical load dispatch (load curve) of each generating unit in consideration of the generation characteristic of each power unit according to the above decision.

Moreover, the appropriate operating reserved capacity such as spinning reserve, etcshall. also be secured to do steady supplies against the margin of demand forecast errorand the power supply dropout, etc.

Though the power plant operates according to the load curve of the above-mentioned, when the power plant doesn't obtain the load curve by some reasons, the power plant shall report on the situation to the national or the local load dispatch centerwhich has the right to control. The load dispatch center that receives the above report shall send the concerned load curve again or execute dispatch command to control the output of generators in consideration of the demand and supply balance etc.

Article 392. Frequency of power system

Refer to the frequency control of the guideline of Article 386 for the maintenance target of the frequency of the power system.

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Article 393. Voltage of power system

Each load dispatch center shall provide the target voltage of power system in which the matter shown in the guideline of Article 386 is considered, and execute operation based on the following items to keep the target voltage of various place and to allocate the reactive power reasonably.

(1)To decrease the reactive power flow of the transmission transformer as much as possible within the range of the target voltage of the transformer.

(2)The system voltage shall be kept high level as much as possible within the range of the target voltage, to decrease the transmission loss and the voltage drop at the time of power system fault.

(3)As for the operation of the interconnection transmission line between local power systems, both dispatch centers shall control the system voltage and reactive power flow concertedly according to the concerned agreement.

Article 394. Stop procedure of various control system

When the various protection systems and theload dispatch systems, etc are stopped, it is necessary to submit the plan that describes thestop device, the stop period, and the stop reason, etc. to theload dispatch center that operates equipment concerned, in order to avoid a decrease service reliability.

In addition, the load dispatch center shall confirm the submitted plan, and decide the stop plan of the system concerned after considering the following matters.

Table 394 Consideration matter when system stop is adjusted

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Article 395. Unscheduled repair

It is necessary to submit the document that describes the stop equipment, the stop period, and the stop reason, etc. to the load dispatch center that operates equipment concerned when it is necessary to stop equipment by unexpected equipment failure etc.

In addition, the above mentioned procedure can be omitted when emergencysituations occur, such as the problem of a human safety and the equipment maintenance, etc.

Article 396. Allowable time in the request

It shall be necessary to describe the following items for theoutage period in the application of the equipment outage.

-Required time to the stop operation of equipment under operation

-Required time to the inspection and the repair

-Required time to the restoration operation after the inspection and the repair, etc.

When the stop period changes by extending working hours, it shall be necessary to report prior to the load dispatch center that has jurisdiction, and to obtain approval.

Article 397. Stop of operation

The owner of equipment shall begin the operation of equipmentoutage and the work after the contacting the load dispatch center that has isdiction,jur discussing a necessary matter among the following items, and obtaining the approval of the load dispatch center.

(1)Responsible person

(2)Area of equipment outage

(3)Work content

(4)Installation place of grounding

(5)Operational procedure of equipment outage

(6)Estimated time of the initiation and termination of working

(7)While work discontinuance condition and emergency restoration estimated time

(8)Other necessary information

Article 398. Fault clearance procedures

The owner of the equipment and the system operator shall make theoperation manual to be able to execute the restoration operation promptly for each power station and substation when the failure occurs in the power system. In addition, the following failure modes are targeted.

(1)Transmission line failure (For each circuit and two or more circuit simultaneous failure by the case where the protective relay for transmission lines operates)

(2)Black out failure

(3)Bus failure (For each bus and two or more bus simultaneous failure by the case where the bus protection relay operates)

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